Temporal trends in 6-minute walking distance for older Japanese adults between 1998 and 2017

Background:The 6-minute walking distance(6 MWD) is an excellent measure of both functional endurance and health.The primary aim of this study was to estimate temporal trends in 6 MWD for older Japanese adults between 1998 and 2017;the secondary aim was to estimate concurrent trends in body size(i.e.,height and mass) and self-reported participation in exercise/sport.Methods:Adults aged 65-79 years were included.Annual nationally representative 6 MWD data(n=103,505) for the entire period were obtained from the Japanese Ministry of Education,Culture,Sports,Science and Technology.Temporal trends in means(and relative frequencies)were estimated at the gender-age level by best-fitting sample-weighted linear/polynomial regression models,with national trends estimated by a post-stratified population-weighting procedure.Temporal trends in distributional variability were estimated as the ratio of coefficients of variation.Results:Between 1998 and 2017 there was a steady,moderate improvement in mean 6 MWD(absolute=45 m(95% confidence interval(95%CI):43-47);percent=8.0%(95%CI:7.6%-8.4%);effect size=0.51(95%CI:0.48-0.54)).Gender-and age-related temporal differences in means were negligible.Variability in 6 MWD declined substantially(ratio of coefficients of variation=0.89,95%CI:0.87-0.92),with declines larger for women compared to men,and for 75-79-year-olds compared to 65-74-year-olds.Correspondingly,there were moderate and negligible increases in mean height and mass,respectively,and negligible increases in the percentage who participated in exercise/sport at least3 days per week and at least 30 min per session.Conclusion:There has been a steady,moderate improvement in mean 6 MWD for older Japanese adults since 1998,which is suggestive of corresponding improvements in both functional endurance and health.The substantial decline in variability indicates that the temporal improvement in mean 6 MWD was not uniform across the distribution.Trends in 6 MWD are probably influenced by corresponding trends in body size and/or participation in exercise/sport.