Beschreibung:
<jats:p>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<jats:sup><jats:bold>+</jats:bold></jats:sup>]<jats:sub>v</jats:sub>) 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<jats:sup><jats:bold>+</jats:bold></jats:sup>]<jats:sub>v</jats:sub>were induced by randomly varied workloads. After 15 min of warming up, the M‐wave area increased to 124.9 ± 19.6% (<jats:italic>P</jats:italic>< 0.001) in comparison with the control value. Simultaneously, the [K<jats:sup><jats:bold>+</jats:bold></jats:sup>]<jats:sub>v</jats:sub>decreased from 4.1 ± 0.3 to 3.6 ± 0.3 mmol l<jats:sup>−1</jats:sup>(<jats:italic>P</jats:italic>< 0.01). During both SE and DE, there were marked intensity‐dependent signs of fatigue. The [K<jats:sup><jats:bold>+</jats:bold></jats:sup>]<jats:sub>v</jats:sub>correlated with changes of the integrated EMG (<jats:italic>r</jats:italic>= 0.87,<jats:italic>P</jats:italic>< 0.001 for both DE and SE). Changes in the M‐wave area during the exercise bouts correlated inversely with the [K<jats:sup><jats:bold>+</jats:bold></jats:sup>]<jats:sub>v</jats:sub>(<jats:italic>r</jats:italic>=−0.73,<jats:italic>P</jats:italic>< 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 (<jats:italic>r</jats:italic>=−0.73 for SE,<jats:italic>r</jats:italic>=−0.47 for DE,<jats:italic>P</jats:italic>< 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<jats:sup><jats:bold>+</jats:bold></jats:sup>].</jats:p>