Six weeks of isocaloric moderate- and heavy-intensity continuous training improves fitness but does not alter plasma cytokines in healthy young adults.

OBJECTIVES: The anti-inflammatory effects of exercise training are hypothesized to involve changes in circulating cytokine concentrations, however the influence of exercise intensity is unclear. We determined the impact of exercise intensity, prescribed relative to lactate threshold (LT), on changes in fitness and plasma cytokines in a 6-week randomized controlled trial. DESIGN: RCT. METHODS: Healthy, young adults (N = 56, 27 males/29 females, age: 22 ± 3 y, peak oxygen consumption [VO2peak]: 38.4 ± 9.5 mL∙kg-1∙min-1) were randomized (2:2:1) to 6 weeks of thrice weekly isocaloric continuous cycling in the moderate (MICT; n = 21) or heavy (HICT; n = 24) intensity domain, or no-exercise control (CTRL; n = 11). Fasting plasma interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α, and fitness were assessed at baseline and post-training. RESULTS: There was no impact of training or intensity (all p > 0.05) on changes in IL-6 (MICT +0.03 pg∙mL-1 95% CI -0.08, 0.13; HICT +0.03 pg∙mL-1 95% CI -0.08, 0.13; CTRL -0.14 pg∙mL-1 95% CI -0.30, 0.01), IL-10 (MICT +0.05 pg∙mL-1 95% CI -0.01, 0.11; HICT +0.02 pg∙mL-1 95% CI -0.05, 0.08; CTRL -0.02 pg∙mL-1 95% CI -0.11, 0.08), or TNF-α (MICT +0.12 pg∙mL-1 95% CI -0.01, 0.26; HICT +0.07 pg∙mL-1 95% CI -0.06, 0.21; CTRL -0.03 pg∙mL-1 95% CI -0.22, 0.17). VO2peak (absolute and relative) and power at LT increased with training (p < 0.002) with no significant differences between MICT and HICT (p > 0.331). CONCLUSIONS: In conclusion, 6 weeks of isocaloric, LT-prescribed training in the moderate and heavy domains improves fitness but does not appear to impact fasting plasma cytokine concentrations in healthy young adults.