title: Predicting metabolic rate during level and uphill outdoor walking using a low-cost GPS receiver.
abstract: The objective of this study was to assess the accuracy of using speed and grade data obtained from a low-cost global positioning system (GPS) receiver to estimate metabolic rate (MR) during level and uphill outdoor walking. Thirty young, healthy adults performed randomized outdoor walking for 6-min periods at 2.0, 3.5, and 5.0 km/h and on three different grades: 1) level walking, 2) uphill walking on a 3.7% mean grade, and 3) uphill walking on a 10.8% mean grade. The reference MR [metabolic equivalents (METs) and oxygen uptake (V̇o2)] values were obtained using a portable metabolic system. The speed and grade were obtained using a low-cost GPS receiver (1-Hz recording). The GPS grade (Δ altitude/distance walked) was calculated using both uncorrected GPS altitude data and GPS altitude data corrected with map projection software. The accuracy of predictions using reference speed and grade (actual[SPEED/GRADE]) data was high [R(2) = 0.85, root-mean-square error (RMSE) = 0.68 MET]. The accuracy decreased when GPS speed and uncorrected grade (GPS[UNCORRECTED]) data were used, although it remained substantial (R(2) = 0.66, RMSE = 1.00 MET). The accuracy was greatly improved when the GPS speed and corrected grade (GPS[CORRECTED]) data were used (R(2) = 0.82, RMSE = 0.79 MET). Published predictive equations for walking MR were also cross-validated using actual or GPS speed and grade data when appropriate. The prediction accuracy was very close when either actual[SPEED/GRADE] values or GPS[CORRECTED] values (for level and uphill combined) or GPS speed values (for level walking only) were used. These results offer promising research and clinical applications related to the assessment of energy expenditure during free-living walking.
authors.affiliation: Movement, Sport and Health Laboratory (EA 1274), Faculty of Sport Sciences, University of Rennes 2, Rennes, France;
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: de Müllenheim
authors.affiliation: Movement, Sport and Health Laboratory (EA 1274), Faculty of Sport Sciences, University of Rennes 2, Rennes, France;
authors.forename: Rémy
authors.initials: R
authors.lastname: Dumond
authors.affiliation: Laboratory for Vascular Investigations and Sports Medicine, University Hospital, Angers, France; Laboratory of Physiology, Institut National de la Santé et de la Recherche Médicale UMR 1083, Centre National de la Recherche Scientifique UMR 6214, Medical School, University of Angers, Angers, France;
authors.forename: Marie
authors.initials: M
authors.lastname: Gernigon
authors.affiliation: Clinical Investigation Center, Institut National de la Santé et de la Recherche Médicale CIC 1414, Rennes, France; Heart Vessels Imaging Team, University Hospital, Rennes, France; University of Rennes 1, Rennes, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Mahé
authors.affiliation: Clinical Investigation Center, Institut National de la Santé et de la Recherche Médicale CIC 1414, Rennes, France; Laboratory of Experimental and Clinical Pharmacology, Medical School, University of Rennes 1, Rennes, France;
authors.forename: Audrey
authors.initials: A
authors.lastname: Lavenu
authors.affiliation: Laboratory for Vascular Investigations and Sports Medicine, University Hospital, Angers, France;
authors.forename: Sandrine
authors.initials: S
authors.lastname: Bickert
authors.affiliation: Movement, Sport and Health Laboratory (EA 1274), Faculty of Sport Sciences, University of Rennes 2, Rennes, France; Department of Sport Sciences and Physical Education, Ecole normale supérieure de Rennes, Campus de Ker Lann, Bruz, France;
authors.forename: Jacques
authors.initials: J
authors.lastname: Prioux
authors.affiliation: Laboratory for Vascular Investigations and Sports Medicine, University Hospital, Angers, France; Laboratory of Physiology, Institut National de la Santé et de la Recherche Médicale UMR 1083, Centre National de la Recherche Scientifique UMR 6214, Medical School, University of Angers, Angers, France; Institute of Physical Education and Sports Sciences (IFEPSA), Université Catholique de l'Ouest, Les Ponts-de-Cé, France; and.
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Noury-Desvaux
authors.affiliation: Movement, Sport and Health Laboratory (EA 1274), Faculty of Sport Sciences, University of Rennes 2, Rennes, France; Clinical Investigation Center, Institut National de la Santé et de la Recherche Médicale CIC 1414, Rennes, France; Department of Sport Sciences and Physical Education, Ecole normale supérieure de Rennes, Campus de Ker Lann, Bruz, France; alexis.lefaucheur@ens-rennes.fr.
authors.forename: Alexis
authors.initials: A
authors.lastname: Le Faucheur
mesh_terms: D056044:Actigraphy / Q000379:methods*; D000328:Adult; D000465:Algorithms; D003198:Computer Simulation; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D040362:Geographic Information Systems; D006801:Humans; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016138:Walking / Q000502:physiology*
keywords: energy expenditure; equations; global positioning system; grade; wearable activity monitors