Force sense of the knee is not affected by fatiguing the knee extensors and flexors

: Knee injuries commonly occur in later stages of competition indicating that fatigue may influence dynamic knee stability. Force sense (FS) is a submodality of proprioception influenced by muscle mechanoreceptors, and, if negatively affected by fatigue, may results in less effective neuromuscular control. OBJECTIVES: To determine the effects of peripheral fatigue on FS of the quadriceps and hamstrings. DESIGN: Quasi-experimental study design. PARTICIPANTS: Twenty healthy and physically active females and males (age: 23.4±2.7 years, mass: 69.5±10.9kg, height: 169.7±9.4cm) participated. INTERVENTIONS: Fatigue was induced during a protocol with two sets of 40 repetitions, and the last set truncated at 90 repetitions or stopped if torque production dropped below 25% of peak torque. MAIN OUTCOME MEASURES: FS of the hamstrings and quadriceps was tested on separate days before and after three sets of isokinetic knee flexion and extension to fatigue by examining the ability to produce a target isometric torque (15% MVIC) with and without visual feedback (FS Error). Electromyographic data of the tested musculature were collected in order to calculate and determine median frequency shift. T-tests and Wilcoxon Signed Rank tests were conducted to examine pre-fatigue and post-fatigue FS Error for flexion and extension. RESULTS: Despite verification of fatigue via torque production decrement and shift in median frequency, no significant differences were observed in FS Error for either knee flexion (pre=0.54±2.28 N·m; post=0.47±1.62 N·m) or extension (pre=-0.28±2.69 N·m; post=-0.21±1.78 N·m) pre-fatigue compared to the post-fatigue condition. CONCLUSIONS: Although previous research has demonstrated that peripheral fatigue negatively affects TTDPM, it did not affect FS as measured in this study. The peripheral fatigue protocol may have a greater effect on the mechanoreceptors responsible for TTDPM than those responsible for FS. Further investigation into the effects of fatigue across various modes of proprioception is warranted.