Muscle Fascicle Behavior During Cross-country Skiing

Abstract

The repetitive extension/flexion patterns are typical of muscle stretch-shortening cycles (SSC) and are commonly observed in sport movements such as running, jumping. In cross-county (x-c) skiing, relatively little evidence collected with kinematics, ground reaction force and electromyography (EMG) recordings suggests that SSC-like behavior can be identified in diagonal stride of classical technique x-c skiing. PURPOSE: The purpose of the present study was to examine the muscle-tendon unit (MTU) and muscle fascicle behaviors simultaneously during the diagonal stride of classical technique x-c skiing. METHODS: The muscle fascicle behavior was measured by the portable ultrasound machine (Prosound C3cv, Aloka Japan) in natural skiing conditions in the Vuokatti ski tunnel. The ultrasound machine with the weight of 5 kg was put on the rucksack of the skier and the probe was attached on the skin of the following muscles: vastus lateralis, rectus femoris, triceps brachii, medial gastrocnemius and soleus. Each fascicle behavior during skiing was studied separately using the same skiing speed of 4.5 m s-1, approximately. An experienced skier was used as a subject. The measurements included also EMGs from the same muscles as the ultrasound scanning was recorded. The 3D kinematics and the ground reaction force recordings were also preformed. RESULTS: Most of the measured fascicles were stretched in the MTU stretching phase followed by shortening in the MTU shortening phase. However, the relative stretching and shortening amplitudes of the fascicles and MTU were muscle specific. Additionally, the rectus femoris muscle showed interesting activation patterns and fascicle behavior during x-c skiing. SSC type behavior was observed in two different phases of the stride, emphasizing the role of the rectus femoris both in knee extension and hip flexion. The knee extension occurred from the end of the braking phase to the early push-off phase and the hip flexion during the early swing phase immediately following the push-off phase. This can explain quite logically why rectus femoris may show greater fatigue as compared to the vastus lateralis and medialis muscles in x-c skiing. CONCLUSIONS: Our results clearly showed the SSC-type fascicle and MTU behavior during x-c skiing as well as the double SSC behavior of the rectus femoris