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OBJECTIVES: The aims of this study were (i) to examine the independent associations of the time spent in daily activities measured by multi-sensor pattern-recognition with frailty and physical functioning (PF); and (ii) to analyze how relocating time between these daily activities is associated with frailty and PF in a sample of older adults. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: The study sample consists of 436 (287 women) high-functioning community-dwelling older adults, aged 65 to 92 years, who participated in the IMPACT65+ Study. MEASUREMENTS: Frailty was calculated as a continuous measure; based on the five widely recognized Fried's criteria. PF was assessed using the SF-12 questionnaire. The time in daily activities was assessed by the Intelligent Device for Energy expenditure and Activity (IDEEA). Independent associations of daily activities with frailty and PF were examined using linear regression models adjusting for potential confounders. The isotemporal substitution models for estimate the effect of replacing time in one activity with the same amount of time in another activity while holding wake time constant. RESULTS: Time spent lying was directly associated, while time in walk at average and brisk pace was inversely associated with frailty. The independent associations for PF were similar to lying, walk at average pace and walk at brisk pace. Isotemporal substitution analyses revealed a clear beneficial effect of hypothetically replacing 30 min/day of sedentary behaviors or light physical activity by the same amount of moderate-to-vigorous physical activity for frailty and PF. CONCLUSION: This is the first study examining the activity-specific and isotemporal association of daily activities with frailty and PF in older adults. Isotemporal substitution analyses showed that replacing sedentary behaviors (lie, recline, passive sit) by light-intensity activities (active sit, stand and walk at slow pace), as well as light-intensity activities by activities at MVPA such as walk at brisk pace, may produce theoretical improvements in frailty and PF. These findings are important for the development of effective interventions focused on reducing age-related frailty and declines in PF.

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Tools for measuring walking time make use of objective and subjective methods. One subjective approach is to administer physical activity questionnaires (PAQ), mainly because they are inexpensive and easy to give to large groups. The European Prospective Investigation into Cancer and Nutrition (EPIC) study has a brief PAQ (EPIC-PAQ) and includes one question referencing walking time. The objective of this study was to assess the validity of the question about time spent walking included in the EPIC-PAQ. The sample included 200 older adults (113 women). To assess daily walking time, participants responded to the EPIC-PAQ in an interview and wore a portable gait analysis system and physical activity monitor for 48 consecutive hours in free-living condition. Results indicated that the mean of bias between the EPIC-PAQ and objetive measurement was -64.6 min/day. Also, the correlation was low compared to an objective measurement (rho = 0.196) and was positively correlated with the time spent at speeds below 2.5 mph but the correlation was low (slow walking rho = 0.154 and pace walking rho = 0.163). The EPIC-PAQ shows low correlations with the objective measurement of walking time, that suggests it may be inaccurate and affecting the estimate of the EPIC-PAQ's PA energy expenditure in this age group.

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Usual gait speed has been shown to have very good reliability and convincing predictive validity for evaluating older adults' gait skills, but its criterion validity is unknown. We examined the criterion validity of the 8-feet (i.e., 2.44 meters) test in a laboratory environment to assess usual gait speed by comparing its results with the Intelligent Device for Energy Expenditure and Activity (IDEEA) monitor. Participants were 200 well-functioning community-dwelling adults aged 65 and older (113 women; 87 men; mean [M] age = 71.8, standard deviation [ SD] = 5.6 years). Participants wore the IDEEA monitor for 48 consecutive hours, and we used the participants' average usual gait speed for the analysis. The Spearman correlation of usual gait speed using both the 8-feet test and IDEEA monitor was moderate and statistically significant (ρ = .364, p < .001). The mean difference between both methods was 0.20 ( SD = 0.27) meters/second, and the corresponding limits of agreement were 0.73 and -0.33 meters/second. There was a small systematic bias when the difference between the two methods was correlated with usual gait speed as measured by the IDEEA (ρ = -.20, p = .011). The perfect agreement (weighted kappa) of both instruments for classifying usual gait speed into tertiles, quartiles, and quintiles was 48.3% ( k = 0.17), 30.9% ( k = 0.23), and 25.4% ( k = 0.29), respectively. Our results indicate that the 8-feet test showed moderate criterion-related validity for evaluating and assessing usual gait speed test in older adults.

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