Author(s): CLARK, B., ELLIOTT, J.D., PÉRIARD, J.D., Institution: UNIVERSITY OF CANBERRA, Country: AUSTRALIA, Abstract-ID: 1733

INTRODUCTION:
Sleep is integral to effective recovery in training and competition, whereas heat acclimation (HA) is critical to preparation for competition in hot environments. However, data on the impact of HA on sleep is limited. The aim of this study was to examine the effects of HA on indices of sleep duration and quality in well-trained endurance athletes.
METHODS:
Ten well-trained runners (3 females) participated in this study (mean ± SD: age = 30 ± 10 yr, height = 1.76 ± 0.09 m, body mass = 67.1 ± 10.9 kg, V̇O2max = 60 ± 7 mL·kg·min−1). Participants completed six weeks of normal (NORM) training followed by six weeks of HA. In NORM training, participants completed coach prescribed training in their typical training environment. During HA, participants substituted three weekly one-hour runs with a treadmill run in an environmental chamber set to 38°C and 40% RH. The HA intervention was designed in consultation with coaches and athletes to be more ecologically valid for high performance athletes, who may not be able to complete daily HA exposures. Sleep was monitored via wrist worn activity monitor in week one of NORM and in weeks one (HA1) and six (HA6) of HA. Participants also completed a brief sleep diary immediately before bed and after waking. Data from sleep diaries was used to confirm bedtime and wake time and activity monitor data was scored for time in bed (TIB), total sleep time (TST), sleep efficiency (SE), sleep onset latency (SOL) and wake after sleep onset (WASO) using the Cole–Kripke algorithm.
RESULTS:
Over the duration of the sleep monitoring periods, compliance rate for daily completion of the sleep diary was 96% and for use of the activity monitor 85%. TIB was 7.5 h [7.0, 7.9] in NORM, increased to 7.7 h [7.2, 8.2] (P<0.001) in HA1, then decreased in HA6 7.4 h [6.9, 7.9] (P=0.019). TST in NORM was 6.8 h [6.3, 7.3], which was lower than HA1 (7.0 [6.5, 7.5], P=0.02), but similar to HA6 (6.6 [6.2, 7.0], P=0.09). SE was 90.7% [88.6, 92.7] in NORM, which was similar to both HA1 (90.5% [88.6, 92.3], P=0.65) and HA6 (89.1% [87.5, 90.7], P=0.14). SOL was 3.9 min [1,4, 6.4] in NORM, which was similar to HA1 (2.8 min [0.7, 4.9], P=0.21) and HA6 (1.3 min [0.3, 2.8], P=0.10). WASO was 37.4 min [29.6, 45.2] in NORM, 41.3 [33.7, 48.9] in HA1 and 47.2 [39.1, 55.4] in HA6, which was higher than NORM (P=0.02) but not HA1 (P=0.09).
CONCLUSION:
Well-trained runners increased TIB during the first week of low density, ecologically valid HA, with a concomitant increase in TST. There was no impact of HA on SOL or SE, though WASO was greater in week 6 of HA relative to NORM training. The changes in TIB and TST were resolved by week 6 of HA and given these were modest, they are likely not of practical relevance for coaches, athletes and practitioners. Future research should investigate the influence of other HA interventions on sleep, including those using more frequent active, and passive heat exposure.