Isokinetic muscle function in COPD

Aim: Exercise limitation in patients with COPD has been attributed to impaired ventilation and reduced skeletal muscle function. We have previously used a combination of FEV₁ and leg muscle function (work achieved during a 30-s isokinetic sprint test) to predict progressive exercise capacity. However, the 30-s test may not be well tolerated in patients with advanced lung disease. We studied the relationship between progressive exercise capacity, FEV₁, and isokinetic work in patients with COPD and in healthy control subjects to assess whether the work accomplished at time intervals of < 30 s could also be used to predict progressive maximal exercise capacity (Wmax). Methods: Twenty-seven patients with COPD and 29 control subjects underwent anthropometric measures, spirometry, progressive cycle ergometry, and 30-s isokinetic cycling. Results: There was no significant difference for weight, height, or body mass index between the groups. The COPD group was slightly older and had a significantly lower FEV₁ than control subjects. They also had a lower Wmax (56 ± 28.3 W vs 141.9 ± 46.7 W) and isokinetic work accomplished over 10 s (W10), over 15 s (W15), over 20 s (W20), over 25 s (W25), and over 30 s (W30). Wmax correlated in both patients with COPD and in control subjects with W10, W15, W20, W25, W30, and FEV₁. Combining FEV₁ and isokinetic work (W10, W15, W20, W25, or W30) in a two-factor model to predict Wmax, the coefficients of determination (r²) for patients with COPD were 0.57, 0.57, 0.58, 0.59, and 0.58, and for control subjects were 0.69, 0.69, 0.71, 0.71, and 0.73, respectively. Wmax correlated with weight only in control subjects. Conclusions: Both ventilatory function and leg muscle function contribute to exercise limitation, and a 20-s isokinetic test can be utilized to assess leg function in patients with COPD.