The metabolic cost of producing submaximal cycling power has been reported to vary with pedaling rate. Pedaling rate, however, constrains two physiological phenomena known to influence metabolic cost and efficiency: the frequency of muscle activation/relaxation and muscle shortening velocity. The purpose of this investigation was to determine the relative influence of those two phenomena on metabolic cost during submaximal cycling. Nine trained male cyclists performed submaximal cycling at power outputs intended to elicit 30, 60 and 90% of their individual lactate threshold at 4 pedaling rates (40, 60, 80, 100 rpm) with 3 different crank lengths (145, 170, and 195mm). The combination of 4 pedaling rates and 3 crank lengths produced 12 pedal speeds ranging from 0.61 to 2.04 m/s. Metabolic cost was determined by indirect calorimetery, and power output and pedaling rate were recorded. A stepwise multiple linear regression procedure selected mechanical power output, pedal speed, and pedal speed squared as the main determinants of metabolic cost (R²=0.990±.01). Neither pedaling rate nor crank length significantly contributed to the regression model. The cost of unloaded cycling and delta efficiency were 150 metabolic watts and 24.7% when data from all crank lengths and pedal speeds were included in a regression. Those values increased with increasing pedal speed and ranged from a low of 73±7 metabolic watts and 22.1±0.3% (145mm cranks, 40 rpm) to a high of 297±23 metabolic watts and 26.6±0.7% (195mm cranks, 100 rpm). These results suggest that mechanical power output and pedal speed, a marker for muscle shortening velocity, are the main determinants of metabolic cost during submaximal cycling, whereas pedaling rate (i.e. activation/ relaxation rate) does not significantly contribute to metabolic cost.