First thing in the morning, during your lunch break or in the evening? Science has some answers.
There's been plenty written about what men should do when they exercise, and whether it should be long slogs or short, sharp sessions, cardio or resistance training, gym or the great outdoors.
What's less commonly discussed is when men should exercise. But some experts believe that the timing of your workouts can have a major impact on the success of your fitness regime. Now a new study appears to back them up.
Here's why 'when' may be as important as 'what' when it comes to working out.
Exercise before breakfast
According to the new study, exercising first thing in the morning is better than later in the day. More specifically, it found that men hitting the gym or streets before breakfast lost more weight than men exercising for the same duration and intensity after their fry-up or cornflakes.
The study asked 10 men to attend Glasgow University's Institute of Cardiovascular and Medical Sciences for breakfast three times. On the first visit, they didn't do any exercise, on the second they took a brisk walk before breakfast and on the third they walked after breakfast.
Unsurprisingly, those who exercised at either time burned more calories than those who didn't exercise at all, but those who exercised before eating burned 33% more calories than the men who walked after their toast or cereal.
The early exercisers also experienced a bigger drop in the blood fats than can contribute to heart disease.
So why does working out on an empty stomach appear to be particularly good for us? Dr Jason Gill, who conducted the research, said it forced the body to draw on its fat reserves for energy. The more stored fat we burn, the more weight we lose.
All this might sound counterintuitive to those who think they need to put some energy in their bodies - in the form of food - before they exercise. But according to Dr Gill, our bodies have around 90 minutes to two hours of readily accessible energy stores, so strenuous exercise on an empty stomach is perfectly possible.
Still, Dr Gill is at pains to point out that the biggest difference in the study was between those who exercised - at any time - and those who didn't. "If you are going to do something, then there is a slight advantage in doing it in a fasted state," he added.
"But if you find you keel over because you can't do exercise before you have your slice of toast, then do it afterwards. You are still going to get a huge benefit."
Exercise in the morning
Plenty of experts would agree that exercising early is the best idea, but for different reasons.
Most importantly, early exercise gets it over and done with. So there's less chance of something happening during the day that will interrupt your plans to work out.
And if you plan to exercise in the evening, you have a whole day to talk or think yourself out of it. The earlier you exercise, the less chance you have of seeing your drive and motivation drain away or get lost in the bustle of the day. Research has found that early exercisers are more consistent.
Exercise in the evening
But though early exercise is clearly better for us in some ways, that's not the whole story.
In fact, a study a few years ago by researchers at the University of Chicago found that the chemical composition of men's blood was better after evening workouts. Evening workouts led to raised levels of the hormones cortisol and thyrotropin, while blood glucose dropped.
"These are signs that your metabolism is adapting well to regular exercise and suggests it may be better to train after work rather than first thing in the morning," said one of the study's authors.
There's also some evidence that we can work out harder in the evenings, after our muscles have had a day to warm up and when hormones that aid exercise are at an optimal level. Research from the University of North Texas found that anaerobic performance, such as sprinting, improves by about 5% in the late afternoon, and endurance improves by around 4%.
It could be that many of us have better workouts in the late afternoon and early evening.
It depends on what you want to achieve
It seems that the evidence is mixed and so to a large extent the best time to exercise is the one that suits your lifestyle. For some of us that will be first thing in the morning, for some at lunchtime and for some after work.
It's also true that working out at any time is far better than not working out at all.
But for an optimal workout, it may depend on what you want to achieve. As the new study suggests, fat burning may be better achieved first thing in the morning. But muscle and endurance building could be more effective when our muscles are warm and our body temperature is at its highest, which is in the late afternoon.
So timing is important, and there are a couple of things all experts agree on. Firstly, don't exercise shortly before bed (it will keep you awake). And secondly, the very best time for your workout is any time you're going to stick to.