What is the consequence of having no ATP during muscle contraction?

When there is no ATP available during muscle contraction, the primary consequence is that muscle fibers cannot relax. Muscle contraction relies on the interaction of actin and myosin filaments within the sarcomeres, which is powered by ATP.

In the absence of ATP, myosin heads remain attached to the actin filaments after they complete a power stroke, leading to a state known as "rigor mortis" in post-mortem muscles. This sticking prevents the detachment of myosin from actin, which is necessary for the muscle fibers to return to their relaxed state.

Without the energy provided by ATP to facilitate the separation of actin and myosin, muscles become locked in a contracted position. This reflects a fundamental requirement of ATP for both the contraction and relaxation phases of muscle activity, highlighting its critical role in muscle physiology.