ORIGINAL ARTICLE Effects of isolated locomotor muscle fatigue on pacing and time trial performance Helma M. de Morree • Samuele M. Marcora Received: 10 December 2012 / Accepted: 30 May 2013 / Published online: 12 June 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Purpose Locomotor muscle fatigue impairs exercise performance during time to exhaustion tests. However, its effect on self-regulation of power output (pacing) is unknown. The primary aim of this study was to investigate the effects of locomotor muscle fatigue on pacing and time trial performance. Methods Ten healthy recreationally active men com- pleted a 15-min time trial on a cycle ergometer 30 min after undergoing an eccentric fatiguing protocol designed to induce a substantial strength loss in the knee extensor muscles without inducing significant metabolic stress. This fatigue condition was compared with a control condition, using a randomly counterbalanced AB/BA crossover design. Results Total work completed during the 15-min cycling time trial was significantly reduced by 4.8 % in the fatigue condition compared with the control condition. This was caused by a significant reduction in power output. Rating of perceived exertion was significantly higher in the fatigue condition compared with the control condition only during the first 3 min of the time trial. Heart rate and vastus lateralis integrated electromyogram were not significantly different between the two conditions. Conclusion The results show that participants with fati- gued locomotor muscles reduce their pace but do not change their pacing strategy. As a result, there was a sig- nificant reduction in time trial performance. As predicted by the psychobiological model of exercise performance, a slower pace may be a behavioral response to compensate for the significant increase in perception of effort induced by locomotor muscle fatigue. Keywords Perception of effort Á Cycling exercise Á Eccentric fatigue Á Pacing strategy Á Exercise tolerance Á Electromyography Introduction Pacing refers to the self-regulation of speed/power output during endurance competitions and exercise performance tests in which the participant is free to vary the workload (time trials). Many physiological, psychological, and environmental factors are known to affect time trial per- formance and/or pacing (Tucker and Noakes 2009). These include hypoxia (Clark et al. 2007), environmental tem- perature (Peiffer and Abbiss 2011), hydration status (Dugas et al. 2009), caffeine ingestion (Wiles et al. 2006), moti- vation (Corbett et al. 2012), and music (Atkinson et al. 2004). The effects of locomotor muscle fatigue on pacing and time trial performance are, however, poorly under- stood. This is surprising if we consider that an exercise- induced reduction in muscle strength/power is considered by many as the ultimate factor limiting exercise perfor- mance (Allen et al. 2008; MacIntosh and Shahi 2011; Communicated by Toshio Moritani. H. M. de Morree Á S. M. Marcora School of Sport, Health and Exercise Sciences, Bangor University, Bangor, UK H. M. de Morree Department of Medical and Clinical Psychology, Center of Research on Psychology in Somatic Diseases (CoRPS), Tilburg University, Tilburg, The Netherlands S. M. Marcora (&) Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Chatham, Kent ME4 4AG, UK e-mail: s.m.marcora@kent.ac.uk 123 Eur J Appl Physiol (2013) 113:2371–2380 DOI 10.1007/s00421-013-2673-0