[Purpose] To investigate reliability and discriminant validity of a single question
about total lying time for assessing physical inactivity in community-dwelling older
people. [Participants and Methods] The participants were 54 healthy older individuals
(mean age, 72.5 years), who were asked to recall retrospectively their mean total lying
and sleep times per day in the previous week (7 days). The total lying and sleep times per
day in the forthcoming week (7 days) were also investigated prospectively after confirming
the mean total lying and sleep times per day in the previous week, and their mean values
per day were calculated. [Results] Intraclass reliability of total lying and sleep times
per day in the forthcoming week were acceptable [ICC (1, 1) for total lying time=0.835,
ICC (1, 1) for sleep time=0.707]. No significant difference in average total lying time
between the previous (8.4 ± 2.0 hours/day) and forthcoming (8.7 ± 1.7 hours/day) weeks was
seen. In the forthcoming week, average total lying time was significantly higher than
average sleep time (7.1 ± 1.3 hours/day). There was low significant correlation between
total lying time and sleep time. [Conclusion] Total lying time can be measured with
acceptable reliability and discriminant validity, and is a different outcome than sleep
time in community-dwelling older adults.