Your circadian rhythms are governed by the Earth's 24-hour cycle, with their ebb and flow influencing important bodily functions such as blood pressure, heart rate, body temperature, and hormone levels. Because people react differently to these rhythms, it's important to use your own body as a guide when deciding when to hit the gym. For example, if you're the kind of person who doesn't need an alarm to get up at the crack of dawn, it only makes sense to use this time wisely by working out. On the other side of the coin, it you have more energy or feel stronger in the evening, it only makes sense to exercise at the end of the day. 

While individual preferences are the most important consideration when choosing a time to exercise, according to some experts, there are some objective factors worth considering. For example, morning routines may be the best time to exercise for anyone who has have trouble with consistency. According to Cedric Bryant, PhD, chief science officer with the American Council on Exercise in San Diego, "Research suggests in terms of performing a consistent exercise habit, individuals who exercise in the morning tend to do better ... The thinking is that they get their exercise in before other time pressures interfere ... I usually exercise at 6 a.m., because no matter how well-intentioned I am, if I don't exercise in the morning, other things will squeeze it out."

On the other side of the spectrum, afternoon and evening workouts can be a great way to relieve stress after a hard day at the office. Countless studies have linked weight gain to the release of cortisol and increased stress levels. People who work out at the end of the day can provide a healthy way to release these daily stresses, with an hour at the gym or a relaxing yoga class a far better option than happy hour at the local pub. People who workout in the P.M also have more opportunities to fuel their body throughout the day, something that is especially important for high intensity cardio or strength routines.

Regardless of when you workout, it's important to time your exercise with your food intake. "Don't exercise immediately following a meal," says Bryant, adding "The blood that needs to go to your muscles is going to your digestive tract. Give yourself 90 minutes after a heavy meal." Sleep is also important if you want your exercise to count, with your body's urge to sleep sabotaged when you exercise or eat too late. It's important to get your body ready for sleep, which may mean not exercising or eating too much in the late evening to avoid raising your heart rate and temperature. 

When it comes to exercise - consistency is key. While A.M and P.M workouts both have their advantages, they mean nothing unless you find time to make exercise a regular part of your life. People who are just starting out and exercising at random times are more likely to drop out, with people who are already consistent often changing the type of exercise they do and the time of day they do it in order to stay fresh. While dusk and dawn workouts can both be used to your advantage, the right mix of consistency and variety is more important than the time of day.

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