Oxygen cost of breathing and breathlessness during exercise in nonobese women and men

Introduction: Although it has been reported that the work of breathing may be higher in women, inconsistencies among studies leaves this important question unresolved. Also, the association between the oxygen cost of breathing and rating of perceived breathlessness (RPB) during exercise has not been examined between women and men. Purpose: This study aimed to measure oxygen cost of breathing during eucapnic voluntary hyperpnea and RPB (Borg 0-10 scale) during 6 min of constant work rate cycling at 60 and 90 W, respectively, in healthy, nonobese women and men. Methods: A total of 9 women (27 yr, body mass index = 21 kg•m ^-1) and 10 men (29 yr, body mass index = 25 kg•m ^-1) participated. All subjects underwent pulmonary function testing, exercise cycling, and determination of oxygen cost of breathing during eucapnic voluntary hyperpnea. Oxygen cost of breathing was obtained from the slope of the oxygen uptake (mL•min ^-1) and ventilation (L•min ^-1) relationship. RPB and cardiorespiratory measures were collected during minute 6 of the exercise. Data were analyzed by independent t-test and regression analysis. Results: Age and pulmonary function were similar between the nonobese women and men. Oxygen cost of breathing was similar between the nonobese women (1.17 ± 0.26 mL•L) and men (1.21 ± 0.42 mL•L). RPB during exercise was similar between the women (2.1 ± 1.3) and men (2.6 ± 1.2) and was correlated (P < 0.05) with relative oxygen uptake (r = 0.55) but not the oxygen cost of breathing. Conclusions: In nonobese women and men, oxygen cost of breathing is not different over the ventilatory ranges studied and RPB is similar at the same relative exercise intensity. In addition, the oxygen cost of breathing was not associated with RPB during constant work rate exercise.