During a squat, how is the lowering phase best described in terms of muscle action?

The lowering phase of a squat is best described as eccentric muscle action because during this phase, the muscles are lengthening while generating force. Specifically, when you squat down, your quadriceps, hamstrings, and glutes are actively engaged to control the descent. This controlled lowering of the body requires the muscles to elongate while still exerting tension, which is characteristic of eccentric contraction.

Eccentric actions play a significant role in deceleration and stability, helping to manage the forces acting on the joints and maintain balance throughout the movement. This phase is essential for muscle strength development and is often associated with muscle soreness following intense workouts due to the microscopic damage created in the muscle fibers.

The other terms refer to different types of muscle actions. Isometric muscle action involves the muscles generating tension without changing length, which doesn't occur during the lowering phase of a squat. Concentric muscle action happens when muscles shorten while producing force, which is seen as you rise back up from the squat position. Auxotonic refers to a situation where both tension and length change simultaneously, which is more complex and not a direct descriptor for this specific part of the squat movement.