Blood-flow-restricted Training Augments Improvements In Muscle K+ Handling, Antioxidant Capacity And Exercise Performance In Men

Abstract

Exercise performance is partly limited by the muscle potassium ion (K+) transport capacity, which is determined by the function of the Na+,K+-ATPase (NKA). Studies in vitro suggest high levels of reactive oxygen species (ROS) compromise NKA function, and increased antioxidant content protects against NKA dysfunction. However, it remains unknown in humans if ROS affect muscle K+ handling, and if this capability is related to the antioxidant capacity. Exercise with reduced muscle blood flow (blood flow restriction, BFR) promote ROS production, which is important for increases in NKA and antioxidant content. Whether BFR may augment increases in muscle K+ handling and NKA content in humans are yet to be explored. PURPOSE: To examine if BFR can augment training-induced improvements in muscle K+ handling and exercise performance, and if these changes are related to an increased antioxidant capacity in men. METHODS: Ten healthy men (25 ± 4 y) performed 6 weeks of interval cycling without (CON-leg) or with BFR (170 mmHg, BFR-leg). Before and after training, catheters were inserted into the fem. artery and vein in both legs, and blood flow was assessed by ultrasound Doppler, to determine thigh K+ release during single-legged, knee-extensions at 25% (Ex1) and 90% Wmax (Ex2) under intravenous infusion of placebo (saline) or N-acetylcysteine (NAC). A muscle biopsy was collected before and after Ex2 to assess catalase activity, and NKA and antioxidant content in type-I and II fibres. RESULTS: Performance of the CON-leg (11%) and BFR-leg (23%) increased with training (p<0.05), with a greater increase in BFR-leg (p<0.05, 12%). After training, K+ release was attenuated in Ex2 in the BFR-leg (p<0.05), but not in CON-leg (p>0.05). Before training, NAC attenuated K+ release in Ex1 (p<0.05), but not in Ex2 (p>0.05), in both legs. After training, the effect of NAC was blunted and catalase activity increased in the BFR-leg only (p<0.05). NKA-isoform and antioxidant content are currently being analysed. CONCLUSION: BFR training augments improvements in muscle K+ handling and exercise performance in men. These effects are related to an increased muscle antioxidant capacity. In addition, ROS appear involved in the regulation of muscle K+ release during submaximal exercise in humans. Supported by the Danish Ministry of Culture (FPK.2015-0017)