Vastus lateralis muscle fascicles actively lengthen during human walking

The energetic cost of muscle force production depends on the contraction type. For example, during mid stance of human walking, the calf muscles show relatively isometric fascicle behaviour, which is thought to be one reason why human walking is highly economical. As fascicle behaviour of the knee extensor vastus lateralis (VL; which has the largest relative quadriceps’ PCSA) during human walking is unclear, a gait analysis investigating its fascicle behaviour was conducted. We found active fascicle lengthening of the VL fascicles in early stance during human walking and propose that this behaviour is favoured because energy must be absorbed by the joint and isometric fascicle behaviour would presumably require greater muscle activity or altered knee kinematics so that fascicles are not stretched.