Constant Work-Rate Test to Assess the Effects of Intradialytic Aerobic Training in Mildly Impaired Patients With End-Stage Renal Disease: A Randomized Controlled Trial

Objective: To investigate if high-intensity constant work rate (CWR) would constitute a more appropriate testing strategy compared with incremental work rate (IWR) to assess the effectiveness of intradialytic aerobic training in patients with end-stage renal disease (ESRD). Design: Randomized controlled trial. Setting: Nephrology unit at the university hospital. Participants: Patients (N=28; 47.0 +/- 11.9y) under hemodialysis (4.4 +/- 4.3y) were randomly assigned to exercise and control groups. Intervention: Patients included in the exercise group underwent a moderate-intensity intradialytic aerobic training program 3 times per week for 12 weeks. Main Outcome Measures: Cardiopulmonary and perceptual responses were obtained during an IWR and a high-intensity CWR test to the limit of tolerance on a cycle ergometer. Results: Training-induced increases in peak oxygen uptake (Vo(2)peak) and time to exercise intolerance (Tlim). Mean improvement in Tlim (97.4%+/- 75.6%) was significantly higher than increases in Vo(2)peak (12%+/- 11.3%) (P<.01); in fact, while Tlim improved 50% to 200% in 9 of 12 patients, Vo(2)peak increases were typically in the 15% to 20% range. CWR test revealed lower metabolic, ventilatory, cardiovascular, and subjective stresses at isotime; in contrast, submaximal responses during the incremental work rate (at the gas exchange threshold) remained unaltered after training. Conclusions: A laboratory-based measure of endurance exercise capacity (high-intensity CWR test to Thin) was substantially more sensitive than oxygen uptake at the peak IWR test to unravel the physiologic benefits of an intradialytic aerobic training program in mildly impaired patients with ESRD.