By Dr. Mercola
It's important to make time for exercise on a regular basis, and for many this means squeezing in a workout early in the morning, during a lunch hour, and even late at night, just before bed.
It's commonly suggested that you should, ideally, avoid exercising at night, however, as the increases in your adrenaline levels, heart rate, and body temperature may make it difficult to fall asleep.
Without a doubt, there are many people who are sensitive to late-night exercise, such that a vigorous session will keep them awake. For some, however, and possibly even the majority, exercise at night may not necessarily be so bad...
Some People Report Exercise at Night Helps Them Sleep Better
One of the benefits of exercise overall is improved sleep quality, but it's typically recommended that you not exercise within three hours of bedtime so you have adequate time to wind down.
A study published in 2011, however, found that when people exercised vigorously for 35 minutes right before bed they slept just as well as on nights when they didn't exercise.1 Another study, a poll by the National Sleep Foundation, found that 83 percent of people said they slept better when they exercised (even late at night) than when they did not.2
More than half of those who exercised moderately or vigorously said they slept better on workout days than non-workout days, and just three percent of late-day exercises said their sleep quality was worse when they exercised than when they did not. The National Sleep Foundation concluded that exercise is good for sleep, regardless of the time of day it's performed, noting:
"While some believe exercising near bedtime can adversely affect sleep and sleep quality, no major differences were found between the data for individuals who say they have done vigorous and/or moderate activity within four hours of bedtime compared to their counterparts (those who did vigorous or moderate activity more than four hours before bedtime).
According to the 2013 Sleep in America® poll, the conclusion can be drawn that exercise, or physical activity in general, is generally good for sleep, regardless of the time of day the activity is performed."
Afternoon Exercise May Help Regulate Your Circadian Rhythm
There's a case to be made for exercise at virtually any time of day, including in the afternoon. A study published in the Journal of Physiology found that exercise helps regulate your circadian rhythms, and the effect may be most profound if it's done in the middle of the day.3
Researchers designed a study comparing the circadian rhythm effects of exercising at various times of day, using two groups of mice: one healthy group and one group with biologically induced circadian disruptions.
There are potentially serious health consequences of disrupted circadian rhythms, such as increased risk of diabetes, obesity, hypertension, memory loss, headaches, indigestion, mood disorders, learning problems, and even certain types of cancer.
Disrupted sleep cycles have the potential to stimulate cancer growth by altering hormone levels, such as melatonin, for instance, showing just how important it is to regulate your circadian rhythm.
Interestingly, the study found that all of the mice showed positive benefits from exercising, regardless of what time of day they exercised (for mice, exercising meant running on a wheel). But the benefits were much higher for the mice whose internal clocks were impaired in the first place.
For those discombobulated mice, after several weeks of running, their internal clocks were much more robust, particularly among the mice that exercised in the afternoon. This finding was a real surprise to researchers who expected to see the most benefit from morning exercise, which tends to be favored by athletes.
Mice exercising in the late evening showed the least benefit, with some developing even more circadian disruptions, including poor sleep (which is contrary to the featured article's findings).
Could it be that exercise has different types of benefits, depending on the time of day it's performed? From a circadian point of view, it makes sense to see higher benefits from afternoon exercise. Circadian rhythms control your body temperature, which has an impact on your workout.
Your body temperature tends to be a degree or two warmer in the afternoon than in the morning, resulting in better muscle performance and decreased risk of injury. You are also generally more alert in the afternoon. Plus, if you tend to hit that "wall" around 1:00 or 2:00 pm, going to the gym might be a good way to get over it. That being said, there's also reason to believe that exercise first thing in the morning may be equally beneficial, if not more so.
The Case for Morning Exercise
Personally, I prefer exercising in the morning for a number of reasons, the first being that your workout will be completed early on, leaving less chance for other obligations to eat up your exercise time. Additionally, exercising in the morning makes it easy to exercise while fasting, which will amplify the benefits you receive.
Research has shown that exercising on an empty stomach is useful for preventing both weight gain and insulin resistance, which is a hallmark of countless chronic diseases.
One of the explanations for this is that your body's fat burning processes are controlled by your sympathetic nervous system (SNS), and your SNS is activated by exercise and lack of food. The combination of fasting and exercising maximizes the impact of cellular factors and catalysts (cyclic AMP and AMP kinases), which force the breakdown of fat and glycogen for energy. This is why training on an empty stomach will effectively force your body to burn fat.
Intermittent fasting calls for you to exercise in late morning or early afternoon, and fasting (or eating only light raw foods, vegetable juice and/or whey protein, or eggs) until 30 minutes after your workout. If you have trouble exercising on an empty stomach, you can include 20 grams of a fast-assimilating protein like a high-quality whey protein concentrate 30 minutes before your workout.
Exercise and fasting result in acute oxidative stress, which keeps your muscles' mitochondria, neuro-motors, and fibers intact. You may have heard of oxidative stress before in a negative light, and when it is chronic it can lead to disease. But acute oxidative stress, such as that which occurs due to short intense exercise or periodic fasting, actually benefits your muscle. In fact, according to fitness expert Ori Hofmekler:
"[Acute oxidative stress] is essential for keeping your muscle machinery tuned. Technically, acute oxidative stress makes your muscle increasingly resilient to oxidative stress; it stimulates glutathione and SOD production in your mitochondria along with increased muscular capacity to utilize energy, generate force and resist fatigue.
Hence, exercise and fasting help counteract all the main determinants of muscle aging. But there is something else about exercise and fasting. When combined, they trigger a mechanism that recycles and rejuvenates your brain and muscle tissues."
The mechanism he refers to is triggering genes and growth factors, including brain-derived neurotropic factor (BDNF) and muscle regulatory factors (MRFs), which signal brain stem cells and muscle satellite cells to convert into new neurons and new muscle cells, respectively. This means that exercise while fasting may actually help to keep your brain, neuro-motors, and muscle fibers biologically young. The combined effect of both intermittent fasting and short intense exercise like Peak Fitness may go way beyond helping you to burn more fat and lose weight; it may help you to:
Turn back the biological clock in your muscle and brain
Boost growth hormone
Improve body composition
Boost cognitive function
Morning Exercise Might Reduce Your Food Cravings for the Rest of the Day
Another reason to schedule your workouts first thing in the morning? Research shows that 45 minutes of moderate-to-vigorous exercise in the morning may actually reduce your food cravings, both immediately afterward and throughout the day.4 The study included 18 women of normal weight and 17 who were clinically obese. Their neural activity in response to images of food was measured on a morning following exercise and on a morning when they did not exercise. The women's attentional responses to images of food decreased significantly after a morning workout, suggesting that exercise might affect how people respond to food cues.
In other words, you're likely to have an easier time resisting a doughnut or slice of pizza if you've exercised earlier in the day, such as after a brisk walk on the treadmill. Also important, morning exercise resulted in an increase in total physical activity that day, and the women did not compensate for the energy expenditure by eating more later in the day, which suggests morning exercise may also help you keep moving even after your workout, which is another key to optimal health.
What's the Best Time of Day to Exercise? The Answer Depends on You
Even though there are discrepancies in the scientific literature about the best time of day to work out, most experts will agree that the best time for YOU to exercise is when you will do it consistently! One thing is certain: any exercise is better than none, regardless of when you do it. If you enjoy exercising in the morning and have successfully organized your schedule around it, then don't change it. Do be mindful that if you're getting up early to exercise, you don't want to sacrifice sleep to do so, so you'll want to go to bed earlier to accommodate it.
The most important thing is to choose a time of day you can stick with, so that exercise becomes a habit. I would generally discourage exercising in the evening, especially if it's vigorous exercise like Peak Fitness or you struggle with your sleep. Exercise raises your heart rate and body temperature, which are not conducive to sleeping. However, if evening is the most convenient time of day for you to exercise and you find that it does not interfere with your sleep, then you should continue.
Alternatively, reserve your evening exercise sessions for gentle, relaxing exercises like yoga, while scheduling more vigorous workouts for morning or afternoon. If you're not sure which time of day you prefer, you can do some experimentation of your own. Perhaps try a month of exercising in the morning, followed by a month of exercising in the afternoon, as your schedule allows. You can also change the time you exercise daily to better accommodate your schedule. Ultimately, listen to your body and let it be your guide in choosing what time of day works best for you.