Objective: To investigate the quadriceps strength in patients with stable chronic obstructive pulmonary disease (COPD), and the characteristics of quadriceps dysfunction in COPD patients.
Methods: All participants including 71 (male 54, female 17) patients with stable COPD and 60 (male 21, female 39) normal subjects underwent lung function tests, anthropometric measurements, quadriceps function assessments and physical activities evaluation. Quadriceps function was assessed by measurement of the maximal isometric volitional contraction (QMVC), endurance time and the maximal twitch tension. SPSS 12.0 was used to perform statistics. The results were presented as the (-x) +/- s for all variables that were normally distributed. Differences between the two groups (i.e., patients vs. controls) were analyzed using a two-tailed grouped t test. Differences between the groups within the COPD patients were analyzed using one-way ANOVA, and q-test was used to analyze the differences between them. Linear regression analysis was used to investigate the relationships between variables.
Results: The mean QMVC was (42 +/- 8) kg, endurance time was (81 +/- 27) s, the maximal twitch tension was (13.9 +/- 6.7) kg in normal men, while they were (23 +/- 6) kg, (51 +/- 18) s and (7.0 +/- 2.3) kg respectively in their COPD counterparts (t value was 5.89 - 10.73, all P < 0.01). The mean QMVC was (29 +/- 5) kg, endurance time was (83 +/- 32) s and the maximal twitch tension was (7.4 +/- 2.1) kg in normal female subjects, while they were (16 +/- 4) kg, (56 +/- 8) s and (4.2 +/- 0.9) kg respectively in female COPD patients (t value was 3.47 - 9.35, all P < 0.01). Correlation analysis showed that QMVC positively correlated with lung function variables, body mass index and mid-thigh muscle circumference in COPD patients (r value was 0.27 - 0.76, all P < 0.01).
Conclusions: Our data showed that quadriceps dysfunction was common in COPD patients. QMVC was impaired to a greater extent than isometric endurance, and QMVC positively correlated with the severity of airflow obstruction. The maximal twitch tension induced by magnetic femoral nerve stimulation was an objective method to assess quadriceps strength.