Energetics of activation in frog skeletal muscle at sarcomere lengths beyond myofilament overlap.

Experiments were designed to gain information about the effects of extremely long sarcomere lengths (greater than 3.8 microns) on muscle activation. The amount of energy liberated in an isometric twitch by muscles stretched to sarcomere lengths where myofilament overlap is vanishingly small (greater than 3.6 microns) is thought to be an indirect measure of the Ca2+ cycled during contraction. The effects of altering sarcomere length from 3.8 to 4.3 microns on the amount of Ca2+ cycled was measured using twitch energy liberation as an indicator of the Ca2+ cycled. Twitch energy liberation decreased by approximately 20% over this sarcomere length region, suggesting that the amount of Ca2+ released by a single action potential is not altered dramatically when a muscle is stretched to extreme lengths.