Upper intensity limit for prolonged aerobic exercise in chronic heart failure.

Introduction: The highest power sustainable in VO2 and blood lactate steady-state conditions is named "critical power" (CP) and marks the upper limit for prolonged aerobic exercise performance. CP is thus of particular interest for continuous aerobic training prescription, but no data are available as to CP in chronic heart failure (CHF) patients, that is, a population in which aerobic training is a widely accepted nonpharmacologic treatment. The aim of this study was to evaluate CP in a group of CHF and in two groups of age-matched untrained (UT-N) and trained (TR-N) normal subjects.

Methods: Fifteen untrained CHF, five UT-N, and five TR-N underwent one incremental and five very high/severe-intensity constant-power cardiopulmonary exercise tests (CPT). Power versus time to exhaustion data from CPT were fitted by a hyperbola, whose power asymptote is CP. Subsequently, all participants exercised at CP with blood lactate sampling every 2 min.

Results: CP was 80 ± 21, 129 ± 17, and 199 ± 35 W in CHF, UT-N, and TR-N, respectively (all comparisons P < 0.005). These values corresponded to 66% ± 6%, 66% ± 6%, and 74% ± 3% of peak power in CHF, UT-N, and TR-N, respectively (TR-N vs both CHF and UT-N, P < 0.05) and to 81% ± 26%, 91% ± 11%, and 83% ± 9% of HR reserve in CHF, UT-N, and TR-N, respectively (NS). All participants exercised for 30 min in VO2, blood lactate, ventilation, and HR steady-state conditions at CP but not at the lowest-power CPT (>CP ~ 10%).

Conclusions: The upper intensity limit for prolonged aerobic exercise, that is, CP, is equal to 65% of peak power in CHF patients. This finding provides a physiologically meaningful reference for continuous aerobic training prescription in this population.