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The relationships between plasma potassium, muscle excitability and fatigue during voluntary exercise in humans
Author(s) -
Shushakov Vladimir,
Stubbe Christian,
Peuckert Antje,
Endeward Volker,
Maassen Norbert
Publication year - 2007
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2006.036384
Subject(s) - medicine , endocrinology , potassium , chemistry , exercise intensity , intensity (physics) , muscle fatigue , physical exercise , sodium , electromyography , cardiology , heart rate , physical medicine and rehabilitation , blood pressure , physics , organic chemistry , quantum mechanics
The relationships between extracellular potassium elevation and EMG variables in relation to muscle fatigue were investigated during handgrip exercise in humans. Acid–base state, lactate, potassium ([K + ] v ) and sodium in venous plasma, as well as variables of surface voluntary and evoked (M‐wave) EMG were determined during repeated dynamic (DE) and static (SE) exercise (1 min exercise, 4 min rest). The different rises of [K + ] v were induced by randomly varied workloads. After 15 min of warming up, the M‐wave area increased to 124.9 ± 19.6% ( P < 0.001) in comparison with the control value. Simultaneously, the [K + ] v decreased from 4.1 ± 0.3 to 3.6 ± 0.3 mmol l −1 ( P < 0.01). During both SE and DE, there were marked intensity‐dependent signs of fatigue. The [K + ] v correlated with changes of the integrated EMG ( r = 0.87, P < 0.001 for both DE and SE). Changes in the M‐wave area during the exercise bouts correlated inversely with the [K + ] v ( r =−0.73, P < 0.001). The M‐wave area did not decrease below the control value at any intensity. The median frequency of the EMG decreased during exercise, depending on the exercise intensity ( r =−0.73 for SE, r =−0.47 for DE, P < 0.001) with a maximal decrease to about 80% after SE with the maximal workload. The muscle action potential propagation velocity changed in the range of about ±2%. For the first time, a negative relationship between venous potassium and M‐wave area was shown during voluntary exercise. However, there was no evidence that the decrease in muscle performance was mainly caused by a decrease in sarcolemmal excitability resulting from a high extracellular [K + ].