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Introduction

Endurance training leads to an improved ability of muscle to utilize oxygen. This is related to an increased density and function of mitochondria. The biogenesis and adaptation of mitochondria is a complex process mediated by various signalling pathways and seems to be highly sensitive to the type of exercise and the local environment in the muscle. Changes in the muslce environment in terms of altered metabolism and substrate accumulation are affected by changes in acid/base balance in response to exercise. Recent studies have shown that changes in acid/base balance may affect the regulation of mitochondrial adaptation to acute exercise; however, how this responds to training and relates to performance adaptations in humans is unclear. Similarly, the effect of acid/base balance on mechanisms underlying mitochondrial biogenesis is unclear. The objectives of this study were to examine the relationship between acid/base balance, mitochondrial biogenesis and adaptation.

Methods

Nineteen recreationally active men undertook a six-week periodised high-intensity interval training programme, a protocol known to produce increases in mitochondrial biogenesis. Participants were matched for aerobic fitness and randomly assigned to one of two different training groups. One group ingested sodium bicarbonate (alkaline) and the other group ingested a placebo prior to each training session. Performance test results, blood samples and muscle biopsies were collected before and after the six week training period and assessed for changes in aerobic fitness, blood metabolites and muscle markers of mitochondrial function and biogenesis. Changes in gene expression associated with mitochondrial biogenesis were also examined. 

Results

After the training period, there were significant (P < 0.05) improvements in TTF, Wmax and LT in both groups, citrate synthase activity in the alkaline group and VO2peak in the placebo group. Improvements were also seen in citrate synthase activity in the placebo group and VO2peak in the alkaline group, however these did not reach significance (P = 0.089 and 0.066 respectively).Despite these significant changes within groups in response to training, there were no significant differences between groups.

Discussion

Both training groups showed substantial changes in performance and physiological measures following the training period, however, suppressing exercise-induced acidosis during training did not significantly improve mitochondrial adaptations or performance in comparison to the placebo condition. However, there was a large degree of individual variation in the response and there were trends towards greater adaptations when exercise-induced acidosis was attenuated.