Ecological momentary assessment (EMA) has the potential to yield new insights into the prediction and modeling of physical activity (PA) and sedentary behavior (SB). The objective of this study was to determine the feasibility and validity of an EMA protocol to assess older adults’ PA and SB. Feasibility was determined by examining factors associated with EMA survey compliance and if PA or SB were impacted by EMA survey compliance. Validity was determined by comparing EMA-reported PA and SB to objectively measured PA and SB at the EMA prompt. Over 10 days, older adults (n = 104; Age_range = 60–98 years) received 6 randomly prompted EMA questionnaires on a smartphone each day and wore an ActivPAL activity monitor to provide a device-based measure of PA and SB. Participants reported whether they were currently engaged in PA or SB. Older adults were compliant with the EMA and ActivPAL protocol on 92% of occasions. Differences in EMA compliance differed by weight status. Among overweight and obese older adults EMA compliance differed by sex (OR = 3.15, 95% CI: 1.43, 6.92) and day of week (OR = 1.79, 95% CI: 1.33, 2.41). Among normal weight older adults, EMA compliance differed by time of day (OR = 1.52, 95% CI: 1.02, 2.30). EMA compliance did not differ for device-based PA or SB in the 15 min before versus the 15 min after the EMA prompt, suggesting that these behaviors did not influence likelihood of responding and responding did not influence these behaviors (ps > 0.05). When PA was reported through EMA, participants engaged in less device-based PA in the 15 min after compared to the 15 min before the EMA prompt (p = 0.01), suggesting possible reactance or a disruption of PA. EMA-reported PA and SB were positively associated with higher device-based PA and SB in the ±15 min, respectively, supporting criterion validity (ps < 0.05). The assessment of older adults’ PA and SB through EMA is feasible and valid, although there may be PA reactance to EMA prompting. Therefore, EMA represents a significant methodological tool that can aid in our understanding of the environmental, social, and psychological processes regulating older adults’ PA and SB in the context of everyday life.

Objective: A 10-day ecological momentary assessment (EMA) study was conducted to test a dual-process model of older adults’ sedentary behavior. Design: Older adults (n = 104, 60–98 years) answered 6 EMA questionnaires/day to assess conscious processes (i.e. momentary intentions, self-efficacy to limit sedentary behavior over the next two hours) and wore an activPAL accelerometer to measure sedentary behavior. Habit strength for sedentary behavior, a non-conscious process, was self-reported at an introductory session. Main outcome measure: Time spent sitting in the two hours after the EMA prompt. Results: Older adults engaged in less sedentary behavior on occasions when their intentions (b = −1.63, p = 0.02) and self-efficacy (b = −2.01, p = 0.003) to limit sedentary behavior were stronger than one’s average level of intentions or self-efficacy, respectively; however, older adults’ average level of intentions (b = −5.30, p = 0.05) or self-efficacy (b = 2.77, p = 0.27) to limit sedentary behavior were not associated with sedentary behavior. Older adults with stronger sedentary behavior habits engaged in greater sedentary behavior in the two hours following the EMA prompt (b = 2.04, p = 0.006). Conclusion: Sedentary behavior is regulated by conscious and non-conscious processes. Interventions targeting older adults’ sedentary behavior should promote momentary intention formation and self-efficacy beliefs to limit sitting as well as content to disrupt habitual sedentary behavior.