Isotemporal substitution of sedentary time with physical activity and its associations with frailty status

Koutatsu Nagai,1 Kayoko Tamaki,2 Hiroshi Kusunoki,2 Yosuke Wada,3 Shotaro Tsuji,4 Masako Ito,5 Kyoko Sano,5 Manabu Amano,6 Soji Shimomura,7 Ken Shinmura2 1Department of Physical Therapy, School of Rehabilitation, Hyogo University of Health Sciences, Kobe, Japan; 2Department of General Medicine, Hyogo College of Medicine, Nishinomiya, Japan; 3Department of Rehabilitation, Hyogo College of Medicine Sasayama Medical Center, Sasayama, Japan; 4Department of Orthopaedic Surgery, Hyogo College of Medicine Sasayama Medical Center, Sasayama, Japan; 5Department of Occupational Therapy, School of Rehabilitation, Hyogo University of Health Sciences, Kobe, Japan; 6School of Pharmacy, Hyogo University of Health Sciences, Kobe, Japan; 7Department of General Medicine and Community Health Science, Hyogo College of Medicine Sasayama Medical Center, Sasayama, Japan Objectives: Recently, isotemporal substitution has been developed to substitute activity time for an equivalent amount of another activity. This study employed this method to demonstrate the effects of replacing sedentary behavior (SB) time with an equivalent amount of light-intensity physical activity (LPA) and moderate-to-vigorous intensity physical activity (MVPA) on the risk for different severities of frailty.Methods: A total of 886 older adults (average age 73.6 years, female 70%) participated in this cross-sectional study. Frailty status was assessed according to the cardiovascular health study criteria.Main outcome measures: Wrist-worn accelerometers were used to measure SB, LPA, and MVPA. Isotemporal substitution models were applied to show the estimated effects of substituting 30 min of SB with an equal amount of time spent in LPA or MVPA on the risk for pre-frailty and frailty.Results: The physical activity level and SB were not associated with the incidence of pre-frailty. However, a 16% (OR: 0.84; 95% CI: 0.78–0.90) and 42% (OR: 0.58; 95% CI: 0.37–0.92) decrease in frailty risk was noted when SB was substituted with LPA and MVPA, respectively, in the crude model. In the adjusted model, the significant effect was sustained for LPA (OR: 0.86; 95% CI: 0.80–0.92) but not for MVPA (OR: 0.74; 95% CI: 0.47–1.17).Conclusions: This study indicates that replacing 30 min of SB with an equivalent amount of LPA decreases the risk for frailty in older adults. Moreover, increasing LPA seems more feasible than increasing MVPA in older adults, with substantial benefit. Keywords: isotemporal substitution, frailty, physical activity, sedentary behavio