The effectiveness of stretch-shortening cycling in upper-limb extensor muscles during elite cross-country skiing with the double-poling technique

摘要

This investigation was designed to evaluate the effectiveness of stretch-shortening cycling (SSC_(EFF)) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSC_(EFF) was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (V_(max)). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of V_(max)). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMG_(FLEX), EMG_(EXT)), as well as prior to pole plant (EMG_(PRE)). SSC_(EFF) was defined as the ratio of aEMG_(FLEX) to aEMG_(EXT). EMG_(PRE) and EMG_(FLEX) increased with velocity for both muscles (P<0.01), as did SSC_(EFF) (from 0.9±0.3 to 1.3±0.5 for the triceps brachii and from 0.9±0.4 to 1.5±0.5 for the latissimus dorsi) and poling force (from 253±33 to 290±36N; P<0.05). Furthermore, SSC_(EFF) was positively correlated to V_(max), to EMG_(PRE) and EMG_(FLEX) (P<0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers.