title: Influence of individual energy cost on running capacity in warm, humid environments.
abstract: OBJECTIVE
  Challenging environmental conditions including heat and humidity are associated with particular risks to the health of runners and triathletes during prolonged events. The heat production of a runner is the product of its energy cost of running (C r) by its velocity. Since C r varies greatly among humans, those individuals with high C r are more exposed to heat stress in warm and humid conditions. Although risk factor awareness is crucial to the prevention of heat stroke and potential fatalities associated therewith, how C r affects the highest sustainable velocity (V) at which maximal heat loss matches heat production has not been quantified to date.
  
  
  METHODS
  Here, we computed in virtual runners weighting 45-75 kg, the influence of C r variability from 3.8 to 4.4 J·m(-1)·kg(-1) on V. Heat loss by radiation, convection, and conduction was assessed from known equations including body dimensions, running velocity (3.4-6.2 m·s(-1)), air temperature (T a, 10-35 °C) and relative humidity (r h, 50, 70 and 90 %).
  
  
  RESULTS
  We demonstrated a marked and almost linear influence of C r on V in hot and humid conditions: +0.1 J·kg(-1)·m(-1) in C r corresponded to -4 % in V. For instance, in conditions 25 °C r h 70 %, 65-kg runners with low C r could sustain a running speed of 5.7 m·s(-1) as compared to only 4.3 m·s(-1) in runners with high C r, which is huge.
  
  
  CONCLUSIONS
  We conclude that prior knowledge of individual C r in athletes exposed to somewhat warm and humid environments during prolonged running is one obvious recommendation for minimizing heat illness risk.
authors.affiliation: Centre de Recherche Cardio-Thoracique de Bordeaux, U1045, Univ. Bordeaux, 33000, Bordeaux, France, laurent.arsac@u-bordeaux2.fr.
authors.forename: Laurent M
authors.initials: LM
authors.lastname: Arsac
authors.forename: Veronique
authors.initials: V
authors.lastname: Deschodt-Arsac
authors.forename: Jean-René
authors.initials: JR
authors.lastname: Lacour
mesh_terms: D000328:Adult; D001833:Body Temperature Regulation; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008297:Male; D010807:Physical Endurance; D012420:Running / Q000502:physiology*