Metabolic and muscular factors limiting aerobic exercise in obese subjects
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The aim of the present study was to understand the role of central (cardiovascular O2 delivery) and peripheral factors (muscle level) in limiting the maximal aerobic performance in obese (OB) subjects.
Fifteen OB (mean age ± SD 25 ± 7 years; BMI 43 ± 7 kg/m2) and 13 lean sedentary subjects (CTRL, age 27 ± 7 years; BMI 22 ± 3 kg/m2) participated in this study. Oxygen uptake (VO2), hearth rate (HR) and cardiac output (CO) were measured during cycle ergometer (CE) and knee extension (KE) incremental tests. Maximal voluntary contractions (MVCs) of knee extensor muscles were performed before and immediately after the two tests.
VO2peak, HR peak and CO peak were significantly higher in CE than KE (+ 126%, + 33% and + 46%, respectively, p < 0.001), both in OB and CTRL subjects, without differences between the two subgroups. Maximal work rate was lower in OB than CTRL (191 ± 38 vs 226 ± 39 W, p < 0.05) in CE, while it was similar between the two subgroups in KE. Although CE and KE determined a reduction of MVC in both subgroups, MVC resulted less decreased after CE than KE exercises (− 14 vs − 32%, p < 0.001) in OB, while MVC decrements were similar after the two exercises in CTRL (− 26% vs − 30%, p > 0.05, for CE and KE, respectively).
The lower muscle fatigue observed in OB after CE compared to KE test suggests that central factors could be the most important limiting factor during cycling in OB.
KeywordsObesity Exercise tolerance Knee extension Small muscles exercise Aerobic function
- a − vO2 diff
Arteriovenous oxygen difference
Body mass index
Maximal voluntary contraction changes in percentage
Knee extension exercise
Maximal voluntary contractions of the knee extensor muscles
MVC immediately after the end of incremental exercise
Time to exhaustion
Pulmonary O2 uptake
MUSCLE thigh volume
The authors thank the patients and control subjects who agreed to participate in the study. The study was supported by Progetti di Ricerca Corrente, Istituto Auxologico Italiano (Milan); and by Fondazione Pittini (Italy).
All authors conceived and designed research. FV, MF, GT and RDM conducted experiments. FV and MF analyzed data. FV wrote the manuscript with the help of MF. SL and AS revised the manuscript. All authors read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
No conflicts of interest, financial or otherwise, are declared by the author(s).
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