Electromyographic analysis of single-leg, closed chain exercises: Implications for rehabilitation after anterior cruciate ligament reconstruction

Objective: Many knee rehabilitation studies have examined open and closed kinetic chain exercises. However, most studies focus on 2-legged, closed chain exercise. The purpose of our study was to characterize 1-legged, closed chain exercise in young, healthy subjects. Subjects: Eighteen normal subjects (11 men, 7 women; age, 24.6 +/- 1.6 years) performed unsupported, 1-legged squats and step-ups to approximately tibial height. Measurements: Knee angle data and surface electromyographic activity from the thigh muscles were recorded. Results: The maximum angle of knee flexion was 111 +/- 23degrees for squats and 101 +/- 16degrees for step-ups. The peak quadriceps activation was 201 +/- 66% maximum voluntary isometric contraction, occurring at an angle of 96 +/- 16degrees for squats. Peak quadriceps activation was 207 +/- 50% maximum voluntary isometric contraction and occurred at 83 +/- 12degrees for step-ups. Conclusions: The high and sustained levels of quadriceps activation indicate that 1-legged squats and step-ups would be effective in muscle rehabilitation. As functional, closed chain activities, they may also be protective of anterior cruciate ligament grafts. Because these exercises involve no weights or training equipment, they may prove more cost effective than traditional modes of rehabilitation.