Exercise-induced signs of muscle overuse in children

Signs of overuse after intense muscular exertion are well described in adul ts, while little research has been conducted in children. The aim of the st udy was to investigate some indirect markers of muscle damage in 13 years o ld boys following two different protocols of one-leg stepping exercise to e xhaustion. This stepping exercise was performed by two experimental groups with different contributions of concentric and eccentric contractions in a 1 :1 vs 1 :2 ratio of timing. Subjective soreness perception and maximum vo luntary isometric force of the knee extensor muscles were measured immediat ely prior to and immediately following the exercise, and at 1, 3, 24, 48, 7 2, 96 hours post exercise. Metabolic markers of exercise stress were taken at similar time intervals and included plasma glutathione concentrations as a marker for oxidative stress, circulating leukocyte numbers, and plasma c reatine kinase (CK) activity. All parameters studied demonstrated a higher level of muscular exertion, with more evident signs of overuse in the group with the more eccentric contribution. Complete recovery was achieved betwe en 72 and 96 hours after exertion. However, in this group of boys, the CK a ctivity did not show the typical adult-lilte increase. Therefore the wide u se of CK as an indicator of intense muscle exertion was not supported in th is group of children. It can be concluded that children, like adults, exper ience similar degrees of muscle disturbances following intense exercise and that they may recover more quickly from such exercise.