There are also, of course, competing camps of personal trainers and fitness gurus who shout from the rooftops, "You must work out first thing in the morning — before you eat breakfast! — or you'll shortchange your results!" Or, alternatively, "You must work out in the afternoon or early evening, when you'll perform your best and reduce your likelihood of injury!"
So, who's right?
Amanda Dale, a personal trainer and exercise instructor (and a woman after my own heart) cuts through the mess and says simply, "When my clients ask me what the best time of day to work out is, my stock answer is this, 'Whenever you'll actually do it.'" Amen, sister, I concur.
She goes on to explain, "Whether you're a morning person, night person or something in between, find the time that works for your lifestyle — it's more important to exercise when you can, than when you 'feel like it' — and make it a part of your daily routine."
That's a very wise woman. So, what's the deal, then? Why do some experts have such competing views?
The challenge is multi-layered. First, circadian rhythms — your body's varied level of wakefulness throughout the day — tends to be fairly consistent from human-to-human. For instance, most people naturally want to be awake and productive during daytime hours before winding down in the evening and sleeping through the night. Unfortunately, this is, in fact, just a generalization. Most people may function best by sleeping through the night and working during the day, but not all people. Some people's circadian rhythms are just plain different (damn you outliers!), which makes sweeping statements about the "best" time to work out pretty impossible to make.
But the challenge is that generalizations are generalizations because there's some truth to them. Scientists who study sleep patterns and human performance tend to find that consistent changes in body temperature and hormone levels contribute to varying levels of physical output, mental alertness and overall performance.
While you might think these generalizations must, then, point to a generalized "best" time to work out (we all want answers in black and white, amiright?) — they, in fact, can't. This is because the "best" time still varies depending on personal goals.
Dale points to several studies to explain, "A 2014 Chinese study published in the International Journal of Sport Nutrition and Exercise Metabolism suggests that exercising in the afternoon or evening can have greater protective benefits against heart disease compared with exercising in the morning. Likewise, a 2014 study of elite rugby players found that competitive performance was better in the evenings due to higher core temperatures, which meant there was less of a 'warm up' delay to reach peak performance." But, before you schedule your next workout for after work, the next study puts a wrench in the system, "A 2013 thesis published by Heather Husmer at the University of Connecticut found that resistance training in the morning is more effective due to a decrease in perceived fatigue and exertion, resulting in higher total workload."
Just to make things a little more confusing, Dale points to the current commentary of the American College of Sports Medicine, which highlights several interesting facts: First, if you're focusing on exercise adherence (just sticking with a program), those who exercise in the morning tend to achieve greatest success. Second, those who exercise consistently, regardless of time of day, tend to perform the best at the time they're most used to exercising. And finally, to come full-circle, the commentary states, "Although most physiological variables demonstrate circadian variation, many do not significantly fluctuate during the segment of the day when athletic endeavors typically occur. Therefore, many types of performance remain constant during normal daylight hours."
In other words, with a few exceptions, the best time to work out is anytime during normal waking hours — as long as you'll do it and do it consistently.
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