title: Changes in Running Mechanics During a 6-Hour Running Race.
abstract: OBJECTIVE
  To investigate changes in running mechanics during a 6-h running race.
  
  
  METHODS
  Twelve ultraendurance runners (age 41.9 ± 5.8 y, body mass 68.3 ± 12.6 kg, height 1.72 ± 0.09 m) were asked to run as many 874-m flat loops as possible in 6 h. Running speed, contact time (tc), and aerial time (ta) were measured in the first lap and every 30 ± 2 min during the race. Peak vertical ground-reaction force (Fmax), stride length (SL), vertical downward displacement of the center of mass (Δz), leg-length change (ΔL), vertical stiffness (kvert), and leg stiffness (kleg) were then estimated.
  
  
  RESULTS
  Mean distance covered by the athletes during the race was 62.9 ± 7.9 km. Compared with the 1st lap, running speed decreased significantly from 4 h 30 min onward (mean -5.6% ± 0.3%, P < .05), while tcincreased after 4 h 30 min of running, reaching the maximum difference after 5 h 30 min (+6.1%, P = .015). Conversely, kvertdecreased after 4 h, reaching the lowest value after 5 h 30 min (-6.5%, P = .008); taand Fmaxdecreased after 4 h 30 min through to the end of the race (mean -29.2% and -5.1%, respectively, P < .05). Finally, SL decreased significantly (-5.1%, P = .010) during the last hour of the race.
  
  
  CONCLUSIONS
  Most changes occurred after 4 h continuous self-paced running, suggesting a possible time threshold that could affect performance regardless of absolute running speed.
authors: Nicola
authors: N
authors: Giovanelli
authors: Paolo
authors: P
authors: Taboga
authors: Stefano
authors: S
authors: Lazzer
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001827:Body Height; D015992:Body Mass Index; D005684:Gait / Q000502:physiology*; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*; D013997:Time Factors; D013996:Time and Motion Studies
keywords: ground-reaction force; kinematics; pacing strategy; ultraendurance; ultramarathon