Daytime naps and night-time sleep quality in athletes and the general population

Theoretically, the relationship between daytime napping and night-time sleep can be reciprocal, with napping compromising nightly circadian sleep pressure, while the resulting degraded sleep quality increases nap propensity. However, while this relationship has been suggested as a perpetuating factor for insomnia disorder and the principal mechanism mediating nap behaviour in elite athletes, it is not strongly supported by empirical evidence. The aim of this thesis was to explore the causes and consequences of napping behaviour in elite athletes, non-elite athletes and non-athletes. The programme utilised quantitative and qualitative data collection, combined cross-sectional and longitudinal designs, and developed hypotheses from conclusions and assumptions reflected in the present sport and sleep literature. Following a detailed review of the epidemiological literature on napping prevalence and natural history, a cross-sectional online survey (Study 1) mapped the napping behaviour of competitive athletes (N=158) and healthy non-athletes (N=82) in relation to sleep quality and quantity, daytime sleepiness and fatigue, and levels of arousal. Both athlete and non-athlete nappers showed higher levels of daytime sleepiness. However, independent of athlete/non-athlete status, cognitive arousal demonstrated a significant moderating effect on sleepiness, with the nappers that showed lower levels of pre-sleep arousal reporting lower levels of sleepiness than the nappers with higher levels of pre-sleep arousal. Athletes also shared the same risk factors for insomnia symptoms as non-athletes: 1) higher age; 2) higher levels of anxiety symptoms; 3) and higher levels of pre-sleep arousal. Study 2 responded to the unique opportunity, created by mandatory home confinement, to explore the daytime napping, sleep schedules and sleep-related characteristics, and insomnia symptoms of elite athletes (N=74) in the absence of the typical athletic lifestyle (using pre-confinement and confinement measures). Results from pre-confinement showed levels and patterns of napping similar to those reported in Chapter 2, and confirmed the interactive role of sleepiness and pre-sleep arousal in mediating naps. The Covid-19 confinement period was associated with: 1) a significant phase delay; 2) significant increases in time in bed and sleep duration; 3) a significant reduction in social jet lag; 4) a mean sleep efficiency consistent with good quality sleep for most athletes; 5) a reduced prevalence of insomnia symptoms (from 74.3% to 48.6%); 6) and a reduced prevalence of napping (from 50% to 31.1%). These results suggest the expression of phenotypic preferences in the absence of routine demands from elite sport. Studies 1 and 2 offered some evidence of napping-insomnia linkage from cross-sectional studies of specialised samples. Using data from a 1-year (baseline to 12-month follow-up) longitudinal study of 488 adults in the United States (all good sleepers at baseline), Study 3 explored the role of napping, individually and when considered as time in bed over 24-h, in the onset and patterning of insomnia. Regression modelling showed that napping (reported at baseline) increased the risk of insomnia symptoms at 1-year, while longitudinal modelling indicated that increases in both napping and 24-h time in bed, resulted in a tendency to present insomnia later in the year. Finally, Study 4 used qualitative and quantitative approaches to clarify the life circumstances, personal experience and the perceived mechanisms by which napping athletes actually transition from good sleep to insomnia. From 12 interviews conducted amongst competitive younger athletes (18+) thematic analysis identified common themes: 1) the emergence of sleep problems and the adoption of napping occurring with the start of university; 2) the adoption of napping in response to both poor sleep, and as a strategy to optimise performance; 3) cognitive arousal listed as the main reason for napping failure; and 4) recognition of napping as potentially harmful to broader sleep management.

From these 4 studies, the following key findings address present hypotheses and can guide future research: 1) napping and non-napping behaviours are complex predispositions influenced by sleep pressure (sleepiness) and cognitive arousal; 2) among nappers, higher levels of pre-sleep arousal can be compensated for by higher levels of sleepiness; 3) in terms of prevalence, causes and consequences, naps among athletes share the same general dynamics as naps within the general population.