Psychometric evaluation of the exercise self-regulatory efficacy scale using objective measures of physical functioning in persons with chronic obstructive pulmonary disease

Abstract

Introduction: Physical activity (PA) promotion is an essential component of managing chronic obstructive pulmonary disease (COPD). Exercise self-efficacy is a primary indicator of exercise engagement. The Exercise Self-Regulatory Efficacy scale (Ex-SRES) was developed and validated in persons with COPD recruited at pulmonary rehabilitation programs who self-reported exercise behaviors. Our study evaluates its psychometric properties using objective assessments of PA and exercise capacity.

Methods: Secondary analyses were performed on baseline assessments of U.S. Veterans with COPD who participated in two PA intervention studies (N = 210; age M = 69 ± 8; 97 % male; 91.9 % White). The Ex-SRES asked how confident participants felt they could exercise 3X/week for 20 min given 16 barriers. The Omron HJ-720 or Fitbit Zip pedometer assessed daily step counts for 7-10 days and the 6-min walk test (6 MWT) assessed exercise capacity. Breathlessness was assessed with the Modified Medical Research Council Dyspnea Scale (mMRC). The St. George Respiratory Questionnaire (SGRQ) assessed health-related quality of life; participants self-reported confidence and motivation for exercising regularly. Exploratory factor analysis (EFA) assessed the underlying factor structure of the Ex-SRES and internal consistency reliability. Convergent validity was evaluated through correlations with objective and subjective measures.

Results: EFA resulted in a one-factor structure accounting for 58.28 % of the common variance. The Ex-SRES demonstrated convergent-type validity: daily step counts (ρ = .17), 6 MWT distance (ρ = .22), mMRC (ρ = -.15), SGRQ (ρ = -.24), motivation (ρ = .42), and confidence (ρ = .58) (p's < .05) and internal consistency reliability (Cronbach's α = .95) CONCLUSION: Objective measures of PA and exercise capacity confirm the psychometric properties of the Ex-SRES.

Keywords: Chronic obstructive pulmonary disease; Exercise; Exercise self-regulatory efficacy; Physical activity. psychometric properties; Validation study.