“What causes task failure during a fatiguing contraction? ” This approach is described by considering how variation in the type of load supported and contraction intensity influence both the time to task failure and the centrally mediated adjustments in reflex activity and motor unit behavior. Keywords: central nervous system, electromyogram, force task, motor units, position task, reflexes INTRODUCTION: WHAT CAUSES MUSCLE FATIGUE? Muscle fatigue is defined as an exercise-induced reduction in the maximal force capacity of the muscle (10). The classic approach used to identify the cause of muscle fatigue has been to distinguish between neural and muscular mechanisms.

Abstract: This study was designed: (1) to test the reliability of surface electromyography (sEMG) recording of the diaphragm and external intercostals contractions response to cervical magnetic stimulation (CMS), (2) to examine the amount and the types of inspiratory muscle fatigue that developed after maximum voluntary ventilation (MVV) maneuvers.Ten male college students without physical disability (22.1±2.0 years old) participated in the study and each completed a control (quiet breathing) trial and a fatigue (MVV maneuvers) trial sequentially. In the quiet breathing trial, the subjects maintained quiet breathing for five minutes. The subjects performed five maximal static inspiratory efforts and received five CMS before and after the quiet breathing. In the MVV trial, subjects performed five maximal inspiratory efforts and received five CMS before, immediately after, and ten minutes after two sets of MVV maneuvers performed five minutes apart. Maximal inspiratory pressure (PImax), sEMG of diaphragm and external intercostals during maximal static inspiratory efforts and during CMS were recorded. In the quiet breathing trial, high intraclass correlation coefficients (ICC=0.95-0.99) were observed in all the variables. In the MVV trial, the PImax, the EMG amplitude and the

Objectives: A recent editorial in Medicine and Science in Sports and Exercise concludes that the study of Hawkins and colleagues confirms ‘‘beyond any doubt the proposition of Hill and Lupton’’. It is not clear which of Hill and Lupton’s propositions have been proved ‘‘beyond any doubt’’. Methods: A review of all the relevant publications of A V Hill and his colleagues. Results: Hill and Lupton believed (i) that myocardial ischaemia limits maximal exercise performance by inducing circulatory failure; (ii) that a ‘‘governor’ ’ protects the ischaemic heart by causing a ‘‘slowing of the circulation’ ’ during maximal exercise; (iii) that the oxygen cost of running increases exponentially at speeds above 16 km per hour; and (iv) that humans reach their highest