Respiratory and Perceptual Responses to High Intensity Interval Exercise in Obese Adults

Purpose: Obese adults experience low lung volume breathing at rest and during exercise, which provokes ventilatory constraints and dyspnea on exertion. High-intensity interval exercise (HIIE) has emerged as an alternative to continuous exercise (CE); however, the effects of HIIE on lung volumes, ventilatory constraints and dyspnea on exertion have not been studied in obese adults and thus tolerability of HIIE remains unknown. Therefore, the purpose of this study was to examine the differences in respiratory and perceptual responses during HIIE versus CE in obese adults when compared with nonobese adults. Methodology: Ten healthy, nonobese (24.1 ± 6.2 yr., BMI: 23 ± 1.3kg/m2) men (N=5) and women (N=5) and ten otherwise healthy obese (24.2 ± 3.8 yr., BMI: 37 ± 4.6kg/m2) men (N=5) and women (N=5) participated in this study. All participants completed a pulmonary function test, an incremental exercise test, and a verification test at 105% of peak work rate (WR). Participants also completed HIIE, which included eight 30 s intervals at 80% of peak WR rate with 45 s of recovery, as well as 6 min of CE below ventilatory threshold (Vth) and 6 min of CE above Vth. The HIIE and CE sessions were completed on separated visits in a random order. Ventilation, gas exchange, heart rate, pulse oxygen saturation, breathing pattern, and exercise tidal flow volume loops were assessed during exercise. Inspiratory capacity (IC) measurements were conducted during exercise by instructing participants to inhale until achievement of total lung capacity (TLC). Operating lung volumes (i.e., end-expiratory lung volume [EELV] and end-inspiratory lung volume [EILV]) were calculated and expressed as a percent of TLC. Expiratory flow limitation (EFL) was assessed as the overlap between exercise tidal flow volume loops and the maximal expiratory flow volume loop. Dynamic hyperinflation (DH) was assessed as the difference in EELV from rest to exercise; an increase in EELV indicated DH. Ratings of perceived breathlessness and exertion (RPB and RPE) were assessed during exercise. Affective and negative emotional responses to breathlessness using a visual analog scale as well as enjoyment of exercise using the physical activity enjoyment scale (PACES) were recorded immediately after exercise cessation. Results: Functional residual capacity (FRC) and TLC (%predicted) were lower in obese when compared with nonobese participants. Cardiorespiratory fitness did not statistically differ between obese and nonobese participants. EELV was lower in obese (HIIE: 39.6 ± 5.8, CE below Vth: 37.6 ± 8.2, CE above Vth: 37.2 ± 4.6%TLC) when compared with nonobese (HIIE: 49.2 ± 5.6, CE below Vth: 48.4 ± 5.5, CE above Vth: 48.2 ± 5.2%TLC; P = 0.001 for each comparison). V̇ O2, V̇ CO2 and V̇ E were significantly higher during HIIE in the obese when compared with the nonobese participants (P \u3c 0.05). During HIIE, four obese participants experienced EFL and three experienced DH. In obese participants, RPE was highest in HIIE (15.2 ± 3.4 Borg units), followed by CE above Vth (10.8 ± 2.8), and then CE below Vth (8.2 ± 1.7; P \u3c 0.05). In obese participants, RPB was highest in HIIE (5.3 ± 2.4 Borg units), followed by CE above Vth (2.5 ± 1.6), and then CE below Vth (0.9 ± 0.7; P \u3c 0.05). During HIIE, unpleasantness associated with breathlessness was higher in obese (4.2 ± 3.0) when compared with nonobese participants (0.6 ± 1.3; P = 0.005). During HIIE, unpleasantness associated with breathlessness was inversely correlated with inspiratory reserve volume (r2= 0.596; P = 0.015) in obese participants. PACES score did not differ between exercise protocols for obese and nonobese participants. Conclusion: CE completed below or above Vth results in a lower ventilatory demand and lower ratings of perceived breathlessness and exertion when compared with HIIE in obese adults. Therefore, CE may be preferable to HIIE in obese adults