How much mechanical stress can a skeletal muscle bear?
In the movie- Saw, for the last trap Bobby was told to insert metallic hooks into his pectoralis major muscle. In his fake story Bobby has raised himself successfully, but when he was "really" trapped, his muscles were broken under his own weight.
Is it true, that muscles can be broken so easy? When human is pulling up on the bar, aren't these muscles undergo much more tension, because of lever effect made by his arms?
Also, what if Bobby insert hooks under his ribs, would he die immediately due to pneumothorax?
The question is biological, no interest of how it was possible to overcome trap with mechanical means.
DimsDims
$\begingroup$ Can you edit this to make it more about biology and less about a fictional character in a movie? Are you interested in the tensile strength of vertebrate muscle? $\endgroup$ – kmm May 26 '14 at 2:13
$\begingroup$ I don't watch the SAW series. But with regard to muscle tear, it depends on a lot of factors like the weight applied (was this Bobby heavy or muscular) and whether he moved around a lot. You might have heard of crocodiles rolling around to tear off flesh of their prey. So if he was thin or was muscular and did not move around much, the muscle should be able to handle the weight. $\endgroup$ – The Last Word May 26 '14 at 4:28
The skeletal muscle is not isotropic and therefore the effect of stress would be different from different axes. The strength also depends on the density of fibers and the composition of tendons (aponeurosis) that connect the muscle tissues; these can change (positively) with long term exercise [ref].
In this article the authors show the effect of different mechanical stresses on the skeletal muscle tissue — digitorum longus, from rabbit hindlimbs.
Tests were performed on extensor digitorum longus (EDL) muscles, chosen for its regular cross-section and low pennation angle (Lieber and Blevins, 1989). To ensure that only muscle tissue was tested, aponeuroses were carefully dissected away
Figure from the same article by Morrow et al. (2010)
You can notice that the yielding point to longitudinal extension is somewhere near 180kPa. It can be assumed that a hook into the tissue on pulling would generate longitudinal extension stress (unless the hook pierces through the muscle tissue or has sharp edges that can rip the muscle transversely). The stress in the Bobby situation would be: $$\frac{\text{weight (mass)}\times \text{gravitational acceleration}\ (9.8\ ms^{-2})}{\text{area of the muscle covered by the hook} \times \text{number of hooks}}$$
This is the best I can answer your question based on data; this cannot be directly extrapolated to the Bobby situation because:
The muscle tissue is different
The strength of the tissue depends on how much has Bobby exercised his muscles.
There would be additional mechanical stresses in other directions because of his movement while being suspended from the hook.
Ribs are not very strong bones and attempt to hook something on it may cause punctured lungs, not pneumothorax. Death will depend on the severity of the wound.
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