Current literature discusses whether an earlier activation of the Vastus lateralis (VL) compared to the Vastus edialis obliquus (VMO) calculated relative to the heelstrike during running can be associated with the Patellofemoral Pain Syndrome (PFPS). The present study investigated the onset of the activity of both Vasti for a healthy control group (n = 12) and subjects suffering from PFPS (n = 14) during barefoot, shod running, and running with insoles (if
available). Based on repeated measurements of the healthy subjects it was estimated that time differences between individual onsets of muscle activation and the later activation of the VMO related to the VL should be at least 25–30 ms to exclude to a high probability an interpretation biased by the given variance of the measurement performed with surface electrodes. The present results show that time differences of the onset of the activity of the Vasti between the two investigated groups were all between 5 and 10 ms on average, not significant, and not clearly distinguishable from the given variance of the measurement. Furthermore, using insoles did not result in a more simultaneous activation of the Vasti before heelstrike.
Thus, an earlier activation of the VL compared to the VMO can not be considered as a single characteristic of patellofemoral pain.
However, future work should investigate whether the muscular
coordination of the Vasti in combination with the kinematics and kinetics of the lower extremity can biomechanically explain the occurrence of individual patellofemoral pain.