Men in their twenties and thirties sleep better the more energy they use up during the day, write researchers at the Dutch Radboud University Nijmegen Medical Centre in Gerontology. This is not the case however for men in their sixties and seventies.
Sleep is the most underestimated lifestyle factor in our contemporary – activity fixated – culture. For ninety percent of humanity, more and better sleep means more testosterone, a stronger immune system, improved stamina, quicker reactions, longer lifespan, less fat and more muscle. So there you go. That explains our interest in ways of improving and increasing the quantity and quality of sleep.
Like exercise. Dutch researchers, who were actually searching for a relationship between fitness and sleep, stumbled upon exercise as a sleep-enhancing factor when they compared the sleep of 12 younger men, average age 27, with that of 21 older men whose average age was 69.
Fitness was not a factor that affected sleep quality the researchers discovered. But, among the young men at least, total daily energy expenditure did correlate with their sleep efficiency [the percentage of the time spent in bed that you are actually asleep]. The more energy young men expend, the greater their sleep efficiency.
The researchers also did another experiment in which they got men [average age 69] to cycle three times a week for 45 minutes at a constant speed, but this did not result in improved quality of sleep.
"Increased daily energy expenditure will deplete energy stores, leading to a larger energy restoration during sleep, which consequently is associated with an enhanced sleep efficiency", is one theory that the Dutch researchers put forward.
"High catabolic activity during exercise is associated with a higher energy expenditure, which leads to elevated anabolic activity during sleep", is another theory. "The higher anabolic activity is believed to promote energy use for tissue restoration, but also improves sleep efficiency."
This last theory may explain why training sessions don't work with older men. The older you are, the less keen your body is on anabolic activity. It's not without reason that older strength athletes have to work harder and harder to achieve any progression at all. Maybe the results of the experiment would have been different if the researchers had got the men to do interval or strength training.