Caroline Praz1,2, Benedikt Fasel3, Philippe Vuistiner2,4, Kamiar Aminian3, Bengt Kayser5. 1. Institute of Sports Sciences and Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Géopolis, Campus Dorigny, Lausanne, 1015, Switzerland. 2. Institute for Research in Rehabilitation, SuvaCare Rehabilitation Clinic, Sion, Switzerland. 3. Laboratory of Movement Analysis and Measurement, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. 4. Institute of Social and Preventive Medicine (IUMSP), University Hospital of Lausanne (CHUV), Lausanne, Switzerland. 5. Institute of Sports Sciences and Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Géopolis, Campus Dorigny, Lausanne, 1015, Switzerland. bengt.kayser@unil.ch.
Abstract
PURPOSE: The aim of this study is to describe the effects of speed and gradient during uphill ski mountaineering on energy expenditure, to relate any changes to changes in stride characteristics, and to determine an optimal gradient and speed allowing minimization of energy expenditure. METHODS: 11 subjects were tested on snowy trails using their mountaineering skis (fitted with skins), boots and poles, at three gradients (7, 11 and 33 %) at 80 % of maximum heart rate (HRmax), and at 11 % also at 90 and 100 % of HRmax. Energy expenditure was calculated by indirect calorimetry to derive energy cost of locomotion (EC), vertical energy cost (ECvert) and mechanical efficiency, while stride length, stride frequency, relative and absolute thrust phase duration, and slope gradient were measured with an inertial sensor-based system. RESULTS: At 11 % there was no change with speed in EC, ECvert and mechanical efficiency, while stride length and frequency increased and absolute thrust phase duration decreased. There was an effect of gradient on EC, ECvert and mechanical efficiency, while speed, stride length and stride frequency decreased and absolute and relative thrust phase duration increased. The most economical gradient (lowest ECvert) was the steepest one. CONCLUSION: During ski mountaineering uphill at shallow gradient (11 %), EC, ECvert and mechanical efficiency do not vary with speed, while at steeper gradient (33 %) economy is improved. It follows that to minimize energy expenditure and optimize performance to reach a place located at a higher altitude, an athlete should choose a steep gradient, if he/she is able to maintain a sufficient speed.
PURPOSE: The aim of this study is to describe the effects of speed and gradient during uphill ski mountaineering on energy expenditure, to relate any changes to changes in stride characteristics, and to determine an optimal gradient and speed allowing minimization of energy expenditure. METHODS: 11 subjects were tested on snowy trails using their mountaineering skis (fitted with skins), boots and poles, at three gradients (7, 11 and 33 %) at 80 % of maximum heart rate (HRmax), and at 11 % also at 90 and 100 % of HRmax. Energy expenditure was calculated by indirect calorimetry to derive energy cost of locomotion (EC), vertical energy cost (ECvert) and mechanical efficiency, while stride length, stride frequency, relative and absolute thrust phase duration, and slope gradient were measured with an inertial sensor-based system. RESULTS: At 11 % there was no change with speed in EC, ECvert and mechanical efficiency, while stride length and frequency increased and absolute thrust phase duration decreased. There was an effect of gradient on EC, ECvert and mechanical efficiency, while speed, stride length and stride frequency decreased and absolute and relative thrust phase duration increased. The most economical gradient (lowest ECvert) was the steepest one. CONCLUSION: During ski mountaineering uphill at shallow gradient (11 %), EC, ECvert and mechanical efficiency do not vary with speed, while at steeper gradient (33 %) economy is improved. It follows that to minimize energy expenditure and optimize performance to reach a place located at a higher altitude, an athlete should choose a steep gradient, if he/she is able to maintain a sufficient speed.
Entities:
Keywords:
Biomechanics; Climbing; Endurance; Energy expenditure; Skiing
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