title: Force-time course parameters and force fatigue model during an intermittent fatigue protocol in motorcycle race riders.
abstract: Fatigue in forearm muscles may be critical for motorcycle riders in relation to performance and forearm disorders. Force-time course parameters were examined to better characterize the reduction in the maximal force generating capacity (MVC) during an intermittent fatigue protocol (IFP) specifically designed for motorcycle riders. Also, a mathematical force fatigue model is proposed. Forty motorcyclists (aged 27.6 ± 6.8 years) performed an IFP that simulated the braking gesture and posture of a rider. Fatigue was confirmed by a 40% decrement of the normalized MVC in comparison with basal value. Contraction time increased in comparison with basal condition (P ≤ 0.034). Relaxation kinetics presented two phases: (a) a pre-fatigue phase where half relaxation time (HRTraw ) and normalized (HRTnor ) decreased (P ≤ 0.013) while relaxation rate (RRraw ) remained unchanged; and (b) a fatiguing phase where HRTraw , HRTnor increased and RRraw decreased (P ≤ 0.047). Normalized RRraw (RRnor ) declined progressively (P ≤ 0.016). The proposed nonlinear force fatigue model confirmed a satisfactory adjustment (R(2)  = 0.977 ± 0.018). This mathematical expression derived three patterns of force fatigue: three-phase, exponential and linear, representing 70%, 13%, and 17% of the participants, respectively. Overall, these results provided further support to force fatigue theoretical and applied proposals.
authors.affiliation: INEFC Barcelona, Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Marina
authors.affiliation: Facultad Biologia (UB), Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Rios
authors.affiliation: INEFC Barcelona, Barcelona, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Torrado
authors.affiliation: School of Health Science, Universitat Pompeu Fabra, Mataro, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Busquets
authors.affiliation: INEFC Barcelona, Barcelona, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Angulo-Barroso
mesh_terms: D000328:Adult; D004576:Electromyography; D005542:Forearm; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008962:Models, Theoretical; D009049:Motorcycles; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018908:Muscle Weakness / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult
keywords: Handgrip; contraction time; relaxation rate; relaxation time