Fig. 4. Electromyography (EMG) data showed decreasing burst durations and increasing amplitudes as a function of swing frequency. (A) Medial hamstring (MH) and (B) rectus femoris (RF) average burst durations, , decreased in inverse proportion to swing frequency f (P<0.05; R²=0.72 and 0.94, respectively), as expected. Burst durations were determined from rectified EMG (as shown by inset diagram). Root-mean-square (RMS) amplitudes of (C) MH and (D) RF increased with leg swing frequency (R²=0.67 and 0.86, respectively), roughly similar to hip torque amplitude (Eqn 5). RMS amplitudes were determined from low-pass filtered, rectified EMG. Data shown (filled and unfilled circles) are means ± s.d. (N=6 for A-C; N=3 for D). Model fits were performed in accordance with predicted trends (f^-1 and Eqn 5, respectively), with coefficients determined by least-squares fits.