Circadian rhythm phase shifts caused by timed exercise vary with chronotype

Abstract

BACKGROUNDThe circadian system entrains behavioral and physiological rhythms to environmental cycles, and modern lifestyles disrupt this entrainment. We investigated a timed exercise intervention to phase shift the internal circadian rhythm.METHODSIn 52 young, sedentary adults, dim light melatonin onset (DLMO) was measured before and after 5 days of morning (10 hours after DLMO; n = 26) or evening (20 hours after DLMO; n = 26) exercise. Phase shifts were calculated as the difference in DLMO before and after exercise.RESULTSMorning exercise induced phase advance shifts (0.62 ± 0.18 hours) that were significantly greater than phase shifts from evening exercise (-0.02 ± 0.18 hours; P = 0.01). Chronotype also influenced the effect of timed exercise. For later chronotypes, both morning and evening exercise induced phase advances (0.54 ± 0.29 hours and 0.46 ±0.25 hours, respectively). In contrast, earlier chronotypes had phase advances from morning exercise (0.49 ± 0.25 hours) but had phase delays from evening exercise (-0.41 ± 0.29 hours).CONCLUSIONLate chronotypes - those who experience the most severe circadian misalignment - may benefit from phase advances induced by exercise in the morning or evening, but evening exercise may exacerbate circadian misalignment in early chronotypes. Thus, personalized exercise timing prescription, based on chronotype, could alleviate circadian misalignment in young adults.TRIAL REGISTRATIONTrial registration can be found at www.clinicaltrials.gov (NCT04097886).FUNDINGFunding was supplied by NIH grants UL1TR001998 and TL1TR001997, the Barnstable Brown Diabetes and Obesity Center, the Pediatric Exercise Physiology Laboratory Endowment, the Arvle and Ellen Turner Thacker Research Fund, and the University of Kentucky.

Keywords: Behavior; Clinical Trials.

Conflict of interest statement

Conflict of interest: The authors have declared that no conflict of interest exists.

Figures

Figure 1. CONSORT diagram for this randomized trial.

Sixty-seven participants were randomized to morning or evening exercise, and 11 participants subsequently withdrew. Fifty-two participants were included in the analytic data set (after removing 4 participants because phase could not be determined from the melatonin data).

Figure 2. Morning exercise advances the phase of the internal circadian rhythm.

Young sedentary adults exercised for 5 days either in the morning (n = 26) or evening (n = 26). Phase shift was calculated as the difference in the timing of DLMO before and after 5 days of exercise and was adjusted for the difference in baseline DLMO between the groups. Data points are raw data. Bars are mean ± SEM from the 1-way ANCOVA model including exercise group and DLMO. *P = 0.01

Figure 3. Phase shift is correlated with internal phase in evening exercisers.

Baseline DLMO, which is marker of internal phase and a proxy for chronotype, was plotted relative to phase shift by morning (A, n = 26) or evening (B, n = 26) exercise. Data were analyzed by 2-tailed Pearson correlation.

Figure 4. The effects of timed exercise on phase shifts depend on chronotype.

Chronotype was dichotomized with a median split, and the effect of morning (n = 26) and evening (n = 26) exercise on phase shift was separately analyzed in earlier (n = 26) and later chronotypes (n = 26). Data points are raw data. Bars are mean ± SEM from 2-way ANCOVA model with exercise group and dichotomized DLMO. *P < 0.05 vs. all other groups.

Figure 5. Study protocol.

During consent, participants completed questionnaires, were measured for height and weight, and began wearing an actigraphy device. One to 9 days later, we measured baseline circadian phase with the dim light melatonin onset (DLMO) assay. Next, we took anthropometric (Anthro) and body composition (Body comp) measures and performed a maximal graded exercise test (GXTmax) to determine peak oxygen consumption (VO2peak). Participants then performed 5 days of treadmill exercise, where they maintained a heart rate corresponding to 70% VO2peak for 30 continuous minutes, in the morning or evening. One day after the final day of exercise, postexercise circadian phase was assessed by the DLMO assay.