High altitude-induced borderline pulmonary hypertension impaired cardiorespiratory fitness in healthy young men.

•We studied the impact of altitude induced borderline PH on cardiorespiratory fitness in healthy subjects.•299 healthy Chinese young men with normal pulmonary artery pressure were consecutively studied.•Borderline PH presents in about one third of the healthy participants following exposure to high altitude.•Borderline PH compromises cardiorespiratory fitness, which was associated with the elevated mPAP.