[ Truncated abstract] The purpose of this series of studies was to further our understanding of the relationship between muscle buffer capacity and training. Study one was performed to determine if there were differences in muscle buffer capacity (βmin-vitro) between females of differing training status (i.e., team-sport, endurance-trained and untrained subjects). Studies two and three were then performed to determine if short-term training could improve muscle buffer capacity and what type of training best improves this muscle characteristic (i.e., high-intensity, moderate-intensity or resistance training). Studies four and five were performed to determine if the accumulation of H+ during exercise was a mechanism by which training improved muscle buffer capacity. Below is a summary of these five studies. Study 1. The team-sport group had a significantly higher βmin-vitro than either the endurance-trained or the untrained groups (181 ± 27 v 148 ± 11 v 122 ± 32 'mol H+?g dm-1?pH-1 respectively; P<0.05). The team-sport group also completed significantly more relative total work (299 ± 27 v 263 ± 31 v 223 ± 21 J?kg-1, respectively; P<0.05) and absolute total work (18.2 ± 1.6 v 14.6 ± 2.4 v 13.0 ± 1.9 kJ, respectively; P<0.05) than the endurance-trained or untrained groups during a repeated sprint ability (RSA) test. There was a significant correlation between βmin-vitro and RSA (r=0.67; P<0.05). These findings show that young females competing in team sports have a larger βmin-vitro than either endurance-trained or untrained females. This may be the result of the intermittent, high-intensity activity during training and the match play of team-sport athletes... Conclusions. Our results show that training intensity is an important determinant of muscle buffer capacity. High-intensity interval training (120-150% LT) improved muscle buffer capacity (9 27%), however, neither moderate-intensity or resistance training improved muscle buffer capacity. In contrast higher training intensity (150-180% LT) may negatively affect muscle buffer capacity. Differences in the accumulation of H+ during high-intensity interval training does not appear to be the underlying mechanism for changes to muscle buffer capacity, however changes to this muscle characteristic were associated with pre-training muscle buffer capacity.