The Rolling Resistances of Roller Skis and Their Effects on Human Performance during Treadmill Roller Skiing

Modern ski-treadmills allow cross-country skiers, biathletes and ski-orienteers to test their physical performance in a laboratory environment using classical and freestyle techniques on roller skis. For elite athletes the differences in performance between test occasions are quite small, thus emphasising the importance of knowing the roller skis’ rolling resistance coefficient, μR, in order to allow correct comparisons between the results, as well as providing the opportunity to study work economy between different athletes, test occasions and core techniques. Thus, one of the aims of this thesis was to evaluate how roller skis’ μR is related to warm-up, mass, velocity and inclination of the treadmill. It was also necessary to investigate the methodological variability of the rolling resistance measurement system, RRMS, specially produced for the experiments, with a reproducibility study in order to indicate the validity and reliability of the results. The aim was also to study physiological responses to different μR during roller skiing with freestyle and classical roller skis and techniques on the treadmill as a case in which all measurements were carried out in stationary and comparable conditions. Finally, the aim was also to investigate the work economy of amateurs and female and male junior and senior cross-country skiers during treadmill roller skiing, i.e. as a function of skill, age and gender, including whether differences in body mass causes significant differences in external power per kg due to differences in the roller skis’ μR. The experiments showed that during a warm-up period of 30 minutes, μR decreased to about 60-65% and 70-75% of its initial value for freestyle and classical roller skis respectively. For another 30 minutes of rolling no significant change was found. Simultaneous measurements of roller ski temperature and μR showed that stabilized μR corresponds to a certain running temperature for a given normal force on the roller ski. The study of the influence on μR of normal force, velocity and inclination produced a significant influence of normal force on μR, while different velocities and inclinations of the treadmill only resulted in small changes in μR. The reproducibility study of the RRMS showed no significant differences between paired measurements with either classical or the freestyle roller skis. The study of the effects on physiological variables of ~50% change in μR, showed that during submaximal steady state 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 significantly changed 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.