Saturday, October 22, 2011

Growth Factors and Muscle Subtractors : Myostatin, IGF-1 and your workouts by Jerry Brainum

Myostatin, a protein discovered by scientists at Johns Hopkins Medical School in 1997, prevents muscular growth. It also works in concert with cortisol and thyroid hormones to increase muscle catabolism, or the breakdown of muscular tissue. Insulinlike growth factor 1 (IGF-1), so named because it has a structure similar to that of insulin, provides potent anabolic effects in muscle, just as insulin does. A condition that favors a decrease in myostatin with an increase in IGF-1 should result in increased muscular growth—shouldn’t it?

   A recent study examined the relationship between myostatin, IGF-1 and muscular growth.1 The study featured two groups of men. Group one trained all the major muscles of the body, while group two trained only their biceps. The subjects trained twice a week for 10 weeks. The hypothesis was that training a larger percentage of muscles would lead to greater levels of growth-promoting hormones, in this case IGF-1. In light of recent studies examining the effect of weight training on myostatin, the authors figured that myostatin levels would decrease.

   Both programs led to significant increases in muscular growth of the biceps, but neither group showed any changes in IGF-1. The researchers were measuring systemic release of IGF-1, but it’s also produced locally in muscle, which appears to account for its anabolic effects in muscle. The fact that both groups showed significant decreases in myostatin levels underscores other findings indicating that weight training is an effective natural myostatin inhibitor. Interestingly, both groups—those doing the isolated biceps exercises and those training their entire bodies—had about the same decrease in systemic myostatin.

   Another study, involving rats as subjects, found that a high-protein diet leads to a greater production of myostatin.2 At the same time that myostatin is increasing, so is another factor, called myogenin, that would normally promote muscle growth. The increase in myostatin cancels the effects of myogenin. Does that mean that those who seek more muscle growth are working against themselves if they’re on a high-protein diet?

   Not at all. The increase in myostatin is only a small part of the picture. Other hormones also increase. Exercise generates localized production of IGF-1 in the muscle, which would cancel myostatin’s inhibition of muscular growth. In fact, protein is the primary nutrient that regulates IGF-1 production.

   Another study looked at two types of exercise to figure out which produced the greatest response of IGF-1 release.3 Twenty-four male subjects divided into two groups exercised three days a week for six weeks. The first group used pure strength training with maximum muscular contractions. The second used a combination program involving maximum contractions and ballistic and stretch exercises.

   Those in the strength-only group showed a 475 percent increase in IGF-1 mRNA, while those in the combo group showed a 135 percent increase. Since the combo group used lighter weights, this study shows that a primary impetus to increased IGF-1 release is exercising with heavier weights.

1 Walker, K.S., et al. (2004). Resistance training alters plasma myostatin but not IGF-1 in healthy men. Med Sci Sports Exerc. 36:787-93.

2 Koichi, N., et al. (2004). A high-protein diet stimulates myostatin mRNA expression in rat skeletal muscles. Med Sci Sports Exer. 36:S193-S194.

3 Necker, A., et al. (2004). IGF-1 responses in human muscle to strength training. Med Sci Sports Exerc. 36:S184.


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