Background: Many papers showed that long-lasting exposure to hypobaric hypoxia changed the metabolic cost of work and substrate contribution, elevating exercise energy expenditure and carbohydrates utilization. Only few of them have shown how long this adaptive changes are maintained. The aim of the study was to assess the impact of prolonged sojourn at high altitude on the physiological cost of sub-maximal work performed at the sea level.Material/Methods: Eight members of two high altitude expeditions (Lenin Peak 7,134 m a.s.l. and Somoni Peak 7,495m a.s.l.), 7 males and 1 female, mean age 26 (±4.1) years, volunteered for this study. Aerobic performance was measured by a direct method (breath-by-breath) using an expiratory gas analyser (Oxycon Pro, Jaeger) with an incremental exercise test till exhaustion. The sea level examinations were performed 7 days before the expedition (BEx) and 7 days after (AEx) the last day at over 2,500m a.s.l. Participants spent 32 (±3) days over 2,500m a.s.l. at the mean altitude of 4,712m a.s.l. (±499m).Results: Prolonged sojourn at high altitude has changed the ventilatory parameters of sub-maximal work measured at the sea level. The sojourn resulted in an increase in the ventilatory volume (tidal volume, minute ventilation and breath frequency) during the sub-maximal work performed with the same workload. However, the respiratory exchange ratio remained at a high level compared to the baseline.Conclusions: We suggest that the adaptive changes introduced during the sojourn remain at the sea level and cause increased carbohydrate metabolism.