AUTHOR=Jabbour Georges , Majed Lina 

TITLE=Mechanical Efficiency at Different Exercise Intensities Among Adolescent Boys With Different Body Fat Levels

JOURNAL=Frontiers in Physiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.00265

DOI=10.3389/fphys.2019.00265

ISSN=1664-042X

ABSTRACT=<p>This study investigated the mechanical efficiency (ME) and associated factors in obese, overweight, and normal-weight adolescent boys during incremental cycle exercise test to exhaustion. Forty-five sedentary adolescent boys (13–14 years old) were separated in three groups according to the percentage of fat mass as follows: 15 normal-weight (NW) (body fat: 16.0 ± 1.9%), 15 overweight (OW) (body fat: 24.0 ± 1.6%), and 15 obese (OB) (body fat: 31.0 ± 3.0%). All groups completed an incremental cycle exercise to exhaustion in which energy consumption (E, W), ME (%), lipid oxidation rate (LO, %), plasma epinephrine and norepinephrine concentrations were determined consecutively at rest and at three intensity levels corresponding to 50 and 75% of each participant’s maximal heart rate (50%HRmax and 75%HRmax) and peak oxygen consumption (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="italic">V</mml:mi></mml:mrow><mml:mrow><mml:mo mathvariant="italic">˙</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2peak</sub>). During the incremental cycle exercise test, plasma epinephrine, and norepinephrine responses as well as ME determined at 50%HRmax, 75%HRmax, and at VO<sub>2peak</sub> stages were significantly lower in OB compared to NW and OW individuals (<italic>ps</italic> &lt; 0.01). Multiple linear regressions showed that body weight (ß = -0.64, <italic>p</italic> &lt; 0.001), energy consumption (ß = -0.24, <italic>p</italic> &lt; 0.05) and lipid oxidation (ß = 0.69, <italic>p</italic> &lt; 0.01) were significant predictors of ME at 50%HRmax. However, at 75%HRmax and <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="italic">V</mml:mi></mml:mrow><mml:mrow><mml:mo mathvariant="italic">˙</mml:mo></mml:mrow></mml:mover></mml:mrow></mml:math></inline-formula>O<sub>2peak</sub>, significant predictors of ME were epinephrine (ß = 0.34, ß = 0.49, respectively, <italic>ps</italic> = 0.01), norepinephrine (ß = 0.26, ß = 0.60, respectively, <italic>ps</italic> &lt; 0.05) and power output (ß = 0.62, ß = 0.71, respectively, <italic>ps</italic> &lt; 0.01). These findings suggest that excess in body weight exerts a negative effect on ME at a low intensity by increasing energy consumption for obese and overweight adolescent boys, while at higher intensities (75%HRmax and VO<sub>2peak</sub>) the lower ME could be better explained by the lower power output and catecholamine responses that were attenuated among obese and overweight adolescent boys.</p>