Relationship between six-minute walk test distance with submaximal and peak oxygen uptake in older breast cancer survivors

Abstract Introduction Cardiorespiratory fitness is an important predictor of all-cause mortality among breast cancer (BC) survivors. Cardiopulmonary exercise testing (CPET) is the gold standard for measuring peak oxygen uptake (VO2peak); however, it is resource-intensive and not always feasible in clinical settings. The six-minute walk test (6MWT) is a simple-to-administer, low-cost measure of aerobic endurance, however its ability to estimate VO2 during the test or predict VO2peak in older BC survivors remains unknown. Purpose This study examined whether the distance walked during a 6MWT is associated with (1) VO2 during the test and (2) VO2peak in older female BC survivors, and to develop a regression equation that could be used to predict 6MWT VO2 and VO2peak. Methods Female BC survivors aged ≥60 years and ≥1 year post-anthracycline or HER2-targeted therapy completed a 6MWT and CPET (cycle-ergometer ramp protocol), during which VO2 and heart rate were measured. VO2 (ml/kg/min) and heart rate during the 6MWT was defined as the average of the last 2 minutes of exercise, while VO2peak was defined as the highest 30-second average obtained during the final minute of the test. Pearson correlations and backward linear regression models were used to evaluate associations among 6MWT distance, submaximal walking VO2, and VO2peak. Results Thirty-nine women participated in this study (mean age: 69±5 years; 13±7 years post–breast cancer therapy; 161±7cm; BMI 28±5). The mean six-minute walk distance was 548 ± 76 m during which time, mean VO2 was 15 ± 4 ml/kg/min and mean heart rate was 127± 19 bpm. Mean cycle VO2peak was 19±4ml/kg/min (82±17% of VO2peak). Six-minute walk distance was moderately correlated with walking VO2 (r = 0.716, p < 0.001) and with cycle VO2peak (r = 0.643, p < 0.001). In regression analyses, 6MWT distance, height, and heart rate independently predicted walking VO2 (adjusted R² = 0.642; VO2peak = 14.53 + (-0.175 x height [cm]) + (0.042 x distance walked [m]) + (0.047 x heart rate [bpm]), p < 0.001). For VO2peak, walk distance was the only significant predictor (adjusted R² = 0.395; VO2peak = −1.335 + (0.037 × distance [m]), p < 0.001). Conclusion The 6MWT is a practical, less demanding alternative to maximal exercise testing for estimating aerobic endurance and peak cardiorespiratory fitness in older BC survivors.