Fig. 5. Time from first stimulus to 50% and 100% peak force and time from last stimulus to 50% peak force during relaxation in isometric stimulations. Each point is the mean of observations made on one fibre preparation. +, time to peak force; x, time to 50% peak force; s, time to 50% relaxation. (A) Results from eight red fibre preparations using tetanus stimulation. Regressions: for time to 50% peak force, y=(0.174±0.017)+(0.02±0.03)x, r²=0.067, P=0.535; for time to 100% peak force, y=(0.459±0.010)+ (0.01±0.02x)x, r²=0.091, P=0.460; for time to 50% relaxation, y=(0.281±0.039)+(0.07±0.07)x, r²=0.140, P=0.360, where y is time in seconds and x is fraction of body length. Values are means ± S.E.M. (B) Results from 13 white fibre preparations using twitch stimulation. The lines are regressions: for time to 50% peak force, y=(0.039±0.011)+(0.0002±0.0002)x, r²=0.050, P=0.464; for time to 100% peak force, y=(0.075±0.020)+(0.0003±0.0004)x, r²=0.055, P=0.441; for time to 50% relaxation, y=(0.170±0.054)+(0.0009±0.0011)x, r²=0.066, P=0.395.