Evaluation of a graded exercise test to determine peak fat oxidation in individuals with low cardiorespiratory fitness:Estimating maximal capacity for fat oxidation

The maximal capacity to utilise fat (peak fat oxidation [PFO]) may have implications for health and ultra-endurance performance, and is commonly determined by incremental exercise tests employing 3-minute stages. However, 3-minute stages may be insufficient to attain steady-state gas kinetics, compromising test validity. We assessed whether 4-minute stages produce steady-state gas exchange and reliable PFO in adults with V̇O2peakThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese

Context Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness. Objective To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism. Design (1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study). Setting General community. Participants Men with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg⋅m-2 for Acute Study, 30.9 ± 4.5 kg⋅m-2 for Training Study). Interventions Moderate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion. Results Acute Study—exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: –3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs –21 ± 32 mL⋅min-1⋅m-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05). Conclusions Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia

Evaluation of a graded exercise test to determine peak fat oxidation in individuals with low cardiorespiratory fitness:Estimating maximal capacity for fat oxidation

The maximal capacity to utilise fat (peak fat oxidation, PFO) may have implications for health and ultra-endurance performance and is commonly determined by incremental exercise tests employing 3-min stages. However, 3-min stages may be insufficient to attain steady-state gas kinetics, compromising test validity. We assessed whether 4-min stages produce steady-state gas exchange and reliable PFO estimates in adults with peak oxygen consumption &lt; 40 mL·kg −1·min −1. Fifteen participants (9 females) completed a graded test to determine PFO and the intensity at which this occurred (FAT MAX). Three short continuous exercise sessions (SCE) were then completed in a randomised order, involving completion of the graded test to the stage (i) preceding, (ii) equal to (SCE equal), or (iii) after the stage at which PFO was previously attained, whereupon participants then continued to cycle for 10 min at that respective intensity. Expired gases were sampled at minutes 3–4, 5–6, 7–8, and 9–10. Individual data showed steady-state gas exchange was achieved within 4 min during SCE equal. Mean fat oxidation rates were not different across time within SCE equal nor compared with the graded test at FAT MAX (both p &gt; 0.05). However, the graded test displayed poor surrogate validity (SCE equal, minutes 3–4 vs. 5–6, 7–8, and 9–10) and day-to-day reliability (minutes 3–4, SCE equal vs. graded test) to determine PFO, as evident by correlations (range: 0.47–0.83) and typical errors and 95% limits of agreement (ranges: 0.03–0.05 and ±0.09–0.15 g·min −1, respectively). In conclusion, intraindividual variation in PFO is substantial despite 4-min stages establishing steady-state gas exchange in individuals with low fitness. Individual assessment of PFO may require multiple assessments. </p