THE EFFECTS OF MUSCLE FATIGUE ON NEUROMUSCULAR FUNCTION AND ANTERIOR TIBIAL TRANSLATION IN HEALTHY KNEES

We investigated the effect of quadriceps and hamstring muscle fatigue on anterior tibial translation and muscle reaction time in 10 healthy subjects. The six men and four women had an average age of 21.3 years and had no known pathologic knee conditions. Each patient underwent a knee examination, arthrometer measurements of tibial translation, subj ective functional assessment, and an anterior tibial translation stres s test before and after quadriceps and hamstring muscle-fatiguing exer cise. The recruitment order of the lower extremity muscles in response to anterior tibial translation did not change with muscle fatigue. Ho wever, the results showed an average increase of 32.5% in anterior tib ial translation (range, 11.4% to 85.2%) after fatigue. Muscle response s in the gastrocnemius, hamstring, and quadriceps originating at the s pinal cord and cortical level showed significant slowing and, in some cases, an absence of activity after the quadriceps and hamstring muscl es were fatigued. The increases in displacement after fatigue strongly correlated (0.62 to 0.96) with a delay in cortical-level activity (in termediate and voluntary). Muscle fatigue, which appears to affect the dynamic stability of the knee, alters the neuromuscular response to a nterior tibial translation. Therefore, fatigue may play an important r ole in the pathomechanics of knee injuries in physically demanding spo rts.