Alternative strategies for exercise critical power estimation in patients with COPD.

Exercise critical power (CP) has been shown to represent the highest sustainable work rate (WR) in patients with chronic obstructive pulmonary disease (COPD). Parameter estimation, however, depends on 4 high-intensity tests performed, on different days, to the limit of tolerance (T(lim)). In order to establish a milder protocol that would be more suitable for disabled patients, we contrasted CP derived from 4, 3 and 2 tests (CP4, CP3 and CP2) in 8 males with moderate COPD. In addition, CP was calculated from 2 single-day tests performed on an inverse sequence (CP(2AB) and CP(2BA)): CP values within 5 W from CP4 were assumed as "clinically-acceptable" estimates. We found that [CP4-CP3] and [CP4-CP2] differences were within 5 W in 8 and 6 patients, respectively (95% confidence interval of the differences = -1.3 to 3.5 W and -11.5 to 6.5 W). There was a systematic decline on T(lim) when an exercise bout was performed after a previous test on the same day (P<0.05). Consequently, substantial differences were found between CP4 and any of the CP estimates obtained from single-day tests. In conclusion, clinically-acceptable estimates of CP can be obtained by using 3 or, in most circumstances, 2 constant WR tests in patients with moderate COPD--provided that they are not performed on the same day.