Figure 4. Impact of stretch on twitch kinetics.

Average twitch kinetics at the 75% (top), 50% (middle) and 10% (bottom) twitch force level at: baseline sarcomere length (left pair of bars), immediately following stretch (middle pair of bars), and 5.5 min following the stretch when the Slow Force Response is fully developed (right pair of bars). Data were recorded in wild-type (WT; open bars; n=5) and homozygous giant titin mutant (HM; hatched bars; n=8) muscles. Time durations were normalized to the first twitch immediately following the stretch (i.e. the middle pair of bars representing the immediate response to SL stretch was set to 100%). In both muscle groups and at all three force levels, stretch per se induced an increase in time to reach peak twitch force (activation, left panels) and between the peak of the contraction down to a given twitch force level (relaxation, middle panels), and the overall duration of the twitch (total duration, right panels); prolonged maintained stretch (5.5 minutes), in contrast, did not affect twitch kinetics. [Ca²⁺]_o=0.4 mM; temperature=25 °C; stimulus frequency=1.0 Hz.