Resting Myokine Concentrations Are Reduced With Resistance-exercise Training But Blood Flow-restricted Resistance-exercise Response Is Unchanged.

Abstract

Myokines are proteins and peptides produced and secreted by skeletal muscle; some are postulated to contribute to skeletal muscle hypertrophy. PURPOSE: To evaluate systemic myokine concentrations following acute blood-flow restricted resistance-exercise (BFR-RE) after a twelve-week traditional strength-training protocol in younger and older males. METHODS: Untrained males (younger: 24.7 ± 3.9 yrs, n = 8; older: 68.3 ± 4.6 yrs, n = 7) performed full-body BFR-RE before and after 12 weeks of progressive full-body strength training. At rest, immediately after, and 3, 6, 24 and 48 hours following each BFR-RE session, venous blood was collected and analyzed in duplicate to determine concentrations of interleukin-4 (IL-4), IL-6, IL-7, irisin, Leukemia Inhibitory Factor (LIF) and nitrate/nitrite. Area under the curve was calculated and a 2-way (age × training status) repeated measures ANOVA was conducted. RESULTS: For older males, IL-4 (untrained = 6996.9 ± 9260.2 AUC vs. trained = 5681.2 ± 8133.6 AUC; p = 0.038) and IL-6 (untrained = 819.2 ± 1104.5 AUC vs. trained = 636.5 ± 952.8 AUC; p = 0.016) were higher in the untrained condition than trained but did not differ for younger males. A significant age effect was identified for irisin, as younger males had higher concentrations than older (mean difference = 9423.8 ± 12546.8 AUC; p = 0.012). However, when AUC was calculated with baseline values subtracted, participants had higher IL-7 in the untrained condition compared to trained (mean difference = 33.5 ± 56.9 AUC; p = 0.04). Other myokines showed no training differences. CONCLUSION: Younger males had higher circulating irisin, and strength training decreased IL-4 and IL-6 in older males. The disappearance of age-related changes in IL-4 and IL-6 after baseline subtraction suggests those differences were due to lower baseline concentrations following the strength training program. Thus, IL-4 and IL-6 levels did not respond differently to BFR-RE in the untrained and trained conditions. Also, the lower response of IL-7 to BFR-RE in the trained vs. the untrained condition indicates that myokine secretion is affected by an individual’s level of training. Funding: This project was supported by grants (SMC & JEA) from the University Collaborative Research Program and Faculty of Science Collaborative - University of Manitoba.