Why do muscles shake when tired? Doesn’t that take even more energy?
In: Biology
Muscles contract when a certain neurotransmitter (acetylcholine) activates the muscular cross bridge. Briefly, acetylcholine allows calcium to enter the muscle cell, alter the ‘shape’ of the muscle cell, and something called a power stroke occurs. This leads to muscle contraction.
When you’ve completed a very hard workout, the buildup of acetylcholine is too much for its enemy (acetylcholine esterase) and you end up with an altered signal within the muscle, leading to extra twitches or even muscle cramps.
PS: just because I’ve seen it mentioned a few times in the comments, it’s not lactic acid. Low pH leads to pyruvate turning into lactate, but that is to maintain functional pH levels. Lactate is actually incredibly beneficial to exercise, not only serving as a pH buffer, but as another substrate to be turned into glucose via the Cori Cycle. Also, lactic acid is typically fully restored to baseline within 30 minutes of ceasing exercise.
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