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 measure ments of tibial translation, subjective functional assess ment, and an anterior tibial translation stress test be fore and after quadriceps and hamstring muscle- fatiguing exercise. The recruitment order of the lower extremity muscles in response to anterior tibial trans lation did not change with muscle fatigue. However, the results showed an average increase of 32.5% in ante rior tibial translation (range, 11.4% to 85.2%) after fatigue. Muscle responses in the gastrocnemius, ham string, and quadriceps originating at the spinal cord and cortical level showed significant slowing and, in some cases, an absence of activity after the quadri ceps and hamstring muscles were fatigued. The in creases in displacement after fatigue strongly corre lated (0.62 to 0.96) with a delay in cortical-level activity (intermediate and voluntary). Muscle fatigue, which ap pears to affect the dynamic stability of the knee, alters the neuromuscular response to anterior tibial transla tion. Therefore, fatigue may play an important role in the pathomechanics of knee injuries in physically de manding sports.