Are the rectus femoris and the vastus lateralis concurrently recruited during walking?

The aim of the study was the quantitative assessment of the concomitant recruitment of rectus femoris (RF) and vastus lateralis (VL) in a group of 11 healthy young adults during walking. To this aim, Statistical gait analysis, a recent methodology performing a statistical characterization of gait by averaging spatial-temporal and surface-EMG-based parameters over numerous strides, was performed in each subject. Superimpositions between RF and VL activity were detected from terminal swing to the following loading response in 99.0±25.8% of strides. This superimposition could be intended as a synergic action of the two muscles for controlling weight bearing, to assist knee extension and to control knee flexion. A further infrequent (<5% of the strides) superimposition was detected in mid and terminal stance, suggesting that the two muscles are working on different joints: RF activity could be interpreted as active participation in hip flexion, while VL activity as the main contribution in modulating rapid knee flexion. These findings have the merit to provide a novel data on the variability of the reciprocal role of RF and VL during walking, allowing a deeper insight in the physiological mechanisms that regulate the knee flexion/extension.