INTRODUCTION: The human musculoskeletal system is well adapted to use energy efficient muscle-tendon mechanics during walking and running 1, but muscle behaviour during snow locomotion is unknown. The presence of a stretch-shortening cycle during diagonal style skiing 2 indicates the potential for similar mechanisms as during running. Therefore, we hypothesised uncoupled muscle behaviour from that of the muscle-tendon unit during diagonal style roller skiing and increased muscle activity at greater speed and incline. METHODS: We synchronised ultrasound with motion capture, electromyography and ski-binding force measurements to assess lower leg muscle and muscle-tendon unit mechanics in thirteen high-level skiers during treadmill roller skiing. Participants skied using diagonal style in three speed and incline conditions (2.5 and 3.5 m/s at 5°, 2.5 m/s at 10°). RESULTS: We found an uncoupling of muscle and joint behaviour during most parts of the propulsive kick phase in all conditions (P < 0.01). Gastrocnemius muscle fascicles actively shortened ~9 mm during the kick phase, while the muscle-tendon unit went through a stretch-shortening cycle. Peak muscle-tendon unit shortening velocity was five times higher than fascicle velocity (375.3 vs 74 mm/s, P < 0.01, Figure 1). Increased incline was met by greater muscle activity (24%, P = 0.04) and slower fascicle shortening velocities (34 vs 45 mm/s, P < 0.01). Increased speed was met by greater peak muscle activity (23%, P < 0.01) and no change in fascicle shortening velocity. DISCUSSION/CONCLUSION: Our data show uncouped muscle behaviour from the joint movement, which enables beneficial contractile conditions and energy utilisation during diagonal style at different slopes and speeds. Active preloading at the end of the glide phase may benefit the mechanisms. REFERENCES: 1 Roberts, T. & Azizi, E., 2011. J Exp Biol 2 Komi, P.V. & Norman, R.W., 1987. Int J Sports Med
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