Abstract
Maneuvering a motorcycle in racing conditions or for prolonged time is sufficiently demanding that on many occasions forearm muscles reach a state of functional failure when riders cannot properly brake or operate the throttle. This study intends to discriminate which ones of the several dynamometric parameters used in the literature to characterize the Force-time (F-t) curve during voluntary contractions are more sensitive to neuromuscular fatigue in simulated motorcycle-riding conditions. Thirty-three adults performed an intermittent fatiguing protocol (IFP) that simulated the brake-pulling and throttle-twisting actions, by using a hydraulic system equipped with a pressure sensor. Sixty pressure-time (P-t) curve parameters, including the rate of pressure development (RPD) and area under the curve were measured to characterize the time course of the braking maximal voluntary contraction (MVC). Two types of variables were used to analyze the P-t curve: 1) Times interval (from 0 to 30-50-100-500-1000 and 2000 ms); 2) Percentages of MVC (10-30-60-90%MVC). Overall significant (p ≤ 0.05) fatigue-related declines were observed only at time intervals longer than 100 ms and contraction intensities higher than 30%MVC. Strong and significant linear declines (p < 0.001) were observed at 500 ms and 1 s for normalized pressures, as well as for the ratio RPD60%MVC/MVC (p < 0.003) throughout the IFP. Our results suggest considering RPD at time windows of 0–500 ms and 0–1 s, and contraction intensities comprised between 30% and 60% of MVC, as more suitable criteria to study fatigue-related decrements in performance rather than the classical MVC force.
Highlights
The braking gesture on a motorcycle can be considered as a handgrip task
In comparison to baseline condition, maximal voluntary contraction (MVC) pressure decreased to 62% ±17% of its initial value in the last round of the intermittent fatiguing protocol (IFP) (p < 0.001)
Ten minutes after the end of the IFP, MVC pressure was still reduced by 19% ± 14% (p < 0.001)
Summary
The braking gesture on a motorcycle can be considered as a handgrip task. Because such repetitive movements occur in many contexts and situations such as in music, sport, or industrial work, scientific research studies reproduced them to investigate neuromuscular fatigue during continuous [1,2,3,4,5] and intermittent [2, 6,7,8] contractions. Fatigue induced by repetitive braking on a motorcycle
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