Muscular Fatigue Influences Patellofemoral Joint Reaction Force During Cutting In Healthy Females

The patellofemoral joint plays a critical role in tibiofemoral joint function, especially in activities with significant knee flexion. Changes in tibiofemoral joint mechanics can impact patellofemoral joint reaction force (PFJRF), potentially causing lower extremity injuries like patellofemoral pain or osteoarthritis. While various factors influencing PJRF have been identified, muscular fatigue is often overlooked. Muscular fatigue may diminish the lower extremity muscles' energy absorption capacity, leading to reduced neuromuscular control and altered tibiofemoral mechanics, ultimately impacting PFJRF. Given the inevitability of muscular fatigue in sports, understanding its impact on PFJRF is essential. PURPOSE: To determine if whole-body muscular fatigue influences patellofemoral joint reaction force during cutting in healthy females. METHODS: Seven healthy (23.0 ± 2.6 yrs, 69.2 ± 6.9 kg; 1.66 ± 0.6 m) recreationally active females completed five pre-fatigue box land-and-cut trials. Participants then completed a laboratory-based whole-body fatigue protocol, before performing five additional box land-and-cut trials. A 12-camera motion capture system and force plates were used to collect marker coordinate and GRF data, respectively. Peak knee flexion angle (KFA) and knee extension moment (KEM) were calculated. Musculoskeletal modeling was used to estimate muscle activation patterns and PFJRF during all box land-and-cut trials. Pre- and post-fatigue lower extremity mechanics were compared using paired samples t-tests. Significance for all tests were a priori set at p < 0.05. RESULTS: Peak PFJRF was lowered after the fatigue protocol (6.6 ± 1.3 BW) compared to the pre-fatigue condition (8.8 ± 1.8 BW; p = 0.038). Post-fatigue peak KFA (-41.2 ± 8.0 deg) and peak KEM (2.2 ± 0.4 Nm/kg) were also reduced compared to pre-fatigue states (KFA: -50.7 ± 6.2 deg, p = 0.020; KEM: 2.8 ± 0.6 Nm/kg, p = 0.012). CONCLUSION: Whole-body muscular fatigue decreased KFA and KEM, which led to reductions in PFJRF. Patellofemoral joint articular cartilage is highly sensitive to abnormal loading patterns (i.e., under -/overloading), which can lead degradation in overall cartilage composition. As such, chronic reductions in PFJRF may have implications in increasing future lower extremity injury risk.