Introduction: The development of cross country ski technique has increased the contribution of the upper body on the total power. Consequently, there is an increased interest in the development of highly advanced ergometers that measure force output and movement velocities in the specific action of cross country skiing. Evaluation and training of upper body power is usually performed by means of a traditional strength training apparatus. The movements performed on this equipment are however quite different from the specific motion. In order to reach a better reproducibility of the ski gesture, a new upper body ergometer (UB Ergo) has been built. The new apparatus is constituted by a system of cables, pulleys and an electric motor that act as load and is actively controlled by a personal computer on the basis of force and velocity sensors. This equipment would avoid some of the main limitation of the traditional strength training apparatus. Indeed the new ergometer has been designed in way that the force is required only during concentric contraction and each pulling cycle starts by a null velocity. The purpose of this study to assess the reliability of this new device for cross country ski specific test comparing the ski performance with the power evaluated with the new ergometer. Methods: 9 well trained cross-country male skiers (mean age 21.7 ±3.12; B.W. 72.2 ±3.8 kg), competing at the international level, participated in this study. The athletes performed two different test: 1- ski test: 3 controlled sprint on the 2006 Olympic track length 1,2 km with 15 minutes of recovery between trials, athletes were forced by means of acoustic warnings to performed the trials at about 95-97% of previous determined maximum. In last tract (180 m. avg. slope 1.37%) was requested the maximal effort and to use double poling technique. Velocity of this tract was used to quantify the performance in ski test. 2- UB Ergo test: 50 sec. double poling exercise. Force and velocity has been measured for each arm; from these data a post processing software calculates the mean power of each cycle. Results: Ski length cycle is significantly lower than ergometer (0.80±0.09 s vs. 1.31±0.19 s; p<0.001). The mean value measured for velocity is 6.69±0.64 m/s and the mean values calculated for power is 678±134 W. The data shows that there are a good correlation (R2=0.744, p<0.005) between average power measured with new upper body ergometer and the performance in ski specific action. Normalizing the power to the body weight the correlation between power and ski velocity become lower remaining however quite good (R2=0.59, p<0.05). Discussion and Conclusion: The difference of cycle length indicates that in the considered part of Olympic ski track the athletes don`t express maximal power to promote high velocity suggesting that in this case the ergometer correlation would be improved in a steeper track. This hypothesis could be supported considering that the power normalized to body weight leads to a decrease of the correlation with the velocity that could reflect the poor role of body weight on flat track performance. Weight normalizations have to be however considered on steeper track where it would be meaningful for the prediction of ski performance. The good correlation between ski velocity and the measured upper body power shows that the UB Ergo could be an effective tools to predict double poling ski performance. It could be therefore introduced in the evaluation protocols for elite cross country skiers.
© Copyright 2005 International Congress Mountain & Sport. Updating study and research from laboratory to field. 11th-12th November 2005. Rovereto (TN) - Italy. Programme and book of abstracts. Published by Centro Interuniversitario di Ricerca in Bioingegneria e Scienze Motorie. All rights reserved.