When Is The Best Time To Exercise?

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There is a long-running debate on when is the best time to exercise. Some people say late afternoon or early evening, because research indicates physical endurance is greatest between 4 pm and 7 pm. However, your hormones seem to favor a morning workout, because that is when cortisol is at its peak.

Cortisol is the antithesis of testosterone, breaking muscle down instead of building it up. The presence of cortisol also halts testosterone production in men and estrogen in women. Finally, cortisol inhibits insulin, so that glucose cannot be stored and is available for energy.

At the same time, hormone that stimulates appetite, ghrelin, has been in production from midnight to early morning. This means you are likely to wake up hungry and your body will be in a mode to burn energy.  If you eat but do not exercise, when insulin rises, it tells the body to store it for later use. If this cycle continues throughout the day, particularly as stress-caused eating, you will pack on weight. And you body will begin to become insulin resistant, which is the beginning of type 2 diabetes.

If, on the other hand, you consume  a piece of fruit and then do some intense exercise, your cortisol will use that blood glucose (from fruit sugar, or fructose) for energy. Exercise stimulates growth hormone, cortisol, and testosterone, a combination which turns available fat and protein into muscle. If you are overweight, the growth hormone plus insulin will burn fat. If you are of normal weight, the growth hormone will look for a source of energy to build protein. It is recommended that you eat some to eat a small amount of easily digested protein (2 eggs) to use for muscle, and complex carbs to be used slowly throughout the morning for energy.

If you run in the early evening, you will tend to burn muscle instead of fat, because your body will not have available glucose. When you eat dinner later, the calories will then be stored as fat. More fat cells (receptors) mean a greater ability of the body to store glucose as fat. Worse, while cortisol production is not increased by exercise, if you consume an energy drink (caffeine and sugar) it will spike cortisol and increase fat storage. You can modulate these effects the same way you do in the morning –– by what and when you eat.

What you can’t change is the impact of exercise upon your circadian rhythm. This is the 24-hour biological clock that regulates the production of many hormones, including growth hormone and cortisol. When you exercise late in the day, you elevate cortisol which interferes with sleep and with the production of growth hormone. This sets you up for throwing your circadian rhythm out of whack.

If you eat a light evening meal and then go for a leisurely walk, you will boot growth hormone slightly. Exposure to dark will help your melatonin production, which makes sure you sleep well and produce the right amount of growth hormone at the correct time.