The impact of the time of day on metabolic responses to resistance exercise in healthy adults: a randomised controlled trial
Anas Dighriri, Hannah Lithgow, Greig Logan, Brendan Gabriel, Lynsey Johnston, James Boyle, Stuart Gray
Introduction:
Resistance exercise has many health benefits, including stimulation of glucose metabolism. However, the optimal time of day to perform resistance exercise is still unknown. The current study sought to determine the impact of the time of day on metabolic responses to resistance exercise in healthy adults in a randomised controlled trial.
Methods
We recruited 17 participants, inclusion criteria age between 18-45 years old with body mass index (BMI) >23.0kg/m². Exclusion criteria included having undergone surgery for weight loss, had prior history of heart, lung, cancer, kidney, endocrine, or liver disease. Participants were randomised into either a control, exercise in the morning (8:00-10am) or exercise in the evening (4:00-8:00pm) group. Those in the exercise group performed 8 resistance exercises (1 set to failure) 3 times over a one-week period, at their allocated time of day. Interstitial glucose responses were measured using a flash glucose monitoring (FGMs) for a one-week period prior to any exercise (habitual activity) and during the one-week exercise period with data compared between groups in time periods 6h post-exercise time and over 24h periods (both on exercise and non-exercise days), and over a 7-day period (exercise and non-exercise weeks).
Results
Participants were randomised to morning exercise n= 5; evening exercise; n= 6 or control group n=6. No time (exercise or no exercise days), group (control, morning or evening) or time*group interactions were seen for with mean glucose or glucose variability (measured as glucose standard deviation (SD)) in the 6h post-exercise period (all p>0.05). When comparing the 24h period no time (p=0.909), group (p=0.334) or time*group (p=0.911) interactions were seen for mean glucose. No time (p=0.537) or group (p=0.510) effects were seen for SD but a significant time*group interaction (p=0.008) was seen. Post-hoc tests revealed a lower (p=0.012) SD on exercise (0.65(0.05)) compared to no-exercise days (0.74(0.10)) within the evening group. No other differences were seen in post-hoc tests. Comparing data over a 7-day period no time, group or time*group (all p>0.05) interactions were seen for mean glucose and SD (all p>0.05).
Conclusion
The current data is part of an ongoing study, but our preliminary data indicates that there is no effect of the time of day mean glucose levels, although exercise may reduce measures of glucose variability.