Respiratory and skeletal muscle strength in chronic obstructive pulmonary disease: impact on exercise capacity and lower extremity function.
OBJECTIVE
We sought to quantify the impact of respiratory muscle and lower extremity strength on exercise capacity and lower extremity function (LEF) in patients with chronic obstructive pulmonary disease (COPD).


METHODS
In 828 persons with COPD, we assessed the impact of reduced respiratory (maximum inspiratory pressure, MIP) and lower extremity muscle strength (quadriceps strength, QS) on exercise capacity (6-minute walk test, 6MWT), and LEF (short physical performance battery). Multiple regression analyses taking into account key covariates, including lung function and smoking, tested the associations between muscle strength and exercise and functional capacity.


RESULTS
For each 0.5 SD decrement in QS, men walked 18.3 m less during 6MWT (95% confidence interval [CI], -24.1 to -12.4); women 25.1 m less (95% CI, -31.1 to -12.4). For each 0.5 SD decrement in MIP, men walked 9.4 m less during 6MWT (95% CI, -15.2 to -3.6); women 8.7 m less (95% CI, -14.1 to -3.4). For each 0.5 SD decrease in QS, men had a 1.32 higher odds (95% CI, 1.11-1.15) of poor LEF; women had a 1.87 higher odds (95% CI, 1.54-2.27). Lower MIP (per 0.5 SD) was associated with increased odds of poor LEF in women (odds ratio = 1.18; 95% CI, 1.00-1.39), but not in men (odds ratio = 1.10; 95% CI, 0.93-1.31).


CONCLUSIONS
In COPD, reduced respiratory and lower extremity muscle strength are associated with decreased exercise and functional capacity. Muscle weakness is likely an important component of impairment and disability in patients with COPD.
Division of Pulmonary, Critical Care, Allergy, and Sleep Medicine, Department of Medicine, University of California, San Francisco, California 94143, USA. jon.singer@ucsf.edu
Jonathan
J
Singer
Edward H
EH
Yelin
Patricia P
PP
Katz
Gabriela
G
Sanchez
Carlos
C
Iribarren
Mark D
MD
Eisner
Paul D
PD
Blanc
D000328:Adult; D015331:Cohort Studies; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000502:physiology*
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