Talk:Muscle (muscle)

Strength per unit area

I can't believe that "vertebrate muscle typically produces approximately 25 N (5.6 lbf) of force per square centimeter of muscle cross-sectional area". If that were all muscles could do, then how can it be that "The 1992 Guinness Book of Records records the achievement of a bite strength of 4,337 N (975 lbf) for 2 seconds"? Certainly the jaw muscle does not have a couple hundred square centimetres of cross section! Eric Kvaalen (talk) 17:43, 8 September 2014 (UTC)

Look at the shape of the temporalis and masseter muscles, particularly the former - a big, fan-shaped muscle with lots of attachment area, like the pectoralis major. Some back-of-the-envelope calculations show that if the bite force was measured at the back of the jaw (mechanical advantage of 1) and both temporalis muscles were equally active (but no masseter activity), you'd only need a 4"x4" patch of temporalis on each side of your head. Having dissected a fair few (mostly elderly) humans, I can say that's big but reasonable for a healthy adult (clench your teeth and feel the side of your head to get a general idea of area). And remember, this is all excluding the masseter, a fairly prominent and strong muscle in its own right, and some contribution from the medial pterygoid muscle.

That said, the value of 25 should probably be a range up to 33, at least based on in vitro experimental preps.HCA (talk) 18:19, 8 September 2014 (UTC)

Someone might have a temporalis 4 inches broad, but certainly not 4 inches thick as well. And the masseter is nowhere near that big in cross section. I find it hard to believe that someone could have 4337/25=173.48 square centimetres of jaw muscle. Also, with my biceps I can lift around 25 kilograms, which is about 250 newtons, in my hand. My biceps has only a couple square centimetres of cross section, so that would make 50 newtons at the tendon. At my hand there would be much less force because of "mechanical disadvantage". I'm gonna take out the number since there's no reference and it seems wrong.

By the way, I'll bet you are the person mentioned in this article. Eric Kvaalen (talk) 07:24, 11 September 2014 (UTC)

Yep, that's me. As for the areas, think of the muscles like people pulling on ropes. If you and I are trying to pull a heavy box down a hallway, if I pull the rope attached to your belt and you pull the rope attached to the box, we only get 1 person's worth of force, because if I pull too hard, you'll slip towards me (or vice versa). If we both stand side-by-side and pull, we get two people-force on the box. If we recruit a bunch of people, eventually we get to the point where only so many can stand shoulder-to-shoulder pulling in parallel in the hallway (maybe 6 people-force). But if we're outside, we can have dozens of people pulling, arranged in a loose semi-circle; sure, some of the force of those at the edges is wasted, but on the whole the force increases a lot because we can fit more people. But that's just the top layer of fibers - in a real muscle, there are multiple layers of fibers, all attached to the bone. Imagine our box is in a football arena. All the people in the front row of seats covering a 60 degree span have ropes to the box, but so do all the people in the second row, and the third, and the fourth. Now, imagine you're trying to calculate how many person-forces the box experiences. You could cut the cross-section perpendicular to the ground, but that wouldn't quite be right, because of the angled layout. Your best metric would be the number of seats, an area on the surface of the concave depression of the arena bowl. That's actually a pretty good approximation of the layout of the temporalis, if you imagine the seating area is the side of the skull (the sky would be towards the skin, the ground the rest of the skull, the box would be the coronoid process, and the ropes would be the temporal aponeurosis (connective tissue linking the layers of muscle fiber to the insertion on the jaw). The effective cross-sectional area of the temporalis isn't the area when you just cut it in half, but the entire area where it attaches to the skull. That's why many mammals have a much stronger relative bite force than we do - their temporalis covers the entire side of the skull and many even have saggital crests that increase the surface area still more.

Also, I think your measurement of the biceps cross-section is either in error or you're just a lot smaller and thinner than me. I just measured mine with some big calipers (8 cm diameter, accounting for the skin etc over it), and using the muscle tension more typical of in vivo mammal muscle (33 N/cm), I calculate a force of 1658 N, a total of 372 lbs at the tendon. Given a rough mechanical advantage of 0.1, that's 37 lbs, equivalent to lifting 4 and a half 1-gallon jugs of water (seems about right from my days of "I will carry all the groceries inside in one trip even if it kills me"). Of course, all of this ignores the brachialis, which is actually pretty comparable in size to the biceps (but underneath it, so most people never see it like they see the biceps). HCA (talk) 14:53, 11 September 2014 (UTC)

Individual muscle fiber strength is incorrect

The listed number (which lacks citation) is 0.3 micronewtons.

This is off by at least a factor of 10.

In (http://web.mit.edu/smik/www/413.pdf) you can find reference to values closer to ~4 micronewtons for cardiac myocytes.

In table 1 of (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2269928/) you can see values for both cardiac and skeletal muscle fibers.

A group of 5 slow-twitch skeletal fibers is shown to produce 485 +/- 62 micronewtons of force. Putting the average between 84 and 109 micronewtons.

I suggest most people interested in the muscle strength section are interested in numbers related to skeletal muscle and so listing a range closer to 80 or 90 uN / fiber would be appropriate.

eye exercises?

"...eye muscles are exercised nightly during rapid eye movement sleep."

The article on REM Sleep doesn't mention that at all. — Preceding unsigned comment added by 23.119.204.117 (talk) 05:08, 3 October 2016 (UTC)

REM means "rapid eye movement", referring to movement of the eyes, and the eyes are moved by muscles. So, that's sort of obvious. --EncycloPetey (talk) 05:25, 3 October 2016 (UTC)

body

hi — Preceding unsigned comment added by 80.4.223.77 (talk) 19:42, 6 October 2016 (UTC)

Move discussion in progress

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