The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise

Eur J Appl Physiol The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise 0 School of Human and Health Sciences, University of Huddersfield , Huddersfield , UK 1 Department of Sport, Exercise and Rehabilitation, Faculty of Health and Life Sciences, Northumbria University , Newcastle upon Tyne NE1 8ST , UK 2 Communicated by Peter Krustrup 3 Water Research Group, School of Environmental Sciences and Development, Northwest University , Potchefstroom , South Africa 4 Department of Sport, Health and Nutrition, Leeds Trinity University , Leeds , UK 5 Institute of Cellular Medicine, Newcastle University , Newcastle , UK Purpose This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions. Methods Ten male amateur football players completed a 120  min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response. Results At HT, FT, and ET, reductions in maximal voluntary force (MVC; −11, −20 and −27%, respectively, P ≤ 0.01), potentiated twitch force (−15, −23 and −23%, respectively, P < 0.05), voluntary activation (FT, −15 and ET, −18%, P ≤ 0.01), and voluntary activation measured with TMS (−11, −15 and −17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6-11%; ICC2,1 0.830.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5-18%; ICC2,1 0.63-0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3-6%; ICC2,1 0.90-0.98). Conclusion Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms. Brain; Central nervous system; Intermittent exercise; Muscle; Performance Mmax Maximal M-wave VATMS Association football (soccer) is a team based, high-intensity, intermittent-sprint sport typically played over 90 min. However, in certain knockout tournament scenarios (e.g., FIFA World Cup or UEFA Champions League) when a match is tied at 90 min, but requires an outright winner, an additional 30  min period of play termed extra time (ET) is required. Recently, negative impacts of this additional period of play have been shown on technical (Harper et al. 2014) and physical (Penas et al. 2015; Russell et al. 2015) performance, as well as aspects of metabolism and hydration status (Harper et al. 2016a, b, d). These negative consequences are concurrent with the greatest occurrence of contact related injuries during this time (Aoki et al. 2012). Participation in soccer results in high levels of metabolic (Rampinini et  al. 2011), mechanical (Akenhead et  al. 2013), and perceptual stress (Impellizzeri et al. 2004). The aetiology of soccer-specific fatigue, which manifests transiently during simulated and actual match-play, has been hypothesised to be due to several putative mechanisms including, compromised excitation–contraction coupling (Clarke et  al. 2015; Rampinini et  al. 2011), depletion of endogenous fuel sources (Bendiksen et al. 2012), ionic disturbances (Bangsbo et  al. 2006), and dehydration (Laitano et al. 2014). Despite these investigations, the precise mechanisms of fatigue are yet to be delineated. Fatigue in soccer has been the subject of several reviews (Bangsbo et  al. 2007; Mohr et  al. 2005; Nedelec et  al. 2012) and experimental study (Andersson et al. 2008; Oliver et al. 2008; Rahnama et al. 2006; Robineau et al. 2012), however, a limited number of investigations have attempted to quantify the neuromuscular fatigue response, with equivocal results (Girard et al. 2015; Marshall et al. 2014; Nybo et  al. 2013; Rampinini et  al. 2011). Fatigue is classically defined as an exercise-induced reduction in the ability of a muscle or muscle group to generate maximal force (Gandevia 2001), which stems from peripheral and central mechanisms. Peripheral fatigue is the loss in muscle force caused by disturbances in sites at or distal to the neuromuscular junction, whereas central fatigue is defined as a progressive, exercised-induced reduction in the voluntary activation (VA) of muscle (Gandevia 2001). Simulated and actual soccer match-play has been shown to elicit substantial peripheral fatigue (Clarke et  al. 2015; Girard et  al. 2015; Rampinini et  al. 2011) likely attributable to alterations in excitation–contraction coupling. Soccer match-p (...truncated)