Guest guest Posted July 9, 2002 Report Share Posted July 9, 2002 > Quick question about the squat. I have a high school > football player who is very inflexible and > uncoordinated in the hip, groin, trunk and low back > area, however he is relatively strong in most > movements in the weight room. He cannot squat 225 or > less below parallel without his heels coming up and > turning inward. However, you put 315+ on the bar and > his heels stay down and stable while executing a good, > below parallel squat. The heavier weight seems to > eliminate his inflexibility or force his body > structure to stretch properly. He obviously has > trouble performing many of our agility drills also. > What can I implement into his training to correct his > instability and flexibility? We've tried dynamic > stretch, overhead squats, 1 leg squats, dynamic > hurdles and box squatting, but to little avail. Any > help would be greatly appreciated. Thank You, > Alford > Rowlett, Texas Have him box squat to a height that he can keep good form to and lower the box every two weeks for however long it takes for him to reach paralell with good form. Kruse Carmel IN USA > > __________________________________________________ > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted December 21, 2009 Report Share Posted December 21, 2009 Here are various resources regarding the squat: Knee biomechanics of the dynamic squat exercise. Med Sci Sports Exerc. 2001 Jan;33(1):127-41. Escamilla RF. PURPOSE: Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise. METHODS: Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. RESULTS: Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60 degrees knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50 degrees knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100 degrees knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. CONCLUSIONS: The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat. ---------------------- Research: Med Sci Sports Exerc 2001 Jun;33(6):984-98 A three-dimensional biomechanical analysis of the squat during varying stance widths Escamilla RF, Fleisig GS, Lowry TM, Barrentine SW, s JR PURPOSE: The purpose of this study was to quantify biomechanical parameters employing two-dimensional (2-D) and three-dimensional (3- D) analyses while performing the squat with varying stance widths. METHODS: Two 60-Hz cameras recorded 39 lifters during a national powerlifting championship. Stance width was normalized by shoulder width (SW), and three stance groups were defined: 1) narrow stance squat (NS), 107 ± 10% SW; 2) medium stance squat (MS), 142 ± 12% SW; and 3) wide stance squat (WS), 169 ± 12% SW. RESULTS: Most biomechanical differences among the three stance groups and between 2-D and 3-D analyses occurred between the NS and WS. Compared with the NS at 45 degrees and 90 degrees knee flexion angle (KF), the hips flexed 6-11 degrees more and the thighs were 7-12 degrees more horizontal during the MS and WS. Compared with the NS at 90 degrees and maximum KF, the shanks were 5-9 degrees more vertical and the feet were turned out 6 degrees more during the WS. No significant differences occurred in trunk positions. Hip and thigh angles were 3-13 degrees less in 2-D compared with 3-D analyses. Ankle plantar flexor (10-51 N.m), knee extensor (359-573 N.m), and hip extensor (275-577 N.m) net muscle moments were generated for the NS, whereas ankle dorsiflexor (34-284 N.m), knee extensor (447-756 N.m), and hip extensor (382-628 N.m) net muscle moments were generated for the MS and WS. Significant differences in ankle and knee moment arms between 2-D and 3-D analyses were 7-9 cm during the NS, 12-14 cm during the MS, and 16-18 cm during the WS. CONCLUSIONS: Ankle plantar flexor net muscle moments were generated during the NS, ankle dorsiflexor net muscle moments were produced during the MS and WS, and knee and hip moments were greater during the WS compared with the NS. A 3-D biomechanical analysis of the squat is more accurate than a 2-D biomechanical analysis, especially during the WS. ---------------- Res Q Exerc Sport 1989 Sep; 60(3):201-8 A preliminary comparison of front and back squat exercises PJ, SJ The purpose of this study was to compare the knee extensor demands and low back injury risks of the front and back squat exercises. Highly strength-trained college-aged males (n = 8), who performed each type of squat (Load = 75% of front squat one repetition maximum), were filmed (50 fps) from the sagittal view. The body was modeled as a five link system. Film data were digitized and reduced through Newtonian mechanics to obtain joint forces and muscle moments. Mean and individual subject data results were examined. The maximum knee extensor moment comparison indicated similar knee extensor demands, so either squat exercise could be used to develop knee extensor strength. Both exercises had similar low back injury risks for four subjects, but sizable maximum trunk extensor moment and maximum lumbar compressive and shear force differences existed between the squat types for the other subjects. The latter data revealed that with the influence of trunk inclination either exercise had the greatest low back injury risk (i.e., with greater trunk inclination: greater trunk extensor demands and lumbar shear forces, but smaller lumbar compressive forces). For these four subjects low back injury risk was influenced more by trunk inclination than squat exercise type. ---------------------- J Biomed Eng 1988 Jul;10(4):312-8 Potential of lumbodorsal fascia forces to generate back extension moments during squat lifts McGill SM & Norman RW The lumbodorsal fascia (LDF) has been implicated in numerous biomechanical interpretations of low back mechanics as a tissue that provides support to the lumbar spine during demanding load bearing. One hypothesis is that oblique abdominal muscle forces contribute to trunk extensor moment by transforming lateral abdominal tension into longitudinal tension via the LDF. However, a review of the anatomical literature supports the hypothesis that extensor forces in the LDF result from tension within the latissimus dorsi muscle. The purpose of our work was to evaluate the potential of the LDF to generate trunk extensor moment using two mathematical models: one that activated the LDF with the abdominals and another that activated the LDF with the latissimus dorsi. Efforts were made to represent the anatomy as accurately as possible. The results from three subjects performing six squat lifts each, suggested that the potential of the LDF to contribute significant extensor moment has been overestimated. In fact, the issue of whether the LDF is activated by the abdominals or the latissimus dorsi is irrelevant because neither strategy appeared able to generate sizable extensor moments in the type of lift studied. ------------------- Eur J Appl Physiol 2001 Mar; 84(3):227-32 Force/velocity and power/velocity relationships in squat exercise Rahmani A, Viale F, Dalleau G, Lacour JR The purpose of this study was to describe the force/velocity and power/velocity relationships obtained during squat exercise. The maximal force (F0) was extrapolated from the force/velocity relationship and compared to the isometric force directly measured with the aid of a force platform placed under the subject's feet. Fifteen international downhill skiers [mean (SD) age 22.4 (2.6) years, height 178 (6.34) cm and body mass 81.3 (7.70) kg] performed maximal dynamic and isometric squat exercises on a guided barbell. The dynamic squats were performed with masses ranging from 60 to 180 kg, which were placed on the shoulders. The force produced during the squat exercise was linearly related to the velocity in each subject (r2 = 0.83-0.98). The extrapolated F0 was 23% higher than the measured isometric force, and the two measurements were not correlated. This may be attributed to the position of the subject, since the isometric force was obtained at a constant angle (90 degrees of knee flexion), whereas the dynamic forces were measured through a range of movements (from 90 degrees to 180 degrees). The power/velocity relationship was parabolic in shape for each subject (r2 = 0.94-0.99). However, the curve obtained exhibited only an ascending part. The highest power was produced against the lightest load (i.e., 60 kg). The maximal power (Wmax) and optimal velocity were never reached. The failure to observe the descending part of the power/velocity curve may be attributed to the upper limitation of the velocities studied. Nevertheless, the extrapolation of Wmax from the power/velocity equation showed that it would be reached for a load close to body mass, or even under unloaded conditions. ------------------- Med Sci Sports Exerc 1986 Aug;18(4):469-78 Biomechanics of the squat exercise using a modified center of mass bar Lander JE, Bates BT, Devita P The purpose of the study was to investigate the effects of load height on selected performance characteristics of a squat exercise. A lower center of mass bar was designed that allowed the integrity of the squat exercise to be maintained while possibly reducing the chances of injury. Five trials were performed with the center of mass of the bar was set at shoulder height (C1) and lowered 18% (C2) and 36% (C3) of the subject's height below the normal bar position using the inverted " U " bar. All trials were filmed as the subjects lifted on a force platform. A balloon catheter was inserted into the subject's recta to monitor intra-abdominal pressure (IAP). High correlations were found between IAP, joint moment, and force data. Many of the critical parameters occurred just after the lowest squat position. Significant differences in trunk angle excursion and trunk angular velocity indicated a greater ease of hip extension for the center of mass bar conditions. No differences were observed between conditions for thigh and knee angles and joint moments indicating kinematic similarity for the lower extremity. IAP was always least for C2 and C3, while compression, shear, and back muscle forces did not differ. It was estimated that the greater IAP was responsible for relieving back muscle forces and compression by up to 15 and 21%, respectively, and increased stress with the weight at shoulder height stimulated a response for greater IAP to help alleviate the stresses on the spine. ---------------------- Med Sci Sports Exerc 1990 Feb;22(1):117-26 The effectiveness of weight-belts during the squat exercise Lander JE, Simonton RL, Giacobbe JK The purpose of this study was to examine the effectiveness of weight- belts during the performance of the parallel squat exercise. Six subjects were filmed (40 fps) as they performed three trials at each of three belt conditions (NB, none; LB, light; HB, heavy) in random order and three load conditions (70, 80, 90% 1RM (one repetition maximum] in increasing order. The parameters examined were collected and interfaced to a computer via an analog-to-digital (A/D) converter: ground reaction forces, intra-abdominal pressure (IAP), and EMG for the rectus abdominus (RA), external oblique (EO), and erector spinae (ES) muscles. Most differences were observed during the 90% 1RM condition, and only they are presented in this paper. Maximum IAP values were always greater (P less than 0.05) for the weight-belt conditions (LB, 29.2; HB, 29.1 greater th an NB, 26,8 kPa). Similar results were observed for the mean IAP. The integrated EMG (iEMG) activity of the muscles and adjusted mean values for back compressive force and back muscle force followed a similar but opposite pattern, with NB being the greatest. ES mEMG/(L5/S1) values for HB (18.1%) were the least, followed by LB (20.01%) and NB (22.3%). Few differences were observed between belt types. These data suggest that a weight-belt can aid in supporting the trunk by increasing IAP. ------------------- Med Sci Sports Exerc 1985 Oct; 17(5):613-20 Lumbar spine loading during half-squat exercises Cappozzo A, Felici F, Figura F, Gazzani F Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load. ----------------- Med Sci Sports Exerc 1989 Oct; 21(5):613-8 Effect of load, cadence, and fatigue on tibio-femoral joint force during a half squat Hattin HC, Pierrynowski MR, Ball KA Ten male university student volunteers were selected to investigate the 3D articular force at the tibio-femoral joint during a half squat exercise, as affected by cadence, different barbell loads, and fatigue. Each subject was required to perform a half squat exercise with a barbell weight centered across the shoulders at two different cadences (1 and 2 s intervals) and three different loads (15, 22 and 30% of the one repetition maximum). Fifty repetitions at each experimental condition were recorded with an active optoelectronic kinematic data capture system (WATSMART) and a force plate (Kistler). Processing the data involved a photogrammetric technique to obtain subject tailored anthropometric data. The findings of this study were: 1) the maximal antero-posterior shear and compressive force consistently occurred at the lowest position of the weight, and the forces were very symmetrically disposed on either side of this halfway point; 2) the medio-lateral shear forces were small over the squat cycle with few peaks and troughs; 3) cadence increased the antero-posterior shear (50%) and the compressive forces (28%); 4) as a subject fatigues, load had a significant effect on the antero-posterior shear force; 5) fatigue increased all articular force components but it did not manifest itself until about halfway through the 50 repetitions of the exercise; 6) the antero-posterior shear force was most affected by fatigue; 7) cadence had a significant effect on fatigue for the medio-lateral shear and compressive forces. ----------------------- Med Sci Sports Exerc 1997 Apr; 29(4):532-9 EMG analysis of lower extremity muscle recruitment patterns during an unloaded squat. Isear JA Jr, kson JC, Worrell TW. During an unloaded squat, hamstring and quadriceps co-contraction has been documented and explained via a co-contraction hypothesis. This hypothesis suggests that the hamstrings provide a stabilizing force at the knee by producing a posteriorly-directed force on the tibia to counteract the anterior tibial force imparted by the quadriceps. Research support for this hypothesis, however, is equivocal. Therefore, the purposes of this study were 1) to determine muscle recruitment patterns of the gluteus maximus, hamstrings, quadriceps, and gastrocnemius during an unloaded squat exercise via EMG and 2) to describe the amount of hamstring-quadriceps co-contraction during an unloaded squat. Surface electrodes were used to monitor the EMG activity of six muscles of 41 healthy subjects during an unloaded squat. Each subject performed three 4-s maximal voluntary isometric contractions (MVIC) for each of the six muscles. Electrogoniometers were applied to the knee and hip to monitor joint angles, and each subject performed three series of four complete squats in cadence with a metronome (50 beats.min-1). Each squat consisted of a 1.2-s eccentric, hold, and concentric phase. A two-way repeated measures ANOVA (6 muscles x 7 arcs) was used to compare normalized EMG (percent MVIC) values during each arc of motion (0-30 degrees, 30-60 degrees, 60-90 degrees, hold, 90-60 degrees, 60-30 degrees, 30-0 degrees) of the squat. Tukey post- hoc analyses were used to quantify and interpret the significant two- way interactions. Results revealed minimal hamstring activity (4-12% MVIC) as compared with quadriceps activity (VMO: 22-68%, VL: 21-63% of MVIC) during an unloaded squat in healthy subjects. This low level of hamstring EMG activity was interpreted to reflect the low demand placed on the hamstring muscles to counter anterior shear forces acting at the proximal tibia. --------- *** The following study showed that if you wish to exercise the glutes, then a full depth squat is highly recommended. J Strength Cond Res 2002 Aug; 16(3): 428-32 The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. Caterisano A, Moss RF, Pellinger TK, Woodruff K, VC, Booth W, Khadra T. The purpose of this study was to measure the relative contributions of 4 hip and thigh muscles while performing squats at 3 depths. Ten experienced lifters performed randomized trials of squats at partial, parallel, and full depths, using 100-125% of body weight as resistance. Electromyographic (EMG) surface electrodes were placed on the vastus medialis (VMO), the vastus lateralis, (VL), the biceps femoris (BF), and the gluteus maximus (GM). EMG data were quantified by integration and expressed as a percentage of the total electrical activity of the 4 muscles. Analysis of variance (ANOVA) and Tukey post hoc tests indicated a significant difference in the relative contribution of the GM during the concentric phases among the partial- (16.9%), parallel- (28.0%), and full-depth (35.4%) squats. There were no significant differences between the relative contributions of the BF, the VMO, and the VL at different squatting depths during this phase. The results suggest that the GM, rather than the BF, the VMO, or the VL, becomes more active in concentric contraction as squat depth increases. ---------------- *** This study concluded that that stance width does not cause significant isolation within the quadriceps but does influence muscle activity on the medial thigh and buttocks. Med Sci Sports Exerc 1999 Mar;31(3):428-36 Stance width and bar load effects on leg muscle activity during the parallel squat. McCaw ST, Melrose DR. PURPOSE: Altering foot stance is often prescribed as a method of isolating muscles during the parallel squat. The purpose of this study was to compare activity in six muscles crossing the hip and/or knee joints when the parallel squat is performed with different stances and bar loads. METHODS: Nine male lifters served as subjects. Within 7 d of determining IRM on the squat with shoulder width stance, surface EMG data were collected (800 Hz) from the rectus femoris, vastus medialis, vastus lateralis, adductor longus, gluteus maximus, and biceps femoris while subjects completed five nonconsecutive reps of the squat using shoulder width, narrow (75% shoulder width), and wide (140% shoulder width) stances with low and high loads (60% and 75% 1RM, respectively). Rep time was controlled. A goniometer on the right knee was used to identify descent and ascent phases. Integrated EMG values were calculated for each muscle during phases of each rep, and the 5-rep means for each subject were used in a repeated measures ANOVA (phase x load x stance, alpha = 0.05). RESULTS: For rectus femoris, vastus medialis, and vastus lateralis, only the load effect was significant. Adductor longus exhibited a stance by phase interaction and a load effect. Gluteus maximus exhibited a load by stance interaction and a phase effect. Biceps femoris activity was highest during the ascent phase. CONCLUSION: The results suggest that stance width does not cause isolation within the quadriceps but does influence muscle activity on the medial thigh and buttocks. ----------------- *** This study confirmed that there are significant differences in muscle recruitment patterns between the trunk extensor and hip extensor strategies of squatting throughout the range of movement. Unfortunately many personal trainers and fitness " authorities " are sufficiently aware of these differences. Spine 1994 Mar 15;19(6):687-95 Electromyographic activity of selected trunk and hip muscles during a squat lift. Effect of varying the lumbar posture. Vakos JP, Nitz AJ, Threlkeld AJ, Shapiro R, Horn T. Electromyographic (EMG) activity of selected hip and trunk muscles was recorded during a squat lift, and the effects of two different lumbar spine postures were examined. Seven muscles were analyzed: rectus abdominis (RA), abdominal obliques (AO), erector spinae (ES), latissimus dorsi (LD), gluteus maximus (GM), biceps femoris (BF), and semitendinosus (ST). The muscles were chosen for their attachments to the thoracolumbar fascia and their potential to act on the trunk, pelvis, and hips. Seventeen healthy male subjects participated in the study. Each subject did three squat lifts with a 157-N crate, with the spine in both a lordotic and kyphotic posture. The lift was divided into four equal periods. EMG activity of each muscle was quantified for each period and normalized to the peak amplitude of a maximal voluntary isometric contraction (MVIC). A two-way analysis of variance (ANOVA) for repeated measures was used to analyze the effects of posture on the amplitude and timing of EMG activity during the lift. Two patterns of EMG activity were seen: a trunk muscle pattern (RA, AO, ES, and LD) and a hip extensor pattern (GM, BF, ST). 1. In the trunk muscle pattern (TP), EMG activity was greatest (in RA, AO, ES, and LD) in the first quarter and decreased as the lift progressed. 2. In the hip extensor pattern (HP), EMG activity was least (in GM, BF, ST) in the first quarter, increased in the second and third quarters, and decreased in the final phase of the lift. Differences were seen among subjects and in the timing of the muscle activity in all muscles. ---------------- *** This study showed that there are major differences in muscle recruitment and joint torque between Weightlifting and Powerlifting squats. In particular, Weightlifters distribute the load more equally between hip and knee, whereas Powerlifters put relatively more load on the hip joint. The thigh muscular activity was found to be slightly higher for powerlifters. Note that Sumo style squats were not examined in this study, but it would probably have been found that this places even greater load on the hips as compared with the knees. Med Sci Sports Exerc 1996 Feb;28(2):218-24 High- and low-bar squatting techniques during weight-training. Wretenberg P, Feng Y, Arborelius UP. Eight Swedish national class weightlifters performed " high-bar " squats and six national class powerlifters performed " low-bar " squats, with a barbell weight of 65% of their 1 RM, and to parallel- and a deep-squatting depth. Ground reaction forces were measured with a Kistler piezo-electric force platform and motion was analyzed from a video record of the squats. A computer program based on free-body mechanics was designed to calculate moments of force about the hip and knee joints. EMG from vastus lateralis, rectus femoris, and biceps femoris was recorded and normalized. The peak moments of force were flexing both for the hip and the knee. The mean peak moments of force at the hip were for the weightlifters 230 Nm (deep) and 216 Nm (parallel), and for the powerlifters 324 Nm (deep), and 309 Nm (parallel). At the knee the mean peak moments for the weightlifters were 191 Nm (deep) and 131 Nm (parallel), and for the powerlifters 139 Nm (deep) and 92 Nm (parallel). The weightlifters had the load more equally distributed between hip and knee, whereas the powerlifters put relatively more load on the hip joint. The thigh muscular activity was slightly higher for the powerlifters. -------------- ***The following study concluded that the use of a weight belt during squats may affect the path of the barbell and speed of the lift without altering electric activity of the muscles. This suggests that the use of a weight belt may increase explosive power by increasing the speed of the movement without compromising the joint range of motion or overall lifting technique. So much for all the claims about belts being of no value in lifting. J Strength Cond Res 2001 May;15(2):235-40 The effects of a weight belt on trunk and leg muscle activity and joint kinematics during the squat exercise. Zink AJ, Whiting WC, WJ, McLaine AJ. Fourteen healthy men participated in a study designed to examine the effects of weight-belt use on trunk- and leg-muscle myoelectric activity (EMG) and joint kinematics during the squat exercise. Each subject performed the parallel back squat exercise at a self- selected speed according to his own technique with 90% of his IRM both without a weight belt (NWB) and with a weight belt (WB). Myoelectric activity of the right vastus lateralis, biceps femoris, adductor magnus, gluteus maximus, and erector spinae was recorded using surface electrodes. Subjects were videotaped from a sagittal plane view while standing on a force plate. WB trials were completed significantly faster than NWB trials over the entire movement and in both the downward phase (DP) and upward phase (UP). No significant differences in EMG were detected between conditions for any of the muscle groups or for any joint angular kinematic variables during either phase of the lift. The total distance traveled by the barbell both anteriorly and vertically was significantly greater (p 0.01) in the WB condition than the NWB condition. The velocity of the barbell was significantly greater both vertically and horizontally during both the DP and UP in the WB condition as compared with the NWB condition. These data suggest that the use of a weight belt during the squat exercise may affect the path of the barbell and speed of the lift without altering myoelectric activity. This suggests that the use of a weight belt may improve a lifter's explosive power by increasing the speed of the movement without compromising the joint range of motion or overall lifting technique. From Dave Sandler's presentation Biomechanics of the Lifts (2001?) Kinematic Squat Analysis • McLaughlin, et. al.(1977) – all lifters showed a " sticking point " – greater horizontal hip and knee displacement in less-skilled lifters (LSL) – greater trunk angle in LSL – bar velocity on descent greater in LSL creating greater " bounce " – ascent bar velocity is similar at initial drive but less during sticking point in (LSL) ========================= • Fry, A. (1993a, – slight angle outward in feet allow knee to track in line with feet and also to attain squat depth – an upright posture is preferred – forward lean is necessary, however, to obtain proper mechanics – low bar squats result in greater forward lean =========================== • Escamilla, R. (2001) – Powerlifters use more hip force then knee as compared to other lifters • Greater trunk lean involves more hip and back – Low bar squats elicit greater contribution from the hamstrings, decreasing ACL strain, as well as shear and compressive knee forces – Vasti muscles are more active then rectus femoris – Hamstrings more active in ascent ============================ Kinetic Squat Analysis • McLaughlin, et. al (1978) – Trunk extensors produce more torque than thigh and lower leg – Trunk lean affects torque distribution inversely – Highly-skilled lifters maintain a more erect trunk position, causing thigh extensor dominant lifting – These results suggest a lifting paradox exists with trunk lean and thigh and trunk contribution ========================== Kinetics of Soft Tissue • Escamilla R. (2001) – Quads generate 2000N to 8000N of force – Ultimate failure of PCL and ACL are estimated at 4000N and 2160N respectively – Failure of the patellar tendon is estimated between 10,000N and 15,000N – Quadriceps rupture unlikely: quadriceps tendon strength is greater then that of the patellar tendon (about 35%- 40% thicker). – Knee shear no different in narrow vs wide stance, however, tibial compressive force is greater in wide stance – suggests foot modification absorbs sheer at the knee due to tracking changes =========================== Patellar Kinetics in Squats • Escamilla R. (2001) – Patella compressive force is greater as depth of squat increases (max force between 50o and 80o) – Patella compressive force is greater eccentrically – No difference in patella compressive force with feet angled out or in – Patella compressive force is greater in wide stance squatting – Powerlifters had lower patella compressive force – Low bar squat produces greater hip extensor torques while high bar squats produced greater knee extensor torques – Powerlifters show less patellar compressive force SQUATS AND MYTHS (1995) Dr Mel C Siff School of Mechanical Engineering University of the Witwatersrand, South Africa My comments on squatting technique have drawn a mixed bag of agreement and upset, which is always the case with fundamental exercises which tend to be surrounded by years of superstitious application. GENERAL COMMENTS Rest assured that this type of analysis is not meant to belittle. Heaven knows how many times we are all challenged at lectures, conferences and lifting platform about the appropriateness of our technique. I thank those who have chosen not to be politically correct and kind to me over the years, otherwise I would have been happily contented with the same old myths forever. Argumentation, analysis, refutation, rebuttal and counterproposal are all time-tested ways of research and teaching. Regrettably we often feel that if someone attacks ideas we believe in, then we are being personally attacked. Most of the time we did not even create the offending idea, yet we have used it so often that we become emotionally attached to it. In the case of religion, politics and sex, criticism invariably leads to such passionate encounters that even families become split up and nations go to war. Even science is not immune to this belief fervor - just try to argue about evolution and you will see what I mean. In the world of fitness, a similar scene rules and it is inordinately easy to tread on toes. The one merit of the Internet is that everyone can attend (unlike some costly conferences and some forbidding lecturers) and become involved and for that we thank fellow list member, Pansy. She prodded all of us into a series of encounters from which we will all emerge enriched, if personality clashes do not cloud the content. So, those of us such as myself who have analyzed your comments in some depth still appreciate your willingness to become involved. SOME SPECIFICS That having been said, it is still essential to comment on one of the worst beliefs that one encounters at virtually every fitness convention and in every popular publication, namely: " This exercise is for the average person or beginner and is not meant for athletes or experts " While the sentiments are well founded, they often tend to insult the 'average' person - who on earth always wants to be just 'average'? None of my clients wants to stay 'average' or 'novice' - that's why they are visiting a professional - they want to move out of averages and progress to something far greater. Of course, we start with carefully graded sequences of exercises, beginning with no added loading, and then progress cyclically to greater heights to achieve mutually agreed-upon goals, but we must never lose sight of the fact that any beginner HAS to be moving progressively onto significant resistance (or duration, degree of difficulty, range of movement etc.) - and this is where the problems begin. Research has shown that skills developed with minimal loading do not necessarily transfer effectively and safely to situations with greater loading. Moreover, learning a skill using movements which are similar to, but not the same as the actual exercise being taught, causes the same sort of motor problem, because the controlling program being instilled into the central nervous system is different for every different variant or pattern of movement. Thus learning of the half squat, power clean or machine bench press does not properly prepare the beginner for safety and efficiency with heavier loads. In fact, the well-meaning, but misguided advice to do certain 'safe' movements can actually lead to the dangerous situation in which the client may be MORE vulnerable to injury if he/she by chance is called upon to execute the banned form of that exercise. ADAPTATION AND OVERDESIGN Just as one overdesigns roads and buildings with a greater " Safety Factor " than 1 to withstand greater loads in earthquake zones such as San Francisco, so we should overdesign the body just in case it is sometimes called upon to do that dread activity that all the fitness authorities cautioned us against. So we have to teach, modify or relearn the skill each time we are exposed to some noticeable change in its characteristics, such as degree of resistance, range, speed, duration and pattern. If one is likely to be exposed to fatigue with an exercise, then we have to ensure that the client knows the different skills of learning and coping under conditions of fatigue. It is highly misleading to believe that there is only one specific skill for a given exercise at a given time for every single person. It is also misleading to lump all squats together. Even though they all involve knee, hip and spinal actions, the powerlifting and weightlifting or deep-knee bend squats differ very significantly in execution and distribution of forces through range of movement. There tends to be an irrational fear associated with deeper-than-parallel squats, even though most of this is based on theoretical analysis and is usually contradicted by clinical studies which show that even more knee injuries occur in activities which do not flex the knee anywhere near parallel (such as running and jumping). Others show that partial squats can traumatize the knees even more than full squats! Do the critics not appreciate that full squats executed under appropriate control throughout the movement actually produce adaptation (that is what all training is about, anyway!), enhanced strength, better stability and greater resistance to unexpected loading? That is what the principle of Gradual Progressive Overload is about, isn't it? THE REAL DANGERS The sooner folk realize that safety of execution does not depend primarily on the exercise alone, but the technique with which it is executed. Thus, a full squat executed slowly over full range may produce smaller patellar tendon forces than a part-range squat done a bit more rapidly. As a matter of fact, the patellar tendon force is frequently much greater during step aerobics, running, jumping, kicking and swimming than during controlled full squats with a load even exceeding twice bodymass. The dangers of a squat (even a part-range one) lie more in inward rotation of the knees, unequal thrusting with one leg, loss of stability with fatigue or poor concentration, unskilled use of ballistic action or the use of some object to raise the heels and increase the stress on the patella and its tendon. Does this mean that we should then advise against all these activities? Of course not! If we presented a table of the stresses and strains acting on all the tissues of the body during apparently innocuous daily activities (including the pressure in smaller blood vessels subjected to the pumping pressure of the heart), we would never get out of bed. Sorry, these arguments of great forces and stresses and so forth have to be looked at in context - the body grows, adapts and flourishes in response to an optimal level of regularly imposed stress. It is also misleading to talk about forces and tensions being large, because we should only do so in the context of knowing something about how big, strong and dense the tissues are upon which they are acting. If the tendon has a large cross-sectional area and the connective tissue comprising it is strong and extensible, then we have far less to worry about than if the tendons were not like that. Remember that a knowledge of the STRESS (force averaged over the cross-sectional area of the tissue) and STRAIN (how much the tissues lengthen relative to their original length) is far more relevant than the force itself. Forget about forces being quoted out of context - we have to be far more specific than that before we can condemn some poor exercise to death. SOME DISCUSSION OF DISAGREEMENTS GENERAL < Like I said above, at no time did I suggest this was appropriate for actual training but was trying to create an idea of overall form. When did I ever say " significant weight " or bouncing or doing it fast? Remember my objective was to help in form, in bodily placement, not in an actual weight training program . > ***EVERYTHING is part of training and appropriate or inappropriate for training. My comments about overall form are answered by my analysis of how much the skills of execution vary all the time and that beginner methods may not necessarily be enough to ensure that efficiency and safety continue to reign. In terms of the two criteria applied to problem-solving situations, those initial drills may be NECESSARY, but they are not SUFFICIENT for learning squats which gradually increase in degree of difficulty (even if the difficulty is because one is growing older and weaker!) If the next response is that the client is never going to add a load and remain at the same level and number of reps, I must say no more and go my way in peace. But if progressive increase in fitness is the aim, well, all the preceding commentary remains relevant. <When did I ever say significant weight? Again, I was trying to get across placement not an actual training routine. > ***Another little problem lurks in this comment. It is commonly believed that adding an external load is the only way to produce really significant loads on the joints and tissues. This myth has beset resistance training for decades and many coaches and doctors still believe that non-load bearing exercise has to be safer than load-bearing exercise. If we wander back to Newton's 2nd Law (Force F = Mass x Acceleration), we learn that the force may be increased either by adding load or by accelerating the action. In fact, since it is easier to move faster or accelerate more rapidly with a heavy load, many folk expose themselves to greater force under unloaded conditions! If one accelerates rapidly, the effective weight or load imposed on the body DOES become significant! This is always something we have to watch out for with beginners or those who believe in using light weights. < With this present myth of 90 degree angle, are you then suggesting that it is appropriate for a beginner to do a deep knee bend? > *** Do the persons suffer from any pre-existing knee problems or weakness? Do they ever squat in daily life to put on shoes or play with youngsters? Do they ever run, jump or kick without experiencing knee pain or disability? Is there any good medical reason which definitely indicates that slow, controlled full squats without major bouncing are dangerous for them? Do they always want to have a limited range of functional knee flexion for the rest of her life? Do they believe that the body was created or evolved NOT to be used in a controlled fashion (and sometimes for emergencies) over the full range of its capabilities? If the answer to all those questions is yes, then let them continue to treat themselves as if they are ready for the grave! Also entirely relevant to the 90 degree story is the fact that more research is emerging which shows that this limited range squatting can actually place GREATER stress on the various structures of the knee joint than full range movement. My old Bulgarian weightlifting coach used to try to convince me that I should even used a controlled bounce at the bottom of all of my squats in the clean and snatch to ensure that I did not damage my knees!! He and many of his colleagues did this for years with loads of as much as 240kg and after several decades of lifting they still had no obvious knee dysfunction. I have not come across any research which supports his advice, but it would appear that he was recommending that one must involve the elastic structures of the joints to augment the 'pure' muscle contraction characteristic of slow controlled squats. Why rely just on muscles, when you can use stored elastic potential energy as well and spare the poor old muscle, seemed to be his view? I await information from others in this regard. POSITION OF THE TORSO Other contributors stressed the importance of squatting with the trunk vertical, which is another one of those horrible myths about squatting. To analyze this advice, let us return to the training chair that started all this discussion. Sit erect with knees in front of you (or a bit to the side), shoulder width or so apart, hands folded across the chest, according to the advice we have just read. Without leaning forwards or shifting the feet further back and flexing the knees more, try to stand up without leaning forwards or bouncing! You will find that this is impossible. To stand up, you either have to spread your legs very wide apart, like the Sumo squat position of the powerlifter, or move the feet backwards and lean forward. For most 'average' folk and serious lifters, the latter position quite naturally teaches you your individual degree of forward trunk lean for squatting and deadlifting. You HAVE to lean forward to squat or deadlift (now don't quote some of those weird 19th century lifts with the load behind the ankles to prove this wrong!); that is determined by the biomechanics of the movement! And never forget to hold the breath, even without a load, for this is what nature decreed should happen to stabilize the trunk and protect the lower spine! Your blood pressure will rise in proportion to the size of the load and the amount of effort that you are willing to put into the action. If you have cardiocirculatory problems, and you insist on squatting with weights, then keep your mouth open and gradually breathe out to prevent intrathoracic and intra-abdominal pressure from increasing too much - and avoid using maximal loads! < Regarding to POSITION OF THE TORSO during squatting: I believe many people get confused by the advice to keep one's back " straight. " Dr. Siff is right, in my experience -- you can't keep your torso perpendicular to the floor without some sort of odd foot position. But you MUST keep an arch in your back. The technique I've always used is to keep the arch in the lower back and neck buy sort of " pushing out " the chest and abdomen and looking slightly upwards. The belief that the spine must be straight during squats and deadlifts is another one of those confusing snippets of ill-explained training lore. > STRAIGHT BACK? The 'advisers' probably mean that the spine should not be flexed forwards or extended backwards, in some sort of hypothetical straight line. When challenged on this point, some of them state that this is their simplified way of stating that the spine should be kept in its neutral position, whatever that means in the context of a dynamic lift involving a line of action which changes all the time relative to the direction of the gravitational pull. PATTERNS AND RHYTHMS Some authors (e.g. Cailliett 'Low Back Pain & Disability') refer simplistically to a lumbar-pelvic rhythm that must be followed to ensure safe lifting (or squatting), but we have to look at the whole body as a linked system to appreciate that the actions of squatting and lifting involve many more actions than those of the pelvis and lumbar spine alone. However, these authors are correct in identifying that there is a characteristic rhythm or timed pattern of anatomical (kinesiological) action for the optimal and safe execution of every exercise. In the case of the squat, there is a definite rhythm of how the different joints (ankle, knee, hip, spine) become involved in producing an efficient and safe movement. This rhythm or timed pattern is really like an exquisitely orchestrated symphony conducted under automatic and voluntary control of our brain and nervous system. Every instructor or coach has to conduct a client's orchestra to produce individualized nervous programs in the brain so that the muscles will obey the commands to execute an exemplary squat. POSTURE AND NEUTRALITY One must maintain a definite lumbar curve during the squat, but this is where some authorities differ. Some consider that this constitutes lumbar hypertension and can damage the spine, so they talk about neutral posture, even though neutrality is defined to apply under static standing upright. As soon as you lie down or tilt the spine relative to gravity, then we can attempt to maintain the three natural mobile curvatures of the spine (cervical, thoracic and lumbar), but this necessitates increasing muscle tension and changes in other joint angles to approach this standard of 'neutrality'. So, the appearance of neutrality is quite different under different actions. Even though the spine looks like it is structurally in the same relative shape, functionally the muscles, ligaments and other tissues are in radically different states of tension and operation. In other words, the concept of neutrality (like all the ideas about pelvic tilt) is not at all as clear-cut as out medical and physiotherapeutic colleagues would have us believe. APPROPRIATE LUMBAR POSITIONING To resolve the issue of lumbar 'hyperextension' during squatting or lifting, we must analyze what stabilizes the spine under different conditions. The muscles act as dynamic or static active stabilizers (since they can contract), while the ligaments act as passive stabilizers (they cannot contract). In maintaining the three natural spinal curvatures, it is pleasing to know that both the muscles and the ligaments (and other tissues such as the fascia, as well as the pressurised trunk) all cooperate to stabilize the spine. However, we cannot say that the loading is distributed equally between muscles (e.g. erector spinae) and ligaments. This ratio is determined by one's way of squatting. So, if one tightens the erector muscles as much as possible, this may cause some of the ligaments to slacken, thereby placing a greater load on the muscles. If one avoids tensing the erector muscles too much or allows the lumbar spine to arch forwards, then the ligaments may bear much greater stress and the muscles tend to decrease their strength output. DYNAMIC STABILIZATION It happens that there is an optimal balance between these two undesirable extremes which allows the contribution by muscles and ligaments to dynamically adjust to different phases of the squat from the starting to the end position. The trainee or lifter learns this optimal dynamic balance by tons of experience, some of which is by the bitter way of making painful or damaging errors. There is not one precise static position of the spine or hips, though there is a typical ratio at each set of joint angle (knees, hips, spine, neck etc.). The ratios change over the range of movement and one learns to develop great proprioceptive skills to enable you to adjust rapidly and automatically. So, we can now appreciate how inadequate it is in the overall picture to learn by squatting onto a seat or in a part range movement from which we are told never to deviate, because one must use a specific single type of pelvic tilt, lumbar angle of concavity, knee angle and so forth. OBVIOUS ADVICE We can, of course, make cautionary statements about avoiding actions which have been seen to have caused serious injuries during squats and all exercises, for that matter - such as rounding the lower back and twisting simultaneously, bouncing vigorously in an uncontrolled fashion on totally relaxed, using a weight which is too heavy to maintain appropriate technique, bouncing the buttocks off a seat while using a significant load or accelerating rapidly and squatting when one is fatigued, sore or injured. Such advice is wise and advisable. But first and foremost are the rules that perfection of technique and intuitive sensitivity to any changes will go a long way to preventing injury and ensuring progress. = Woodhouse: Sports Science MSc Squatting and the Implications of Technique on Muscle Function Introduction The squat has been described as the 'King of Exercises' since it activates the largest, most powerful muscles in the body and is the greatest test of lower body strength (4, 6, 12). The major muscles that are activated are the ankle, knee and hip extensors, the spinal erectors and the abdominals. As a result the squat is one of the most popular exercises for development of lower body strength and power. It constitutes one of the three competitive lifts in the sport of Powerlifting and the front squat variation is also a component of the 'Clean' lift in weightlifting. The 'Sticking Point' Phenomena When load is near maximal, squat technique may be adjusted to permit a successful completion of the lift. This results in an asymmetric lift when descending and ascending components are compared (6). The point of minimal bar velocity during the ascent is often described as the 'sticking point'. The sticking point is thought to result from the force-length properties of muscles and the torque produced by the load (6). The quadriceps' ability to produce tension decreases as they extend and hence so does their net extensor moment. At the sticking point, they are no longer able to produce sufficient force to continue extending the knees (6). Hip flexion at this point occurs to shorten the load's moment arm at the knee joints and enables the quadriceps to extend them (17) (and also lengthen the hamstrings). The vasti muscles of the quadriceps group all show similar peak EMG activity during ascent and decent (12). The rectus femoris is the only bi-articular muscle in the quadriceps group, it creates a hip flexor moment. and shows ~30% greater activation during the descent yet still significantly less than the vasti (12). The vasti each have specific length tension relationships, and it may be a weakness in the lateralis that contributes to the sticking point since the medialis is most active at the latter stages of knee extension (15) The moment arm at the hip increases as it flexes at the sticking point but lengthening of the gluteal and hamstring muscles is advantageous for producing force since it improves their length tension relationships and hence increases net torque (6). The hamstrings are a bi-articular muscle, crossing both knee and hip joints, during the ascent they shorten at the hip and lengthen at the knees. However the shortening at the hip is disproportionate to the lengthening at the knee, and therefore their ability to produce tension is improved by hip flexion (6). Hip flexion increases the moment arm of the load and therefore requires an increase in the isometric tension produced in the spinal erectors. At the beginning of the ascent some lifters (particularly in the front squat) hyperextend the spine to shorten the hip's moment arm and also to help keep the load-body centre of gravity over the feet (4). Hyperextension of the lumbar spine places greater stress on the facet joints and may increase the risk of chronic lower back pain (8). Repeated training in this hyperextended position may cause an exaggeration of the lumbar curve - lordosis (8). At the sticking point however the spine generally flattens and in some cases may partially flex. This allows the knees to extend fractionally without any increase in bar height (4). As the spine flexes, the spinal erector's length tension relationship moves closer to optimum but the net extensor torque decreases because there is a significant decrease in the angle the logissimus and iliocostalis muscle fibres make with the spine. This compromises their ability to support shear forces and hence, at full flexion, those forces are transferred to passive tissues, (i.e. ligaments and spinal disks) significantly increasing the risk of injury (13). Powerlifters may allow their spine to flex to within two or three degrees of full flexion hence preventing injury yet maximising the ability to negotiate the 'sticking region' (14). Squatting typically stresses the spinal erectors isometrically in an extended position. Due to the specificity of this mode of training there is little cross over to the shorter muscle fibre lengths involved in spinal flexion (4). Therefore, if a lifter has not been conditioned to partially flex the spine, the muscles may not be able to maintain sufficient tension and it may 'buckle' (14). When squatting lifters employ the Vasalva manoeuvre, that is a voluntary increase in pressurisation of the abdominal cavity achieved by closing the epiglottis and activating trunk and abdominal muscles (11). The effect of increasing intra abdominal pressure is increased stability of the spine though the mechanism is not fully understood (10). An early theory was that a hydrostatic force within the abdominal cavity induced an extensor moment by pushing down on the pelvic floor and up on the diaphragm (10). However contraction of rectus abdominis, and the internal/external oblique muscles causes a flexor moment that offsets the extensor moment caused by intra-abdominal pressure (3). It is now believed that increased co-activation of spinal flexor and extensor muscles increases spinal stiffness and hence spinal stability (3). This means that increased intra-abdominal pressure is simply a useful by-product that negates the flexor moment caused by the abdominal and oblique muscles as discussed above (3). The changes in technique at the sticking point highlight the influence of load on technique. This is important when designing protocols to examine the kinematics of the lift. Also the sticking point phenomena has implications for training to improve squatting strength, for example lifters might train isometrically at the sticking point to improve strength specifically at that joint angle (4). Width of Stance A wide stance is typical of Powerlifters whilst weightlifters typically use a narrower stance (although not narrow as defined by the research) Typically in the research a narrow stance was defined to be ~75% of shoulder width whilst wide stance was defined to be ~140% shoulder width. Commonly lifters show greater lateral rotation of their feet as stance width increases but this variable has not been shown to influence any muscle activities (6). Research involving EMG has shown no significant difference in quadriceps activation between narrow and wide stances (12). Adductor activation has been shown to increase with a wide stance (12). This is because the thigh shows increased abduction and lateral rotation during the descent with a wide stance and, during the ascent, the adductors are therefore activated to draw the thigh back to the midline of the body and also medially rotate it back to a neutral position (12). Gluteus maximus and hamstring activation also increases with a wide stance (6). It has been suggested, for the former, that this is due to the positioning of its' distal attachment, which causes the gluteus to lengthen with thigh abduction (12). This lengthening shifts it away from its' optimum position on the length-tension curve and hence greater activation is required to create the same tension as the narrower stance (12). Greater activation of hip extensor muscles may also occur because width stance effects torso inclination (see later). Narrow stance caused greater forward knee movement and hence greater plantar flexion at the ankle as the shank inclined (6). This caused an increase in activity of the gastrocnemius during the ascent phase and since the gastrocnemius is a bi-articular muscle crossing both ankle and knee joints there is an increased knee flexion moment (6). Intuitively greater quadriceps activity is expected to counteract this but as discussed above this is not the case. This implies that either this moment is negligible or that the kinematics are altered. The increased forward knee movement also increases knee shear force due to more acute angle formed by thigh and shank (6). These findings, have implications for training for example, for greater development of the adductors and to minimise shear forces, a wide stance may be preferable. In contrast, a narrower stance may be more beneficial to increase activation of the gastrocnemius. Powerlifters have found that a wider stance is one factor that permits them to lift greater loads, however they need only squat to a position where the thighs break parallel and a wide stance may be less efficient for deeper variations of the lift. Bar Position There are three major methods of supporting the barbell when performing a squat lift. 'Low bar' where the bar lies across the spine of the scapula. 'High bar', the traditional technique, where the bar rests on top of the posterior deltoids and trapezius muscles, and 'Front bar' where the barbell rests on the anterior deltoids and clavicals. The load is posterior to the body's line of gravity with low and high bar but anterior with front bar. Low bar is the technique utilised by powerlifters, whilst front bar is used directly in weightlifting during the clean. High bar is the most common technique in strength training for sport since it has the lowest flexibility and skill requirement. Whilst there are correlations between bar position and the kinematics of the lift these are subject to individual differences in technique (16). The major difference is the degree of trunk inclination. Increased trunk inclination, increases the moment arm at the hip but decreases it at the knee and (as discussed previously) the greater the moment arm, the greater the muscle activation required to extend the joint. Bar position also directly influences the moment arm since the distance of the bar to the hip increases from low bar to high bar and again from high bar to front bar (16). Typically the front bar causes the most erect trunk posture since over inclination would cause the bar to fall forward off the chest (4, 17). Since the spine is more resistant to compressive forces (directed axially) than to shear forces, an erect trunk posture reduces risk of lower back injury (16). In the high bar the load is typically positioned centrally between knee and hip joints (17). Low bar allows the greatest hip flexion and hence the shortest moment arm at the knee. This latter bar position is therefore the most mechanically efficient and hence permits the greatest loads (17). At the present time there is no research to show whether bar position effects other factors such as intra-abdominal pressure. There may also be some interaction between other variables such as stance and depth. Cadence Increased lifting speed causes higher maximum, and greater variation in, shear and compressive force in the knee and spine (9). This is because a faster decent requires greater deceleration forces from the knee and hip extensors in order to slow and stop the weight at the bottom of the descent (6). Slower cadences during the descent may therefore be preferred since they decrease risk of injury and also increase the time under tension hence increasing the training effect (4). Cadence has not however been shown to significantly effect intra-abdominal pressure (7). Other factors There are many other factors, outside the scope of this paper, that influence squat kinematics. For future work however these include the depth of squat, segmental length, fatigue and equipment such as shoes, lifting belts and suits. References 1. Ariel, B. G. Biomechanical analysis of the knee joint during deep knee bends with heavy loads. In: Biomechanics IV, R. and C. Morehouse (Eds.). Baltimore: University Park Press, 1974, pp. 44-52 2. Bird, M. and J. Hudson. Mearsurement of elastic like behaviour in the power squat. Journal of Science and Medicine in Sport. 1(2):89-99, 1998 3. Cholewicki, J., J. Kishna and and S. M. McGill. Intra Abdominal pressure mechanism for stabilizing the lumbar spine. Journal of Biomechanics. 32: 13-17, 1999 4. Dreshler, A. In The Weightlifting Encyclopedia, S. Heath (Ed.). A is A Communications, 1998 5. Escamilla, R. F., N. Zheng, G. S. Fleisig, et al. The effects of technique variations on knee biomechanics during the squat and leg press. Med. Sci. Sports Exerc. 29:S156, 1997 6. Escamilla, R. F., G. S. Fleisig, T. M. Lowry, S. W. Barrentine and J. R. s. A three-dimensional biomechanical analysis of the squat during vaying stance widths. Med. Sci. Sports Exerc. 33: 984-998, 2000 7. Hall, S. J. Effect of attempted lifting speed on forces and torque exerted in the lumbar spine. Med. Sci. Sports Exerc. 17:440-444, 1985 8. Hall, S. J. In Basic Biomechanics IV, V. Malinee (Ed.). McGrraw-Hill, 2002 pp. 275-305 9. Hattin, H. C., M. R. Pierrynowski, and K. A. Ball. Effect of load, cadence and fatigue on tibio-femoral joint force during a half squat. Med. Sci. Sports Exerc. 21:613-618, 1989 10. Hodges, P. W., A. G. Cresswell., K. Daggfeldt. and A. Thostensson. In vivo measurement of the effect of intra-abdominal pressure on the human spine. Journal of Biomechanics 34: 347-353, 2001 11. Enoka, R. M. In Neuromechanical Basis of Kinesiology II, L. Galasyn- (Ed.). Human Kinetics, 1994, pp. 56-59 12. McCaw, S. T., and D. R. Melrose. Stance width and bar load effects on leg muscle activity during the parallel squat. Med. Sci. Sports Eerc. 31(3):428-436, 1999 13. McGill, S. M, R. L. Hughson, and K. Parks. Changes in lumbar lordosis modify the role of the extensor muscles, Clin. Biomech. 15:777, 2000 14. McGill, S. M. Low. Back stability: From formal descriptions to issues for performance and rehabilitation. Exerc. And Sport Sci. 29:26, 2001 15. Palastanga, N., D. Field, and R. Soames. In Anatomy and Human Movement 16. , P. J., and S. J. . A preliminary comparison of front and back squat exercises. Res. Q. 60:201-208, 1989 17. Wretenberg, P., Y. Feng, and U. P. Arborelius. High and low bar squatting techniques during weight training. Med. Sci. Sports Exerc. 28:218-224, 1996 18. , G. a., T. H. Delong, and G. Gehlsen. Electromyographic activity of the hamstrings during performance of the leg curls, stiff-leg deadlifts, and back squat movements. J. Strength Cond. Res. 13:168-174, 1999 ============== Carruthers Wakefield, UK Quote Link to comment Share on other sites More sharing options...
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