title: Changes in leg spring behaviour, plantar loading and foot mobility magnitude induced by an exhaustive treadmill run in adolescent middle-distance runners.
abstract: OBJECTIVE
  This study aimed to determine adjustments in spring-mass model characteristics, plantar loading and foot mobility induced by an exhaustive run.
  
  
  METHODS
  Within-participants repeated measures.
  
  
  METHODS
  Eleven highly-trained adolescent middle-distance runners ran to exhaustion on a treadmill at a constant velocity corresponding to 95% of velocity associated with VO₂max (17.8 ± 1.4 kmh(-1), time to exhaustion=8.8 ± 3.4 min). Contact time obtained from plantar pressure sensors was used to estimate spring-mass model characteristics, which were recorded (during 30 s) 1 min after the start and prior to exhaustion using pressure insoles. Foot mobility magnitude (a composite measure of vertical and medial-lateral mobility of the midfoot) was measured before and after the run.
  
  
  RESULTS
  Mean contact area (foot to ground), contact time, peak vertical ground reaction force, centre of mass vertical displacement and leg compression increased significantly with fatigue, while flight time, leg stiffness and mean pressure decreased. Leg stiffness decreased because leg compression increased to a larger extent than peak vertical ground reaction forces. Step length, step frequency and foot mobility magnitude did not change at exhaustion.
  
  
  CONCLUSIONS
  The stride pattern of adolescents when running on a treadmill at high constant velocity deteriorates near exhaustion, as evidenced by impaired leg-spring behaviour (leg stiffness) and altered plantar loading.
authors.affiliation: ASPIRE Health Centre - ASPETAR, National Sports Medicine Programme, Doha, Qatar. Electronic address: francois.fourchet@aspire.qa.
authors.forename: François
authors.initials: F
authors.lastname: Fourchet
authors.affiliation: Sport Science Department, ASPETAR - Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Olivier
authors.initials: O
authors.lastname: Girard
authors.affiliation: Sport Science Department, ASPETAR - Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Luke
authors.initials: L
authors.lastname: Kelly
authors.affiliation: ASPIRE Health Centre - ASPETAR, National Sports Medicine Programme, Doha, Qatar.
authors.forename: Cosmin
authors.initials: C
authors.lastname: Horobeanu
authors.affiliation: ISSUL Institute of Sport Sciences-Department of Physiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Grégoire P
authors.initials: GP
authors.lastname: Millet
mesh_terms: D000293:Adolescent; D056352:Athletes; D005528:Foot / Q000502:physiology; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D012420:Running / Q000502:physiology*; D016474:Weight-Bearing
keywords: Fatigue; Medial arch; Spring mass model; Stride mechanics