Figure 6. Peak force reached during muscle stretch (F_peak) for different conditions.

All peak forces were normalized relative to the corresponding isometric reference forces and pooled for each stretch condition and across all subjects. A, Protocol 1: the peak forces during stretch were greater for stretch amplitudes of 20 and 30 deg than those for 10 deg during electrical stimulation. F_peak was found to be greatest for stretch amplitudes of 20 deg for the voluntary contractions. Significance (* P < 0.05) is presented separately for electrically induced (continuous line) and for voluntary (dashed line) contractions because a significant interaction (stimulation method × stretch condition) was found. B, Protocol 2: F_peak increased with increasing speeds of stretch for the electrical and voluntary contractions. Means were collapsed across the stimulation methods and significance (* P < 0.05) is presented only for different stretch conditions, as no interaction (stimulation method × stretch condition) was found. F_peak, peak force produced during active stretching.