title: Optimal slopes and speeds in uphill ski mountaineering: a laboratory study.
abstract: OBJECTIVE
  The purpose of this study was to estimate the energy cost of linear (EC) and vertical displacement (ECvert), mechanical efficiency and main stride parameters during simulated ski mountaineering at different speeds and gradients, to identify an optimal speed and gradient that maximizes performance.
  
  
  METHODS
  12 subjects roller skied on a treadmill at three different inclines (10, 17 and 24 %) at three different speeds (approximately 70, 80 and 85 % of estimated peak heart rate). Energy expenditure was calculated by indirect calorimetry, while biomechanical parameters were measured with an inertial sensor-based system.
  
  
  RESULTS
  At 10 % there was no significant change with speed in EC, ECvert and mechanical efficiency. At 17 and 24 % the fastest speed was significantly more economical. There was a significant effect of gradient on EC, ECvert and mechanical efficiency. The most economical gradient was the steepest one. There was a significant increase of stride frequency with speed. At steep gradients only, relative thrust phase duration decreased significantly, while stride length increased significantly with speed. There was a significant effect of gradient on stride length (decrease with steepness) and relative thrust phase duration (increase with steepness).
  
  
  CONCLUSIONS
  A combination of a decreased relative thrust phase duration with increased stride length and frequency decreases ECvert. To minimize the energy expenditure to reach the top of a mountain and to optimize performance, ski-mountaineers should choose a steep gradient (~24 %) and, provided they possess sufficient metabolic scope, combine it with a fast speed (~6 km h(-1)).
authors.affiliation: Department of Physiology, Faculty of Biology and Medicine, Institute of Sports Sciences, University of Lausanne, Géopolis, Campus Dorigny, 1015, Lausanne, Switzerland.|Institute for Research in Rehabilitation, SuvaCare Rehabilitation Clinic, Avenue Grand-Champsec 90, 1950, Sion, Switzerland.
authors.forename: Caroline
authors.initials: C
authors.lastname: Praz
authors.affiliation: Laboratory of Movement Analysis and Measurement, Ecole Polytechnique Fédérale de Lausanne, EPFL STI IBI-STI, ELH 134, Station 11, 1015, Lausanne, Switzerland.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Fasel
authors.affiliation: Institute for Research in Rehabilitation, SuvaCare Rehabilitation Clinic, Avenue Grand-Champsec 90, 1950, Sion, Switzerland.|Institute of Social and Preventive Medicine (IUMSP), University Hospital of Lausanne (CHUV), Lausanne, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Vuistiner
authors.affiliation: Laboratory of Movement Analysis and Measurement, Ecole Polytechnique Fédérale de Lausanne, EPFL STI IBI-GE ELH 132, Station 11, 1015, Lausanne, Switzerland.
authors.forename: Kamiar
authors.initials: K
authors.lastname: Aminian
authors.affiliation: Department of Physiology, Faculty of Biology and Medicine, Institute of Sports Sciences, University of Lausanne, Géopolis, Campus Dorigny, 1015, Lausanne, Switzerland. bengt.kayser@unil.ch.
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009051:Mountaineering / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology; D012865:Skiing / Q000502:physiology*
keywords: Biomechanics; Endurance; Energy expenditure; Skiing