Expiratory flow limitation is a primary characteristic in chronic obstructive pulmonary disease (COPD) and asthma. Increased airway resistance occurs due to bronchoconstriction, destruction of elastic tissue in the airways, and mucus hypersecretion from goblet cells caused by irritation of the epithelium. As a result, the airways become narrowed. Obstruction can lead to dynamic hyperinflation, dyspnea, and exercise intolerance. However, increased airway resistance is just one of many abnormalities in COPD and asthma – COPD in particular is an exceedingly heterogeneous disease. Isolating the effects of expiratory airflow limitation, alone, is therefore challenging. In order to study abnormal lung mechanics in isolation, we aimed to test whether adjustable imposed expiratory resistance in young healthy volunteers produced deficits in the flow-volume relationship similar to that of patients with COPD or asthma. PURPOSE Measure pulmonary function in young healthy volunteers with and without imposed expiratory resistance. METHODS Twenty-seven participants (27 ± 5 years, 170 ± 11 cm, 71.4 ± 13.0 kg) completed standard pulmonary function testing according to the ATS/ERS standards. The testing included three conditions in random order: control, imposed expiratory resistance of 7 cmH2O/L/s, and imposed expiratory resistance of 11 cmH2O/L/s. Resistance was imposed with a threshold inspiratory muscle trainer (Vacumed, Ventura, CA) installed in reverse in the spirometer (Parvo Medics, Sandy, UT). RESULTS FEV1 was reduced (F[1.492, 38.79] = 66.94, p < 0.05) with 7 and 11 cmH2O/L/s of resistance vs control (3.21 ± 0.88 and 3.24 ± 0.91 L, respectively, vs. 4.05 ± 0.15 L). FVC was also reduced (F[1.599, 41.57] = 68.11, p < 0.05) at 7 and 11 cmH2O/L/s vs control (4.11 ± 1.09 and 4.14 ± 1.12 L, respectively, vs. 5.07 ± 1.35 L). FEV1/FVC was not different (F[1.865, 48.48] = 3.611, p < 0.05) between resistance conditions. PEF was reduced (F[1.534, 39.89] = 63.61, p < 0.05) with 7 and 11 cmH2O/L/s of resistance vs control (6.01 ± 1.73 and 6.20 ± 1.92 L, respectively, vs. 8.71 ± 2.83 L). CONCLUSIONS Imposed expiratory resistance reduced key variables (FEV1, FVC, PEF) measured during pulmonary function testing. FEV1/FVC ratio was not affected by either resistance condition. A concave expiratory flow-volume relationship was consistently absent – a key limitation for model comparison with pulmonary function in COPD. This is most likely due to the imposed resistence being applied outside of the airways, leading to higher airway pressures. The higher airway pressures are likely to resist dynamic airway compression and either maintain the equal pressure point position or possibly move it proximally.