That is probably because the fibers are handing off work to each other like a baton race, "I'm pooped, take over for me". You might get triple strength - at the

That is probably because the fibers are handing off work to each other like a baton race, "I'm pooped, take over for me". You might get triple strength - at the cost of sudden collapse a few seconds later when the whole muscle runs out of resources at once. Edit: in this context, consider the muscle prostration of a person who has been tazed (which forces total contraction electrochemically).