Exercise is recommended for the treatment and prevention of type 2 diabetes. However, the most effective time of day to achieve beneficial effects on health remains unknown. We aimed to determine whether exercise training at two distinct times of day would have differing effects on 24 h blood glucose levels in men with type 2 diabetes.
Eleven men with type 2 diabetes underwent a randomised crossover trial. Inclusion criteria were 45–68 years of age and BMI between 23 and 33 kg/m 2 . Exclusion criteria were insulin treatment and presence of another systemic illness. Researchers were not blinded to the group assignment. The trial involved 2 weeks of either morning or afternoon high-intensity interval training (HIIT) (three sessions/week), followed by a 2 week wash-out period and a subsequent period of the opposite training regimen. Continuous glucose monitor (CGM)-based data were obtained.
Morning HIIT increased CGM-based glucose concentration (6.9 ± 0.4 mmol/l; mean ± SEM for the exercise days during week 1) compared with either the pre-training period (6.4 ± 0.3 mmol/l) or afternoon HIIT (6.2 ± 0.3 mmol/l for the exercise days during week 1). Conversely, afternoon HIIT reduced the CGM-based glucose concentration compared with either the pre-training period or morning HIIT. Afternoon HIIT was associated with elevated thyroid-stimulating hormone (TSH; 1.9 ± 0.2 mU/l) and reduced T 4 (15.8 ± 0.7 pmol/l) concentrations compared with pre-training (1.4 ± 0.2 mU/l for TSH; 16.8 ± 0.6 pmol/l for T 4 ). TSH was also elevated after morning HIIT (1.7 ± 0.2 mU/l), whereas T 4 concentrations were unaltered. Conclusions/interpretation
Afternoon HIIT was more efficacious than morning HIIT at improving blood glucose in men with type 2 diabetes. Strikingly, morning HIIT had an acute, deleterious effect, increasing blood glucose. However, studies of longer training regimens are warranted to establish the persistence of this adverse effect. Our data highlight the importance of optimising the timing of exercise when prescribing it as treatment for type 2 diabetes. Open image in new window Open image in new window Fig. 1 CGM-based glucose levels in response to HIIT. CGM-based glucose levels were assessed during the pre-training period and on exercise days (Exercise) and subsequent days (Rest). Blood glucose readings on Exercise days in ( a ) week 1 ( n = 11) and ( b ) week 2 ( n = 9), and on Rest days in ( c ) week 1 ( n = 11) and ( d ) week 2 ( n = 8). Red lines and symbols, morning exercise; blue lines and symbols, afternoon exercise; grey lines and symbols, matched pre-training days. Red arrows, time of morning exercise; blue arrows, time of afternoon exercise; grey arrows, snack offered. Using two-way ANOVA: § p < 0.05 for the effect of time; ¶ p < 0.05 for the interaction between exercise and time. Using Tukey’s multiple comparison test: * p < 0.05 for the difference between exercise trials; † p < 0.05 for the difference between morning exercise trial and pre-training period; ‡ p < 0.05 for the difference between afternoon exercise trial and pre-training period. Values are means + SEM Notes
Some of the data were presented as an abstract at the 54th annual meeting of the European Association for Study of Diabetes in 2018. The authors wish to thank J. Larsson and K. Mattsson (SATS Sports Club Sweden AB, Stockholm, Sweden) for assistance with exercise supervision and for access to the training facilities, D. Fiuza-Sanches (Clinical Physiology, Karolinska University Hospital, Stockholm, Sweden) for exercise testing, and P. Odenblad (Clinical Physiology, Karolinska University Hospital, Stockholm, Sweden) for assistance with study coordination.
The authors are supported by grants from Novo Nordisk Foundation (NNF14OC0011493 and NNF14OC0009941), Swedish Diabetes Foundation (DIA2015-052), Wenner-Gren Foundation, Swedish Research Council (2015-00165), Strategic Research Program in Diabetes at Karolinska Institutet (2009-1068), Stockholm County Council (SLL20150517 and SLL20170159) and Swedish Heart Lung Foundation (20150423).
MS and BMG designed the study, collected and analysed the data and wrote the manuscript. JS and TF collected and analysed the data and critically revised the manuscript. MB, KC and PSA designed the study, collected the data and critically revised the manuscript. AK, JRZ and HWH designed the study, analysed the data and critically revised the manuscript. All authors approved the final version of the manuscript for publication. HWH is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
The authors declare that there is no duality of interest associated with this manuscript.
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