Neuromuscular fatigue and tibiofemoral joint biomechanics when transitioning from non-weight bearing to weight bearing

Context: Fatigue is suggested to be a risk factor for anterior cruciate ligament injury. Fatiguing exercise can affect neuro-muscular control and laxity of the knee joint, which may render the knee less able to resist externally applied loads. Few authors have examined the effects of fatiguing exercise on knee biomechanics during the in vivo transition of the knee from non-weight bearing to weight bearing, the time when anterior cruciate ligament injury likely occurs. Objective: To investigate the effect of fatiguing exercise on tibiofemoral joint biomechanics during the transition from non-weight bearing to early weight bearing. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: Ten participants (5 men and 5 women; age = 25.3 ± 4.0 years) with no previous history of knee-ligament injury to the dominant leg. Intervention(s): Participants were tested before (preexer-cise) and after (postexercise) a protocol consisting of repeated leg presses (15 repetitions from 108-408 of knee flexion, 10 seconds' rest) against a 60% body-weight load until they were unable to complete a full bout of repetitions. Main Outcome Measure(s): Electromagnetic sensors measured anterior tibial translation and knee-flexion excursion during the application of a 40% body-weight axial compressive load to the bottom of the foot, simulating weight acceptance. A force transducer recorded axial compressive force. Results: The axial compressive force (351.8 ± 44.3 N versus 374.0 ± 47.9 N; P =.018), knee-flexion excursion (8.0° ± 4.0° versus 10.2° ± 3.7°; P =.046), and anterior tibial translation (6.7 ± 1.7 mm versus 8.2 ± 1.9 mm; P <.001) increased from preexercise to postexercise. No significant correlations were noted. Conclusions: Neuromuscular fatigue may impair initial knee-joint stabilization during weight acceptance, leading to greater accessory motion at the knee and the potential for greater anterior cruciate ligament loading.