Insulin and Muscle Mass
March 5, 2011 by Jerry Brainum

Insulin, testosterone and growth hormone for monster size.

Why do we lose muscle as we age? The obvious answer for most people is lack of sufficient exercise. Muscles work on a use-it-or-lose-it basis, as do most of the organs and tissues of the body. Without the stimulation provided by exercise, the neuromuscular connections between the brain and the muscular system gradually fade, and muscles atrophy, or shrink. The loss of muscle mainly affects the type 2 muscle fibers, those linked to muscular size and strength, and the balance between type 1s, the weaker, so-called endurance muscle fibers, and the more powerful type 2 fibers veers toward a dominance of type 1s. That explains much of the frailty associated with the aging process.

Besides a lack of exercise that places stress on type 2 fibers, namely resistance exercise, such as weight training, a major cause of muscle loss with aging is the gradual decline in the synthesis and secretion of anabolic hormones, including testosterone, growth hormone and insulin. There’s crossover between anabolic hormones and exercise, since regular exercise helps maintain measures of the hormones with age. Inevitably, of course, they drop to some extent in most people.

People who are clinically deficient in any of the anabolic hormones often experience dramatic beneficial changes in body composition and strength when the missing hormones are supplied. That explains the current popularity of growth hormone therapy to treat aging symptoms. Giving GH to an older person who’s deficient in it results in significant improvements in such factors as skin thickness and bodyfat, which in turn often leads to a subjective feeling of turning back the clock.

Testosterone is even more important for those who want to maintain or develop muscle with age. Without adequate testosterone, you simply won’t make any gains. Testosterone begins to decline about age 40, as does GH, while muscle gains begin to significantly slow. The drop of testosterone—that is, T—with age is most noticeable in those who are sedentary, but it also affects many of those still engaged in regular exercise. I’ve spoken with countless men over the years who were diagnosed with low T. In those who also lifted weights regularly, taking supplemental testosterone produced often dramatic changes in body composition and muscular strength.

While testosterone and growth hormone therapy are commonly used to treat symptoms of aging, the only accepted medical use for insulin is to treat diabetes mellitus. Type 1 diabetics lack the pancreatic cells to synthesize insulin, so they must take insulin injections. The more common type of diabetes, type 2, can often be treated with oral medications, exercise and diet, although in some cases insulin injections are required to control elevated blood glucose.

In recent years athletes have used insulin for several reasons. A common side effect of using large doses of GH is elevated blood glucose, which can be controlled with an insulin-injection kicker. Insulin also triggers amino acid uptake into muscle for use in muscle protein synthesis. Insulin activates the primary enzyme that converts carbohydrate into glycogen, which aids muscle recovery after training and gives the muscle a fuller appearance to muscle; each gram of glycogen is stored with 2.7 grams of water.

So, is insulin an anabolic hormone? It certainly is if you want to gain bodyfat. Indeed, insulin is the most potent fat-stimulating hormone in the body. It’s often referred to as a “storage hormone” because it promotes energy storage both as fat and as carbohydrate in the form of glycogen. In relation to muscle, insulin is conditionally anabolic, meaning that in the presence of large amounts of amino acids in the blood, it aids in amino acid uptake into muscle, which facilitates muscle protein synthesis, a definite anabolic effect.