Buffer capacity and lactate accumulation in skeletal muscle of trained and untrained men

Abstract

Buffer capacity (.beta.) of skeletal muscle has been determined in trained (n = 7) and in sedentary subjects (n = 8). The trained subjects were active in ball games where a high degree of anaerobic energy utilization is required. Percentage fiber type occurrence in the thigh muscle was not significantly different in the 2 groups. However, there was a tendency towards a higher proportion of type I (slow-twitch) fibers (61.5 .+-. 11.6% vs. 50.2 .+-. 12.5%) and a lower proportion of type IIB fibers (2.1 .+-. 3.5% vs 14.1 .+-. 16.3%) in the trained subjects. The proportion of the cross-sectional area of the muscle biopsies that was made up of type I or type II fibers was not different in the 2 groups. All subjects performed an isometric contraction of the knee extensors to fatigue at 61% of their maximal voluntary contraction force. Muscle biopsies were taken from the quadriceps femoris muscle at rest and immediately after contraction. The buffer capacity of muscle was calculated from: .beta. = (Muscle lactate (work)-Muscle lactate (rest))(Muscle pH(rest)-Muscle pH (work)). A higher buffer capacity (P < 0.05) was observed in the trained subjects (.beta. = 194 .+-. 30 mmolxpH-1xkg-1 dry wt.) compared to the sedentary group (.beta.=164 .+-. 20) (mean .+-. SD). An unexpected finding was that muscle lactate after contraction to fatigue was lower (30%, P < 0.01) and muscle pH was higher (6.80 .+-. 0.06 vs. 6.61 .+-. 0.12, P < 0.01) in the trained subjects than in the sedentary controls. Creatine phosphate stores were almost completely depleted in both groups. Post-exercise lactate values were related to the proportion of type II fibers in the muscle (P < 0.01). There was, however, no statistical correlation between .beta. and fiber type occurrence (P > 0.05). Skeletal muscle buffer capacity can evidently be changed by training in man. The lower lactate accumulation and pH decline after an isometric contraction to fatigue that was observed in the trained compared to the sedentary subjects is related to the training per se. However, the tendency towards a lower type I (slowtwitch) fiber percentage in the trained subjects is likely to have contributed to the observed differences.