The Relationship Between Length and Active Force for Submaximal Skeletal Muscle Contractions: a Review.

The force-length relationship is usually obtained for isometric contractions with maximal activation, but less is known about how sarcomere length affects force during submaximal activation. During submaximal activation, length-dependent alterations in calcium sensitivity, owing to changes in cross-bridge kinetics (rate of attachment and/or detachment), result in an activation-dependent shift in optimal length to longer sarcomere lengths. It is known that sarcomere length, as well as temperature and phosphorylation of the regulatory light chains of myosin, can modify Ca⁺ sensitivity by altering the probability of cross-bridge interaction.

Plyometric exercise enhances twitch contractile properties but fails to improve voluntary rate of torque development in highly trained sprint athletes.

: The objective of this study was to evaluate a plyometric conditioning activity (3 sets of 5 countermovement jumps, [CA]) for twitch properties and voluntary knee extension. : After a familiarization session, fourteen highly trained sprint athletes, 12 men (23.25 ± 7.

Does postactivation potentiation (PAP) increase voluntary performance?

The transient increase in torque of an electrically evoked twitch following a voluntary contraction is called postactivation potentiation (PAP). Phosphorylation of myosin regulatory light chains is the most accepted mechanism explaining the enhanced electrically evoked twitch torque. While many authors attribute voluntary postactivation performance enhancement (PAPE) to the positive effects of PAP, few actually confirmed that contraction was indeed potentiated using electrical stimulation (twitch response) at the time that PAPE was measured.