EMG profiles of ACL-deficient patients during walking: the influence of mild fatigue

The purpose of this study was to determine muscle activities after ACL rupture during walking and running and to investigate the influence of mild fatigue (10 min walking) on these activities. A group of 12 patients with ACL-ruptures was compared with a control group (healthy volunteers) of 15 persons. Linear envelopes of EMG-activity from vastus medialis, vastus lateralis, biceps femoris and medial hamstrings were measured. Patients and control persons walked on a treadmill at speeds of 1.2 m/s (samples at t = 2 min and t = 12 min) and 2.8 m/s i.e. running (sample at t = 15 min). The patient group showed significantly lower muscle activities of vastus lateralis (p < 0.001) and medial hamstrings (p < 0.05) for both the injured and uninjured leg during running compared to the control group. After 10 minutes walking, the mean-EMG of biceps femoris (p < 0.05) and medial hamstrings (p < 0.01) decreased as did the activity time of biceps femoris (p < 0.05), medial hamstrings (p < 0.01) and vastus medialis (p < 0.001) for the injured leg of the patient group. Control persons showed no significant changes. Thus, mild fatigue did effect only the EMG-pattern of the patients. Patients with ACL-ruptures should be trained not only on strength and stabilisation, but also on endurance. A decrease in hamstrings activity during walking might be a sensitive measure for evaluation of the rehabilitation process, as those muscles may be able to substitute ACL-deficiency.