מדוע אנו מרגישים קושי ומאמץ בעת כיווץ שריר

מדוע אנו מרגישים קושי ומאמץ בעת כיווץ שריר בעוד ההשקעה האנרגטית נעשית בהרפיית השריר

At the end of the power stroke the actomyosin complex is remains intact until ATP becomes available. ATP binding to myosin is a very exergonic reaction, with the result that ATP displaces actin from the myosin head as indicated by the equation below. Thus, it is often said that ATP is required for muscle relaxation. It is important to note that in relaxed muscle, myosin is in its high-energy conformational state. Note that the final product (M-ATP) is also the first reactant shown in the first equation above, completing the reactions of the contractile cycle. מתוך http://themedicalbiochemistrypage.org/muscle.html