Effect of intensified training on muscle ion kinetics, fatigue development, and repeated short-term performance in endurance-trained cyclists.

摘要

The effects of intensified training in combination with a reduced training volume on muscle ion kinetics, transporters, and work capacity were examined. Eight well-trained cyclists replaced their regular training with speed-endurance training (12 X 30 s sprints) 2-3 times per week and aerobic high-intensity training (4-5 X 3-4 min at 90-100% of maximal heart rate) 1-2 times per week for 7 wk and reduced training volume by 70% (intervention period; IP). The duration of an intense exhaustive cycling bout (EX2; 368 +- 6 W), performed 2.5 min after a 2-min intense cycle bout (EX1), was longer (P < 0.05) after than before IP (4:16 +- 0:34 vs. 3:37 +- 0:28 min:s), and mean and peak power during a repeated sprint test improved (P < 0.05) by 4% and 3%, respectively. Femoral venous K~+ concentration in recovery from EX1 and EX2 was lowered (P < 0.05) after compared with before IP, whereas muscle interstitial K~+ concentration and net muscle K~+ release during exercise was unaltered. No changes in muscle lactate and H~+ release during and after EX1 and EX2 were observed, but the in vivo buffer capacity was higher (P < 0.05) after IP. Expression of the ATP-sensitive K~+ (K_(ATp)) channel (Kir6.2) decreased by IP, with no change in the strong inward rectifying K~+ channel (Kir2.1), muscle Na~+-K~+ pump subunits, monocarboxylate transporters 1 and 4 (MCT1 and MCT4), and Na~+/H~+ exchanger 1 (NHE1). In conclusion, 7 wk of intensified training with a reduced training volume improved performance during repeated intense exercise, which was associated with a greater muscle reuptake of K~+ and muscle buffer capacity but not with the amount of muscle ion transporters.