The effect of posture on maximal oxygen uptake in active healthy individuals.PURPOSE
 Semi-supine and supine cardiopulmonary exercise testing (CPET) with concurrent cardiac imaging has emerged as a valuable tool for evaluating patients with cardiovascular disease.  Yet, it is unclear how posture effects CPET measures.  We aimed to discern the effect of posture on maximal oxygen uptake (VO2max) and its determinants using three clinically relevant cycle ergometers.


 In random order, 10 healthy, active males (Age 27 ± 7 years; BMI 23 ± 2 kg m2) underwent a ramp CPET and subsequent constant workload verification test performed at 105% peak ramp power to quantify VO2max on upright, semi-supine and supine cycle ergometers.  Doppler echocardiography was conducted at peak exercise to measure stroke volume (SV) which was multiplied by heart rate (HR) to calculate cardiac output (CO).


 Compared to upright (46.8 ± 11.2 ml/kg/min), VO2max was progressively reduced in semi-supine (43.8 ± 10.6 ml/kg/min) and supine (38.2 ± 9.3 ml/kg/min; upright vs. semi-supine vs. supine; all p ≤ 0.005).  Peak HR decreased progressively from upright to semi-supine to supine (186 ± 11 vs. 176 ± 13 vs. 169 ± 12 bpm; all p < 0.05).  Peak SV and CO were lower in supine relative to semi-supine and upright (82 ± 22 vs. 92 ± 26 vs. 91 ± 24 ml and 14 ± 3 vs. 16 ± 4 vs. 17 ± 4 l/min; all p < 0.01), but not different between semi-supine and upright.


 CONCLUSION
 VO2max is progressively reduced in reclined postures.  Thus, posture should be considered when comparing VO2max results between different testing modalities.
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