Some people swear by a morning sweat session, while others prefer later in the day to help relieve the stress of the day.
The truth is, any exercise is better than none at all! However, to obtain the best possible results from your workout, it all boils down what your health goals are: Is it weight loss, improve performance, or to manage stress?
To help end the debate, I've rounded up both sides of the argument.
THE PERKS OF THE MORNING
Studies have shown that people who exercise in the morning are more consistent with regard to forming a regular exercise habit, and when you also consider that it's done and dusted before everything in your day (evening plans, commuting, late nights in the office, family distractions) takes priority, it makes sense. Fatigue from a long day can also lead to skipped evening workouts.
Another benefit of dragging yourself out of bed is that the energy you create by exercising will sustain you throughout the day and may even improve concentration and mental alertness for back-to-back meetings. This is partly due to enhanced blood flow. More blood means more energy and oxygen, which makes our brain sharper.
Break the fast
A nutritional benefit is that you're less likely to skip breakfast because exercise stimulates an appetite. Say, for example, you start the day with a morning jog, this is often followed by a post-workout meal and an increased water intake all morning long.
Be it eggs, wholegrain cereal, or a green smoothie, breakfast also provides an opportune time to get a wide variety of daily nutrients: calcium, fibre, quality carbohydrates, protein and heart-healthy fats - a combination that helps to stabilise blood sugar levels and ward off the midmorning munchies.
Burn body fat
This is debatable. Few studies show that morning workouts (in a fasted state) will prime the body for an all-day fat burn, while other studies have shown that the same amount of fat is burned during a workout regardless whether you've eaten or not.
There are caveats, of course. Exercising on an empty stomach is unlikely to improve your performance. Why? Carbohydrates are the preferred (and most efficient) source of fuel for the working muscles to access, so exercising when blood glucose levels are low may mean that exercise performance will suffer and fewer total calories may be burned due to a less intense workout.
On the contrary, exercising on a full stomach can be uncomfortable (as most athletes would attest). Digestion requires the blood that your working muscles will want. But if you often feel like you're running on empty, try experimenting with a light snack such as a piece of fruit or a glass of milk to take the edge off.
Exercising too close to bedtime may interfere with sleep and may cause insomnia. Exercise stimulates the body and raises body temperature, which is the opposite of what you want near bedtime, because a cooler body temperature is associated with sleep. Besides, knowing you have a morning sweat session may motivate you to hit the hay sooner.
WHEN EXERCISING LATER IS BETTER
Body temperature is at its lowest just before waking, so the likelihood of injury increases when you exercise upon rising. You can easily overcome this by allowing more time to warm up the body to reduce the risk of pulling a hamstring.
An individual who works out later in the day has the opportunity to eat and fuel the body for a tougher, more intense workout. And as body temperature is at its highest, so does enzyme activity and muscular function, so you can work out at your peak between the hours of 2pm and 6pm.
We've all heard of 'stress eating' and studies have linked weight gain to increased stress levels, due to the release of cortisol, which in turn can result in poor eating habits. Letting off some steam at the end of the day can provide a healthy way to release daily stresses - a far better option than happy hour.
The most important thing is that you stay active and make it a regular part of your life, no matter what time of day - so find the time that suits your motivation levels and schedules, and stick to it!
Kathleen Alleaume is a nutrition and exercise scientist.