Regional Hypertrophy

[Guest guest]

Dr.J.Parks "

Re: Muscle Fiber Type and Training Reps?

> This study would seem to agree with doing different movements for

> rehabilitation as well as repitition and load modificaction for development.

>

> Eur J Appl Physiol 1998 Aug;78(3):219-25

> Muscles within muscles: the neuromotor control of intra-muscular

> segments. Wickham JB, Brown JM Dept of Biomedical Science, University of

> Wollongong, NSW, Australia.

>

> The aim of this investigation was to anatomically identify, and then

> determine the function of, individual segments within the human deltoid

> muscle. The anatomical structure of the deltoid was determined through

> dissection and/or observation of the shoulder girdles of 11 male cadavers

> (aged 65-84 years).

>

> These results indicate that the deltoid consists ofseven anatomical segments

> (D1-D7) based upon the distinctive arrangement of

> each segment's origin and insertion. Radiographic analysis of a cadaveric

> shoulder joint suggested that only the postero-medial segment D7 has a line

> of action directed below the shoulder joint's axis of rotation. The

> functional role of each individual segment was then determined utilising an

> electromyographic (EMG) technique. Seven miniature (1 mm active plate; 7 mm

> interelectrode distance) bipolar surface electrodes were positioned over the

> proximal portion of each segment's muscle belly in 18 male and female

> subjects (18-30 years). EMG waveforms were then recorded during the

> production of rapid isometric shoulder abduction and adduction force

> impulses with the shoulder joint in 40 degrees of abduction in the plane of

> the scapula. Each subject randomly performed 15 abduction and 15 adduction

> isometric force impulses following a short familiarisation period. All

> subjects received visual feed back on the duration and amplitude of each

> isometric force impulse produced via a visual force-time display which

> compared subject performance to a criterion force-time curve. Movement time

> was 400 ms (time-to-peak isometric force) at an intensity level of 50%

> maximal voluntary contraction. Temporal and intensity analyses of the EMG

> waveforms, as well as temporal analysis of the isometric force impulses,

> revealed the neuromotor control strategies utilised by the CNS to control

> the activity of each muscle segment.

>

> The results showed that segmental neuromotor control strategies differ across

> the breadth of the muscle and that individual segments of the deltoid can be

> identified as having either " prime mover " , " synergist " , " stabiliser " or

> " antagonist " functions; functional classifications normally associated with

> whole muscle function.

>

> Therefore, it was concluded that the CNS can " fine tune " the activity of at

> least six discrete segments within the human deltoid muscle to efficiently

> meet the demands of the imposed motor task.

>

> [Note that this reference was posted and discussed a long time ago, so it

> might be useful to read through the archives for more info. Mel Siff]

An extrapolation of the results from this study and other more recent work from

the same laboratory

indeed do validate the mainly anecdotal evidence of regional skeletal muscle

hypertrophy. We have

found significant differences in segmental (portions) onset times, %MVC and

durations for segments of

the pectoralis major, latissimus dorsi and the aforementioned deltoid.

Specifically by doing various

static and dynamic shoulder joint movements whilst measuring the surface EMG

from subpopulations of

motor units within the pectoralis major, latissimus dorsi and deltoid numerous

(more than previously

cited) independently activated segments of these muscles became apparent.

The critical factor influencing which part of the muscle contracted first and

with the most intensity

was the relationship between the movement plane and the line of action of a

segment. The more

efficient the line of action of the segment the greater the intensity it would

contract and the

earlier it would turn on (onset).

For instance, by doing shoulder joint abduction movements in the plane of the

scapula (30 degrees

anterior to the coronal plane) the anterolateral (D2-D3) segments of the deltoid

showed the highest

contraction intensity. Compare this with abduction in the coronal plane (a 30

degree difference in

movement direction) where the more lateral (D3-D4) segment displayed

significantly (p<0.05) higher

contraction intensities and onsets. To extrapolate these results to the weight

room it would mean

that say lateral raises done in different planes even varying as little as 30

degrees significantly

changes the area of the deltoid being 'worked'. More anterior lateral raises

more anterior segments

worked, more posterior (towards the back) movement more posterior segments

worked. No rocket science

here.

To cite another example, for the latissimus dorsi we have found that the lower

segments (it was

divided into six segments L1-L6 superior to inferior) turn on first at higher

contraction intensities

when doing static shoulder joint adduction movements at 90 degrees of abduction.

When adduction (arm

moved towards body from the side) movements were performed with the arm closer

to the side of the body

(20 degrees abduction) the more middle to upper segments of the muscle now

displayed higher

contraction intensities when compared with the more lower segments. So to

extrapolate these results

it would seem that doing lat pulldowns empasing the lower phase of the movement

would recruit more so

the upper to middle portions of this muscle whereas emphasing the upper phase of

the movement (arm

more horizontal) would recruit more so the lower segments of the latissimus

dorsi.

Finally for the pectoralis major we have found that only upper segments P1-P2

(it was also divided into

six segments P1-P6 superior to inferior respectively) are activated in a static

shoulder flexion

(towards the front) movement at low intensities (25% of max force) with the

whole muscle being

activated at higher intensities of contraction (75%MVC). This was with the

upper limb at the side of

the body. Actually the clavicular fibres of the pectoralis major were activated

before the anterior

deltoid (D1-D2) in this flexion movement, emphasing the importance of these

fibres for this particular

task.

So as a final note the results of this work (later of which is in press) suggest

that varying movement

direction and contraction intensity does have an effect on the outcome of which

segment of the

particular muscle you are training will be recruited first and contract the

'hardest'. Something I'm

sure most knew but is scientifically validated by this work. Science catching

up with practice.

Dr Wickham

Lecturer

Dept of Anatomy & Physiology

j.wickham@...

School of Human Biosciences

La Trobe University

VIC 3086