Afternoon exercise best for blood sugar control in those at diabetes risk: Study

The circadian rhythmicity is regulated by a central clock, which is located in the hypothalamic suprachiasmatic nucleus (SCN), but also by multiple peripheral molecular clocks, located in distal organs such as skeletal muscle, liver, and adipose tissue. While the central clock is entrained by daily light-dark cycles, the peripheral molecular clocks are robustly entrained by non‐photic environmental signals (zeitgebers) such as exercise and feeding. Previous studies have shown that a rapid day-night shift, as a model for shiftwork or jetlag, leads to disturbed glucose homeostasis and skeletal muscle insulin resistance in humans, illustrating the indisputable role that central and peripheral molecular clocks play in regulating systemic energy homeostasis. As such, integrating different external cues at optimal times can potentially be used to improve metabolic health. However, the effect of the timing of exercise was not previously analyzed. Therefore, researchers of the Maastricht University Medical Center, Netherlands, conducted a study to compare the metabolic health effects of morning versus afternoon exercise training in metabolically compromised subjects enrolled in a 12‐week exercise training program.

It was a retrospective comparative study on 32 adult men who were at risk for or diagnosed with type 2 diabetes performed 12 weeks of supervised exercise training either in the morning (8.00–10.00 a.m., N = 12) or in the afternoon (3.00–6.00 p.m., N = 20). Researchers assessed the before, during, and after 12 weeks of exercise training maximal workload (Wmax) and maximal aerobic capacity (VO2max) during a graded cycling test with ECG monitoring until exhaustion. They used dual X‐ray absorptiometry to assess body composition.

Key findings of the study were:

♦ After 12 weeks, researchers found that compared to participants who trained in the morning, participants who trained in the afternoon experienced better effects on

              • Peripheral insulin sensitivity (+5.2 ± 6.4 vs. −0.5 ± 5.4 μmol/min/kgFFM),

              • Insulin‐mediated suppression of adipose tissue lipolysis (−4.5 ± 13.7% vs. +5.9 ± 11%),

              • Fasting plasma glucose levels (−0.3 ± 1.0 vs. +0.5 ± 0.8 mmol/l),

              • Exercise performance (+0.40 ± 0.2 vs. +0.2 ± 0.1 W/kg) and

              • Fat mass (−1.2 ± 1.3 vs. −0.2 ± 1.0 kg, p = .03).

♦ They also found that exercise training in the afternoon also tended to elicit superior effects on basal hepatic glucose output.

The authors concluded, "Our findings suggest that metabolically compromised subjects may reap more pronounced metabolic benefits from exercise training when this training is performed in the afternoon versus morning".Our findings suggest that the timing of an exercise training session is a crucial environmental cue when aiming to improve blood sugar control in metabolically compromised subjects and elucidates that performing afternoon exercise training might be more optimal than exercising at morning hours

For further information:

https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.14669