Benefits of Rest and Sleep on Metabolic Process.

Exercise researchers uniformly agree on the importance of getting sufficient sleep to aid recovery. What we don't know is the precise function of sleep. Theories abound on this subject. One suggests that the brain neutralizes the accumulated effects of daytime stress during sleep, while another states that sleep is vital for proper immune function, an idea bolstered by the fact that a lack of sufficient sleep results in a 40 percent suppression of immunity.

In terms of bodybuilding and other forms of exercise, sleep is important because of the oft-repeated notion that you grow during rest. Science confirms this premise, as research clearly shows an ebb and flow of anabolic hormones during the night (assuming, of course, that you sleep at night). These include growth hormone and testosterone. At other times cortisol, a catabolic hormone, is secreted. This is particularly trite during the later stages of sleep.

Since all humans secrete these hormones, you may wonder how and if their activity is influenced by exercise. If we accept the idea that muscular growth can occur during sleep, then the possible influence of exercise on anabolic hormone flow becomes a critical issue in terms of the so-called anabolic drive. At least two studies have examined the issue of exercise and night hormones. One study, published in the Journal of Applied Physiology (79; 1461- 1468, 1995), examined the nighttime hormonal consequence of both low-intensity and moderate exercise.

As a control measure the researchers also monitored hormonal release during sleep when subjects hadn't exercised. The subjects consisted of 10 amateur triathletes between the ages of 20 and 26. When they didn't exercise, the men showed a growth hormone peak coupled with a low concentration of cortisol during the initial sleep stages; that is, during the first 90 minutes.

During the second half of the sleep period GH dropped, while testosterone increased. When the subjects performed high-intensity exercise, the testosterone levels decreased.

After moderate exercise the usual early GM release during sleep shifted to the later sleep stages. In addition, cortisol levels peaked earlier than usual but decreased during the second half, again reversing the usual pattern of flow for this hormone. These patterns weren't affected by lower-intensity exercise. Another study, this one published in the European Journal of applied Physiology (72;121 -126, 1995), was more relevant to bodybuilders, since the subjects were described as eight trained male weightlifters.

This study looked at levels of various hormones both right after exercise and during sleep. Testosterone and cortisol increased for 40 minutes after the exercise session ended but returned to resting levels within one hour after the workout.

The researchers noted that their findings were in agreement with those of previous studies in that training larger muscle groups elicited a greater post exercise rise in testosterone. While the weight training didn't affect nocturnal GH release, it did increase testosterone, cortisol and thyroid hormones. The thyroid affected, however, was T4, which is considered far less active metabolically than T3 thyroid hormone. The authors of this study suggest that the early-morning rise of cortisol may occur because of the extended time between meals due to sleep.

Among its other functions cortisol helps maintain a certain level of blood sugar through a liver process called gluconeogenesis that involves a breakdown of proteins and other non-carb sources into glucose.

While some people have cited this morning rise of cortisol as a catabolic effect, the accompanying increase in testosterone serves to balance and neutralize it by inhibiting the binding of cortisol to cellular receptors. The fact that testosterone was elevated by the weight-training session at some points during sleep without the presence of increased cortisol indicates an increased anabolic effect from the weight during sleep.