Association of peak aerobic power with capillary density but not oxidative potential in human vastus lateralis muscle

In this study, we have postulated that in healthy males, peak aerobic power ((V) over dot O-2peak) would associate with muscle capillary density rather than oxidative potential, regardless of fibre type or subtype. To test this, active but untrained volunteers (n = 11) were separated into high (HI) and low (LO) groups based on (V) over dot O-2peak obtained during a progressive cycle task to fatigue. The 26% higher (P < 0.05) (V) over dot O-2peak observed in HI (40.8 +/- 1.5 mL-kg(-1)-min(-1), mean +/- SE) compared with LO (51.4 +/- 0.90 mL.kg(-1).min(-1), mean +/- SE) was not accompanied by differences in age (21.3 +/- 1.2 compared with 21.1 +/- 0.63 years, respectively) or body mass (72.4 +/- 4.6 compared with 71.6 +/- 1.9 kg, respectively). Tissue samples obtained from the vastus lateralis indicated greater (P < 0.05) capillary counts per fibre (CC; +24%) in HI compared with LO, regardless of fibre type (I, IIA, IIX, IIAX). Capillary density (CD) as measured in a field of defined area was also elevated (+22%; P < 0.05), as was the number of capillaries per fibre (+22%; P < 0.05). No differences were observed between the 2 groups in the distribution, area, and the CC/fibre area ratio in the different fibre types and subtypes. Similarly, there was no difference between the HI and LO groups in oxidative potential, as measured by succinic dehydrogenase activity in the different fibre types. It is concluded that the higher capillary density may contribute to improved vascular conductance and the elevated (V) over dot O-2peak observed in the untrained participants.