title: Mechanical Energy and Propulsion in Ergometer Double Poling by Cross-country Skiers.
abstract: OBJECTIVE
  This study aims to investigate fluctuations in total mechanical energy of the body (Ebody) in relation to external ergometer work (Werg) during the poling and recovery phases of simulated double-poling cross-country skiing.
  
  
  METHODS
  Nine male cross-country skiers (mean ± SD age, 24 ± 5 yr; mean ± SD body mass, 81.7 ± 6.5 kg) performed 4-min submaximal tests at low-intensity, moderate-intensity, and high-intensity levels and a 3-min all-out test on a ski ergometer. Motion capture analysis and load cell recordings were used to measure body kinematics and dynamics. From these, Werg, Ebody (sum of the translational, rotational, and gravitational potential energies of all segments), and their time differentials (power P) were calculated. Ptot--the rate of energy absorption or generation by muscles-tendons--was defined as the sum of Pbody and Perg.
  
  
  RESULTS
  Ebody showed large fluctuations over the movement cycle, decreasing during poling and increasing during the recovery phase. The fluctuation in Pbody was almost perfectly out of phase with Perg. Some muscle-tendon energy absorption was observed at the onset of poling. For the rest of poling and throughout the recovery phase, muscles-tendons generated energy to do Werg and to increase Ebody. Approximately 50% of cycle Ptot occurred during recovery for all intensity levels.
  
  
  CONCLUSIONS
  In double poling, the extensive contribution of the lower extremities and trunk to whole-body muscle-tendon work during recovery facilitates a "direct" transfer of Ebody to Werg during the poling phase. This observation reveals that double poling involves a unique movement pattern different from most other forms of legged terrestrial locomotion, which are characterized primarily by inverted pendulum or spring-mass types of movement.
authors.affiliation: 1Center for Elite Sports Research, Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, NORWAY; and 2Swedish Winter Sports Research Center, Department of Health Science, Mid Sweden University, Östersund, SWEDEN.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Danielsen
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Sandbakk
authors.forename: Hans-Christer
authors.initials: HC
authors.lastname: Holmberg
authors.forename: Gertjan
authors.initials: G
authors.lastname: Ettema
mesh_terms: D001696:Biomechanical Phenomena; D004734:Energy Metabolism; D016552:Ergometry; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D009048:Motor Skills / Q000502:physiology; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology; D010101:Oxygen Consumption; D012865:Skiing / Q000502:physiology*; D013710:Tendons / Q000502:physiology; D060726:Torso / Q000502:physiology; D055815:Young Adult