Electromyographic evaluation of closed and open kinetic chain knee rehabilitation exercises

The use of closed kinetic chain knee rehabilitation exercises has been advocated in recent years. The primary reason cited for employing closed kinetic chain exercises is that these exercises result in less anteroposterior (A/P) shear force at the knee joint, when compared with traditionally used open kinetic chain exercises. The purpose of this study was to determine the electromyographical (EMG) activity ratio of quadriceps to hamstrings occurring in the following exercises: unilateral one quarter squats, leg extensions (N-K Table), lateral step-ups, and movements on the Fitter (Fitter International, Inc), Stair-master 4000 (Randal Sports/Medical Products, Inc), and slideboard. Ten female student-athletes participated in this study. EMG surface electrodes were applied over the rectus femoris and biceps femoris muscles. The subjects completed three maximum isometric contractions for both muscle groups to obtain baseline EMG data. They then performed repetitions of each exercise. These movements were videotaped simultaneously with a stationary shuttered video camera operating at 30 Hz. A computer program was used to analyze the videotaped performances for knee joint range of motion (ROM). Three trials of data were averaged. Baseline EMG activity was used to determine percentage of maximum EMG activity for each exercise. There were significant differences (p.<01) among the exercises for the following dependent variables: ROM, maximum angle, percent of maximum contraction, time of contraction, and total EMG (EMG area under the curve). This study suggests that the five closed kinetic chain exercises studied result in minimal A/P shear forces at the knee joint.