A study was recently performed to determine the forces created by closed kinetic chain leg exercises and whether or not these forces are detrimental to the knee after reconstructive surgery. Closed kinetic chain leg exercises entail keeping the foot in a fixed position and accompanying knee movement with hip and ankle motion. Examples of closed chain exercises are the squat, lunge, and front squat, all of which were tested in this study. Results from the study showed that the forces created by closed chain exercises do not exert detrimental forces to an athlete's knee after reconstructive surgery. These findings support other research on the forces exerted during exercises such as the squat that all prove the squat is not hazardous to one's knees when performed properly.
-If you want to increase your strength, muscle mass, muscle tone, flexibility, etc. perform squats or one of its variations. No other exercise has as many benefits.
Stuart, M., et. al. Comparison of Intersegmental Tibiofemoral Joint Forces and Muscle Activity During Various Closed Kinetic Chain Exercises. American Journal of Sports Medicine. 24(6) 1996 792.