Exercise Timing Linked to Cardiorespiratory Fitness in Men With T2D

Timing of bout-related moderate-to-vigorous physical activity (MVPA) is associated with cardiorespiratory fitness and cardiovascular risk among men with type 2 diabetes (T2D), independent of bout-related MVPA volume and intensity, according to research published in Diabetes Care.

Although regular physical activity (PA) is an important component of blood glucose management and overall cardiovascular health in individuals with prediabetes and diabetes, few studies have examined the role that time of day of bout-related MVPA plays in this population.

Using baseline data from the Look AHEAD Study, investigators aimed to characterize the temporal distribution of bout-related MVPA in adults with overweight/obesity and T2D, define whether the timing varies according to sociodemographic or anthropometric factors, and determine associations of timing of bout-related MVPA with baseline cardiorespiratory fitness and risk for coronary heart disease (CHD).

The Look AHEAD Study randomized adults (n = 5145) with overweight/obesity and T2D to an intensive lifestyle intervention or diabetes support and education program. All participants in the current analysis (n = 2035) completed baseline testing prior to randomization, had been diagnosed with T2D, had a body mass index (BMI) of at least 25 kg/m² (or ≥27 kg/m² when taking insulin), and were between the ages of 45 and 76 years.

Throughout the study period (1 week), “participants were instructed to wear the hip-mounted RT3 triaxial accelerometer for 7 consecutive days during waking hours, removing it only for periods of sleep, bathing, showering, or other water-based activities,” and they were instructed not to alter their habitual PA patterns while wearing the device.

To determine intensity of physical activity (expressed in metabolic equivalent tasks [METs]), researchers divided the estimated energy expenditure per minute by estimated resting energy expenditure per minute, computed using the software.

“Periods of MVPA were defined as ≥3 METs. Bout-related MVPA was defined as any activity ≥3 METs and ≥10 minutes in duration, allowing for a 1-2 minutes interruption in MVPA,” the authors wrote. In addition, “Participants were categorized into 6 groups based on the time of day with the majority of bout-related MVPA (MET× min): ≥50% of bout-related MVPA during the same time window (morning, midday, afternoon, or evening), <50% bout-related MVPA in any time category (mixed; the reference group), and ≤1 day with bout-related MVPA per week (inactive).”

Analyses revealed:

• Cardiorespiratory fitness was highly associated with timing of bout-related MVPA (P = .0005), independent of weekly bout-related MVPA volume and intensity, while the association varied by sex (P = .02).
• In men, the midday group had the lowest fitness (β = –0.46; 95% CI, –0.87 to –0.06), while the mixed group in women was the least fit.
• Framingham risk score (FRS) was associated with timing of bout-related MVPA (P=.02), which also differed by sex (P = .0007).
• The male morning group had highest 4-year FRS (2.18%; 95% CI, 0.70%-3.65%), but no association was observed in women.

Overall, men who performed the majority of bout-related MVPA in the midday had the lowest cardiorespiratory fitness, the authors wrote. In comparison, men who were the most active in the morning hours tended to have the highest cardiorespiratory fitness. Additionally, “men who performed the majority of bout-related MVPA in the morning hours had higher 4-year FRS indicating a higher chance of developing CHD in the next 4 years, independent of their overall levels of bout-related MVPA, MVPA bout intensity, and their cardiorespiratory fitness,” the researchers noted.

This finding could be due to the fact that men with higher risk were more likely to perform MVPA in mornings. Other factors such as timing of food intake, sleep duration, or types of occupation may have contributed to this finding but were not measured in the current analysis.

“The general message for our patient population remains that you should exercise whenever you can as regular exercise provides significant benefits for health," said study author Jingyi Qian, PhD. “But researchers studying the effects of physical activity should take into account timing as an additional consideration so that we can give better recommendations to the general public about how time of day may affect the relationship between exercise and cardiovascular health.”

Findings do align with evidence on the link between circadian system and exercise physiology. However, it is unclear why time-specific activity could be associated with different levels of health.

“Interest in the interaction between physical activity and the circadian system is still just emerging," said Qian. "We formed a methodology for quantifying and characterizing participants based on the clock-time of their physical activity, which allows researchers to carry out other studies on other cohorts."

Future longitudinal studies are warranted to further investigate the association between timing of bout-related MVPA and improvement of cardiorespiratory fitness and potential mechanisms, authors concluded.

Reference

Qian J, Walkup MP, Chen S, et al. Association of objectively-measured timing of physical activity bouts with cardiovascular health in type 2 diabetes. Diabetes Care. Published online February 17, 2021. doi:10.2337/dc20-2178