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 (12x30-s sprints) 2-3 times per wk and aerobic high-intensity training (4-5x3-4min at 90-100% of maximal heart rate) 1-2 times per wk for 7 wks, and reduced training volume by 70% (intervention period; IP). The duration of an intense exhaustive cycling bout (EX2; 356±6 W), performed 2.5min 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 to 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 K+ATP channel 2 (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, 7wks of intensified training with a reduced training volume improved performance during repeated intense exercise, which was associated with a greater muscle re-uptake of K+ and muscle buffer capacity but not with the amount of muscle ion transporters.