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.