The six-minute stepper test is related to muscle strength but cannot substitute for the one repetition maximum to prescribe strength training in patients with COPD

Purpose: There are many barriers to pulmonary rehabilitation, including a limited access to evaluation centers. To cope with these difficulties, field tests are often used to prescribe endurance training. As field tests are related to muscle strength, they could also be used to prescribe strength training and increase the access to pulmonary rehabilitation in rural area. However, their validity for this purpose has never been studied. Patients and methods: The relationship between the 6-minute stepper test (6MST), 6-minute walk test, maximal workload achieved during cardiopulmonary exercise testing (Wpeak), and one repetition maximum (1RM) was assessed in 35 patients with COPD through a retrospective chart review to derive predictive equation of the 1RM from these tests. The effectiveness of these equations to prescribe strength training at 70% of the 1RM was assessed in an independent cross-validation group of 34 patients with COPD. Results: There was a moderate relationship between the 6MST, Wpeak and the 1RM (r=0.44 and r=0.41, respectively, both P≤0.01). Whatever the test, the prescription of strength training using the estimated 1RM compared with the measured 1RM resulted in a mean absolute difference and a mean bias of about 30 kg. Conclusion: The use of the 6MST and Wpeak for the prescription of strength training would result in a clinically not acceptable error. Therefore, they should not be used as a substitute for the 1RM to prescribe strength training.