Cross-country skiing is one of the most demanding endurance sports. During the last decade there has been an enhanced emphasize on upper body development which has markedly improved skiers endurance and muscle strength in their arm and torso region and capability to utilize a high fraction of VO2 max in different skiing techniques. These improvements demonstrates a high adaptive potential and that upper body muscles can adapt towards a similar level as leg muscles in well-trained c.c. skiers. Moreover, novel biomechanical development with innovative modifications of skiing techniques has contributed to higher racing velocities, decisive for performance especially in the new sprint events and mass-start. One of the most important racing techniques is double poling (DP), a complex movement involving both the upper and lower body....THIS ABSTRACT IS LONGER THAN ALLOWED IN THIS DATABASE