Physiological correlates of endurance time variability during constant-workrate cycling exercise in patients with COPD

Rationale

The endurance time (T_end) during constant-workrate cycling exercise (CET) is highly variable in COPD. We investigated pulmonary and physiological variables that may contribute to these variations in T_end.

Methods

Ninety-two patients with COPD completed a CET performed at 80% of peak workrate capacity (W_peak). Patients were divided into tertiles of T_end Group 1: <4 min; Group 2: 4–6 min; Group 3: >6 min]. Disease severity (FEV₁), aerobic fitness (W_peak, peak oxygen consumption _peak], ventilatory threshold _VT]), quadriceps strength (MVC), symptom scores at the end of CET and exercise intensity during CET (heart rate at the end of CET to heart rate at peak incremental exercise ratio HR_CET/HR_peak]) were analyzed as potential variables influencing T_end.

Results

W_peak, _peak, _VT, MVC, leg fatigue at end of CET, and HR_CET/HR_peak were lower in group 1 than in group 2 or 3 (p≤0.05). _VT and leg fatigue at end of CET independently predicted T_end in multiple regression analysis (r?=?0.50, p?=?0.001).

Conclusion

T_end was independently related to the aerobic fitness and to tolerance to leg fatigue at the end of exercise. A large fraction of the variability in T_end was not explained by the physiological parameters assessed in the present study. Individualization of exercise intensity during CET should help in reducing variations in T_end among patients with COPD.