Human critical power-oxygen uptake relationship at different pedalling frequencies

Critical power (CP) is lower at faster rather than slower pedalling frequencies and traditionally reported in watts (W). Faster pedalling frequencies also engender a greater metabolic rate (VO2) at low work rates, but with progressive increases in power output, the initial difference in VO2 between fast and slower pedalling frequencies is reduced. We tested the hypothesis that CP represents a unique metabolic rate for any given individual which would be similar at different pedalling frequencies. Eleven collegiate athletes (five cross-country runners, END; six sprinters, SPR), aged 18-23 years, performed exhaustive rides at either 60 or 100 r.p.m. on separate days for the determination of the pedal rate-specific CP. The VO2 at CP (CP-VO2) was determined from an 8 min ride at the CP for each pedal frequency. The group mean CP was significantly lower at 100 r.p.m. (189 +/- 50 W) compared to 60 r.p.m. (207 +/- 53 W, P < 0.05). However, the group mean CP-VO2 values at 60 (2.53 +/- 0.60 l min(-1)) and 100 r.p.m. (2.58 +/- 0.53 l min(-1)) were not significantly different. Critical power was significantly higher in the END athletes (242 +/- 50 W at 60 r.p.m.; 221 +/- 56 W at 100 r.p.m.) compared to SPR athletes at both pedal frequencies (177 +/- 38 W at 60 r.p.m.; 162 +/- 27 W at 100 r.p.m., P < 0.05), but the CP-VO2 was not (P > 0.05). However, when the CP-VO2 was scaled to body weight, the END athletes had a significantly greater CP-VO2 (41.3 +/- 4.1 ml min(-1) kg(-1) at 60 r.p.m.; 40.8 +/- 5.5 ml min(-1) kg(-1) at 100 r.p.m.) compared to the SPR athletes at both pedal frequencies (27.7 +/- 4.6 ml min(-1) kg(-1) at 60 r.p.m.; 29.4 +/- 2.8 ml min(-1) kg(-1) at 100 r.p.m., P < 0.05). We conclude that CP represents a specific metabolic rate (VO2) which can be achieved at different combinations of power outputs and pedalling frequencies.