Author(s): ALESSANDRO, C., NARDON, M., ZANONI, M., BARTESAGHI, M., ZAZA, A., PERIN, C., Institution: UNIVERSITY OF MILANO-BICOCCA, Country: ITALY, Abstract-ID: 2239

INTRODUCTION:
Neuromuscular fatigue is a physiological phenomenon that reduces muscle force and power, affecting neuromuscular strategies during dynamic movements. Research suggests fatigue-induced motor alterations may cause negative effects on lower limb biomechanics [1]. However, whether these alterations increase the risk of musculoskeletal injury is still debated [2]. Here we investigated whether fatigue caused kinematic alterations that increase the risk of anterior cruciate ligament (ACL) rupture, one of the most common injuries during sport activities.
METHODS:
Twenty-three male participants performed at least three repetitions of single-leg hop for distance jumps with both dominant (D) and non-dominant leg (ND), before and after an individualized fatiguing protocol on a cycle ergometer until exhaustion. Cycling power was set 10% above the workload associated to each participant’s anaerobic threshold, previously determined by cardiopulmonary exercise testing. Hence the fatiguing protocol was adapted to the fitness level of each participant. Sagittal and frontal joint lower-limb angles before- and after the cycling protocol were compared using two-ways repeated measure ANOVA and Bonferroni-corrected post-hoc tests, evaluating whether fatigue induced motor alterations typically associated with an increased risk of ACL injury [3].
RESULTS:
Jump length was reduced for both legs following the exercise (D: Δ=-8.5±2.6, ND: Δ=-7.1±3.1 cm; mean ± standard error; p<.001). Joint kinematics were significantly affected by the fatiguing protocol. Following fatigue, there was a reduction of hip and knee flexion angles during the propulsion phase – corresponding to the peak value in the ground reaction force profile (Hip D: Δ=-3.5±1.6°, p=.043; ND: Δ=-3±1°, p=.006; Knee D: Δ=-3.2±0.7°, p<.001; ND: Δ=-2.3±0.7°, p=.003), at foot contact after jumping (Hip D: Δ=-2.6±1.2°, ND: Δ=-2.9±1°, p<.05 ; Knee D: Δ=-1.6±0.6°, ND: Δ=-1.7±0.7°, p<.001), and – just for the hip joint – during landing (D: Δ=-5.4±1.4°, ND: Δ=-5±1.3°, p<.001). Finally, we found a significant and close-to-significance increase in knee valgus during landing, for the dominant (Δ=-1.9±0.6°, p=.004) and non-dominant leg (Δ=-1.2±0.7°, p=.073) respectively.
CONCLUSION:
The reduced knee flexion we observed post-cycling during landing suggests a quadriceps-dominant strategy, typically associated with increased ACL strain [3]. Additionally, the increased knee valgus we observed in the dominant leg at landing is another risk factor for ACL injury [3]. Taken together these results suggest an increased risk of ACL injury after fatigue. Additional analyses on joint moments and muscle activity will be performed to integrate these results.
REFERENCES:
1. Barber-Westin & Noyes. Am J Sports Med. 2017
2. Bourne MN, et al. Sports Med. 2019
3. Hewett TE, et al. N Am J Sports Phys Ther. 2010