Evidence Of Central And Peripheral Fatigue After A Functional Fatigue Protocol

Abstract

Muscle fatigue often occurs during athletic participation, and may lead to injury. The mechanisms that produce muscular fatigue during intermittent, multi-directional exercise (e.g., soccer or basketball) remain unknown. We propose that central activation failure (CAF) will account for a major portion of the decrease in muscle force production that occurs during a functional fatigue protocol (FFP) designed to simulate high-level activities. PURPOSE: To determine the extent of central and peripheral fatigue during a FFP in unimpaired individuals. METHODS: Fourteen (7 M, 7 F) recreationally-active participants volunteered for this study (age: 21±2years, height: 175±9cm, mass: 68±8kg). The FFP consisted of a maximum-effort timed 90m agility course and 5 standing broad jumps for maximum distance. The FFP was repeated (with a 5-sec rest between each repetition) until the time to complete the agility course exceeded 150% of the initial repetition. Voluntary (MVC) and electrically-elicited (EEC) peak isometric quadriceps torque, and maximum vertical jump height (VJ), were measured pre- and post-FFP. Central fatigue was assessed by using the twitch superimposition technique to measure CAF in the quadriceps. A 130V, 10 pulse train of electrical impulses (lasting 100ms) were delivered via two electrodes placed over the quadriceps during a 3s MVC. Peak torque was calculated 100ms prior to, and immediately after the initiation of the electrical pulses. CAF was calculated as the change in peak torque (EEC-MVC) divided by the EEC torque. Peripheral fatigue was assessed by examining the change in EEC torque. Paired t-tests and bivariate correlations were performed to analyze the results between conditions. RESULTS: CAF increased post-fatigue (pre:3.5±2.8%; post:10.2±6.2%, p = 0.004). Both MVC (166.4±40.1Nm to 139.1±42.3Nm, p = 0.010) and EEC (172.7±41.8Nm to 153.7±40.7Nm, p = 0.018) decreased post-fatigue. The change in CAF was highly correlated to the loss of MVC torque (r = 0.797), explaining 59.4% of the variance (p = 0.002). VJ also decreased post-fatigue (48.5±8.3cm to 45.4±11.8cm, p = 0.034). CONCLUSION: This FFP produces significant levels of central and peripheral fatigue and decreases isometric quadriceps force and VJ height. The loss of voluntary muscle force is significantly related to the change in CAF.