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Received July 3, 2003
Revised September 11, 2003
Accepted after revision November 21, 2003
1 August Krogh Institute
2 Institute of Exercise and Sport Sciences
* To whom correspondence should be addressed. E-mail: jbangsbo{at}aki.ku.dk.
A rise in extracellular potassium concentration in human
skeletal muscle may play an important role for
development of fatigue during intense exercise. The aim
of the present study was to examine the effect of
intense intermittent training on muscle interstitial
potassium kinetics and its relationship to the density
of Na+,K+-ATPase subunits and
K+ATP channels as well as exercise
performance in human skeletal muscle. Six male subjects
performed intense one-legged knee-extensor training for
7 weeks. The trained leg (TL) and the control leg (CL)
performed on separate days a 30-min exercise period of
30-W and an incremental test to exhaustion. Frequently
during the exercise periods interstitial potassium
([K+]i) was determined by
microdialysis, femoral arterial and venous blood samples
were drawn and thigh blood flow was measured. Time to
fatigue for TL was 28% longer (p<0.05) than for CL (10.6
±0.7 (mean±SE) vs. 8.3±0.7 min).
The amount of Na+-K+-ATPase
subunits 
1 and 2
was 29.0±8.4 and 15.1±2.7% higher
(p<0.05) in TL compared to CL while the amount of 
1 subunits and K+ATP channels were
the same. In CL [K+]i increased
more rapidly and was higher (p<0.05) throughout the 30-W
exercise bout as well at 60- and 70-W compared to TL,
whereas [K+]i was similar at the
point of fatigue (9.9±0.7 and 9.1±0.5
mmol l-1 respectively). During the 30-W
exercise bout as well as at 50-W exercise femoral venous
potassium concentration ([K+]v)
was higher (p<0.05) in CL than in TL, but identical at
exhaustion (6.2±0.2 mmol l-1).
Release of potassium to the blood was not different in
the two legs. The present data demonstrated that intense
intermittent training reduce accumulation of potassium
in human skeletal muscle interstitium during exercise
probably through a larger re-uptake of potassium due to
a greater activity of the muscle Na+-
K+-ATPase pumps. The lower accumulation of
potassium in muscle interstitium in the trained leg was
associated with delayed fatigue during intense exercise,
supporting the hypothesis that interstitial potassium
accumulation is involved in the development of fatigue.
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