@phdthesis{deSouzaSilveira2017,
  author    = {de Souza Silveira, Raul},
  title     = {Human substrate metabolism at upper oxidative capacities},
  doi       = {10.25932/publishup-42333},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423338},
  school      = {Universit{\"a}t Potsdam},
  pages     = {iii, 85, v},
  year      = {2017},
  abstract  = {Introduction: Carbohydrate (CHO) and fat are the main substrates to fuel prolonged endurance exercise, each having its oxidation patterns regulated by several factors such as intensity, duration and mode of the activity, dietary intake pattern, muscle glycogen concentrations, gender and training status. Exercising at intensities where fat oxidation rates are high has been shown to induce metabolic benefits in recreational and health-oriented sportsmen. The exercise intensity (Fatpeak) eliciting peak fat oxidation rates is therefore of particular interest when aiming to prescribe exercise for the purpose of fat oxidation and related metabolic effects. Although running and walking are feasible and popular among the target population, no reliable protocols are available to assess Fatpeak as well as its actual velocity (VPFO) during treadmill ergometry. Moreover, to date, it remains unclear how pre-exercise CHO availability modulates the oxidative regulation of substrates when exercise is conducted at the intensity where the individual anaerobic threshold (IAT) is located (VIAT). That is, a metabolic marker representing the upper border where constant load endurance exercise can be sustained, being commonly used to guide athletic training or in performance diagnostics. The research objectives of the current thesis were therefore, 1) to assess the reliability and day-to-day variability of VPFO and Fatpeak during treadmill ergometry running; 2) to assess the impact of high CHO (HC) vs. low CHO (LC) diets (where on the LC day a combination of low CHO diet and a glycogen depleting exercise was implemented) on the oxidative regulation of CHOs and fat while exercise is conducted at VIAT. Methods: Research objective 1: Sixteen recreational athletes (f=7, m=9; 25 ± 3 y; 1.76 ± 0.09 m; 68.3 ± 13.7 kg; 23.1 ± 2.9 kg/m²) performed 2 different running protocols on 3 different days with standardized nutrition the day before testing. At day 1, peak oxygen uptake (VO2peak) and the velocities at the aerobic threshold (VLT) and respiratory exchange ratio (RER) of 1.00 (VRER) were assessed. At days 2 and 3, subjects ran an identical submaximal incremental test (Fat-peak test) composed of a 10 min warm-up (70\% VLT) followed by 5 stages of 6 min with equal increments (stage 1 = VLT, stage 5 = VRER). Breath-by-breath gas exchange data was measured continuously and used to determine fat oxidation rates. A third order polynomial function was used to identify VPFO and subsequently Fatpeak. The reproducibility and variability of variables was verified with an intraclass correlation coefficient (ICC), Pearson's correlation coefficient, coefficient of variation (CV) and the mean differences (bias) ± 95\% limits of agreement (LoA). Research objective 2: Sixteen recreational runners (m=8, f=8; 28 ± 3 y; 1.76 ± 0.09 m; 72 ± 13 kg; 23 ± 2 kg/m²) performed 3 different running protocols, each allocated on a different day. At day 1, a maximal stepwise incremental test was implemented to assess the IAT and VIAT. During days 2 and 3, participants ran a constant-pace bout (30 min) at VIAT that was combined with randomly assigned HC (7g/kg/d) or LC (3g/kg/d) diets for the 24 h before testing. Breath-by-breath gas exchange data was measured continuously and used to determine substrate oxidation. Dietary data and differences in substrate oxidation were analyzed with a paired t-test. A two-way ANOVA tested the diet X gender interaction (α = 0.05). Results: Research objective 1: ICC, Pearson's correlation and CV for VPFO and Fatpeak were 0.98, 0.97, 5.0\%; and 0.90, 0.81, 7.0\%, respectively. Bias ± 95\% LoA was -0.3 ± 0.9 km/h for VPFO and -2 ± 8\% of VO2peak for Fatpeak. Research objective 2: Overall, the IAT and VIAT were 2.74 ± 0.39 mmol/l and 11.1 ± 1.4 km/h, respectively. CHO oxidation was 3.45 ± 0.08 and 2.90 ± 0.07 g/min during HC and LC bouts respectively (P < 0.05). Likewise, fat oxidation was 0.13 ± 0.03 and 0.36 ± 0.03 g/min (P < 0.05). Females had 14\% (P < 0.05) and 12\% (P > 0.05) greater fat oxidation compared to males during HC and LC bouts, respectively. Conclusions: Research objective 1: In summary, relative and absolute reliability indicators for VPFO and Fatpeak were found to be excellent. The observed LoA may now serve as a basis for future training prescriptions, although fat oxidation rates at prolonged exercise bouts at this intensity still need to be investigated. Research objective 2: Twenty-four hours of high CHO consumption results in concurrent higher CHO oxidation rates and overall utilization, whereas maintaining a low systemic CHO availability significantly increases the contribution of fat to the overall energy metabolism. The observed gender differences underline the necessity of individualized dietary planning before exerting at intensities associated with performance exercise. Ultimately, future research should establish how these findings can be extrapolated to training and competitive situations and with that provide trainers and nutritionists with improved data to derive training prescriptions.},
  language  = {en}
}