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Combatting the war on sleep: Investigating sleep and recovery in the military

The military setting often includes continuous operations, whether in training or deployed environments. These often-stressful environments present unique challenges for service members to achieve both intra-day and inter-day recovery. This thesis aimed to investigate the physical fitness levels, sleep, and recovery of military personnel (Army, Navy, and Air Force), which have been deemed as essential for daily task completion and safe operation during military training and deployment. The physical fitness levels of trainees entering military service are of major interest internationally. In Study One, 116 participants were assessed for 2.4 km run times, muscular endurance (press-ups and curl-ups), body mass, and Y-balance musculoskeletal screening, before and after a 6-week Joint Officer Induction Course. In general, fitness levels were poor compared to entry-level standards over the last 4–5 years, and it was shown that significant improvements could be made over 6 weeks in aerobic fitness and upper-body and core muscular endurance across all services. Of note, Army personnel performed better in the 2.4 km run and press-ups compared to other services (p < 0.05), and Navy personnel performed better in curls-ups. At completion of the course, there were significant improvements in 2.4 km run time (p = 0.02), press-ups (p = 0.04), and curl-ups (p = 0.01) across all services. However, it was evident that there were poor levels of perceived recovery and sleep over the duration of the 6-week course. In an attempt to improve day-to-day recovery, Study Two investigated the influence of wearing lower-body compression garments (CG) on changes in physical performance, subjective soreness, and sleep quality over 6 weeks of military training. Twenty-seven participants wore CG every evening for 4–6 h, and 28 wore standard military attire (CON), over a 6-week period. Subjective questionnaires (soreness and sleep quality) were completed weekly, while 2.4 km run times, maximum press-ups, and curl-ups were tested before and after 6 weeks of military training. There were small benefits in favour of CG over CON for improvements in 2.4 km run times (d = −0.24) and press-ups (d = 0.36). While not statistically significant, CG provided small to moderate benefits to perceived muscle soreness. Study Two again highlighted that poor sleep was a concern during the initial military training courses. In Study Three, 22 officer-trainees wore wrist actigraphs for 36 nights to monitor sleep, completed subjective well-being questionnaires weekly, and were tested for: 2.4 km run times, and maximum press-ups and curl-ups before and after 6 weeks of training. The sleep mid-point of 6:15 h:min was used to stratify the trainees into two quantile groups, UNDERS (5:51 ± 0:29 h:min [mean ± SD], n = 11) and OVERS (6:27 ± 0:09 h:min, n = 11). Subjective wellbeing scores demonstrated a significant group × time interaction (p < .05), with large effect sizes in favour of the OVERS group for fatigue and soreness at various time points. Sleeping more than 6:15 h:min per night over 6 weeks was associated with small benefits to aspects of physical performance when compared with sleeping less than 6:15 h:min. Given these results in relation to physical performance and well-being with increased sleep, we conducted a follow-up study to investigate interventions to enhance sleep in the military setting. In Study Four, before investigating a sleep intervention (Study Five), we compared manually-scored with automatic-scoring actigraphy devices. Sixty nights of sleep data from 20 healthy adult participants were assessed by concomitantly wearing an automatic scoring device (Fatigue Science Readiband™) and a manually-scored device (Micro Motionlogger®). Sleep indices including total sleep time (TST), total time in bed (TIB), sleep onset latency (SOL), sleep efficiency (SE%), wake after sleep onset (WASO), wake episodes per night (WE), sleep onset time (SOT), and wake time (WT) were assessed between the two devices. There were no significant differences between devices for any of the measured sleep variables (p > 0.05). All sleep indices resulted in very-strong correlations (r's >0.84) between devices. A mean difference between devices of <1 min for TST was associated with a typical error of measurement TEM of 15.5 mins (95% CI, 12.3–17.7 min). Given there were no significant differences between devices in the current study, we identified that these two devices could be used concurrently for the interventional study (Study Five). In the final study, Study Five, 64 officer-trainees wore wrist actigraphs for 6 weeks during initial military training to quantify sleep metrics. Participants were randomly allocated to either: a low-temperature lighting group (LOW, n = 19), standard-temperature lighting with no adjustment to lights but with a placebo ‘sleep-enhancing’ device placed in the barrack room (PLA, n = 17), or a control group of standard-temperature lighting (CON, n = 28). The lighting environments referred to their living quarters, where they resided from 1800h each night during the 6-week training camp. A significant group x time interaction was observed for the 2.4 km run, with the improvement in LOW (Δ92.3 s) associated with a large improvement when compared to CON (Δ35.9 s; p = 0.003; d = 0.95), but not PLA (Δ68.6 s). Similarly, curl-up improvement resulted in a moderate effect in favour of LOW (Δ14 repetitions) compared to CON (Δ6; p = 0.063; d = 0.68). Chronic exposure to low-temperature lighting was associated with benefits to aerobic fitness across a 6-week training period, with minimal effects on sleep measures. In summary, the series of studies in this thesis provides a foundation for better understanding the physical fitness characteristics, as well as sleep and recovery considerations in the military setting. Although trainees present to initial training with low levels of fitness, significant improvements can be made over a 6-week training period. It was also identified that recovery and sleep are generally poor during these initial military training courses. However, the use of recovery interventions, such as CG, can provide some benefits to perceived muscle soreness, physical performance, and improvements in sleep over the duration of these courses that translated into benefits to physical adaptation to training. Results from this thesis enhance our understanding of sleep and recovery in military trainees. This work may help to inform decision-making in the design and implementation of intensive military courses, highlighting the need for a greater emphasis on sleep and recovery practices to enhance both the physical adaptation to training and the overall well-being of recruits.
Type of thesis
The University of Waikato
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