Stress of DB Side Raises

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Some authorities are always warning us about the alleged dangers of doing any

loaded exercises (like dumbbell side raises) above horizontal level,

ostensibly because of " impingement " syndrome and overstressing certain

muscles such as supraspinatus (one of the " rotator cuff " muscles). The

following research project shows that the supraspinatus muscle is heavily

loaded not only in high arm positions above the horizontal during concentric

contraction but also during eccentric contraction in arm positions of only

0-30 degrees of abduction.

Is this finding now likely to have some fitness guru condemning any form of

DB side raises? After all, it is stressful to raise the arms above the

horizontal and it is stressful to resist the load going down to your sides,

especially over the last 30 degrees of the movement. What else is one to do

but expunge that very dubious exercise from the training manuals? Doesn't

that sound logical - at least a lot more logical than drawing the abs in

while you squat or lift heavy loads?

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J Orthop Res 1999 Jul;17(4):546-53

Effects of isokinetic muscle activity on pressure in the supraspinatus muscle

and shoulder torque.

Sporrong H, Styf J

Work-related shoulder pain is an increasing problem. Work in overhead

positions, which causes high pressure in the supraspinatus muscle, has been

shown to increase the shoulder load. It is not known how different types of

muscle activity in the shoulder affect pressure in the muscle. The aim of

this study was to investigate the difference between contraction modes. This

has not been done before for shoulder muscles. The results are relevant from

several aspects, both clinical and experimental.

Pressure in the supraspinatus muscle and torque generation in the shoulder

during isokinetic concentric and eccentric activity were measured in nine

healthy human subjects. Torque and arm position were measured continuously

with a computerized ergonometer. The contraction velocity was 60 degrees per

second, and the range of movement was 0-120 degrees of abduction.

Electromyographic measurements were recorded with a surface electrode above

the supraspinatus muscle belly. Intramuscular pressure was recorded with a

microcapillary infusion technique.

Peak intramuscular pressure did not differ significantly between the two

modes of contraction, but the peak was reached at 115 degrees (SD = 15

degrees) of abduction during concentric activity and at 6 degrees (SD = 7

degrees) of abduction during eccentric activity. The ratio between

intramuscular pressure and torque was 3.0 mm Hg/Nm (0.40 kPa/Nm) during

concentric activity and 2.3 mm Hg/Nm (0.31 kPa/Nm) during eccentric activity.

The peak torque occurred at 44 degrees of abduction during concentric muscle

activity and at 74 degrees of abduction during eccentric activity.

Intramuscular pressure was higher during isometric contraction than during

eccentric and concentric activity, and the torque was in between the two

latter contraction modes.

We conclude that the supraspinatus muscle is heavily loaded not only in high

arm positions during concentric contraction but also during eccentric

contraction in arm positions of 0-30 degrees of abduction.

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Dr Mel C Siff

Denver, USA

http://groups.yahoo.com/group/Supertraining/