Figure 2.

Mean estimated muscle forces (black) and EMG (gray) crossing the knee joint at 0.75 m·s⁻¹, 1.25 m·s⁻¹, and 1.50 m·s⁻¹. Muscles grouped and summed by similar activation patterns: (a) vasti (vasti lateralis, vasti medialis, vastus intermedius), (b) gastrocnemius, (c) rectus femoris, and (d) hamstrings (semimembranosus, semitendinosus, and biceps femoris short/long head). Gracilis, sartorius, and tensor fascia latae not shown due to small force output (<0.10 BW across speeds). The EMG was normalized to peak values recorded during walking at 1.25 m·s⁻¹ and are expressed as a percentage. The EMG is from muscles in bold. Rectus femoris EMG was not available. The mid-gait-cycle hamstring muscle force production was due to the biceps femoris short head, which was not assessed with EMG.