ELECTROMYOGRAPHIC ANALYSIS OF MUSCLE FATIGUE IN ANTERIOR CRUCIATE LIGAMENT DEFICIENT KNEES

The aim of this study was to detect possible differences in muscle fat igue and recovery of knee flexor and extensor muscles in patients with a deficient anterior cruciate ligament compared with patients with a normal anterior cruciate ligament. Surface electromyography of 15 pati ents with anterior cruciate ligament deficiency was performed while th e muscles were under 80% of maximum isometric contraction, and after 1 , 2, 3, and 5 minutes of rest. During the first 60 seconds of contract ion, all muscles recorded significantly decreased mean power frequency and increased amplitude. The rate of decrease of mean power frequency was significantly greater in the injured quadriceps and normal hamstr ings. All muscles except two recovered to the initial mean power frequ ency level after 1 minute of rest. All but two muscles in the injured and normal limb recorded an overshoot of mean power frequency during t he recovery phase. This overshoot phenomenon also was seen for some mu scles in the amplitude analysis. The findings confirm the fatigue stat e in all the muscles, suggest recruitment of more Type II fibers as th e muscle fatigues, and show the physiologic adaptation of the quadrice ps and hamstrings to anterior cruciate ligament insufficiency. The cur rent study indirectly shows a dissociation between low intramuscular p H and mean power frequency during the recovery phase. It also indirect ly suggests that the atrophied thigh muscles have fiber type compositi on similar to that of the normal side.