Muscle buffer capacity and aerobic fitness are associated with repeated-sprint ability in women

In addition to a high aerobic fitness, the ability to buffer hydrogen ions (H⁺) may also be important for repeated-sprint ability (RSA). We therefore investigated the relationship between muscle buffer capacity (βm_{in vivo} and βm_{in vitro}) and RSA. Thirty-four untrained females [mean (SD): age 19 (1) years, maximum oxygen uptake (V̇O_2peak) 42.3 (7.1) ml·kg⁻¹·min⁻¹] completed a graded exercise test (GXT), followed by a RSA cycle test (five 6-s sprints, every 30 s). Capillary blood was sampled during the GXT and before and after the RSA test to determine blood pH (pH_b) and lactate concentration ([La⁻]_b). Muscle biopsies were taken before (n=34) and after (n=23) the RSA test to determine muscle lactate concentration ([La⁻]_i), hydrogen ion concentration ([H⁺]_i) pH_i, βm_{in vivo} and βm_{in vitro}. There were significant correlations between work decrement (%) and βm_{in vivo} (r=−0.72, P<0.05), V̇O_2peak (r=−0.62, P<0.05), lactate threshold (LT) (r=−0.56, P<0.05) and changes in [H⁺]_i (r=0.41, P<0.05). There were however, no significant correlations between work decrement and βm_{in vitro}, or changes in [La⁻]_i, or [La⁻]_b. There were also no significant correlations between total work (J·kg⁻¹) during the RSA test and βm_{in vitro}, βm_{in vivo}, or changes in [La⁻]_i, pH_i, [La⁻]_b, or pH_b. There were significant correlations between total work (J·kg⁻¹) and both V̇O_2peak (r=0.60, P<0.05) and LT(r=0.54, P<0.05). These results support previous research, identifying a relationship between RSA and aerobic fitness. This study is the first to identify a relationship between βm_{in vivo} and RSA. This suggests that the ability to buffer H⁺ may be important for maintaining performance during brief, repeated sprints.