The best time of day to exercise? It depends on your health

Movement at any time of day is essential for good health. But if you want a specific outcome, exercising at a particular time of day might help you achieve it.

Previous research has suggested that the time of day you exercise can affect performance: the greatest aerobic adaptations tend to happen during morning exercise, while the greatest muscular adaptations tend to happen in the afternoon or evening. While this is generally true, the time you naturally rise and go to bed – whether you are a morning or evening person, for instance – also influences when we perform at our best.

Evening exercise may provide more bang for health buck, but not for everyone. Credit: iStock

For health outcomes, however, the time of day may be different again.

A new study published in Diabetes Care examined the movement patterns of nearly 30,000 participants who were at risk of or who have type 2 diabetes and followed up on their health outcomes eight years later.

They found that, regardless of when you exercised, regular moderate-to-vigorous activity reduced the risk of premature death, or death from cardiovascular disease. Among adults with type 2 diabetes, more than half of all deaths are related to cardiovascular disease events.

But they also found that those who did some form of aerobic activity in the evening, such as a brisk walk after dinner, were the least likely (61 per cent less) to die prematurely from any cause or from cardiovascular disease (37 per cent less likely). Why?

While more research is needed to confirm the observational findings, it is to do with our circadian rhythm: the internal clocks by which our body’s systems run each day. Our circadian rhythm is influenced by zeitgeibers (German for “time cues”) such as light, eating and exercise.

In the past five years, researchers have come to understand that aligning our eating patterns with our circadian rhythm might optimise the way our body metabolises food. The idea is that our bodies are primed to handle glucose in the daytime when we are awake and active, but as the sun goes down and our circadian rhythm switches gears, our glucose response becomes worse.

“It was a logical next step to see if exercise could influence some of these metabolic processes that are affected by circadian rhythm,” explains Dr Angelo Sabag, an exercise physiologist at University of Sydney’s Charles Perkins Centre and joint first author of the new research.

One recent systematic review found after-dinner exercise elicited the greatest improvements in glucose.

This may be because physical activity is, as Sabag says, “a really potent stimulator of insulin sensitivity”, so evening exercise offsets the naturally declining glucose response towards the end of the day.

For the new paper, Sabag and his colleagues wanted to understand what this might mean in the long term for those with poor metabolic health.

People with or at risk of type 2 diabetes, such as those with obesity, have a slightly delayed circadian rhythm meaning that the impaired glucose response we all have late in the day is pushed back further, happening around midnight.

This means they wake with high blood glucose levels and the cycle of dysregulation continues. Evening activity, as they predicted, seemed to have the greatest benefit in regulating that spike and influencing health outcomes down the track.

Additionally, the frequency of aerobic bouts further reduced the risk and were more important than the total time a person moved each day.

More frequent episodes of contraction, through movement, may stimulate glucose uptake into skeletal muscle reducing dramatic oscillations throughout the day, the researchers suggested.

Mary MacKillop Institute for Health Research director John Hawley says the findings are powerful, and it’s a large cohort, but it’s still early days.

“I’ve been asked many times what is the best time of day to exercise, but the truth is we don’t have enough studies on populations,” says Hawley, who was not involved with the study. While evening exercise might be the most effective time for those with metabolic conditions, the same is not necessarily true for the rest of us.

Our body has a remarkable capacity to maintain homeostasis and in a normal state of health we can cope with fluctuations. Therefore, the time of day is likely to make little difference – for health outcomes at least.

The capacity to self-regulate diminishes with increased weight and this is where precision may provide extra bang for buck, Sabag adds: “Those people can benefit the most from evening exercise.”

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