The aim of this study was to investigate the effects on pulmonary ventilation and oxygen uptake ( (V) over dot athletes with a very high maximal oxygen uptake (V) over dotO(2)max) and corresponding high ventilation capacity when using a modern metabolic system with relatively high resistance to breathing (HIGH(RES)), compared to a traditional system with low resistance to breathing (LOWRES). Four rowers and three cross-country skiers (without asthma), competing at a high international level, performed in experimental conditions with LOWRE (S)and HIGH(RES) using a rowing ergometer and roller skis on a treadmill. The results showed that (V) over dotO(2), blood lactate, heart rate and respiratory exchange ratio were not different between the LOWRES and HIGH(RES) test conditions during both submaximal and maximal exercise. Also, the athlete's time to exhaustion (treadmill) and mean power (rowing ergometer) from maximal tests were no different between the two conditions. However, ventilation and expiratory O-2 and CO2 concentrations were different for both submaximal and maximal exercise. Thus, the authors have concluded that the differences in resistance to breathing of metabolic systems influence elite endurance athletes (V) over dot(E)at low to very high workloads, thus affecting the expired gas fractions, but not the submaximal (V) over dotO(2), (V) over dotO(2)maxand performance in a laboratory setting at sea level.