Poster Presentation ANZOS-Breakthrough Discoveries Joint Annual Scientific Meeting 2018

Effects of high-intensity interval training performed in the morning or evening on 24 h blood glucose profiles (#237)

Samuel K Pinto 1 , Trine Moholdt 1 2 , Evelyn B Parr 1 , Brooke L Devlin 1 , David W Dunstan 1 3 , John A Hawley 1
  1. Exercise & Nutrition Research Program, Mary MacKillop Institute for Health Research, Australian Catholic University, Fitzroy, Victoria, Australia
  2. Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway
  3. Baker Heart and Diabetes Institute, Melbourne, Victoria, Australia

Exercise and restriction of dietary carbohydrate (CHO) independently reduce daily glycaemia, but their combined effects on glycaemic control are unclear. Furthermore, diurnal rhythms exist in many physiological processes, including glucose metabolism, and it is unknown whether the time of day that exercise is performed alters glycaemic responses. We examined the effects of short-term high-intensity interval-training (HIIT) performed in the morning or evening on 24-h glycaemia during CHO-restriction.

Twenty-four sedentary males with overweight/obesity (age:36±5 y, BMI:31.2±2.3 kg/m2) participated in this randomized, three-armed parallel study (n=8/group). Participants consumed their habitual diet for 3-d (D1-3; Baseline), followed by 5-d of CHO-restriction (D4-8; Diet-only; 15% CHO, 65% fat, 20% protein). Participants completed a further 5-d (D9-13; Diet+Training) of CHO-restriction and either daily cycle ergometer exercise at 0630 h (AM-Ex), daily exercise at 1830 h (PM-Ex), or diet-only (CON). Training consisted of three HIIT sessions (10x1 min at ~90% of peak heart rate) and two continuous cycling sessions (40-60 min at 60-70% of peak heart rate). Interstitial glucose was measured via continuous glucose monitoring from D1-13.

Mean 24-h glucose was reduced in AM-Ex (-0.16 mmol/L, 95%CI:-0.01–0.30, P=0.04) and PM-Ex (-0.30 mmol/L, 95%CI:-0.46–0.14, P<0.001) during Diet-only compared to Baseline, with no difference between Diet-only and Diet+Training for any group. Nocturnal glycaemia was reduced in PM-Ex during Diet+Training compared to Baseline (-0.62 mmol/L, 95%CI:-0.90–0.34, P<0.001) and Diet-only (-0.41 mmol/L, 95%CI:-0.62–0.19, P<0.001), but was unaltered in AM-Ex and CON.

These findings suggest that during CHO-restriction, short-term HIIT performed in the evening, but not the morning, may reduce nocturnal glycaemia in men with overweight/obesity. These effects may be partly due to differences in nutrient availability or hormonal milieu between morning and evening exercise. Targeted exercise with regards to timing may elicit more favourable nocturnal glycaemic control.

Research supported by Novo Nordisk Foundation Challenge Grant NNF14OC0011493.