Cold-water immersion after training sessions: Effects on fiber type-specific adaptations in muscle K+ transport proteins to sprint-interval training in men

Effects of regular use of cold-water immersion (CWI) on fiber type-specific adaptations in muscle K⁺ transport proteins to intense training, along with their relationship to changes in mRNA levels after the first training session, were investigated in humans. Nineteen recreationally-active men (24{plus minus}6 y, 79.5{plus minus}10.8 kg, 44.6{plus minus}5.8 mL∙kg-1∙min-1) completed six weeks of sprint-interval cycling either without (passive rest; CON) or with training sessions followed by CWI (15 min at 10{degree sign}C; COLD). Muscle biopsies were obtained before and after training to determine abundance of Na⁺,K⁺-ATPase isoforms (α_1-3, β_1-3) and FXYD1, and after recovery treatments (+0 h and +3 h) on the first day of training to measure mRNA content. Training increased (p<0.05) the abundance of α₁ and β₃ in both fiber types, β₁ in type-II fibers, and decreased FXYD1 in type-I fibers, whereas α₂ and α₃ abundance was not altered by training (p>0.05). CWI after each session did not influence responses to training (p>0.05). However, α₂ mRNA increased after the first session in COLD (+0 h, p<0.05), but not in CON (p>0.05). In both conditions, α₁ and β₃ mRNA increased (+3 h; p <0.05), β₂ mRNA decreased (+3 h; p<0.05), whereas α₃, β₁, and FXYD1 mRNA remained unchanged (p>0.05) after the first session. In summary, Na⁺,K⁺-ATPase isoforms are differently regulated in type I and II muscle fibers by sprint-interval training in humans, which for most isoforms do not associate with changes in mRNA levels after the first training session. CWI neither impairs nor improves protein adaptations to intense training of importance for muscle K⁺ regulation.