Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development

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Abstract
This study examined the effect of two different intense exercise training regimens on skeletal muscle ion transport systems, performance, and metabolic response to exercise. Thirteen subjects performed either sprint training [ST; 6-s sprints ( n = 6)], or speed endurance training [SET; 30-s runs ∼130% V̇o2 max, n = 7]. Training in the SET group provoked higher ( P < 0.05) plasma K+ levels and muscle lactate/H+ accumulation. Only in the SET group was the amount of the Na+/H+ exchanger isoform 1 (31%) and Na+-K+-ATPase isoform α2 (68%) elevated ( P < 0.05) after training. Both groups had higher ( P < 0.05) levels of Na+-K+-ATPase β1-isoform and monocarboxylate transporter 1 (MCT1), but no change in MCT4 and Na+-K+-ATPase α1-isoform. Both groups had greater ( P < 0.05) accumulation of lactate during exhaustive exercise and higher ( P < 0.05) rates of muscle lactate decrease after exercise. The ST group improved ( P < 0.05) sprint performance, whereas the SET group elevated ( P < 0.05) performance during exhaustive continuous treadmill running. Improvement in the Yo-Yo intermittent recovery test was larger ( P < 0.05) in the SET than ST group (29% vs. 10%). Only the SET group had a decrease ( P < 0.05) in fatigue index during a repeated sprint test. In conclusion, turnover of lactate/H+ and K+ in muscle during exercise does affect the adaptations of some but not all related muscle ion transport proteins with training. Adaptations with training do have an effect on the metabolic response to exercise and specific improvement in work capacity.