Question

if we have a muscle that is 100 mm long when optimally stretched and we attach it to a small weight, if it was to contract maximally, how far can it pull the attached weight?

my answer: it should only be able to contract 30 mm of its attached weight because the muscle being held at constant length by the activation of the muscle must maintain a certain level of force.

Please help me explain/ understand my answer.

Answer 1

Isotonic contractions generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions. A concentric contraction causes muscles to shorten, thereby generating force. Eccentric contractions cause muscles to elongate in response to a greater opposing force. When the muscle contracts at this short resting length, we see a small amount of force development. Now, let's stretch the muscle a little bit, so we increased its resting length by just 1mm. As you can see below, the muscle contracts with more force at this longer resting length. If we stretch the muscle once again to now 2mm beyond what it was originally, it develops even more force.

Thus, the change in tension is due to the number of contracting muscle fibers, not a change in how much tension the individual fibers are generating. Note that stimuli below the minimum strength needed to trigger any of the muscle fibers to reach the threshold and undergo an action potential (i.e., subthreshold stimuli) will not trigger any contraction in the muscle. A threshold is considered to be the level of stimulation required to trigger the smallest measurable contraction resulting from the excitation and contraction of the first few muscle fibers.