Exercise and the GH-IGF-I Axis

Abstract

The effectiveness of physical (exercise) training depends on the training load and on the individual’s ability to tolerate it, and an imbalance between the two may lead to under- or overtraining. Therefore, many efforts have been made to find objective parameters to quantify the balance between training load and the athlete’s ability to tolerate it. One of the unique features of exercise is that it leads to a simultaneous increase of antagonistic mediators. On the one hand, exercise stimulates anabolic components of the growth hormone (GH) insulin like growth factor-I (IGF-I) axis. On the other hand, exercise elevates catabolic pro-inflammatory cytokines such as interleukin-6 (IL-6). The very fine balance between the anabolic and inflammatory/catabolic response to exercise will determine the effectiveness of exercise training and the health consequences of exercise. In this chapter we review the changes in the anabolic-catabolic hormonal balance and demonstrate their usage by athletes and/or their coaches to gauge training and preparation for competition. We also discuss recent advances in the use of hormonal genetic polymorphisms of the GH-IGF-I system as an additional assisting tool for talent identification and sports selection and perhaps also for building effective (i.e., more precise) training programs for athletes.