title: Retrospective study of predictive variables for maximal heart rate (HRmax) in horses undergoing strenuous treadmill exercise.
abstract: BACKGROUND
  Heart rate is one of the most commonly measured variables in equine exercise physiology and relative exercise intensity commonly expressed as % of maximal heart rate. A number of influences affect maximal heart rate (HRmax), including age of the horse but other factors have not been described.
  
  
  OBJECTIVE
  To determine if fitness, health status, gender, breed, athletic use, body mass, in addition to age, are predictive of HRmax in the horse.
  
  
  METHODS
  Maximal heart rate data from 328 horses which underwent treadmill exercise tests at 5 different laboratories were obtained retrospectively. Univariable linear regression analyses were performed on individual variables. Multiple linear regression analysis using a backward elimination modelling procedure was then used to relate the observed HRmax values simultaneously with different predictive variables. Variables were retained in the final regression model if they or any of their categories were significantly predictive of HRmax at P<0.05 and if there was a significant collective contribution to the model from inclusion of each variable, also at P<0.05.
  
  
  RESULTS
  Age, fitness status, laboratory, gender and breed/use (combined category) were all statistically significantly predictive of HRmax. Together these variables accounted for 41% of the variance in HRmax. Age alone accounted for only approximately 13% of the variation between horses in HRmax. Neither body mass nor health status were significantly predictive.
  
  
  CONCLUSIONS
  HRmax in the horse declines with age but is also influenced by other factors. As the factors investigated accounted for only 41% of the variation between horses, other unidentified variables with a strong influence on HRmax remain to be identified.
  
  
  CONCLUSIONS
  Factors such as fitness, age, gender, breed and use need to be considered when interpreting estimates or measurements of HRmax.
authors.affiliation: Hartpury College, Hartpury House, Gloucester, UK.
authors.forename: T L
authors.initials: TL
authors.lastname: Vincen
authors.forename: J R
authors.initials: JR
authors.lastname: Newton
authors.forename: C M
authors.initials: CM
authors.lastname: Deaton
authors.forename: S H
authors.initials: SH
authors.lastname: Franklin
authors.forename: T
authors.initials: T
authors.lastname: Biddick
authors.forename: K H
authors.initials: KH
authors.lastname: McKeever
authors.forename: P
authors.initials: P
authors.lastname: McDonough
authors.forename: L E
authors.initials: LE
authors.lastname: Young
authors.forename: D R
authors.initials: DR
authors.lastname: Hodgson
authors.forename: D J
authors.initials: DJ
authors.lastname: Marlin
mesh_terms: D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000502:physiology; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006304:Health Status; D006339:Heart Rate / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D016014:Linear Models; D008297:Male; D010375:Pedigree; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012737:Sex Factors