Passive cycling, during which a motor drives the pedals, increases energy expenditure above rest. However, little is known about the factors that influence energy expenditure during passive cycling. Our purpose was to quantify how leg mass, cycling cadence, and adaptation influence the energy expenditure during passive cycling. Eleven sedentary to recreationally active non-cyclists (5M, 6F, age 18-30) participated. The role of leg mass was studied by comparing one- and two-leg passive cycling. Cycling trials were performed at both 60 and 90 RPM to study the influence of cycling cadence. Adaptation was studied using multiple cycling trials and a 30-minute passive cycling trial. Rest and active (no load) cycling trials were performed for energy cost comparisons. Passive cycling significantly (p<0.03) increased energy expenditure above rest for all cycling trials. The increases in energy expenditure during passive cycling were greater when two legs were compared to one leg (37% vs. 15% at 60 RPM;​ p=0.008 and 93% vs. 44% at 90 RPM;​ p=0.001). The increase in energy expenditure was greater for 90 RPM compared to 60 RPM two-leg passive cycling (93% vs. 37%;​ p<0.001). The increase in energy expenditure was repeatable over multiple trials and was sustained for exercise durations of 30-minutes. Compared to the passive cycling trials, energy expenditure was significantly greater during active (no load) cycling at 60 and 90 RPM. In conclusion, increases in energy expenditure during passive cycling are directly related to the amount of activated leg mass and cycling cadence and not influenced by adaptation.