Document Detail

Methodological aspects of crossover and maximum fat-oxidation rate point determination.
MedLine Citation:
PMID:  18823806     Owner:  NLM     Status:  MEDLINE    
AIM: Indirect calorimetry during exercise provides two metabolic indices of substrate oxidation balance: the crossover point (COP) and maximum fat oxidation rate (LIPOXmax). We aimed to study the effects of the analytical device, protocol type and ventilatory response on variability of these indices, and the relationship with lactate and ventilation thresholds. METHODS: After maximum exercise testing, 14 relatively fit subjects (aged 32+/-10 years; nine men, five women) performed three submaximum graded tests: one was based on a theoretical maximum power (tMAP) reference; and two were based on the true maximum aerobic power (MAP). Gas exchange was measured concomitantly using a Douglas bag (D) and an ergospirometer (E). RESULTS: All metabolic indices were interpretable only when obtained by the D reference method and MAP protocol. Bland and Altman analysis showed overestimation of both indices with E versus D. Despite no mean differences between COP and LIPOXmax whether tMAP or MAP was used, the individual data clearly showed disagreement between the two protocols. Ventilation explained 10-16% of the metabolic index variations. COP was correlated with ventilation (r=0.96, P<0.01) and the rate of increase in blood lactate (r=0.79, P<0.01), and LIPOXmax correlated with the ventilation threshold (r=0.95, P<0.01). CONCLUSION: This study shows that, in fit healthy subjects, the analytical device, reference used to build the protocol and ventilation responses affect metabolic indices. In this population, and particularly to obtain interpretable metabolic indices, we recommend a protocol based on the true MAP or one adapted to include the transition from fat to carbohydrate. The correlation between metabolic indices and lactate/ventilation thresholds suggests that shorter, classical maximum progressive exercise testing may be an alternative means of estimating these indices in relatively fit subjects. However, this needs to be confirmed in patients who have metabolic defects.
A-S Michallet; J Tonini; J Regnier; M Guinot; A Favre-Juvin; V Bricout; S Halimi; B Wuyam; P Flore
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2008-09-26
Journal Detail:
Title:  Diabetes & metabolism     Volume:  34     ISSN:  1262-3636     ISO Abbreviation:  Diabetes Metab.     Publication Date:  2008 Nov 
Date Detail:
Created Date:  2008-11-21     Completed Date:  2009-02-25     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9607599     Medline TA:  Diabetes Metab     Country:  France    
Other Details:
Languages:  eng     Pagination:  514-23     Citation Subset:  IM    
Laboratoire de recherche-exercice, santé REX-S, IFR 1, hôpital Sud, université Joseph-Fourier Grenoble-1, BP 338, 38043 Echirolles cedex, France; Inserm, ERI17, laboratoire HP2, université Joseph-Fourier Grenoble-1, 38042 Grenoble, France.
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MeSH Terms
Anaerobic Threshold / physiology
Calorimetry, Indirect / methods
Carbon Dioxide / analysis
Dietary Fats / metabolism*
Exercise Test
Leisure Activities
Oxygen Consumption
Pulmonary Gas Exchange / physiology
Pulmonary Ventilation / physiology
Reference Values
Respiratory Mechanics
Young Adult
Reg. No./Substance:
0/Dietary Fats; 124-38-9/Carbon Dioxide

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