The Influence of Eccentric and Concentric Muscle Contractions on Concentration of Growth Factors in Strength Trained Athletes.

The aim of this study was to compare the growth factors (testosterone, growth hormone, insulin growth factor and insulin growth factor binding protein-3) concentrations and physiological responses during eccentric and concentric muscle contractions in strength trained athletes. A group of nine subjects performed an incremental exercise test requiring concentric and eccentric muscle contractions. Serum growth hormone (GH), insulin-like growth factor (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) were assessed, before and after both types of exercise. The concentrations of IGF-I and GH tended to be higher during exercise than at rest and reached the level of statistical significance at maximal exercise intensity (p<0.05 and p<0.01). In summary, the data from this investigation demonstrates that the increase in serum IGF-I concentration occurs after incremental arm exercise but the changes are independent of endogenous growth hormone responses. Therefore this data supports the importance of local variables in the magnitude of the IGF response system. The direct mechanism is more pronounced during eccentric exercise what could stimulate muscle mass and strength after this type of muscle contractions.