Depending on how long we exercise, different hormones, neurotransmitters, local transmitters and pheromones are produced, explains Juleen Zierath, a physiologist at the Karolinska Institute in Sweden. “[These] they have a broad impact on health, influencing sleep, memory, exercise performance and metabolic homeostasis.”
This has led Zierath and other researchers to wonder if they can harness this knowledge to optimize the benefits of exercise. And because the muscle clock is also involved in turning on genes that regulate glucose and fat, several new studies have focused on exercise time as a therapeutic strategy in metabolic diseaseslike type 2 diabetes.
“The best time of day to exercise is when you can! Establishing a daily exercise habit is important for your overall health and well-being,” Zierath emphasizes. “However, the evidence … indicates that there are certain times of the day when one can ‘fine tune’ the response to exercise.”
Earlier this year, Zierath’s research found that, in mice, exercising in the morning led to “a stronger metabolic impact” than in the evening: The mice were better able to break down fats and use carbohydrates.
“This study suggests that timing of exercise during the day may be a valuable therapy for patients with metabolic disorders,” he says.
in a new follow-up studylooked at how exercise in the morning or afternoon affected men with type 2 diabetes.
While changes in body composition were similar, afternoon exercise was better at improving blood glucose levels, while morning exercise seemed better at burning fat.
There could be many reasons for the difference, he says, including the intrinsic daily rhythm of our circadian clock, hormonal differences at different times of the day, or whether someone has eaten before exercise, which is more likely in the afternoon than in the morning.
As her lab tries to uncover these effects, much remains to be learned, says Karyn Esser, a professor of Physiology and Aging at the University of Florida, whose new research also explores the impact of exercise on circadian rhythm and whose review article discusses the evidence around timing exercise and metabolic disorders.
“There’s going to be enough variation between humans and possibly types of exercise that making blanket claims that one time or another is best for everyone won’t be correct,” says Esser. “What we do know is that exercise in [night] would have different metabolomic results than if it were performed in the middle of the day/active period. Is this a risk? Unlikely, it’s my best guess for healthy subjects… but could it increase the risk for people with metabolic diseases? We do not know.
Dr. David Mizrahi, a researcher at The Daffodil Center at the University of Sydney, is circumspect.
Charging
“Although findings showing ‘precision’ or personalized exercise programs based on metabolic health may optimize benefits, I caution that placing full emphasis on this message and instead promoting that any exercise, anytime , is better than none for the general population.”
Regular exercise at any time of day makes tissues more sensitive to insulin, adds Zierath, which benefits everyone, including people with metabolic disorders. However, as a prescription, there may be benefits depending on the time of day.
“In response to afternoon exercise, people with type 2 diabetes may achieve better nighttime glucose control,” he says. “There is also some evidence that in middle-aged men and women, there may be greater gains in strength and aerobic fitness in response to afternoon exercise.”
With more people living with metabolic disorders: the number of Australians living with diabetes almost tripled in the last 20 years and about 90 percent of those cases are type 2 diabetes – understanding how adjustments to diet and exercise can help is a growing focus.
“We’re still in the early stages of learning about the potential benefits (and perhaps risks) of exercising at different times of the day,” says Esser. “In general, exercise when you can, as we know it’s good for us… But time can be important in terms of health and performance.”
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