The best hours of the day to exercise for weight management, according to study

People who exercised in the morning had a lower body mass index and smaller waists than those who did not

Exercising between 7am and 9am may be the key to weight management, new research suggests.

Although evidence regarding the optimal timing of physical activity has been controversial, a new study has found the start of the day appears to be the best time to engage in moderate to vigorous physical activity in order to lose weight.

The study, which was published in The Obesity Society’s (TOS) journal on 4 September, used data from the 2003–2004 and 2005–2006 cycles of the National Health and Nutrition Examination Survey by the Centers for Disease Control and Prevention (CDC). A total of 5,285 participants were cross-sectionally analysed and split into morning, midday and evening exercisers.

The findings revealed that people who engaged in 150 minutes of moderate to vigorous physical activity in the morning group had a lower body mass index and smaller waists than those in the other groups. People in the morning group also reported having healthier diets and consuming fewer calories per unit of body weight, compared with people who exercised later in the day.

According to the findings, people in the morning group spent a significantly higher amount of time sitting or lying down - not moving - than the others. But the researchers found that despite this, the lower body mass index and waist size in the morning group persisted.

Those in the morning group (642 people) were 10 to 13 years older than the two other groups. This cluster also had the highest percentage of women, and the majority of them were primarily non-Hispanic white, had a college or higher education, and had never used tobacco or alcohol.

Tongyu Ma, assistant professor of natural and health sciences at Franklin Pierce University, said: “Our study provided a novel tool to explore the diurnal pattern of physical activity and to investigate its impact on health outcomes.”

“Our findings propose that the diurnal pattern of moderate to vigorous physical activity could be another important dimension to describe the complexity of human movement,” Ma stated in the study.

Clinical psychologist Rebecca Krukowski - professor and co-director of the Community-Based Health Equity centre at the University of Virginia, who was not involved in the study - added: “This is exciting new research that is consistent with a common tip for meeting exercise goals – that is, schedule exercise in the morning before emails, phone calls or meetings that might distract you.”

However, Krukowski pointed out that since it was a cross-sectional study, “it is not known whether people who exercise consistently in the morning may be systematically different from those who exercise at other times, in ways that were not measured in this study.”

“For example, people who exercise regularly in the morning could have more predictable schedules, such as being less likely to be shift workers or less likely to have caregiving responsibilities that impede morning exercise,” she said. “Predictable schedules could have other advantageous effects on weight that were not measured in this study, such as with sleep length/quality and stress levels. In addition, the ‘morning larks’ who consistently rise early enough for morning exercise may be biologically different from their ‘night owl’ counterparts.”

Experts also noted that previous research has focused on the frequency, intensity and duration of physical activity. So far, few studies have investigated the diurnal pattern of accelerometer-measured physical activity to classify the time of day of human movement. It is unclear whether accumulating physical activity at different times of day is equally associated with obesity.

Additionally, it is unclear whether meeting the physical activity guidelines of 150 minutes per week of moderate to vigorous physical activity is equally beneficial for reducing obesity.

Additional reporting from PA.