Roller skis' rolling resistance and grip characteristics influences on physiological and performance measures in cross-country skiers

Sammanfattning: The aim of this thesis was to investigate roller ski characteristics; classical and freestyle roller skis’ rolling resistance coefficients (?R) and classical style roller skis’ static friction coefficients (?S), and to study the influence of different ?R and ?S on cross-country skiers’ performance and both physiological and biomechanical indices. The aim was also to study differences in skiing economy and efficiency between recreational skiers, female and male junior and senior elite cross-country skiers.The experiments showed that during a time period of 30 minutes of rolling on a treadmill (warm-up), ?R decreased significantly (p<0.05) to about 60-65 % and 70-75 % of its initial value for freestyle and classical roller skis respectively. Also, there was a significant influence of normal force on ?R, while different velocities and inclinations of the treadmill only resulted in small changes in ?R.The study of the influence on physiological variables of a ~50 % change in ?R showed that during submaximal steady rate exercise, external power, oxygen uptake, heart rate and blood lactate were significantly changed, while there were non-significant or only small changes to cycle rate, cycle length and ratings of perceived exertion. Incremental maximal tests showed that time to exhaustion was significantly changed and this occurred without a change in maximal power, maximal oxygen uptake, maximal heart rate and blood lactate, and that the influence on ratings of perceived exertion was non-significant or small.The study of classical style roller skis ?S showed values that were five to eight times more than the values of ?S reported from on-snow skiing with grip-waxed cross-country skis.The subsequent physiological and biomechanical experiments with different ?S showed a significantly lower skiing economy (~14 % higher v?O2), higher heart rate, lower propulsive forces coming from the legs and shorter time to exhaustion (~30 %) when using a different type of roller ski with a ?S similar to on-snow skiing, while there was no difference between tests when using different pairs of roller skis with a (similar) higher ?S.The part of the thesis which focused on skiing economy and efficiency as a function of skill, age and gender, showed that the elite cross-country skiers had better skiing economy and higher gross efficiency (5-18 %) compared with the recreational skiers, and the senior elite had better economy and higher efficiency (4-5 %) than their junior counterparts, while no differences could be found between the genders.