Lactate and acid-base exchange during brief intense contractions of skeletal muscle in situ

Our goal was to design a stimulation-contraction paradigm using an isolated in situ dog gastrocnemius muscle preparation that would provide an experimental model for brief intense intermittent (IC) exercise in humans. Second, acid-base and ion exchanges across the muscle were investigated using four 30-s bouts of isotonic tetanic contractions (2 s-1, 100-ms train, 50 impulses/s) with 4 min of rest between bouts. During the bouts, peak power output (W) was 18.2 mW/g in the first bout; it declined by 4.4% by the fourth bout and by 12-16% in each bout. Compared with repetitive continuous contractions (CC) at maximal O2 uptake (VO2), W was greater and VO2 (approximately 3.5 mumol.g-1.min-1) and CO2 production (approximately 4.5 mumol.g-1.min-1) were less with IC. Venous-arterial (v-a) differences and lactate output peaked immediately after each bout and were not different from the values reported for CC at maximal VO2. Thus, with IC, VO2/W was lower and the CO2 production/VO2 and lactate output/VO2 ratios were greater than those seen with CC. These differences suggest that this stimulation-contraction paradigm may be an appropriate model for brief intense exercise. The v-a [H+] difference was a direct result of the v-a PCO2 difference. The venous strong ion difference was always greater than or equal to the arterial strong ion difference because the v-a [Cl-] difference was opposite and greater than the v-a lactate concentration difference, whereas the v-a [Na+] and [K+] differences were small.(ABSTRACT TRUNCATED AT 250 WORDS)