Purpose: In obesity, an increased work of breathing contributes to a higher O2 cost of exercise and negatively affects exercise tolerance. The purpose of the study was to determine whether, in obese adolescents, acute respiratory muscle unloading via normoxic helium–O2 breathing reduces the O2 cost of cycling and perceived exertion. Methods: Nine males [age 16.8 ± 1.6 (x ± SD) years, body mass 109.9 ± 15.0 kg] performed on a cycle ergometer, breathing room air (AIR) or a 21 % O2–79 % helium mixture (He–O2): an incremental exercise, for determination of $$ mathop Vlimits^{.} $$V.O2 peak and gas exchange threshold (GET); 12 min constant work rate (CWR) exercises at 70 % of GET (GET) determined in AIR. Results: $$ mathop Vlimits^{.} $$V.O2 peak was not different in the two conditions. From the 3rd to the 12th minute of exercise (both during CWR < GET and CWR > GET), $$ mathop Vlimits^{.} $$V.O2 was lower in He–O2 vs. AIR (end-exercise values: 1.40 ± 0.14 vs. 1.57 ± 0.22 L min−1 GET). During CWR > GET in AIR, $$ mathop Vlimits^{.} $$V.O2 linearly increased from the 3rd to the 12th minute of exercise, whereas no substantial increase was observed in He–O2. The O2 cost of cycling was ~10 % (GET) lower in He–O2 vs. AIR. Heart rate and ratings of perceived exertion for dyspnea/respiratory discomfort and leg effort were lower in He–O2. Conclusions: In obese adolescents, acute respiratory muscle unloading via He–O2 breathing lowered the O2 cost of cycling and perceived exertion during submaximal moderate- and heavy-intensity exercise.
