Dose–response effects of exercise training on the subjective sleep quality of postmenopausal women: exploratory analyses of a randomised controlled trial

OBJECTIVE: To investigate whether a dose–response relationship existed between exercise and subjective sleep quality in postmenopausal women. This objective represents a post hoc assessment that was not previously considered. DESIGN: Parallel-group randomised controlled trial. SETTING: Clinical exercise physiology laboratory in Dallas, Texas. PARTICIPANTS: 437 sedentary overweight/obese postmenopausal women. INTERVENTION: Participants were randomised to one of four treatments, each of 6 months of duration: a non-exercise control treatment (n=92) or one of three dosages of moderate-intensity exercise (50% of VO(2peak)), designed to meet 50% (n=151), 100% (n=99) or 150% (n=95) of the National Institutes of Health Consensus Development Panel physical activity recommendations. Exercise dosages were structured to elicit energy expenditures of 4, 8 or 12 kilocalories per kilogram of body weight per week (KKW), respectively. Analyses were intent to treat. PRIMARY OUTCOME MEASURES: Continuous scores and odds of having significant sleep disturbance, as assessed by the Sleep Problems Index from the 6-item Medical Outcomes Study Sleep Scale. Outcome assessors were blinded to participant randomisation assignment. RESULTS: Change in the Medical Outcomes Study Sleep Problems Index score at 6 months significantly differed by treatment group (control: −2.09 (95% CI −4.58 to 0.40), 4 KKW: −3.93 (−5.87 to −1.99), 8 KKW: −4.06 (−6.45 to −1.67), 12 KKW: −6.22 (−8.68 to −3.77); p=0.04), with a significant dose–response trend observed (p=0.02). Exercise training participants had lower odds of having significant sleep disturbance at postintervention compared with control (4 KKW: OR 0.37 (95% CI 0.19 to 0.73), 8 KKW: 0.36 (0.17 to 0.77), 12 KKW: 0.34 (0.16 to 0.72)). The magnitude of weight loss did not differ between treatment conditions. Improvements in sleep quality were not related to changes in body weight, resting parasympathetic control or cardiorespiratory fitness. CONCLUSION: Exercise training induced significant improvement in subjective sleep quality in postmenopausal women, with even a low dose of exercise resulting in greatly reduced odds of having significant sleep disturbance. TRIAL REGISTRATION NUMBER: clinicaltrials.gov identifier: NCT00011193.