Posture matters: how body position shapes cardiopulmonary response to maximal exercise testing.

Body posture influences cardiovascular and respiratory responses during exercise, yet in a clinical setting, differences in body positions are not considered when comparing different methodologies analyzing physical effort, such as cardiopulmonary exercise testing (CPET), stress echo, or invasive hemodynamic. We aimed to investigate how upright (UP), semirecumbent (SR), and supine (SP) positions affect key CPET variables and cardiac output (CO) in healthy adults. Twelve healthy volunteers (30.9 ± 4.4 yr; 50% female) performed three randomized CPETs in UP, SR, and SP positions. Breath-by-breath gas exchange data [oxygen uptake (V̇o2) carbon dioxide production (V̇co2), minute ventilation (V̇e), tidal volume (TV), respiratory rate (RR)] and hemodynamic parameters [CO by thoracic bioimpedance, stroke volume (SV), heart rate (HR)] were continuously monitored. Data were analyzed at rest, anaerobic threshold, iso-watt stages, and peak exercise. At rest and submaximal workloads, HR decreased, and SV increased with more reclined positions, maintaining CO. V̇e and TV were lower in SR and SP positions, whereas RR and peripheral oxygen saturation ([Formula: see text]) were unchanged. At peak exercise, V̇o2, V̇co2, workload, and exercise duration declined progressively from UP to SP (V̇o2: 2,587 ± 1,009, 2,520 ± 982, 2,269 ± 847 mL/min; P < 0.001), with lower V̇e driven by reduced TV. Despite reduced metabolic and ventilatory demands, CO was unchanged via increased SV. Dyspnea perception was lower in reclined postures. Body posture modulates cardiopulmonary responses during exercise. Semirecumbent and supine positions reduce V̇o2 and V̇e preserving CO. These findings highlight the importance of posture-specific reference values for accurate interpretation in clinical practice.NEW & NOTEWORTHY Body position during exercise testing profoundly affects cardiopulmonary responses, even in healthy individuals. Results obtained in different postures are not directly comparable. Upright, semirecumbent, and supine exercise produce systematic changes in oxygen uptake, ventilation, workload, and dyspnea, with lower performance in reclined positions. Despite this, cardiac output is preserved through adjustments in heart rate and stroke volume, indicating that posture-rather than cardiac dysfunction-drives differences. Without posture-specific reference values, disease severity may be misinterpreted.