Daily physical activity is reduced in precapillary pulmonary hypertension (PH) but the underlying mechanisms are inadequately explored. We sought to investigate clinical and physiological relations of daily physical activity and profile differences between less and more active patients with precapillary PH. A prospective, cross-sectional study of 20 patients with precapillary PH who undertook a) a comprehensive clinical assessment, b) a preliminary treadmill test, c) 7-day monitoring of daily walking intensity with triaxial accelerometry and d) a personalized treadmill test corresponding to the individual patient mean daily walking intensity with real-time physiological measurements. Significant clinical correlations with individual patient mean walking intensity (1.71±0.27 m/s2) were observed for log N-terminal pro-brain natriuretic peptide (log-NTproBNP: r=-.75, p=<.001), age (r=-.70, p=.001), transfer factor for carbon monoxide %predicted (r=.51, p=0.022) and 6-minute walk distance (r=.50, p=.026). Significant physiological correlations were obtained for heart rate reserve (r=.68, p=.001), quadriceps tissue oxygenation index (Q-StO2: r=.58, p=.008), change in Q-StO2 from rest (r=.60, p=.006) and ventilatory equivalent for oxygen uptake (r=-.56, p=.013). Stepwise multiple regression analyses retained log-NTproBNP (R2=0.55), heart rate reserve (R2=0.44) and Q-StO2 (R2=0.13) accounting for a significant variance in individual walking intensity. Less active patients had greater physical activity-induced cardiopulmonary impairment, worse quadriceps oxygenation profile and compromised health-related quality of life compared to more active patients. These preliminary findings suggest a significant relation between right ventricular and peripheral muscle oxygenation status and reduced daily physical activity in precapillary PH. Further research is warranted to unravel the physiological determinants, establish clinical predictors, and identify beneficial interventions.