The purpose of this study was to examine the effects of external loading on the energy cost and mechanics of roller ski skating. A group of 13 highly skilled male cross-country skiers roller skied at 19.0 ( SD 0.1) km x h(-1) without additional load and with loads of 6% and 12% body mass (mb). Oxygen uptake (VO2), knee and ankle joint kinematics, roller-ski electromyogram (EMG) of the vastus lateralis and gastrocnemius lateralis muscles, and roller ski velocity were recorded during the last 40 s of each 4-min period of roller skiing. One-way repeated measures ANOVA revealed that the VO2 expressed relative to total mass (mtot), joint kinetics, eccentric-to-concentric ratio of the integrated EMG, velocity changes within a cycle, and cycle rate did not change significantly with load. The subsequent analysis of the effect of load on each resistance opposing motion suggested that the power to sustain changes in translational kinetic energy, potential energy, and overcoming rolling resistance increased proportionately with the load. The lack of a significant change in VO2/mtot with external loading was associated with a lack of marked change in external mechanical power relative to mtot. The existence of an EMG signal during the eccentric phase prior to the thrust (concentric phase), as well as the lack of significant delay between the two phases, showed that a stretch-shortening cycle (SSC) occurs in roller ski skating. Taken together, the present results would suggest that external loading up to 12% mb does not increase storage and release of elastic energy of lower limb muscles during SSC in roller ski skating.