12-Week Inspiratory Muscle Training Improves Respiratory Muscle Strength in Adult Patients with Stable Asthma: A Randomized Controlled Trial

Abstract

This study aims to investigate and compare the effects of conventional breathing exercises and an inspiratory muscle training intervention on clinical symptoms in asthma patients. Sixty asthma patients (40-65 years old) were randomly assigned to either the conventional breathing exercises (BTE) or inspiratory muscle training (IMT) group for a 12-week intervention period. Outcome measurements were performed before and after the intervention, including the spirometry data, maximal inspiratory and expiratory pressures (PImax and PEmax), asthma control test, asthma control questionnaire, six-minute walk test, and three-day physical activity log, were recorded. PImax expressed as % of predicted value controlled for age and gender in healthy subjects (% predicted) increased by 16.92% (82.45% to 99.38%, p < 0.05) in the BTE group and by 29.84% (71.19% to 101.03%, p < 0.05) in the IMT group. Except for forced vital capacity, which was reduced in the BTE group, all other measured variables improved in both groups, and no statistically significant between-group differences were found. IMT appears to be more effective than breathing exercise intervention in promoting improvements in respiratory muscle strength. IMT may act as an alternative to conventional breathing exercises for middle-aged and elderly asthma patients.

Keywords: asthma; breathing exercise; forced vital capacity (FVC); inspiratory muscle training; maximal inspiratory pressure (PImax).

Figure 1

Flowchart of the participants throughout the study (CONsolidated Standards Of Reporting Trials (CONSORT) flow diagram) [20].

Figure 2

The experimental procedure and timeframe of the study. ⌂: Pulmonary and respiratory function assessments; ♦: Asthma control assessments; ●: Functional capacity and physical activity assessments; ★: Respiratory visit adjustment (in a monthly interval).

Figure 3

Effects of the breathing exercises (BTE) and inspiratory muscle training (IMT) on the forced vital capacity (FVC) (A) and forced expiratory volume in one second, FEV1 (B). Values are mean ± SD. * denotes the significant differences between the BTE and IMT groups. † denotes the significant “Treatment (Group) × Time” interaction. (p < 0.05).

Figure 4

Effects of the breathing exercises (BTE) and inspiratory muscle training (IMT) interventions on the PImax (A) and PEmax (B). Values are mean ± SD. Pretest is illustrated as a white bar, while posttest is illustrated as a black bar. * denotes the significant differences between pre- and posttest within BTE or IMT group. (p < 0.05).