Imposed expiratory resistance, hyperinflation, and dyspnea are dissociated from locomotor fatigue during moderate exercise

Abstract

Expiratory flow resistance (e.g. asthma, chronic obstructive pulmonary disease) results in dyspnea, dynamic hyperinflation, and premature exercise intolerance during heavy intensity exercise. This cascade seems to be primarily precipitated by abnormal lung mechanics that result in exacerbated symptoms and reduced maximal evocable limb motor activity. We do not know whether this cascade behaves in the same way during moderate exercise where only modest locomotor fatigue is expected to develop.We hypothesized that expiratory flow resistance would result in dynamic hyperinflation, dyspnea, and exacerbated locomotor fatigue during moderate intensity exercise in a similar manner to that during heavy intensity exercise.Volunteers (N=10, 27±6 yr) completed constant power moderate exercise (50% peak ramp power) with 3 levels of imposed expiratory flow resistance (7, 9, 11 cm H2O·L·s−1) or control (no imposed flow resistance). We measured operating lung volumes during exercise with inspiratory capacity maneuvers. Participants reported dyspnea and leg effort using a Borg 10‐point scale. At the termination of exercise we used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power (Piso).Decline in Piso was not different when expiratory flow resistance was imposed (p>0.05). Inspiratory capacity was smaller at the end of exercise in the most severe resistance (11 cm H2O·L·s−1) as compared to control (2.31±1.52 vs. 3.15±0.71 L; p<0.05). Similarly, inspiratory reserve volume was smaller at the end of exercise in the most severe resistance as compared to control (−0.07±1.28 vs. 0.82±0.43 L; p<0.05). Dyspnea was greater at the end of exercise in both mild and severe resistance (7 and 11 cm H2O·L·s−1) as compared to control (5.7±2.5 and 5.2±1.9 vs. 3.7±1.6; p<0.05). Piso was not related to inspiratory reserve volume, inspiratory capacity, or dyspnea (p>0.05).Imposed severe expiratory flow resistance results in hyperinflation and exacerbated dyspnea in healthy volunteers. Unlike what we have found during heavy exercise, however, abnormal lung mechanics and dyspnea were not related to maximal locomotor power during moderate exercise.