What motion is occurring at the knee during the positive phase?

Question

Squat exercise: What motion is occurring at the knee during the positive phase?What muscles are being used during the positive phase? How are these muscles contracting during the positive phase? What motion is occurring during the negative phase? What muscles are being used during the negative phase? How are these muscles contracting during the negative phase? 

Answer 1

Hi Kiah, I realize you asked this question a while ago but hopefully my answer is still helpful.

For the purposes of this question, I am assuming that by positive phase you mean the upward motion and negative phase you mean the downward motion.

Positive phase:

1. Knee extension
2. Quadriceps - rectus femoris, vastus medialis, vastus lateralis, vastus intermedius
3. There are many other muscles at the hip and ankle that are working, but quadriceps are the primary group.
4. Concentric contraction - as you are moving upwards in the squat, your quadriceps are shortening and therefore it is a concentric contraction of the quadriceps

Negative phase:

1. Knee flexion
2. Hamstrings (concentric), Quadriceps (eccentric)
3. Quadriceps are contracting eccentrically as you lower your body with the squat. They are lengthening and controlling the movement which is an eccentric contraction. If you are referring to the hamstrings which flex the knee, it is a concentric contraction.

For questions like these, it is important to know what muscle groups are the focus. Type of contraction (eccentric vs. concentric) can vary for a single movement (i.e. squat) depending on what muscles you are talking about.