Abstract
Brief periods of aerobic exercise training lead to reductions, rather then the expected increases in circulating IGF-I. We hypothesized that intense exercise training in adolescents initially leads to simultaneous increases in proinflammatory cytokines and decreases in activity of the GH/IGF-I axis; and that as exercise training proceeds, levels of proinflammatory cytokines become reduced, and a rebound in IGF-I ensues leading to the higher IGF-I levels. To test this, we evaluated the GH/IGF-I axis and levels of inflammatory cytokines (IL-6, TNF-alpha, IL-1beta, IL-1ra), body composition, and fitness in 13 healthy adolescent boys (mean age 15.9 +/- 0.3 yr) over the course of a high-school wrestling season. Subjects were tested preseason, midseason (6 wk), peak season (12-14 wk), and 4 wk postseason. No significant weight loss was noted throughout the season. During the wrestling season (mid and peak) both total (P < 0.046) and free (P < 0.002) IGF-I levels decreased, whereas proinflammatory cytokines (IL-1ra, P < 0.005; IGFBP-1, P < 0.013; and IGFBP-2, P < 0.025) increased. GHBP (P < 0.018) levels also decreased during the season. In the postseason, there were significant increases in GHBP, and free and total IGF-I, whereas proinflammatory cytokines decreased. An initial catabolic-type hormonal response occurs with intense exercise training in adolescents. This is followed by a rebound in circulating growth factors when the period of heavy training ceases.
Highlights
In support of this idea, we recently demonstrated that a single bout of intense exercise, even in healthy adolescents, can lead to stimulation of interleukin- 6 (IL-6), interleukin-1 (IL-1), and tumor necrosis factor-␣ (TNF-␣)] all of which can directly suppress the GH/IGF-I axis [26]
We hypothesized: 1) that intense exercise training in adolescents would initially lead to simultaneous increases in proinflammatory cytokines and decreases in activity of the GH/IGF-I axis; and 2) that as exercise training proceeds, levels of proinflammatory cytokines would become reduced while an increase in IGF-I ensues
This study demonstrates that the response to a period of exercise training in adolescence is characterized by a remarkable inverse relationship between proinflammatory, predominantly catabolic mediators, and the anabolic hormone IGF-I
Summary
Method: To test this, we evaluated the GH/IGF-I axis and levels of inflammatory cytokines (IL-6, TNF-␣, IL-1, IL-1ra), body composition, and fitness in 13 healthy adolescent boys (mean age 15.9 Ϯ 0.3 yr) over the course of a high-school wrestling season. During the wrestling season (mid and peak) both total (P Ͻ 0.046) and free (P Ͻ 0.002) IGF-I levels decreased, whereas proinflammatory cytokines (IL-1ra, P Ͻ 0.005; IGFBP-1, P Ͻ 0.013; and IGFBP-2, P Ͻ 0.025) increased.
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