The impact of mental fatigue on pacing strategies1 Opinion
An inability to be able to pace yourself can be deleterious to one’s performance, as an individual must be able to carefully select the appropriate distribution of efforts as to avoid falling behind in a race. Originally, the capacity to do so was thought to be controlled by a mechanistic determination based on an athlete’s physiology; as such, a runner may be limited by lactate concentration in the blood. However, latterly it is stipulated that afferent feedback to the brain in response to physiological stimuli such as increases in heart rate, core and skin temperatures, glycogen concentrations and exercise intensity as well as environmental cues including temperature and partial pressure of oxygen of the inspired air, serves to aid the brain in forecasting exercise duration to avoid causing harmful homeostatic derangements (Tucker, 2009).
An anticipatory model has been used to describe how exercise is regulated at a self-selected pace. This theory develops the claim that rate of perceived exertion (RPE) is used as a form of conscious feedback integration against a template anticipatory forecasting in order to make an informed decision of the best pace to select. The acquisition of such complex systems requires previous experience and training as well as afferent inputs from the environment. The athlete is usually aware of the projected distance or time, and based on these factors, the athlete can select an initial exercise intensity which will best suit the exercise and continue to appropriately augment their work-rate and RPE as a means of matching conscious and anticipated RPE (Tucker, 2009).
However, new studies (Brownsberger et al, 2013 & McCarron et al, 2013) are beginning to emerge which suggest that interactions between physical and cognitive effort can be disrupted by previous increments in cognitive load. Research investigating whether mental fatigue influences voluntary effort during self-paced exercise has demonstrated that cognitive fatigation can negatively influence endurance performance, which is purported to be a result of an alteration in perception of effort. Sensations of tiredness can manifest themselves as a reduction in decision making ability as well as affecting attention, motivation and voluntary willingness to suppress fatigue.
Evidence supporting the use of the brain to control pace selection through exercise may lie in the findings from McCarron et al (2013) who found that increasing cognitive load through means of a Wisconsin Card Sorting Task (WCST) during a 5 km run negatively impacted on performance. This propounds the view that pre-frontal regions may have a mediating role on pace regulation during 5 km running. This is premised on the assumption that performance in the WCST is associated with activity in these areas, and individuals with frontal lobe lesions have previously shown more perseverative errors during the WCST than patients with lesions in other parts of the brain or healthy controls.
Similarly, Browsnberger et al (2013) purported that completion of a 90 minute pre-exercise task of continuous cognitive activity resulted in decrements in power production during self-paced exercise. A closer look at the data yielded shows that subjects also exhibited great β-band activation of the frontal lobe. Brownsberger and colleagues (2013) puts forward the view that afferent physiological information may not be the only mediator of voluntary regulation of effort during exercise, but also central factors such as the negative cognitive associations sensations of mental fatigue immediately prior to exercise. Additionally, subject’s heart rates remained similar in both experimental and control conditions, elucidating that physiological stress was similar for that period.
Although there has been relatively little research into this area, current research appears to validate the view that mental fatigue could have a draining effect on exercise, and increase perception of effort. As a result, athletes may perceive the upcoming exercise to be more strenuous than mentally alert athletes and reduce their work-rate or power output. This coincides with psychophysiological studies which postulate that mental fatigue increases effort responses to performance challenges and lowers the level of task difficulty in which individuals are willing to withhold effort (Wright et al, 2008). A possible mechanism underlying this could be that mental fatigue affects the central processing of sensory inputs which generates the perception of effort during exercise. Alternatively, mental fatigue could directly affect the cortical centres in which the cognitive aspects of centre motor command control perceived exertion (Marcora et al, 2009).
This is an important connection to make, as mental fatigue can consequently have negative implications for performance. The premise behind this indicates that the brain does not regard just the afferent peripheral physiological information, for instance muscle soreness, respiratory discomfort or changes in pH; but also psychological factors such as perceived tiredness. This could be used to explain why some athlete do not perform as well in the evening and why they often attribute poor performances to being mentally tired. Further research in this area may include attempting to elucidate whether this novel concept has applications out of endurance exercise and whether sports requiring more cognitive reasoning may result in athletes fatiguing quicker than sports which require less tactical play.
Brownsberger, J., Edwards, A., Crowther, R., & Cottrell, D. (2013) Impact of Mental Fatigue on Self-paced Exercise. Int J Sports Med, 34: 1029-1036.
Marcora, S.M., Staiano, W., & Manning, V. (2009) Mental fatigue impairs physical performance in humans. J Appl Physiol, 106: 857-864.
McCarron, J., & Smith, M.F. (2013) Brain drain: the impact of increased cognitive load on self-paced running performance. In: International Sport Science and Sports Medicine Conference, 21-23 August 2013, United Kingdom.
Tucker, R. (2009) The anticipatory regulation of performance: the physiological basis for pacing strategies and the development of a perception based model for exercise performance. Br J Sports Med, 43: 392-400.
Wright, R.A., Stewart, C.C., Barnett, B.R. (2008) Mental fatigue influence on effort-related cardiovascular response: extension across the regulatory (inhibitory)/non-regulatory performance dimension. Int J Psychophysiol, 69: 127-133.
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Optimising sporting performance through the provision of physiological and nutritional support