The Relationship Between Extracellular Potassium Concentrations and Muscle Membrane Excitability Following a Sustained Submaximal Isometric Quadriceps Contraction

Abstract

The purpose of this study was to relate femoral venous plasma potassium concentrations ([K⁺]) following a fatiguing submaximal isometric quadriceps contraction, to the excitability of the muscle cell membrane as assessed by the compound muscle action potential (M-Wave) . Ten healthy male volunteers (22. 0 ± . 5 yrs) performed a unilateral 3 minute (min) sustained isometric quadriceps contraction at 30% of their maximum voluntary contraction (MVC) . M-Waves, peak evoked twitch torque, plasma lactate concentration ([La⁻]), and plasma potassium concentration ([K⁺]) were measured before, and at predetermined times over the course of a 15 min recovery period following the fatigue paradigm. Immediately post-exercise, twitch torque decreased to 58% of baseline, femoral venous [La⁻] had risen to 10 ± 0.8 mmol/1, and [K⁺] was significantly increased from 4.0 ± 0.1 mmol/1 to 5.9 ± 0.2 mmol/1. M-Wave amplitude illustrated a trend for potentiation increasing 9.5%-from 13.9 ± 2.4 mV pre-exercise, to 15.3 ± 2.8 mV at 1 min 20 seconds post-exercise. M-Wave area exhibited a similar trend from baseline, but values showed no statistical significance during this time. These results suggest that in spite of increased extracellular [K⁺] following this type of fatiguing exercise, muscle membrane excitability is maintained, which is probably due to the electrogenic nature of the highly active Na⁺ /K⁺ pump. This study was supported by the Natural Sciences and Engineering Research Council of Canada.