External dead space explains sex-differences in the ventilatory response to submaximal exercise in children with and without obesity.

We compared the exercise ventilatory response (slope of the ventilation, V̇ and carbon dioxide production, V̇CO relationship) in boys and girls with and without obesity. 46 children with obesity (BMI percentile: 97.7 ± 1.4) and 27 children without obesity (BMI percentile: 55.1 ± 22.2) were included and divided into groups by sex (with obesity: 17 girls and 29 boys; without obesity: 13 girls and 14 boys). A 6 min constant load cycling test at 45 % of peak work rate was performed. The V̇/V̇CO slope was similar (p = 0.67) between children with (32.7 ± 4.3) and without (32.2 ± 6.1) obesity; however, it was higher (p = 0.02) in girls (35.4 ± 5.6) than boys (32.6 ± 4.9). We also examined a corrected V̇/V̇CO slope for the effects of mechanical dead space (V), by subtracting V̇ from V̇ (V̇/V̇CO slope). The V̇/V̇CO slope remained similar (p = 0.37) between children with (26.8 ± 3.2) and without obesity (26.1 ± 3.1); however, no sex differences were observed (p = 0.13). Therefore, V should be accounted for before evaluating the V̇/V̇CO slope, particularly when making between-sex comparisons.