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COPD patients usually present thoracoabdominal asynchrony (TAA) that occurs due to an opposite motion among chest wall compartments decreasing tidal volume; however, the proper effect of TAA on chest wall volume remains unclear. Aim: to compare chest wall volume and respiratory kinematics among healthy and COPD patients with and without TAA. Methods: In this cross-sectional study 22 COPD (FEV 1 40±10%pred) and 13 healthy controls (FEV 1 98±14%pred) were assessed during rest and exercise (70% maximum workload) in a cycle ergometer. TAA was evaluated via optoelectronic plethysmography by calculating the phase angle (Lissajous approach) among upper and lower ribcage and abdomen. COPD patients were classified in two groups: those presenting asynchrony (TAA+) or not (TAA-) based on reference values of phase angle (mean ± 2*standard-deviation from controls). Chest wall volume and compartmental contribution were estimated. ANOVA was used for comparison. Results: Controls and COPD were homogenous for age, gender and BMI. Asynchrony occurred during rest and exercise in the lower ribcage. At rest, lower ribcage contribution was decreased in TAA+ compared to controls (9±10.7 vs. 18±9.2, p Conclusion: Thoracoabdominal asynchrony decreases chest wall volume in COPD and changes respiratory kinematics, decreasing lower ribcage and increasing abdominal contributions during exercise.