A multi-directional exploration of the relationship between sleep, appetite and exercise within middle-aged men

Sleep, eating habits and exercise are three key modifiable lifestyle behaviours that have been examined extensively independent of one another, or the relationship between two domains. However, closer examination of these behaviours collectively suggest synergistic physiological and psychological processes that interact in a complex, multi-directional fashion. Furthermore, evidence exists suggesting that middle-aged men do not currently meet minimum guidelines for sleep, diet or exercise. Therefore, the examination of the physiological and psychological implications these negative behaviours have on this population group warrant exploration. Hence, the aims of the current thesis were to i) identify relationships between sleep, appetite and exercise , ii) examine prolonged (three consecutive days) sleep manipulation on appetite-related hormones, perceived appetite and mood states, iii) examine the effects of short-duration, vigorous exercise on appetite and mood states following sleep curtailment and extension, and iv) investigate the acute sleep and appetite responses to exercise intensity and exercise time-of-day in inactive middle-aged (35 - 60 y) men.The first study (Chapter Three) of this thesis investigated the effects of prolonged sleep manipulation on appetite-related hormones, perceived appetite and mood states in inactive, middle-aged men. This study also aimed to examine whether self-paced vigorous exercise effects upregulated appetite and mood states associated with sleep curtailment (i.e. restriction and fragmentation). Nine men undertook four separate trials in a randomised fashion, which involved three consecutive nights of normal sleep (CONT: 6.5 - 8.5 h), sleep restriction (RES: 4 h), sleep fragmentation (FRAG: 6.5 - 8.5 h with intermittent alarms) or sleep extension (EXT: 10 h). Appetite-related hormones [ghrelin, leptin and total peptide tyrosine tyrosine (PYYtotal)], glucose, perceived appetite (hunger, fullness, desire to eat and prospective food consumption), food cravings (Food Cravings Questionnaire - state: FCQ-S) and mood states (POMS) were assessed after sleep manipulation and after exercise. For the exercise protocol, participants were required to complete a 20 min self-paced cycling bout clamped at a rating of perceived exertion (RPE) of 15 (hard, vigorous). After sleep manipulation and exercise, PYYtotal was lower for RES compared to EXT and FRAG (p ≤ 0.03). Also, following exercise, acylated ghrelin was higher for RES and EXT compared to CONT and FRAG (p ≤ 0.03); however, there were no between-trial differences for leptin (p > 0.05). Desire to eat and prospective food consumption were higher for RES compared to FRAG after sleep manipulation and exercise (p = 0.05). While, desire for sweet foods was higher for RES compared to CONT following sleep manipulation (p = 0.04); however, this difference was no longer present after exercise. Fatigue was higher for RES compared to all other trials after sleep manipulation (p ≤ 0.02); while perceived sleep quality was higher for CONT and RES compared to EXT and FRAG (p = 0.01 - 0.05). Interestingly, stress was higher for EXT compared to RES and CONT (p ≤ 0.02), indicating that for middle-aged adults, increasing sleep duration may not be beneficial but rather improving sleep continuity (e.g. reduce number of awakenings). Lastly, after sleep manipulation, TMD was higher for RES and FRAG compared to CONT and EXT (p ≤ 0.05); however, after exercise, mood results revealed that only fatigue remained higher for RES compared to all other trials (p ≤ 0.05). Collectively, these results suggest that while sleep curtailment may induce detrimental hormone and perceptual appetite and mood responses; short-duration, vigorous-intensity exercise may transiently attenuate these outcomes.Study Two (Chapter Four) investigated the effects of high-intensity interval exercise (HIIE) and moderate-intensity continuous exercise (MICE) on sleep characteristics, appetite-related hormones, perceived appetite and free-living energy intake in inactive, middle-aged men. For this study, 11 overweight men (49 ± 5 y, BMI: 28 ± 3 kg·m2) completed two consecutive nights of sleep assessments to determine baseline (BASE) sleep stages and arousals recorded by polysomnography (PSG). Two trials were randomly assigned on separate afternoons (1400 - 1600 h), which included a 30 min exercise bout of either i) MICE (60 % V̇O2peak) or ii) HIIE (60 s work at 100 % V̇O2peak: 240 s rest at 50 % V̇O2peak). Measures included appetite-related hormones (acylated ghrelin, leptin, PYYtotal) and glucose before exercise, 30 min after exercise and the morning after exercise; PSG recorded sleep following exercise; and actigraphy, and self-recorded sleep and food diaries up to 48 h after exercise. Results indicated that there were no between-trial differences for time in bed (TIB: p = 0.19) or TST (p = 0.99). Although, after HIIE, there was a greater proportion of stage N3 sleep (HIIE: 21 ± 7 %, BASE: 18 ± 7 %, p = 0.02) and the number of arousals during rapid eye movement (REM) sleep (HIIE: 7 ± 5, BASE: 11 ± 7, p = 0.05) were lower compared to BASE. The sleep results also indicated that wake after sleep onset (WASO) for MICE (41 ± 22 min) was lower compared to BASE (56 ± 33 min, p = 0.02). Acylated ghrelin was lower and glucose was higher 30 min after exercise for HIIE compared to MICE (p ≤ 0.05) suggesting favourable reductions in perceived hunger and energy intake. However, there were no significant differences for perceived hunger or fullness, nor did free-living energy intake decrease during the 48 h after exercise. As such, it appears that HIIE is more beneficial than MICE for improving some sleep variables and inducing transient changes in appetite-related hormones in inactive, middle-aged men; however, perceived appetite and energy intake may not be sensitive enough to these acute physiological changes.The final study (Chapter Five) examined the effects of HIIE time-of-day on sleep characteristics, appetite-related hormones, perceived appetite and free-living energy intake. Initially, participants were required to undertake two consecutive nights of PSG sleep assessments to exclude sleep disorders and obtain BASE sleep characteristics. Following BASE, 11 overweight men (49 ± 5 y, BMI: 28 ± 3 kg·m2) completed three separate trials involving 30 min of HIIE (60 s work at 100 % V̇O2peak: 240 s rest at 50 % V̇O2peak) in the i) morning (MORN: 0600 - 0700 h), ii) afternoon (AFT: 1400 - 1600 h), and iii) early evening (EVEN: 1900 - 2000 h). Appetite-related hormones (acylated ghrelin, leptin and PYYtotal) and glucose were measured before exercise, 30 min after exercise and the morning after exercise. Further, overnight PSG recorded sleep was measured the night following exercise; while actigraphy, self-reported sleep and food diaries were recorded for 48 h after exercise. Like Chapter Four, there were no between-trial differences for TIB (p = 0.10) or TST (p = 0.46). Whole-night sleep data indicated greater proportion of stage N3 sleep was recorded for MORN (23 ± 7 %) compared to BASE (18 ± 7 %; p = 0.02). However, during the initial 180 min of sleep data, REM sleep (EVEN: 8 ± 5 %, BASE: 13 ± 5 %) was lower and non-REM (NREM) sleep was higher for EVEN (92 ± 5 %) compared to BASE (87 ± 5 %, p ≤ 0.05). Acylated ghrelin was higher 30 min after exercise for AFT compared to MORN and EVEN (p = 0.01); whereas glucose was higher for MORN compared to AFT and EVEN (p ≤ 0.02). There were no significant between-trial differences for leptin and PYYtotal, perceived appetite or free-living energy intake despite significant reductions in acylated ghrelin, particularly for AFT and EVEN. Nonetheless, these findings show that HIIE can be performed safely in the early evening without subsequent sleep disruptions or detrimental perceived appetite or energy intake responses.Collectively, these studies show that inactive, middle-aged men are vulnerable to detrimental health outcomes related to negative sleep, appetite, exercise and mood behaviours. Simultaneous examination of sleep, appetite and mood revealed that insufficient sleep, and increased negative moods and stress likely result in an upregulated drive for calorie-dense food intake, while vigorous intensity exercise may transiently alleviate these detrimental effects. Further, higher exercise intensities may be required to improve some subsequent sleep and appetite-related hormone responses. However, perceived appetite and free-living energy intake may not be sensitive enough to these acute signals. Nevertheless, HIIE may be performed at any time of day without inducing subsequent detrimental effects on sleep and appetite among middle-aged, inactive men. Thus, eliminating commonly cited exercise barriers and encouraging habitual exercise that may induce improvements in greater sleep, appetite and mood behaviours overtime and reduce the risk of detrimental health outcomes.