title: The application of maximal heart rate predictive equations in hypoxic conditions.
abstract: OBJECTIVE
  Peak heart rate (HRpeak) is a common tool used in exercise prescription for groups in which maximal exercise intensity is contraindicated; however, the application of this method in normobaric hypoxia is unknown. Therefore, this study investigated the response of HRpeak and the application of predictive HRpeak equations to prescribe exercise intensity in acute normobaric hypoxia. Results were used to examine whether age-derived HRpeak predictive equations are valid in hypoxic conditions.
  
  
  METHODS
  Fifteen untrained (eight men) volunteers (age 22 ± 2 years; peak rate of oxygen consumption 46.3 ± 7.0 ml kg(-1) min(-1)) completed incremental cycle ergometer tests (randomised order) to measure HRpeak at sea-level (SL (ambient inspiratory oxygen fraction (FIO2) 0.209)) and four normobaric hypoxic conditions FIO2: 0.185, 0.165, 0.142, 0.125 (≈1,000-4,000 m).
  
  
  RESULTS
  HRpeak was similar across all conditions (SL, 182 ± 13; 0.185, 178 ± 11; 0.165, 177 ± 9; 0.142, 178 ± 9; 0.125, 175 ± 10 b min(-1)) despite a reduction in oxygen saturation with increasing hypoxia (SL, 95 ± 5; 0.185, 95 ± 2; 0.165, 92 ± 2; 0.142, 88 ± 3; 0.125, 82 ± 4 %; P ≤ 0.05). The HRpeak was overestimated by all equations compared to the measured value (P < 0.05). Four equations overestimated HRpeak in all conditions (P < 0.01); two in four conditions (0.185, 0.165, 0.142, 0.125; P < 0.01); and two in three conditions (0.165, 0.142, 0.125; P < 0.01).
  
  
  CONCLUSIONS
  The overestimation of HRpeak by commonly used age-derived predictive equations in normobaric hypoxic conditions suggests that despite possible contraindications researchers should directly measure HRpeak whenever possible if it is to be used to prescribe exercise intensities.
authors.affiliation: Department of Sport and Exercise Sciences, University of Chichester, College Lane, Chichester, West Sussex, PO19 6PE, UK.
authors.forename: Carla A
authors.initials: CA
authors.lastname: Gallagher
authors.forename: Mark E T
authors.initials: ME
authors.lastname: Willems
authors.forename: Mark P
authors.initials: MP
authors.lastname: Lewis
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Myers
mesh_terms: D000531:Altitude; D003627:Data Interpretation, Statistical; D015444:Exercise; D005080:Exercise Test / Q000592:standards*; D005260:Female; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010101:Oxygen Consumption; D012016:Reference Values; D055815:Young Adult