The effects of training intensity on muscle buffer capacity in females

We examined changes in muscle buffer capacity (βm_{in vitro}), \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2peak}}}} \) and the lactate threshold (LT) after 5 weeks of high-intensity interval training (INT) above the LT or moderate-intensity continuous training (CON) just below the LT. Prior to and immediately after training, 16 female subjects performed a graded exercise test to determine \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2peak}}}} \) and the LT, followed 2 days later by a resting muscle biopsy from the vastus lateralis muscle to determine βm_{in vitro}. Following baseline testing, the subjects were randomly placed into the INT (n=8) or CON training group (n=8). Subjects then performed 5 weeks of cycle training (3 days per week), performing either high-intensity INT (6–10×2 min at 120–140% LT with 1 min rest) or moderate-intensity CON (80–95% LT) training. Total training volume was matched between the two groups. After the training period, both groups had significant improvements in \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2peak}}}} \) (12–14%; P<0.05) and the LT (7–10%; P<0.05), with no significant differences between groups. The INT group, however, had significantly greater improvements in βm_{in vitro} (25%; 123±5–153±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹; P<0.05) than the CON group (2%; 130±12–133±7 μmol H⁺·g muscle dm⁻¹·pH⁻¹, P>0.05). Our results show that when matched for training volume, high-intensity interval training above the LT results in similar improvements in \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{{\text{2peak}}}} \) and the LT, but greater improvements in βm_{in vitro} than moderate-intensity continuous training below the LT. This suggests that training intensity is an important determinant of changes to βm_{in vitro}.