Background and aims: The six minute walk test is widely used to measure aerobic exercise capacity in older people, but lack responsiveness to change. We aimed to compare the reliability, responsiveness and completion rates of the six minute walk with a new test of aerobic exercise capacity - the endurance shuttle walk test. Methods: Two groups were studied: 18 patients from a Medicine for the Elderly Day Hospital (study 1) receiving physiotherapy, and 15 community dwelling older people (study 2) receiving caffeine or placebo in a crossover study, followed by a weekly exercise programme. Six minute walk test and endurance shuttle walk test were performed at baseline and after interventions. Intraclass correlation coefficients were calculated for reliability, and Cohen's effect sizes were calculated to characterize responsiveness. Results: 6/18 of patients in study 1 completed the baseline shuttle walk successfully. For those completing baseline and week one shuttle walk, similar intraclass correlation coefficients were seen (shuttle walk 0.97; six minute walk 0.90). In study 2, all attendees completed baseline and follow-up shuttle walk. 7/15 managed the maximum shuttle walk time at baseline. Effect sizes for caffeine intervention (0.29 for six minute walk, 0.01 for shuttle walk) and for exercise intervention (0.15 for six minute walk, 0.24 for shuttle walk) were similarly low for both tests. Conclusion: The endurance shuttle walk is no more responsive to change than the six minute walk in older people, is limited by ceiling effects, and cannot be performed successfully by very frail older people.