Researchers from the University of Sydney, Australia, who tracked the movement of 30,000 people over nearly eight years, found that engaging in most of one’s daily physical activity in the evening is associated with the greatest health benefits for those who are obese.

The researchers classified participants’ physical activity by morning, afternoon, and evening using data from wearable devices. They found that the lowest risk of premature death and cardiovascular disease death occurred in those who primarily engaged in aerobic moderate to vigorous physical activity, which increases heart rate and causes dyspnea.

It also seemed that the frequency of people’s nighttime moderate-to-vigorous physical activity (MVPA), measured in brief bursts lasting three minutes or longer, mattered more than their daily total of physical activity.

The Charles Perkins Center at the University led the study, which was published in the journal Diabetes Care.

According to Dr. Angelo Sabag, Lecturer in Exercise Physiology at the University of Sydney, “Due to a number of complex societal factors, around two in three Australians have excess weight or obesity which puts them at a much greater risk of major cardiovascular conditions such as heart attacks and stroke, and premature death,”

“Exercise is by no means the only solution to the obesity crisis, but this research does suggest that people who can plan their activity into certain times of the day may best offset some of these health risks.”

Although comparable results have been found in smaller clinical trials, the significance of this study lies in the huge number of participants, the use of objective physical activity assessments, and concrete endpoints like premature mortality.

Dr. Matthew Ahmadi, a co-first author of the study, emphasized that it tracked more than simply structured activity. Instead, because prior studies have demonstrated a clear correlation between this kind of exercise, glucose regulation, and a decreased risk of cardiovascular disease as compared to shorter (non-aerobic) bouts, researchers concentrated on monitoring continuous aerobic MVPA in bouts lasting three minutes or more.

Dr. Ahmadi, a postdoctoral research fellow with the National Heart Foundation at the Charles Perkins Center, University of Sydney, said, “We didn’t discriminate on the kind of activity we tracked, it could be anything from power walking to climbing the stairs, but could also include structured exercise such as running, occupational labor or even vigorously cleaning the house,” 

Even though the study’s results are observational, they corroborate the authors’ original hypothesis, which was based on earlier research and proposed that individuals with diabetes or obesity who already have late-evening glucose intolerance may be able to mitigate some of this intolerance and its consequences by engaging in evening physical activity.

How Was the Research Carried Out?

Using data from the UK Biobank, the researchers identified 29,836 adults over 40 who were obese; 2,995 of these individuals also had a type 2 diabetes diagnosis.

Based on when they performed the majority of their aerobic MVPA—as determined by a wrist accelerometer worn continuously for 24 hours a day over seven days at the start of the study—participants were divided into three groups: morning, afternoon, and evening MVPA.

After that, the researchers combined health information from the National Health Services and the National Records of Scotland to track the individuals’ health over a 7.9-year period. They documented 2,162 microvascular dysfunction episodes, 3,980 cardiovascular events, and 1,425 deaths throughout this time.

The researchers took into consideration variables including age, sex, smoking, drinking, eating fruits and vegetables, spending time sedentary, overall MVPA, education, using medications, and sleeping patterns in order to reduce bias. Participants with pre-existing cancer and cardiovascular disease were also disqualified.

Although the length of the study follow-up and further sensitivity analysis, according to the researchers, strengthen the validity of their findings, they are unable to totally rule out the possibility of reverse causation because of the observational design. There’s a chance that some participants’ decreased aerobic MVPA values were brought on by an underlying or undetected illness.

What Makes this Study Significant?

Senior author of the report and director of the Mackenzie Wearables Research Hub at the Charles Perkins Center, Professor Emmanuel Stamatakis, stated that the sophistication of wearables research studies is offering significant insights into the exercise patterns that are most beneficial to health.

“It is a really exciting time for researchers in this field and practitioners alike, as wearable device-captured data allow us to examine physical activity patterns at a very high resolution and accurately translate findings into advice that could play an important role in health care,” stated Professor Stamatakis.

“While we need to do further research to establish causal links, this study suggests that the timing of physical activity could be an important part of the recommendations for future obesity and type 2 diabetes management, and preventive health care in general.”