Evaluation of isokinetic muscle strength of upper limb and the relationship with pulmonary function and respiratory muscle strength in stable COPD patients

Background: Upper limb muscle strength plays an important role in respiratory and pulmonary function, and limited research focuses on the role of strength and endurance of the elbow extensor and flexor. This study was conducted to accurately assess upper limb muscle function and quantified associations with pulmonary function and respiratory muscle strength in patients with stable chronic obstructive pulmonary disease (COPD). Methods: In this cross-sectional study, patients with stable COPD treated in Yue-Yang Integrative Medicine Hospital from March 2014 to March 2016 were recruited. All participants underwent a pulmonary function test (forced expiratory volume in first second/forced vital capacity, FEV1/FVC; percentage value of predicted FEV1, FEV1% pred), a respiratory muscle strength test (maximal inspiratory pressure, MIP; maximal expiratory pressure, MEP), and an isokinetic test of dominant upper limb after a 24-hr interval (peak torque, PT; PT/body weight, PT/BW; total work, TW; endurance ratio, ER). Results: A total of 88 patients with stable COPD (age: 65.5 +/- 8.7 years) were recruited, of which 73% (64 patients) were male. In the multiple stepwise regression analysis, sex remained as significant impactors in the final model for FEV1% pred (adjusted R-2=0.243, P < 0.001). Elbow flexor PT/BW and ER, sex, and BMI remained as significant impactors in the final model for FEV1/FVC (adjusted R-2=0.255, P<0.01). Elbow flexor TW remained as significant impactors for MIP (adjusted R-2=0.112, P=0.001), while elbow extensor PT and PT/BW and sex remained as significant impactors for MEP (adjusted R = 0.385, P<0.01). Conclusion: In stable COPD, pulmonary function and respiratory muscle strength are associated with upper limb muscle strength. In particular, elbow flexor endurance is likely an important impactor for pulmonary function and inspiratory muscle strength, while elbow extensor strength is of importance for expiratory muscle strength.