title: The relationships between plasma potassium, muscle excitability and fatigue during voluntary exercise in humans.
abstract: 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+].
authors: Division of Sports and Work Physiology, Hannover Medical School, Carl-Neuberg Strasse 1, D-30625, Hanover, Germany. chouchakov.vladimir@mh-hannover.de
authors: Vladimir
authors: V
authors: Shushakov
authors: Christian
authors: C
authors: Stubbe
authors: Antje
authors: A
authors: Peuckert
authors: Volker
authors: V
authors: Endeward
authors: Norbert
authors: N
authors: Maassen
mesh_terms: D000200:Action Potentials; D000328:Adult; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011188:Potassium / Q000097:blood*; D012964:Sodium / Q000097:blood; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium