The effects of a multimodal intervention for optimising sleep and internalising symptoms in young adults during British Army Infantry Basic Training.

STUDY OBJECTIVES: We assessed the effectiveness of a multimodal sleep intervention on subjective sleep outcomes, including insomnia symptoms, with secondary analysis of internalising symptoms in Infantry trainees. METHODS: A two-arm parallel design was employed (baseline: weeks 1-3; intervention: weeks 4-12). The evidence-based intervention involved psychoeducation, sleep hygiene optimisation, pre-bedtime routines and extended sleep opportunity. Surveys were completed at training start (pre-training status), end of week-3 (baseline), and week-12 (intervention). Linear mixed models assessed the effects of time and group (participants: age 22 ± 4.9 years; control [CON], n = 40; experimental [EXP], n = 43). The CON group followed the habitual basic training sleep schedule and environment. No women enrolled in basic training during the study period. RESULTS: Both groups experienced chronic sleep restriction, with sleep duration reduced from ~7-hours pre-training to ~5.5-hours during training, driven by earlier wake times. During the intervention, EXP shifted bedtimes ~40-minutes earlier, achieving ~30-minutes more sleep than CON and reporting significantly better sleep quality. Both groups reported increased daytime sleepiness during baseline (11.6±6.1) relative to pre-training (6.4±4.4, p<0.001) but sleepiness was significantly lower in EXP during the intervention (6.2±4.3) compared to CON (13.0±6.2, p<0.001). Controls reported significantly worse insomnia compared to EXP at pre-training (mean Δ = 2.8, p<0.01), with scores converging to subthreshold levels during baseline. EXP reported significantly less severe insomnia (4.7±2.7) compared to CON (9.1±3.7, p <0.001) during the intervention. Compared to CON, EXP reported significantly reduced stress (mean Δ -5.0, p <0.01) and clinically meaningful reductions in depressive symptoms (mean Δ -6.7 points, p<0.001) during the intervention. CONCLUSIONS: The multimodal intervention improved insomnia and internalising symptoms. As no mental health intervention was delivered; symptom improvements likely reflect sleep-mediated effects.