title: A standardized approach to study human variability in isometric thermogenesis during low-intensity physical activity.
abstract: Limitations of current methods: The assessment of human variability in various compartments of daily energy expenditure (EE) under standardized conditions is well defined at rest [as basal metabolic rate (BMR) and thermic effect of feeding (TEF)], and currently under validation for assessing the energy cost of low-intensity dynamic work. However, because physical activities of daily life consist of a combination of both dynamic and isometric work, there is also a need to develop standardized tests for assessing human variability in the energy cost of low-intensity isometric work.
  
  
  OBJECTIVE
  Development of an approach to study human variability in isometric thermogenesis by incorporating a protocol of intermittent leg press exercise of varying low-intensity isometric loads with measurements of EE by indirect calorimetry.
  
  
  RESULTS
  EE was measured in the seated position with the subject at rest or while intermittently pressing both legs against a press-platform at 5 low-intensity isometric loads (+5, +10, +15, +20, and +25 kg force), each consisting of a succession of 8 cycles of press (30 s) and rest (30 s). EE, integrated over each 8-min period of the intermittent leg press exercise, was found to increase linearly across the 5 isometric loads with a correlation coefficient (r) > 0.9 for each individual. The slope of this EE-Load relationship, which provides the energy cost of this standardized isometric exercise expressed per kg force applied intermittently (30 s in every min), was found to show good repeatability when assessed in subjects who repeated the same experimental protocol on 3 separate days: its low intra-individual coefficient of variation (CV) of ~ 10% contrasted with its much higher inter-individual CV of 35%; the latter being mass-independent but partly explained by height.
  
  
  CONCLUSIONS
  This standardized approach to study isometric thermogenesis opens up a new avenue for research in EE phenotyping and metabolic predisposition to obesity.
authors.affiliation: Department of Medicine/Physiology, University of Fribourg Fribourg, Switzerland.
authors.forename: Delphine
authors.initials: D
authors.lastname: Sarafian
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Miles-Chan
authors.forename: Gayathri
authors.initials: G
authors.lastname: Yepuri
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Montani
authors.forename: Yves
authors.initials: Y
authors.lastname: Schutz
authors.forename: Abdul G
authors.initials: AG
authors.lastname: Dulloo
keywords: NEAT; energy expenditure; exercise; isometric; obesity; spontaneous physical activity; static; thermogenesis