Introduction Cost of locomotion (CL) has been shown to increase after endurance running and cycling bouts. The main purpose of this study was to compare, in the same participants, the effect of both modalities on CL when matched for relative intensity and duration. Methods Seventeen recreational athletes performed two incremental tests in running and cycling to determine the first ventilatory threshold then two 3-h bouts of exercise at 105% of threshold, with gas exchange measurements taken for 10 min at the start, middle and end of the 3 h to calculate CL. Neuromuscular fatigue during isometric knee extensor contractions and force-velocity profile on a cycle ergometer were assessed before and immediately after the 3-h trials. Results CL significantly increased at mid (+3.7%, P = 0.006) and end (+7.4%, P < 0.001) of exercise for cycling compared with start, whereas it did not change with time for running. Cardio-respiratory and metabolic variables changed similarly for cycling and running, therefore not explaining the time-course differences in CL between modalities. Changes in CL during cycling correlated significantly with loss of maximal force extrapolated from the force-velocity profile (r = 0.637, P = 0.006) and changes in cadence (r = 0.784, P < 0.001). Conclusions The type of locomotion influences the effects of exercise on energy cost because 3 h of exercise at the same relative intensity caused a significant increase of cycling CL, and no changes in running CL. The changes in CL in cycling are likely due, at least in part, to fatigue in the locomotor muscles.
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