Cycling with blood flow restriction improves performance and muscle K⁺ handling and blunts the effect of antioxidant infusion in humans

Abstract

Key points Here, we provide evidence that reactive oxygen species (ROS) play a role in regulating K + homeostasis in the untrained musculature of humans, as indicated by attenuated thigh K + efflux during exercise with concomitant antioxidant infusion. We also demonstrate that interval training with blood flow restriction (BFR) augments improvements in performance and reduces K + release from contracting muscles during intense exercise  The effect of training with BFR on muscle K + handling appears to be partly mediated by increasing the protection against ROS, since the effect of antioxidant infusion was blunted after training with restricted blood flow. Further, training with BFR resulted in higher abundance of Na + ,K + -ATPase-isoform α1 in type-II (51%), β1 in type-I (33%), and FXYD1 in type-I (108%) and type-II (60%) muscle fibres. This suggests fibre type-specific adaptations in Na + ,K + -ATPase-isoform content are also important for improvements in muscle K + handling by training with BFR in humans. Abstract (max 250 words)We examined if blood flow restriction (BFR) would augment training-induced improvements in muscle K + handling and performance during intense exercise in men, and if these adaptations would be associated with an effect of muscle antioxidant function on thigh K + release and with fibre type-dependent modulation of Na + ,K + -ATPase-isoform abundance and FXYD1 phosphorylation. Ten recreationally-active men (25 ± 4 y, 49.7 ± 5.3 mL•kg -1 •min -1 ) performed 6 weeks of interval cycling, where one leg trained without (control; CON-leg) and the other leg with BFR (BFR-leg, pressure: 178 mmHg). Before and after training, catheters were inserted into the femoral artery and vein, and blood flow was assessed during single-leg kneeextensions at 25% (Ex1) and 90% of leg peak aerobic power (Ex2) with intravenous infusion of N-acetylcysteine (NAC) or saline (placebo), and a resting muscle biopsy was collected.After training, performance during exhaustive exercise increased to a greater extent in BFRleg (23%) than in CON-leg (12%, p<0.05), whereas thigh K + release during Ex2 was attenuated in BFR-leg only (p<0.05). Before training, NAC depressed K + release during Ex1 (p<0.05), but not during Ex2 (p>0.05). After training, this effect was blunted in BFR-leg (p<0.05), whilst the abundance of Na + ,K + -ATPase-isoform α1 in type-II (51%), β1 in type-I (33%), and FXYD1 in type-I (108%) and type-II (60%) fibres was higher in BFR-leg (p<0.05; vs. CON-leg). Thus, interval training with BFR elicits greater improvements in performance and reduces muscle net K + release during intense exercise, which may be caused by elevated ROS scavenging and fibre type-dependent increases in Na + ,K + -ATPase-isoform abundance.

Molecular stressors underlying exercise training‐induced improvements in K+ regulation during exercise and Na+,K+‐ATPase adaptation in human skeletal muscle

“…In agreement, long‐term treatment of kidney cells with H 2 O 2 resulted in upregulation of Na + ‐K + ‐ATPase expression and activity, whereas adding a bolus of the antioxidant apocynin abolished these effects in vitro . In extension of these results, blood flow restriction has been shown to augment increases in oxidative damage to a single exercise session, as well as facilitate training‐induced improvements in Na + ‐K + ‐ATPase‐isoform protein abundance and K + regulation in human skeletal muscle . Adding to this point, rapid and marked perturbations in redox homeostasis effectively increase ROS levels, whereas a single bout of post‐exercise cold‐water immersion, which is likely to temporarily perturb muscle redox state, caused a selective increase in Na + ‐K + ‐ATPase α 2 isoform mRNA expression in skeletal muscle of recreationally‐active men …”

“…In this study, we compared changes in mRNA and activation of signaling proteins (ie AMPK and CaMKII) to exercise sessions performed with reduced muscle blood flow (ie, blood flow restriction; BFR) and in systemic hypoxia (~3250 m altitude). Key observations were that BFR augmented exercise‐induced increases in FXYD1 mRNA content, type‐I fibre AMPK downstream signaling (increased ACC phosphorylation), and in markers of oxidative stress, consistent with an elevated FXYD1 protein abundance and a reduced net thigh K + release (ie improved K + regulation) during exercise following 6 weeks of blood‐flow‐restricted training . In contrast, the session in systemic hypoxia did not result in selective changes in levels of Na + ,K + ‐ATPase‐isoform mRNA transcripts, AMPK or CaMKII downstream signaling, or oxidative stress, despite a similar level of muscle hypoxia (as assessed in vivo by near‐infrared spectroscopy; NIRS) compared to the session with BFR .…”

“…In another experiment using lung tissue of piglets, increases in both global Na + ,K + ‐ATPase mRNA and protein content were evident after breathing hyperoxic gas (inspired oxygen fraction = 0.96) . Consistent with the observations in vitro, we have shown that exercise training with reduced muscle blood flow, which substantially raises muscle oxygen perfusion (>3‐fold) in the recovery from each exercise bout (as assessed in vivo by ultrasound Doppler), augmented training‐induced increases in muscle Na + ,K + ‐ATPase‐isoform abundance ( β 1 in type I, α 1 in type II, and FXYD1 in both fibre types) concomitant with a reduced net thigh K + release during near‐maximal exercise in humans . Together, this evidence suggests that increased oxygen perfusion of contracting muscle fibres may be a key stimulus underlying increases in Na + ,K + ‐ATPase expression and the capacity for K + regulation in human skeletal muscle.…”

“…High doses of ROS have been shown to impair myocytic force development by perturbing ion (eg Ca 2+ and K + ) homeostasis . Accordingly, antioxidant treatment in humans attenuated exercise‐induced increases in arterialised‐venous K + concentration, and thigh K + release, indicating ROS may affect plasma and muscle K + homeostasis in exercising humans. Disturbance of K + homeostasis due to ROS accumulation is likely mediated via oxidative modifications to, and in this case dysfunction, of K + channels and transport systems, including the Na + ,K + ‐ATPase .…”

“…However, most of these reviews go >15 years back and thus lack essential novel inputs, specifically about how different types of exercise training (eg interval‐endurance, sprint‐interval and resistance training regimens), may affect K + regulation and its key determinants, including Na + ,K + ‐ATPase function, content, and isoform expression, in humans. In line with findings in animals, a number of recent discoveries point to a different regulation of Na + ,K + ‐ATPase function and expression by exercise training between different human skeletal muscle fibre types . However, the potential implications of this fibre type‐dependent regulation have been scarcely examined.…”