Interstitial and arterial‐venous [K+] in human calf muscle during dynamic exercise: effect of ischaemia and relation to muscle pain

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Abstract
1 Changes in the concentration of interstitial K+ surrounding skeletal muscle fibres ([K+]I) probably play some role in the regulation of cardiovascular adjustments to muscular activity, as well as in the aetiology of muscle pain and fatigue during high-intensity exercise. However, there is very little information on the response of [K+]I to exercise in human skeletal muscle. 2 Five young healthy subjects performed plantar flexion exercise for four 5 min periods at increasing power outputs (≈1-6 W) with 10 min intervening recovery periods, as well as for two 5 min periods with ischaemia at ≈1 and ≈3 W. Microdialysis probes were inserted into the gastrocnemius medialis muscle of the right leg to measure [K+]I, and K+ release from the plantar flexors during and after incremental exercise was calculated from plasma flow and arterial-venous differences for K+. Calf muscle pain was assessed using a visual analogue scale. 3 On average, [K+]I was 4.4 mmol l−1 at rest and increased during minutes 3-5 of incremental exercise by ≈1-7 mmol l−1 as a positive function of power output. K+ release also increased as a function of exercise intensity, although there was a progressive increase by ≈1-6 mmol l−1 in the [K+] gradient between the interstitium and arterial-venous plasma. 4 [K+]I was lower during ischaemic exercise than control exercise. In contrast to this effect of ischaemia on [K+]I, muscle pain was relatively higher during ischaemic exercise, which demonstrates that factors other than changes in [K+]I are responsible for ischaemic muscle pain. 5 In conclusion, this study has demonstrated that during 5 min of dynamic exercise, [K+]I increases during the later period of exercise as a positive function of exercise intensity, ischaemia reduces [K+]I during rest and exercise, and the increase in [K+]I is not responsible for muscle pain during ischaemic exercise.