Abstract. The effect of exercise on gastric mucosal energy status has not been fully elucidated. The aim of this study was to evaluate the impact of submaximal cycling on gastric mucosal energy balance and its relationship to changes in systemic energy status. Ten healthy volunteers (age 2040years) were investigated at rest (BL), during 30min of submaximal exercise (E) on bicycle ergometry and during the 30min after the completion of cycling. Gastric mucosal PCO2 (PgmCO2) was measured by air tonometry at 10-min intervals and the gastric mucosalarterial PCO2 difference (PCO2gap) was calculated. Hemodynamics, arterial blood gases, lactate and pyruvate were also measured. PCO2gap significantly increased throughout exercise [BL: 0.2kPa (median), 0.10.6kPa (25th75th percentiles); E10min: 1.0kPa, 0.81.7kPa; E20min: 1.35kPa, 0.81.8kPa; E30min: 1.5kPa, 0.92.0kPa]. The early changes in PCO2gap (PCO2gap at E10min minus PCO2 gap at BL) correlated significantly and positively with corresponding changes in arterial lactate (r2=0.58, P0.05) and lactate-to-pyruvate ratio (r2=0.72, P0.05). On recovery, all metabolic parameters normalized within 30min. We conclude that submaximal cycling in volunteers leads to the early derangement of gastric mucosal energy balance. The time course of PCO2gap parallels changes in systemic energy status.