Cross-Sectional Associations of Physical Fitness Performance Level and Sleep Duration among Older Adults: Results from the National Physical Fitness Survey in Taiwan

Research on relationships between physical fitness and sleep duration among older adults is scarce, especially in Taiwanese representative samples of elderly people who undergo physical fitness measurements. This study aimed to determine the associations between physical fitness and short and long sleep durations among older adults in Taiwan. We conducted a cross-sectional study and reviewed data derived from the National Physical Fitness Survey in Taiwan. A total of 24,125 Taiwanese adults aged 65 years and older participated in this study between October 2014 and March 2015. Each individual's sleep duration was recorded with a standard questionnaire method. Sleep duration data were stratified into short (<= 5 h), normal (6-7 h), and long (>= 8 h) sleep duration groups. Physical fitness was assessed by five components: aerobic endurance (2 min step test), muscle strength and endurance (30 s arm curl and 30 s chair stand tests), flexibility (back scratch and chair sit-and-reach tests), body composition (body mass index (BMI) and waist-to-hip ratio (WHR)), and balance (one-leg stance with eye open and 8-foot up-and-go tests). To understand whether a dose-response relationship exists between physical fitness and short or long sleep duration, we analyzed four levels of performance on the basis of quartiles of physical fitness measurements by using logistic regression. The first quartile of physical fitness performance was the baseline level. The odds ratio (OR) for short sleep duration for the third quartile of BMI was 0.8031 times (95% CI, 0.7119-0.9061) lower than the baseline. For the fourth quartile of BMI, the OR was 0.8660 times (95% CI, 0.7653-0.9800) lower than the baseline. The adjusted OR for long sleep duration significantly decreased in the second, third, and fourth quartiles of the 30 s chair stand, back scratch, chair sit-and-reach test, one-leg stance with one eye open, and BMI. The adjusted OR was increased in the third and fourth quartiles of the 8-foot up-and-go and WHR. The results of the current study suggest that physical fitness performance may influence sleep duration as an associated factor, and the relationship is much stronger for long sleep duration than for short sleep duration.