Interstitial pH in human skeletal muscle during and after dynamic graded exercise

Abstract

1. In this study a new method has been used to measure interstitial pH continuously in human muscle during graded exercise. Human subjects performed 5 min of one-legged knee-extensor exercise at power outputs of 30, 50 and 70 W. Muscle interstitial pH was measured continuously in microdialysis dialysate using the pH-sensitive fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(and -6)-carboxyfluorescein (BCECF). 2. The mean interstitial pH at rest was 7.38 +/- 0.02. Interstitial pH gradually reduced during exercise in a nearly linear manner. The mean value (range) of the lowest interstitial pH at 30, 50 and 70 W exercise was 7.27 (7.18-7.34), 7.16 (7.05-7.24) and 7.04 (6.93-7.12), respectively. 3. The lowest pH was obtained 1 min after exercise, irrespectively of the workload, after which interstitial pH recovered in a nearly exponential manner. The mean half-time for recovery was 5.2 min (range 4.1-6.1 min). The changes in interstitial pH exceeded the changes in venous blood pH. 4. The present study showed that interstitial pH decreased during exercise in relation to intensity. These pH changes could have implications for blood flow regulation as well as for modulations of membrane transport systems.

Figure 1. Interstitial acidification during exercise

Individual recordings of interstitial pH during 5 min of knee-extensor exercise are shown. The six panels refer to the six different subjects. The power output was 30 W (green), 50 W (blue) and 70 W (red). Exercise was started 5 min after onset of the recording (marked with horizontal bar). One subject, marked *, became exhausted after 2 min of 70 W exercise.

Figure 2. Peak interstitial pH during exercise at different power outputs

For each subject the line connects pH at rest and pH at peak interstitial acidification obtained at a power output of 30, 50 and 70 W. One subject, marked *, became exhausted after 2 min of 70 W exercise.

Figure 3. Intracellular, interstitial and venous pH during knee-extensor exercise

▪, mean (±s.e.m.) peak interstitial pH obtained in the present study. Data connected by a straight line. •, femoral venous pH during knee-extensor exercise (authors’ unpublished data); each value represents mean from six subjects. ○, femoral venous pH during exhaustive knee-extensor exercise in three studies (Sjøgaard et al. 1985; Bangsbo et al. 1996, 2000). The dashed line represents a regression line for the venous data. ▴, intracellular pH obtained with the homogenisation technique (Sjøgaard et al. 1985; Juel et al. 1990; Bangsbo et al. 1993a, Bangsbo 1996). Data from the literature represent means of five to six subjects.