Background Intact proprioception (joint position sense (JPS), kinaesthesia, force sense (FS)) is critical for optimal neuromuscular control of knee functional joint stability. Fatigue is known to impair knee JPS and kinaesthesia, but research regarding the effect of fatigue on knee FS is lacking.
Objective To determine the effect of functional fatigue on knee extension FS in uninjured, adult, male football players. It was hypothesized that functional fatigue would result in significant impairment of FS.
Design Single-session, pre-/post-intervention repeated measures.
Setting University sensorimotor control and biomechanics laboratory.
Participants University team players (n=21; age (mean±SD) 21.0±1.2 years; height 178.7±7.2 cm; mass 76.8±11.5 kg; training×2/week; match×1/week) without history of knee intra-articular derangement or surgery.
Interventions Functional fatigue was defined/induced using the previously published Functional Agility Short-Term Fatigue Protocol (FAST-FP). The FAST-FP incorporated acceleration-deceleration tasks typical of football training/match play.
Main Outcome Measures Dominant leg (preferred kicking leg) knee extension FS was measured in Newtons (N). Players were seated on an isokinetic dynamometer set to isometric mode, the knee flexed 45°. A knee extension target trial-reproduction trial sequence was repeated five times, the difference between trials designated the absolute error (AE), the average AE used for data analyses. Reliability and measurement error for this procedure has been previously established. Force sense measurements were performed before and immediately after the FAST-FP. The FS and FAST-FP procedures were adjacent in the same laboratory space with minimal transition time between tasks.
Results Force sense AE significantly increased following fatigue (pre-fatigue=10.9±5.8 N; post-fatigue=23.0±9.2 N; difference=12.1±7.9 N; P=0.00; d=1.59).
Conclusions Dominant leg knee extension FS was significantly impaired following functional fatigue. Fatigue-induced impairment of FS could result in sub-optimal neuromuscular control and altered knee functional joint stability that affects knee injury risk.