What action is produced by the quadriceps femora muscles during the concentric phase of the back squat exercise?

The concentric phase of the back squat is the ascent from the bottom position back to standing, during which the knee moves from a flexed to an extended position. The quadriceps femoris group - including the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris - are the primary movers responsible for this knee extension against the load.

Hip flexion occurs during the descent (eccentric phase) and is controlled eccentrically by the hip extensors; the quadriceps' rectus femoris crosses the hip but is not the primary driver of hip action in the squat.

Knee flexion occurs during the eccentric (lowering) phase of the squat and is controlled by the quadriceps acting eccentrically, not concentrically.

Hip extension during the concentric phase is produced primarily by the gluteus maximus and hamstrings, not the quadriceps femoris.