title: How do humans control physiological strain during strenuous endurance exercise?
abstract: BACKGROUND
  Distance running performance is a viable model of human locomotion.
  
  
  RESULTS
  To evaluate the physiologic strain during competitions ranging from 5-100 km, we evaluated heart rate (HR) records of competitive runners (n = 211). We found evidence that: 1) physiologic strain (% of maximum HR (%HRmax)) increased in proportional manner relative to distance completed, and was regulated by variations in running pace; 2) the %HRmax achieved decreased with relative distance; 3) slower runners had similar %HRmax response within a racing distance compared to faster runners, and despite differences in pace, the profile of %HRmax during a race was very similar in runners of differing ability; and 4) in cases where there was a discontinuity in the running performance, there was evidence that physiologic effort was maintained for some time even after the pace had decreased.
  
  
  CONCLUSIONS
  The overall results suggest that athletes are actively regulating their relative physiologic strain during competition, although there is evidence of poor regulation in the case of competitive failures.
authors.affiliation: Department of Exercise Physiology, European University of Madrid, Madrid, Spain.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Esteve-Lanao
authors.forename: Alejandro
authors.initials: A
authors.lastname: Lucia
authors.forename: Jos J
authors.initials: JJ
authors.lastname: deKoning
authors.forename: Carl
authors.initials: C
authors.lastname: Foster
mesh_terms: D000328:Adult; D000531:Altitude; D003163:Competitive Behavior / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D006813:Humidity; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D012420:Running; D013177:Sports; D013312:Stress, Physiological / Q000517:prevention & control*