We all know we should exercise regularly, but it can be difficult to fit exercise into our busy schedules. Most people can only exercise before or after work, so it’s worth examining whether the time of day we exercise affects outcomes such as weight loss and sleep.
To understand why the timing of exercise might be important, we first need to understand how our bodies function over a 24-hour day. Our biological clock helps to regulate sleep patterns, when we eat, blood pressure and body temperature. These circadian rhythms have been associated with many aspects of physical performance, health and well-being.
Exercising before breakfast
Exercising on an empty stomach is different, physiologically, from exercising after a meal. After an overnight fast, our bodies are reliant on fat as its primary fuel source, so if you exercise in the morning, before eating breakfast, you will essentially burn more fat.
Burning more fat during exercise may have a metabolic advantage, but does that make a difference to fat loss over a period of time? Unfortunately, it’s unlikely. Research examined the difference between exercising in a fasted state, compared with after food, for four weeks. While both groups lost fat mass, there was no difference in the amount of fat lost between fasted and fed exercise.
Researchers investigating the impact of six weeks of morning versus evening exercise on energy intake and weight loss found those who exercised in the morning ate less throughout the day, and subsequently, lost 1kg more than those in the evening group.
But some researchers have also found we work harder in the evening. Conceivably, if we are working harder in the evening, over time, we will expend more energy, potentially leading to greater weight loss than with morning exercise.
If you are looking to run faster or lift more weight, you’re most likely to break your personal records in the afternoon. That’s because your metabolism is in full gear.
Past noon, levels of the hormones cortisol and testosterone help muscles process energy more efficiently. Your body temperature is also higher, which is linked to increased strength.
For those who struggle to pry themselves out of bed, an afternoon sweat session may be best. That’s because circadian rhythms and the levels of hormones that influence them, including melatonin and cortisol, differ from person to person. Not everyone is designed to be an early bird.
Overall, you are likely to enjoy exercising more, and work out with more intensity and consistency, if you do it when you feel most energetic.
Exercise and sleep
Exercise increases how awake we feel and raises our core temperature, which, in theory, is contrary to the “optimal” conditions to elicit feelings of sleepiness.
Despite previous recommendations that discouraged exercising within four hours of bedtime, there’s a growing body of evidence to support evening exercise.
Swiss researchers found vigorous exercise performed one-and-a-half hours before bedtime was associated with falling asleep faster, fewer awakenings after sleep onset, and better mood states.
In contrast, to get up early for morning training, some researchers found swimmers are sacrificing sleep, compared to rest days. So, if you’re going to get up at 5am for that pump class, make sure you get to bed a little earlier the night before, so you don’t lose sleep to make it work.
So is there really a better time of day to exercise?
Sticking to a workout plan isn’t easy when we have competing demands like work and family commitments, which can vary week to week. There are advantages to both morning, afternoon and evening exercise. To get the most health benefits from exercise, the best time of day to exercise is when you will actually do it.
What we do know is you are more likely to do it regularly if you select a time and stick to it, regardless of whether it’s morning or evening. Exercising consistently at the same time each day is one of the best predictors of developing a long-lasting exercise habit.