Reliability and validity of 4-metre gait speed in COPD

In community-dwelling older adults, usual gait speed over 4 m (4MGS) consistently predicts greater risk of adverse health outcomes. The aims of the present study were to assess the reliability of the 4MGS and the relationship with established health outcome measures in chronic obstructive pulmonary disease (COPD). Test-retest and interobserver reliability of the 4MGS were measured in 80 and 58 COPD patients, respectively. In 586 COPD patients, the 4MGS, as well as forced expiratory volume in 1 s (FEV1), the incremental shuttle walk (ISW), Medical Research Council (MRC) dyspnoea scale and St George's Respiratory Questionnaire (SGRQ) were measured. Participants were stratified according to "slow" (<0.8 m·s(-1)) or "normal" 4MGS (≥0.8 m·s(-1)). Intra-class correlation coefficients for test-retest and interobserver reliability were 0.97 and 0.99, respectively. There was a significant positive correlation between 4MGS with ISW (ρ = 0.78; p<0.001) and a negative correlation with MRC dyspnoea scale and SGRQ (ρ = -0.55 and -0.44; p<0.001 for both). COPD patients with slow 4MGS had significantly reduced ISW and higher MRC dyspnoea scale and SGRQ than those with preserved walking speed, despite similar FEV1 % predicted. The 4MGS is reliable in COPD, correlates with exercise capacity, dyspnoea and health-related quality of life, and has potential as a simple assessment tool in COPD.