Does Time of Day in Which Exercise Training is Performed Alter Fitness and Health Outcomes in Women?

Abstract

While there is much anecdotal evidence suggesting the importance of time of day (TOD) in which exercise training is performed, there is a paucity of controlled comprehensive studies examining the influence of TOD on training-induced adaptations. PURPOSE: to determine the effect of TOD on mediating training-induced changes in exercise performance, cardio-metabolic health, and body composition in active normal weight women. METHODS: 27 healthy active females (BMI = 24 ± 3 kg/m2; 42±8 yrs) were recruited for this study and randomized to either exercise training in morning (AM) or evening (PM) for 12 weeks. In following recent ACSM guidelines, we employed a multimodal training paradigm (Resistance, Interval, Stretching, and Endurance, RISE). Baseline exercise performance was assessed via abdominal, upper and lower body muscular strength (situps, pushups, 1 RM bench and leg presses), power (jump squats and bench throws), aerobic power (5km cycling time trial), flexibility (sit and reach), and balance (stork stand), cardiovascular health (blood pressure, and augmentation index (AIx)), body composition (iDEXA: Fat free mass, fat mass, abdominal/visceral fat, %body fat), hunger/satiety ratings (visual analog scales), and cardio-metabolic profile (energy expenditure, fasting lipids, glucose, insulin). RESULTS: At baseline, no differences existed between groups in any variable. Training resulted in significant (p<0.05) improvements in exercise performance, cardio-metabolic health, and body composition. However, there were significant interactions (p<0.05) of TOD x training for DBP (-10±1 v. -5±5ΔmmHg), RMR (-130±65 v. -12±36 Δkcal/d), FM (-1.0±0.2 vs. -0.3±0.2 Δkg), Abfat (-2.6±0.3 v. -0.9±0.5 Δkg), 1RM BP (8±2 v. 12±2 Δlb), Pushups (9±1 v. 13±2Δreps), BT power (10±6 v. 45±28 Δwatts), SJ power (135±6 v. 39±8 Δwatts), AM vs. PM, respectively. CONCLUSIONS: The multimodal RISE protocol improved performance, cardiovascular health, and body composition, with the TOD altering the magnitude of exercise training-induced adaptations. Specifically, training in the AM resulted in greater improvements in diastolic blood pressure, fat mass, abdominal fat mass, and lower body peak power. Whereas, training in the PM resulted in greater gains in upper body muscle strength, endurance, and power. Support: Isagenix.