title: Crossover and maximal fat-oxidation points in sedentary healthy subjects: methodological issues.
abstract: OBJECTIVE
  Our study aimed to assess the influence of protocol on the crossover point and maximal fat-oxidation (LIPOX(max)) values in sedentary, but otherwise healthy, young men.
  
  
  METHODS
  Maximal oxygen intake was assessed in 23 subjects, using a progressive maximal cycle ergometer test. Twelve sedentary males (aged 20.5±1.0 years) whose directly measured maximal aerobic power (MAP) values were lower than their theoretical maximal values (tMAP) were selected from this group. These individuals performed, in random sequence, three submaximal graded exercise tests, separated by three-day intervals; work rates were based on the tMAP in one test and on MAP in the remaining two. The third test was used to assess the reliability of data. Heart rate, respiratory parameters, blood lactate, the crossover point and LIPOX(max) values were measured during each of these tests.
  
  
  RESULTS
  The crossover point and LIPOX(max) values were significantly lower when the testing protocol was based on tMAP rather than on MAP (P<0.001). Respiratory exchange ratios were significantly lower with MAP than with tMAP at 30, 40, 50 and 60% of maximal aerobic power (P<0.01). At the crossover point, lactate and 5-min postexercise oxygen consumption (EPOC(5 min)) values were significantly higher using tMAP rather than MAP (P<0.001). During the first 5 min of recovery, EPOC(5 min) and blood lactate were significantly correlated (r=0.89; P<0.001).
  
  
  CONCLUSIONS
  Our data show that, to assess the crossover point and LIPOX(max) values for research purposes, the protocol must be based on the measured MAP rather than on a theoretical value. Such a determination should improve individualization of training for initially sedentary subjects.
authors.affiliation: Research Unit "Sportive practices in School and University and performance", Higher Institute of Sport and Physical Education of Kef, University of Jendouba, Jendouba, Tunisia.
authors.forename: N
authors.initials: N
authors.lastname: Gmada
authors.forename: H
authors.initials: H
authors.lastname: Marzouki
authors.forename: M
authors.initials: M
authors.lastname: Haboubi
authors.forename: Z
authors.initials: Z
authors.lastname: Tabka
authors.forename: R J
authors.initials: RJ
authors.lastname: Shephard
authors.forename: E
authors.initials: E
authors.lastname: Bouhlel
mesh_terms: D000465:Algorithms; D015992:Body Mass Index; D016552:Ergometry / Q000379:methods*; D006339:Heart Rate; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D050356:Lipid Metabolism; D015227:Lipid Peroxidation; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology*; D015656:Respiratory Mechanics; D057185:Sedentary Behavior; D012885:Skinfold Thickness; D055815:Young Adult
chemical_list: D019344:Lactic Acid