title: Contribution of the legs to double-poling performance in elite cross-country skiers.
abstract: OBJECTIVE
  In the classical style of cross-country skiing, the double-poling (DP) technique, which is regarded as an upper-body exercise, is used on the flatter parts of a course. Limited biomechanical and physiological data are available about DP compared with other cross-country skiing techniques. The purpose of the present study was to evaluate the possible role of the lower body during DP.
  
  
  METHODS
  Eleven elite cross-country skiers performed two incremental tests using DP roller skiing at 1 degree inclination on a treadmill with or without locking the knee and ankle joints (DPLOCKED and DPFREE). Maximal and peak oxygen uptake (VO2max and VO2peak) during classic diagonal skiing and DP, respectively, were measured. In addition, heart rate, blood lactate concentration, and maximal DP velocity (Vmax) were determined. Pole-ground reaction forces and joint angles (elbow, hip, knee, and ankle) were analyzed.
  
  
  RESULTS
  The skiers obtained 7.7% higher VO2peak, 9.4% higher Vmax, and 11.7% longer time to exhaustion during DPFREE compared with DPLOCKED (all P < 0.05). There was a higher heart rate and blood lactate concentration in DPLOCKED at submaximal stages (all P < 0.05), with no difference in oxygen consumption. At 85% Vmax, corresponding to approximately 81% VO2peak FREE, the differences in physiological variables were accompanied by a 13.6% higher poling frequency, a 4.9% shorter poling phase, 13.3% shorter recovery phase, and 10.9% lower relative pole force in DPLOCKED (all P < 0.05).
  
  
  CONCLUSIONS
  Movements of the knee and ankle joints are an integrative part in the skillful use of the DP technique, and restriction of the motion in these joints markedly affects both biomechanical and physiological variables, impairing DP performance.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden. hc.holmberg@sok.se
authors.forename: Hans-Christer
authors.initials: HC
authors.lastname: Holmberg
authors.forename: Stefan
authors.initials: S
authors.lastname: Lindinger
authors.forename: Thomas
authors.initials: T
authors.lastname: Stöggl
authors.forename: Glenn
authors.initials: G
authors.lastname: Björklund
authors.forename: Erich
authors.initials: E
authors.lastname: Müller
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D016552:Ergometry; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption; D011187:Posture; D012865:Skiing / Q000502:physiology*