Fuel oxidation in relation to walking speed: influence of gradient and external load

• Published in: European journal of applied physiology Vol. 110; no. 3; pp. 515 - 521
• Main Authors: Entin, Pauline L., Gest, Colleen, Trancik, Susan, Richard Coast, J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.10.2010; Springer; Springer Nature B.V
• Subjects: Adolescent; Adult; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Carbohydrate Metabolism - physiology; Energy Metabolism - physiology; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Human Physiology; Humans; Lipid Metabolism - physiology; Male; Occupational Medicine/Industrial Medicine; Original Article; Oxidation-Reduction; Oxygen Consumption - physiology; Pulmonary Gas Exchange - physiology; Sports Medicine; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Walking - physiology; Weight-Bearing - physiology; Young Adult; Exercise energetics; Carbohydrate usage; Economy of movement; Fuel selection; Preferred walking speed; Physical exercise; Human; Speed; Gradient; Selection; Locomotion; Walking; Carbohydrate; Oxidation
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-010-1523-6

People intuitively walk at a speed that minimizes energy cost per meter. Therefore, the selective advantages of energetic efficiency are thought to drive individuals’ preferred walking speed (PWS). This presumption disregards fuel partitioning, which may, in fact, be significant due to the disparate sizes of the carbohydrate (CHO) and fat reservoirs, coupled with the necessity of CHO for high intensity exercise. Potentially, PWS may reflect CHO conservation more than energetic efficiency per se. This study was designed to determine if PWS over a variety of conditions conforms to the CHO sparing hypothesis. Six subjects walked on a treadmill at five speeds: their PWS and speeds 0.45 and 0.22 m/s below and above PWS, under loads of 0, 10, and 20% of body weight, as well as at grades of −6.25, 0 and +6.25%. Oxygen consumption, carbon dioxide production and respiratory exchange ratio were measured over each 10 min bout to calculate total energy, CHO and fat usage. The subjects’ mean (±SD) unloaded, level PWS was 1.32 ± 0.11 m/s. PWS was reduced by the 20% load and uphill grade, but not affected by the 10% load or downhill grade. Carbohydrate provided ≥50% of required energy in all conditions. The CHO oxidation rate was related to speed such that the gain was greater at speeds above than below the PWS; however, differences in CHO oxidation between conditions did not correspond to differences in PWS. We conclude that CHO sparing is not the primary determinant of PWS during externally loaded or grade walking.