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Randomized Controlled Trial
. 2019 Feb;62(2):233-237.
doi: 10.1007/s00125-018-4767-z. Epub 2018 Nov 13.

Afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes: a randomised crossover trial

Mladen Savikj  1   2 , Brendan M Gabriel  1 , Petter S Alm  1 , Jonathon Smith  1 , Kenneth Caidahl  3   4 , Marie Björnholm  3 , Tomas Fritz  3   4 , Anna Krook  1 , Juleen R Zierath  1   3   5 , Harriet Wallberg-Henriksson  6
Affiliations
Randomized Controlled Trial

Afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes: a randomised crossover trial

Mladen Savikj et al. Diabetologia. 2019 Feb.

Abstract

Aims/hypothesis: 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.

Methods: 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/m2. 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.

Results: 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 T4 (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 T4). TSH was also elevated after morning HIIT (1.7 ± 0.2 mU/l), whereas T4 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.

Keywords: Blood glucose level; Circadian rhythm; Continuous glucose monitoring; Exercise; High-intensity interval training; Type 2 diabetes.

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Conflict of interest statement

The authors declare that there is no duality of interest associated with this manuscript.

Figures

Fig. 1
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
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