title: Factors underlying the perception of effort during constant heart rate running above and below the critical heart rate.
abstract: OBJECTIVE
  This study examined: (1) the sustainability of the critical heart rate (CHR) minus 5 b min(-1) (CHR - 5) and CHR plus 5 b min(-1) (CHR + 5); (2) the ratings of perceived exertion (RPE), velocity, [Formula: see text], minute ventilation ([Formula: see text]), breathing frequency (f b ), and electromyographic amplitude (EMG AMP) and EMG mean power frequency (MPF) responses during treadmill running at CHR - 5 and CHR + 5 to determine what factors underlie the perception of effort when heart rate (HR) is held constant; and (3) the relationships among RPE, [Formula: see text], and HR, to determine which variable(s) reflect exhaustion during exercise performed at a constant HR.
  
  
  METHODS
  The CHR was determined in eight runners (mean ± SD; age = 24 ± 3 years) from a series of four exhaustive, constant velocity runs. The RPE, velocity, [Formula: see text], [Formula: see text], f b , EMG AMP, and EMG MPF responses were recorded during runs at the CHR - 5 and CHR + 5.
  
  
  RESULTS
  At CHR - 5, RPE, f b, and EMG MPF increased, while velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased. At CHR + 5, RPE and f b increased, velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased, and EMG MPF remained constant.
  
  
  CONCLUSIONS
  The close association between f b and RPE throughout the run at CHR - 5 and during the last 50 % of the run at CHR + 5 indicated that muscle afferents may have provided feedback from metabolic and mechanical stimuli that contributed to the perceptual responses. In addition, only RPE consistently indicated exhaustion and the current findings supported its use to monitor exercise performed at a constant HR.
authors.affiliation: Department of Kinesiology and Health Promotion, University of Kentucky, 221 Seaton Building, Lexington, KY, 40506-0219, USA. hbergstrom@uky.edu.
authors.forename: Haley C
authors.initials: HC
authors.lastname: Bergstrom
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Housh
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Kristen C
authors.initials: KC
authors.lastname: Cochrane
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Nathaniel D M
authors.initials: ND
authors.lastname: Jenkins
authors.affiliation: Department of Exercise Science, Creighton University, Omaha, NE, USA.
authors.forename: Jorge M
authors.initials: JM
authors.lastname: Zuniga
authors.affiliation: Department of Health, Exercise, and Recreation Management, University of Mississippi, Oxford, MS, USA.
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Buckner
authors.affiliation: Department of Exercise and Health Promotion, Florida Atlantic University, Boca Raton, FL, USA.
authors.forename: Jacob A
authors.initials: JA
authors.lastname: Goldsmith
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Schmidt
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Glen O
authors.initials: GO
authors.lastname: Johnson
authors.affiliation: Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA.
authors.forename: Joel T
authors.initials: JT
authors.lastname: Cramer
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure; D006339:Heart Rate; D006801:Humans; D008297:Male; D005082:Physical Exertion; D012420:Running / Q000502:physiology
keywords: Constant heart rate exercise; Critical heart rate; Critical power; Critical velocity; Ratings of perceived exertion