Stretch-Shortening Cycle in Roller Ski Skating: Effects of Speed

Abstract

The purpose of this study was to examine the effects of speed on the stretch-shortening cycle (SSC) behavior during roller ski skating. Ten highly skilled male cross-country skiers roller skied at 4.56, 5.33 m · s–1and maximal speed using the V2-alternate technique on a flat terrain. Knee and ankle joint kinematics, and EMG of thevastus lateralis(VL) andgastrocnemius lateralis(GL) muscles were recorded during the last 40 s of each bout of roller skiing. Maximal speed was associated with increases in cycle rate combined with decreases in cycle length. For VL, no significant differences were observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/Conc) and for the stretching velocity over the range of speeds. For GL, stretching velocity and iEMG Ecc/Conc were significantly greater at maximal speed. The analysis of GL EMG activity suggests that speed improved GL stiffness so that more elastic energy was stored, a better force transmission occurred, and coupling time decreased. These findings suggest that the efficiency of roller ski skating locomotion may be increased with speed through a better use of the stretch-shortening cycle pattern in the ankle extensors.