title: Oxygen consumption during walking and running under fractional weight bearing conditions.
abstract: BACKGROUND
  Knowledge of changes in oxygen consumption during reduced body weight loading at different speed levels is important, in particular in astronauts who may lose aerobic fitness as well as in clinical patients (e.g., in obese individuals at walking speeds or in injured athletes at running speeds). Therefore, the aim of this study was to analyze oxygen consumption during unloaded walking and running.
  
  
  METHODS
  Oxygen consumption (Vo2), heart rate (HR), and Borg rating of perceived exertion (Borg RPE) were quantified in 10 healthy young female and male volunteers at 3 body weight (BW) conditions (100%, 66%, and 33% BW) and 4 treadmill speeds (slow walking at 0.4 m x s(-1), comfortable walking at 1.3 m x s(-1), slow running at 2.2 m x s(-1), and moderately fast running at 3.1 m x s(-1)). Unloading was achieved in a waist-high chamber with increased pressure called Lower Body Positive Pressure (LBPP).
  
  
  RESULTS
  All parameters (Vo2, HR, and Borg RPE) decreased during unloaded walking and running. Interestingly, our findings confirm a specific linear relationship between each parameter and treadmill speed for each BW condition with smaller slope angles at higher levels of unloading (e.g., for Vo2, the slope angle decreased from 11.9 at 100% BW to 4.4 at 33% BW).
  
  
  CONCLUSIONS
  Oxygen consumption, heart rate, and Borg rating of perceived exertion are reduced during unloaded exercise with a relatively greater decline at higher treadmill speeds. That is, the higher the treadmill's speed in unloaded conditions, the relatively "easier" it is to exercise.
authors.affiliation: Department of Orthopaedic Surgery, University of California, UCSD Medical Center, San Diego 92103, USA. heidi.ruckstuhl@gmail.com
authors.forename: Heidi
authors.initials: H
authors.lastname: Ruckstuhl
authors.forename: Thomas
authors.initials: T
authors.lastname: Schlabs
authors.forename: Armando
authors.initials: A
authors.lastname: Rosales-Velderrain
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hargens
mesh_terms: D001835:Body Weight; D015444:Exercise / Q000502:physiology; D005080:Exercise Test; D005260:Female; D006305:Health Status Indicators; D006339:Heart Rate; D006801:Humans; D016014:Linear Models; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D010465:Perception; D011312:Pressure; D012420:Running / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult