The relationship between plasma potassium,muscle membrane excitability and force following quadriceps fatigue |
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Authors: | W West A Hicks R McKelvie J O’Brien |
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Institution: | (1) Department of Kinesiology, McMaster University, 1280 Main St. West, Hamilton, Ontario L85 4 K1, Canada, CA;(2) Department of Medicine, McMaster University, 1200 Main St. West, Hamilton, Ontario L8N 375, Canada, CA |
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Abstract: | To examine the simultaneous changes in plasma K+], muscle excitability and force during fatigue, ten male adults (mean age = 22 ± 0.5 years) held an isometric contraction
of their right quadriceps muscle at an intensity of 30% maximum voluntary contraction (MVC) for 3 min. Femoral venous and
brachial arterial K+] were determined from serial samples drawn before, during, and for 15 min following the 3-min contraction. Each blood sample
was synchronized with a maximal stimulation of the right femoral nerve to evoke a twitch and compound muscle action potential
(M-wave). Immediately post-exercise, twitch torque was only 42% of baseline and femoral venous plasma K+] had increased significantly from 4.02 ± 0.08 mmol/l to 5.9 ± 0.22 mmol/l. Femoral venous plasma lactate rose to a peak level
of 10.0 ± 0.8 mmol/l at 1 min post exercise. The recovery of the twitch torque was exponentially related to the recovery of
femoral venous plasma K+] (r
2 = 0.93, P < 0.01). There was no evidence for any loss of muscle membrane excitability during the period of increased extracellular
K+], in fact, the M-waves tended to be potentiated in the early phases of the recovery period. These results suggest that muscle
membrane excitability is maintained in spite of increased extracellular K+] following fatigue induced by a sustained submaximal quadriceps contraction. However, the strong relationship between twitch
torque and femoral venous plasma K+] suggests that K+ may be exerting its effect distal to surface membrane action potential propagation, most likely in the T-tubular region.
Received: 20 April 1995/Received after revision and accepted: 8 January 1996 |
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Keywords: | Muscle fatigue Potassium Muscle membrane excitability M-wave |
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