Effects of Eccentric and Concentric Emphasized Resistance Exercise on IL-15 Serum Levels and Its Relation to Inflammatory Markers in Athletes and Non-Athletes

Cytokines play an important role in modulating the muscle's metabolic and immunological responses to exercise. In the present study, we investigated changes in the serum levels of Interleukin (IL)-15 as well as tumor necrosis factor (TNF)-α and high sensitivity C-reactive protein (hs-CRP), as markers of inflammation, in athlete and non-athlete young men following eccentric (ECC) and concentric (CON) emphasized resistance exercise (RE). This study recruited 28 young males, 14 athletes and 14 non-athletes. Subjects completed two bouts of ECC and CON emphasized RE five days apart. Each bout included seven exercises that emphasized all major muscle groups with weight loads of 70% - 80% of one repetition maximum (1RM) for CON RE and 90% - 100% of 1RM for ECC RE. We analyzed subjects' blood samples before and immediately after each bout of exercise to determine cytokine and hs-CRP serum levels according to enzyme-linked immunosorbent assay. Statistical analysis showed a significant difference between IL-15 serum levels before and after ECC and CON RE in non-athletes (P = 0.03). In athletes, IL-15 serum level only increased after ECC RE (P = 0.01), which was noted to be the highest degree of change in IL-15 levels in all subjects. For athletes, the hs-CRP levels significantly decreased (P < 0.05). The serum levels of both TNF-α and hs-CRP were also significantly down-regulated after ECC RE in non-athletes. These results indicated that fitness level and RE could modulate circulating levels of IL-15 and suggest the potential anti-inflammatory effects of IL-15 during RE.