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ARTICLES: Sandra K. Hunter, Tejin Yoon, Joseph Farinella, Erin E. Griffith, and Alexander V. Ng Time to task failure and muscle activation vary with load type for a submaximal fatiguing contraction with the lower leg J Appl Physiol 2008; 105: 463-472 [Abstract] [Full text] [PDF]

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Muscle fatigue does not cause exhaustion

Samuele M Marcora   (16 June 2008)

Muscle fatigue does not cause exhaustion 16 June 2008
Samuele M Marcora, Senior Lecturer in Exercise Physiology School of Sport, Health and Exercise Sciences, Bangor University, Wales, UK Send letter to journal: Re: Muscle fatigue does not cause exhaustion s.m.marcora{at}bangor.ac.uk Samuele M Marcora	Since the time of AV Hill, the physiological model of exercise performance rests on the assumption that muscle fatigue (defined as an exercise-induced reduction in maximal voluntary force/power) causes task failure/exhaustion (2). In other words, it is assumed that exercise is terminated when the subject is unable to produce with his/her fatigued neuromuscular system the force/power required by the task despite maximal voluntary effort (1, 4). The solid findings presented by Hunter et al. (3) confute this basic assumption. Indeed, immediately after exhaustion, the fatigued neuromuscular system of their subjects could produce 3.5 times the force required by the two submaximal exercise tasks. So what caused exhaustion? According to our psychobiological model of exercise performance based on motivational intensity theory (5), task failure is actually task disengagement. This means that subjects take the conscious decision to withdraw voluntary effort when they perceived it to be equal to the maximal effort they are willing to invest in the task (the so called-potential motivation) or ii) when they believe to have exerted a true maximal effort and, therefore, continuation of the task is perceived as impossible. The data presented in Fig. 7C of Hunter and colleagues’ study are clearly consistent with this motivational theory. Therefore, we believe that a paradigm shift is necessary: physiologists interested in the limits of exercise performance should study the neurobiology of perceived exertion and effort-based decision making rather than the central and peripheral mechanisms of muscle fatigue as dictated by the current physiological model of exercise performance (6). References 1. Allen DG, Lamb GD, Westerblad H. Skeletal muscle fatigue: cellular mechanisms. Physiol Rev. 2008; 88: 287-332. 2. Gandevia SC. Spinal and supraspinal factors in human muscle fatigue. Physiol Rev. 2001; 81: 1725-89. 3. Hunter SK, Yoon T, Farinella J, Griffith EE, Ng AV. Time to Task Failure and Muscle Activation Vary with Load Type for a Submaximal Fatiguing Contraction with the Lower Leg. J Appl Physiol. 2008; doi:10.1152/japplphysiol.90398.2008. 4. Jones AM, Wilkerson DP, DiMenna F, Fulford J, Poole DC. Muscle metabolic responses to exercise above and below the "critical power" assessed using 31P-MRS. Am J Physiol Regul Integr Comp Physiol. 2008; 294: R585-93. 5. Marcora SM, Bosio A, de Morree HM. Locomotor muscle fatigue increases cardiorespiratory responses and reduces performance during intense cycling exercise independently from metabolic stress. Am J Physiol Regul Integr Comp Physiol. 2008; 294: R874-83. 6. McKenna MJ, Hargreaves M. Resolving fatigue mechanisms determining exercise performance: integrative physiology at its finest! J Appl Physiol. 2008; 104: 286-7.