Stretch-shortening cycle in roller ski skating: Effects of speed

The purpose of this study was to examine the effects of speed on the stretc h-shortening cycle (SSC behavior during roller ski skating. Ten highly skil led male cross-country skiers roller skied at 4.56, 5.33 m . s(-1) and maxi mal speed using the V2-alternate technique on a flat terrain. Knee and ankl e joint kinematics, and EMG of the vastus lateralis NL) and gastrocnemius l ateralis (GL) muscles were recorded during the last 40 s of each bout of ro ller skiing. Maximal speed was associated with increases in cycle rate comb ined with decreases in cycle length. For VL, no significant differences wer e observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/C onc) and for the stretching velocity over the range of speeds. For GL, stre tching velocity and iEMG Ecc/Conc were significantly greater at maximal spe ed. The analysis of GL EMG activity suggests that speed improved GL stiffne ss so that more elastic energy was stored, a better force transmission occu rred, and coupling time decreased. These findings suggest that the efficien cy of roller ski skating locomotion may be increased with speed through a b etter use of the stretch-shortening cycle pattern in the ankle extensors.