S. Green et al., Interstitial and arterial-venous [K+] in human calf muscle during dynamic exercise: effect of ischaemia and relation to muscle pain, J PHYSL LON, 529(3), 2000, pp. 849-861
1. Changes in the concentration of interstitial K+ surrounding skeletal mus
cle fibres ([K+](I)) probably play some role in the regulation of cardiovas
cular adjustments to muscular activity, as well as in the aetiology of musc
le 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 planter flexion exercise for four
5 min periods at increasing power outputs (similar to1-6 W) with 10 min int
ervening recovery periods, as well as for two 5 min periods with ischaemia
at similar to1 and similar to3 W. Microdialysis probes were inserted into t
he gastrocnemius medialis muscle of the right leg to measure [K+](I), and K
+ release from the plantar flexors during and after incremental exercise wa
s 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 minu
tes 3-5 of incremental exercise by similar to1-7 mmol l(-1) as a positive f
unction of power output. K+ release also increased as a function of exercis
e intensity, although there was a progressive increase by similar to1-6 mmo
l l(-1) in the [K+] gradient between the interstitium and arterial-venous p
lasma.
4. [K+](I) was lower during ischaemic exercise than control exercise. In co
ntrast to this effect of ischaemia on [K+](I), muscle pain was relatively h
igher 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 positi
ve function of exercise intensity, ischaemia reduces [K+](I) during rest an
d exercise, and the increase in [K+](I) is not responsible for muscle pain
during ischaemic exercise.