Force Sense of the Knee Not Affected by Fatiguing the Knee Extensors and Flexors

Context: 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, which, if negatively affected by fatigue, may result 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: 20 healthy and physically active women and men (age 23.4 +/- 2.7 y, mass 69.5 +/- 10.9 kg, height 169.7 +/- 9.4 cm). Interventions: Fatigue was induced during a protocol with 2 sets of 40 repetitions, and the last set was 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 3 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 to calculate and determine median frequency shift. T tests and Wilcoxon signed-rank tests were conducted to examine prefatigue and postfatigue 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) prefatigue compared with the postfatigue condition. Conclusions: Although previous research has demonstrated that peripheral fatigue negatively affects threshold to detect passive motion (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.