Effect of Exercise Training on Sleep: Implications for the Athlete Population

Sleep is important for physiological and psychological restoration; as such, athletes are encouraged to prioritise sleep following training and competition. Despite this, both team and individual sport athletes appear to achieve inadequate sleep duration and/or quality. Among other potential factors (i.e. schedule, sleep environment and psychological factors), the demands of exercise training are suggested to determine the sleep duration of athletes. However, the effect of exercise training on nocturnal sleep in athletes is not well-understood. Consequently, the aim of this thesis was to elucidate the effect of exercise training on sleep by completing four studies, which tested different training demands encountered by athletes. Chapter 3 compared the sleeping patterns of athletes and non-athletes during a competition week. Thirty athletes (from team sports and individual sports) and non-athletes were monitored for their sleep over 7d via actigraphy and the Consensus Sleep Diary. Internal training load (duration x RPE) was also attained on each day using a diary. The athlete group had a lower sleep efficiency compared to non-athletes (81.7±4.8 vs. 85.3±4.0 %, p = 0.003, ES: 0.81 [moderate effect]) as a result of a longer sleep onset latency (18 vs. 10 min, p = 0.001, ES: 0.19 [small effect]). Athletes also displayed greater intra-individual variability in sleep onset latency compared with non-athletes (13±9 vs. 7±6 min, p = 0.002, ES: 0.78 [moderate effect]). Analysis of the training load diaries revealed team sport athletes, but not individual sport athletes, had a greater daily training load compared to non-athletes (650 vs. 333 AU, p 0.05). Nocturnal heart rate variability was not different between conditions, but average heart rate increased after high intensity interval exercise (50±5 beats·min-1) compared with low intensity exercise (47±5 beats·min-1, p = 0.02, ES: 1.73 [large effect]) and no exercise (47±5 beats·min-1, p = 0.028, ES: 0.98 [moderate effect]). This suggested endurance athletes may perform high and low intensity exercise interchangeably in the early evening without disruption to nocturnal sleep. Chapter 5 investigated the effect of a single high intensity interval training session, previously shown to reduce muscle glycogen stores ( 0.05). There was a reduction in maximum voluntary contraction at post (-6.5±2.6 %, p = 0.001), 24h post (-7.2±6.5%, p = 0.027) and 48h post (-4.4±4.4 %, p = 0.039) compared to pre exercise. Perceived muscle soreness was also higher at post (2±2 AU, p = 0.026), 24h post (4±2 AU, p = 0.027) and 48h post (4±2 AU, p = 0.034) compared to pre exercise (0±1 AU). These findings suggested reduced muscle glycogen stores did not impact sleep the night after exercise, neither did increased muscle damage on the next two nights. Thus, endurance athletes may be able to attain training adaptations using the ‘train high, sleep low’ paradigm without jeopardising subsequent nocturnal sleep. Within Chapter 6, an 8-week case study of an International Taekwondo athlete was conducted to explore the effect of low energy availability on sleep leading into competition. A tailored training and nutritional intervention was designed to achieve a 9.5kg reduction in body mass so the athlete could make weight for competition in the Bantamweight category. Each week, energy availability was calculated and actigraphy was used to measure sleep. Additionally, the athletes’ hydration status was monitored via urine osmolality, whilst their body composition was assessed using dual x-ray absorptiometry and the sum of skinfolds. There was no negative effect of low energy availability on nocturnal sleep based on the average sleep during -8 weeks to -4 and -3 weeks to the pre-cut stage (-2 before competition). Sleep duration and efficiency were within recommended values during these periods (>7h and 85% respectively [National Sleep Foundation]). However, during the days leading into competition (-5d), there was a noticeable reduction in the athletes’ sleep duration, though this was likely a reflection of their internal behaviour (i.e. choosing to make bedtime later). This case study suggested low energy availability does not impact sleep duration or quality. In conclusion, the four studies resulting from this thesis have provided further understanding of the effects of exercise training on subsequent nocturnal sleep within the athlete population. Based on this research, coaches can be more aware of typical situations that alter sleep. Subsequently, this information can be utilised in the organisation of athletes training regimes