Isotemporal Substitution of Sedentary Time With Physical Activity Among Middle-Aged and Older Latinos: Effects on Episodic Memory

Abstract

Purpose

To examine the estimated effects of substituting 30 min of sedentary time with low-light physical activity (LLPA) and high-light physical activity (HLPA) on episodic memory, executive functioning, and working memory among middle-aged and older Latinos.

Design

A cross-sectional study.

Setting

Chicago and Chicagoland suburbs.

Subjects

Middle-aged and older Latinos (n = 61).

Measures

Accelerometer-assessed physical activity. A cognitive battery was administered to assess episodic memory, executive function, and working memory.

Analysis

Isotemporal substitution analyses were conducted, where unstandardized coefficients from linear regression models were used to examine the substitution effect of replacing sedentary time with LLPA and HLPA.

Results

Substitution of sedentary time with LLPA was associated with better episodic memory (Immediate recall, B = .947, P = .008; Delayed recall, B = .857, P = .013). No other significant substitution effects were present.

Conclusion

Middle-aged and older Latinos who replace sedentary time with LLPA may have better episodic memory. Future studies may target light physical activity to address cognition disparities and can inform the development of physical activity interventions that are appealing and accessible for Latinos.

Keywords

physical activity cognition health disparities sedentary behavior

Purpose

It is well established that moderate-to-vigorous physical activity (PA) confers beneficial effects and sedentary behavior confers deleterious effects on cognitive health outcomes.^1,2 Yet, PA participation remains low, especially among Latinos.^3,4 In a qualitative study conducted by Marquez et al,⁵ older community-dwelling Latinos reported fear of crime and lack of social networks as barriers to PA, and middle-aged Latinos cite similar barriers. Despite experiencing these barriers, Latinos do cite a preference for dance and walking instead of higher-intensity exercise like running.³ Engaging in moderate-to-vigorous PA may also initially be too challenging for sedentary populations.⁶ Latinos, on average, spend 11.9 h per day in sedentary behaviors⁴ and independent of PA, it negatively affects health.^7,8 Sedentary behavior differs from physical inactivity, in that physical inactivity is defined as not meeting the PA guidelines⁹ and sedentary behavior is any waking behaviors characterized by low energy expenditure in a sitting, lying down, and reclined position.¹⁰ Findings from a systematic review and harmonized meta-analysis found that higher sedentary time is associated with a higher mortality risk, where risk increases at sedentary times greater than 9.5 h per day.⁷ Thus, it is imperative for populations with high levels of sedentary time to both decrease their sedentary time and increase PA levels. Dogra and colleagues⁶ proposed a “staircase” (stepwise) instead of an “elevator” (skipping steps) approach to increasing PA among sedentary and inactive populations, which may first include decreasing sedentary time and increasing light PA.

Data show that light PA (i.e., activity >1 and <3 METs) may have health benefits especially among older adults.¹¹ Light PA may improve cognitive outcomes like processing speed¹² and short-term memory.¹³ A few studies have also investigated the potential health benefits of replacing sedentary time with light PA.^11,14,15 Using isotemporal substitution analyses, Suzuki et al¹⁴ found that replacing 30 min of sedentary behavior per day with light PA was associated with increased odds of maintaining cognitive function. Buman and colleagues¹¹ also conducted an isotemporal substitution analysis to examine the effect of replacing sedentary behavior with light PA on self-rated health among older adults. For this study, light PA was divided into low-light PA (LLPA) and high-light PA (HLPA). According to the commonly used Freedson threshold,¹⁶ light-intensity activities are categorized as 100-1951 counts/min using accelerometry. Given that this category includes a wide range of activities from standing to leisurely walking, Buman and colleagues¹¹ surmised that activities at the lower and higher ends of light PA may have differential effects on health, and indeed found that replacing 30 min/day of sedentary time with HLPA was associated with better psychosocial health when compared to LLPA.

Currently, cross-sectional studies have demonstrated positive associations between executive functioning and light PA among both young and older adults;^17-20 however, few studies have examined it with other cognitive domains like episodic memory and working memory. Furthermore, PA participation and its associations with episodic memory and not PA intensity have been examined. Hayes and colleagues²¹ found that total PA is positively associated with visual episodic memory among older adults. Intensity was also positively associated with episodic memory, but it was operationalized as a ratio between total steps taken and minutes in light, moderate, and vigorous together, thus making it difficult to determine which intensity is specifically associated with episodic memory. Similarly, in a 14-year follow-up study among older adults, moderate and high PA levels (91-180 min/day and 181 min/day and above, respectively) were associated with better learning, delayed recall, and retention, all measures of episodic memory.²² More studies are needed to investigate whether light PA is associated with episodic memory and working memory. Additionally, few studies focus on Latino populations, a population that engages in high amounts of sedentary behavior and puts them at a high risk for cognitive decline.

The purpose of this study was to examine replacing sedentary behavior with LLPA and HLPA and their associations with episodic memory, executive functioning, and working memory among middle-aged and older Latinos. We hypothesized that replacing sedentary behavior with LLPA and HLPA will be positively associated with episodic memory, executive functioning, and working memory, with HLPA having magnified associations with cognitive outcomes.

Methods

Design and Sample

This study reports secondary findings from a cross-sectional study, that was approved by the University of Illinois Urbana-Champaign Institutional Review Board. All participants provided informed written consent. Participants were eligible if (1) age ≥50 years old, (2) self-identify as Hispanic/Latino, and (3) scored at least a 21 on the Modified Telephone Interview for Cognitive Status (TICS-m).²³ Exclusion criteria included self-reported physical illness or medical condition that would interfere with participation in the study and an inability to walk without regular use of an assistive device (e.g., walker) except for canes.

Measures

Demographics

Demographic variables included age, sex, education, and household income.

Device Assessed PA

Participants wore a GTX3+ accelerometer (ActiGraph, Pensacola, FL) for 7 consecutive days. Participants were asked to wear the monitor on belt or attached to a clip placed on their non-dominant hip during wake times. They were also asked to fill out an accelerometer log to assess wear time. We considered a valid day to have ≥10 h of wear time and included participants with at least 4 valid days.²⁴ Time spent in PA intensity was based on an existing count-based intensity threshold. Moderate-to-vigorous PA ( $\geq$ 1952 counts/minute) and sedentary behavior (<100 counts/minute) thresholds were chosen in this study, and they have been used largely in both calibration and intervention studies.^25-28 All other activity was categorized as light PA (100-1951 counts/minute). Since a wide range of activities fall within light PA (i.e., standing, housework), the Copeland threshold cutpoints²⁹ were used to further divide light PA into LLPA (100-1040 counts/minute) and HLPA (1041-1951 counts/minute). An example of a LLPA may include walking slowly around the store and an example of a HLPA may include playing darts.³⁰ This threshold has been evaluated specifically in older populations,²⁹ so it was also used within this current study.

Cognitive Performance

Episodic Memory

Logical Memory I (Immediate) and II (Delayed)³¹ consists of 2 parts. A brief story was read to the participant who was then asked to retell it immediately (I) and after a 10-min delay filled with other activities (II). The score was the number of 25 story units recalled immediately (I) and after the delay (I).

Executive Function

The Trail Making Test (Parts A & B)³² has 2 parts. An individual sequentially draws lines to connect 24 encircled numbers randomly spread on a page (Part A) and encircled numbers and letters in alternating order (Part B). The score is equivalent to the time it took for the individual to complete each task.

The color task (Stroop C) of the short form³³ of the Stroop Neuropsychological Screening Test³⁴ displays names of colors printed in contrasting ink colors to the participant and they are asked to name the words. The second task, the Color-Word task (Stroop C-W), the participant is shown the names of colors printed in contrasting ink colors (i.e., the word “red” in blue ink) and is asked to name the color of the ink rather than the word. Scores were calculated by subtracting the number of errors from the number of words named correctly in 30 s, and by subtracting the number of errors from the number of colors named correctly in 30 s.³³

The Word Fluency Test³⁵ asks the participant to produce as many examples as possible in separate 60-s trials from 2 semantic categories: animals and fruits and vegetables. The score was calculated by summing the number of animals and the number of fruits and vegetables that the participant named.

During the Symbol Digit Modalities Test,³⁶ the participant was asked to identify and name the digits which belonged with successively presented symbols. The score equaled the number of digits that were correctly paired with the symbols in 90 s.

Working Memory

The Digit Span Test³¹ consists of 2 parts. Digit strings of growing length were read, and the participant was asked to repeat each string forward (Digit Span Forward) or backward (Digit Span Backward). The score equaled the number of correctly retrieved strings from each part.

During the Digit Ordering Test,³³ digit strings of increasing length were read, and the participant was asked to reorder the digits and say them in ascending order. The score was the number of correctly reordered strings.

Statistical Analysis

Isotemporal models represent the effect of replacing the dropped intensity category with other intensity categories entered into the model.^11,37 Incorporating the summary total activity variable in the model inhibits total time, which allows comparisons to be made between intensity category and their impacts on health outcomes of interest. Isotemporal substitution analyses were conducted to examine the effect of substituting sedentary time with LLPA or HLPA on tests of episodic memory, executive functioning, and working memory. This was achieved by entering a total activity time variable (ie, sedentary + LLPA + HLPA + moderate-to-vigorous PA). The intensity category of interest was then dropped from the model. Before the intensity categories were entered into the model, they were divided by a constant of 30 so that a unit increase in outcome of interest represented an increase of 30 min/day within the designated intensity category. This step was done simply for ease of interpretation of the results. Additionally, we conducted a sensitivity analysis where we combined LLPA and HLPA into a total light PA category and repeated the isotemporal substitution analysis. Unstandardized coefficients from linear regression models were used to examine the substitution effect and covariates included in the model were age, sex, education, income, and BMI. All analyses were completed using IBM SPSS Statistics for Windows, Version 28.0.

Results

Of the 61 participants, 50 (82%) completed all cognitive tests. The mean age of participants was 58.98 ± 8.67 years, and the sample was primarily female (n = 47; 77%). Participant characteristics are displayed in Table 1.

Table 1.

Demographic Characteristics (n = 61).

Characteristics	n	%	Mean	SD
Age	61	-	58.98	8.66
BMI	52	-	31.30	5.21
Sex
Female	47	77	-	-
Education
No high school diploma/HS graduate	38	63.3	-	-
Household income
>$40,000	19	31.1	-	-
Accelerometer outcomes
Sedentary time (min/day)	55	-	451.72	84.15
LLPA (min/day)	55	-	268.46	70.78
HLPA (min/day)	55	-	45.93	26.45
MVPA (min/day)	55	-	18.83	17.31
Cognitive outcomes
Logical memory I	50	-	11.56	3.90
Logical memory II	50	-	10.48	3.79
Trail making test A	54	-	44.17	22.04
Trails making test B	54	-	145.81	86.32
Stroop C	54	-	73.76	128.86
Stroop C-W	54	-	21.3	6.41
Word fluency	54	-	39.81	6.79
Symbol digit modalities	54	-	37.52	13.35
Digit span forward	54	-	5.31	1.96
Digit span backward	54	-	4.50	1.67
Digit ordering	54	-	5.80	2.03

Notes: MVPA, Moderate-to-Vigorous Intensity Physical Activity.

Cognitive Performance

Substitution of 30 min/day of sedentary time with LLPA was associated with a higher immediate recall score (B = .947, P = .008) and higher delayed recall score (B = .857, P = .013). Substitution for HLPA (Immediate: B = −1.265, P = .239; Delayed: B = −1.104, P = .287) and MVPA (Immediate: B = −.972, P = .482; Delayed: B = −.975, P = .466) were not significantly associated with episodic memory. There were no significant relationships between the substitutions of sedentary time with LLPA, HLPA, or moderate-to-vigorous PA on any executive function measures. There were no significant relationships between the substitutions of sedentary time with LLPA, HLPA, or moderate-to-vigorous PA on any working memory measures. All isotemporal model results are reported in Table 2. Sensitivity analyses revealed that there were no significant relationships between the substitution of sedentary time with total light PA on any cognitive measures and substitution for MVPA was associated with a lower immediate recall score (B = −2.142, P = .04) (Table 3).

Table 2.

Isotemporal Substitution Models.

	B₀-Sedentary time	B₂-LLPA (SE)	B₃-HLPA (SE)	B₄-MVPA (SE)	B₅-Total time (SE)
Episodic memory
Immediate recall	Dropped	.947* (.338)	−1.265 (1.057)	−.972 (1.369)	−.275 (.206)
Delayed recall	Dropped	.857* (.327)	−1.104 (1.023)	−.975 (1.325)	−.315 (.200)
Executive function
Trail Making-A	Dropped	−1.628 (1.809)	4.731 (5.442)	−6.950 (6.968)	.211 (1.098)
Trail Making-B	Dropped	2.452 (8.563)	−.6873 (25.765)	30.569 (32.992)	−.957 (.855)
Stroop C	Dropped	−2.424 (1.298)	3.931 (3.842)	−4.975 (4.918)	.267 (.775)
Stroop C-W	Dropped	.109 (.567)	−1.802 (1.705)	.141 (2.183)	.028 (.344)
Word fluency	Dropped	.105 (.641)	1.786 (1.930)	−2.248 (2.471)	−.538 (.389)
Symbol digit	Dropped	.933 (1186)	−1.498 (3.568)	1.090 (4.568)	−.406 (.720)
Working memory
Digit span forward	Dropped	.195 (.203)	.499 (.611)	−.991 (.783)	−.130 (.123)
Digit span backward	Dropped	.061 (.177)	.065 (.534)	−.526 (.684)	−.089 (.108)
Digit ordering	Dropped	−.143 (.204)	.875 (.614)	−1.495 (.786)	.049 (.124)

Note. Isotemporal Substitution Models, adjusted for age, race, education, sex, income, and BMI. Sedentary time is dropped. B₁-B₃ represent unstandardized mean change in the variable of interest if substituted with sedentary time. SE, Standard Error; *P $\leq$ .05.

Table 3.

Isotemporal Substitution Models With a Total Light Physical Activity Variable.

	B₀-Sedentary time	B₁- LPA (SE)	B₂-MVPA (SE)	B₃-Total time (SE)
Episodic memory
Immediate recall	Dropped	.188 (.275)	−2.142 (1.016)*	−.229 (.209)
Delayed recall	Dropped	.151 (.272)	−1.870 (1.006)	−.288 (.207)
Executive function
Trail Making-A	Dropped	1.563 (1.000)	−4.265 (3.540)	−.002 (.757)
Trail Making-B	Dropped	1.037 (5.988)	24.341 (21.206)	−.922 (4.534)
Stroop-C	Dropped	−.711 (.948)	−1.458 (3.356)	−.035 (.718)
Stroop C-W	Dropped	−.309 (.354)	−1.617 (1.255)	.211 (.268)
Word fluency	Dropped	.449 (.490)	−1.125 (1.737)	−.627 (.371)
Symbol digit	Dropped	−.377 (.825)	.367 (2.921)	−.323 (.625)
Working memory
Digit span forward	Dropped	.055 (.154)	−.411 (.547)	−.188 (.117)
Digit span backward	Dropped	−.101 (.113)	−.259 (.401)	−.122 (.086)
Digit ordering	Dropped	−.128 (.148)	−.424 (.522)	−.033 (.112)

Discussion

We hypothesized that substituting sedentary behavior with LLPA and HLPA would be positively associated with episodic memory, executive functioning and working memory with magnified associations with HLPA on cognitive outcomes. However, our hypothesis was only partially supported. Our study found that substituting LLPA and not HLPA or moderate-to-vigorous PA was significantly associated with episodic memory; however, we did not find any associations with other cognitive tests.

Our findings show that substituting sedentary behavior with LLPA was significantly associated with better episodic memory among middle-aged and older Latinos, whereas there was a statistically insignificant relationship when substituting sedentary behavior with HLPA. Episodic memory enables a person to remember specific events from one’s personal past³⁸ and declines with aging.³⁹ To date, few studies have investigated relationships between PA intensity and episodic memory. Ruscheweyh et al⁴⁰ conducted an intervention to assess if PA intensity would differentially affect episodic memory among older adults. They found that PA, regardless of intensity, has beneficial effects on memory capacity. The intervention included both Nordic walking and gymnastics, where Nordic walking corresponded with moderate-intensity PA and their gymnastics protocol (i.e., stretching) corresponded with light PA. Their findings somewhat support our results in that engaging in light PA may improve episodic memory, though they also found beneficial effects amongst participation in moderate-intensity PA where our study did not find a significant relationship. An observational study examining PA and episodic memory among middle-aged and older Latinos conducted by Halloway et al⁴¹ found that those who had less of a decline in self-reported light PA maintained episodic memory which, like our findings, suggest that light PA may play a beneficial role in episodic memory. Both of our studies targeted Latinos, a population that engages in high levels of sedentary behavior,⁴ which puts them at a greater risk of cognitive decline. Thus, there is justification for the continued examination of light PA and episodic memory among middle-aged and older Latinos.

Comparable to our findings, Wu et al⁴² found that adults aged ≥45 years, who participated in mild PA, defined as walking at work, home, for travel, and any other walking solely for leisure, had a higher episodic memory score compared with individuals who engaged in no PA. Though, they did find that individuals engaging in moderate PA, defined as activities that make you breathe somewhat harder than normal (Taiji, mopping), also had higher episodic memory than those who engaged in no PA. Currently, there are mixed findings with respect to PA intensity and cognitive function. In a meta-analysis of 36 exercise interventions in adults older than 50 years of age, at least moderate intensity of exercise was associated with improved cognitive function,⁴³ whereas a meta-analysis of prospective studies showed that low-to-moderate intensity was associated with a significantly lower risk of cognitive decline.⁴⁴ One potential reason for mixed findings may include the varied proposals of PA intensity thresholds.⁴⁵

PA intensity is measured according to METs, where 1 MET is the amount of oxygen metabolized while seated at rest and serves as a physiological measure of energy cost for a type of activity.⁴⁶ The Physical Activity Guidelines recommend using the following threshold: >3.0 METs is light-intensity, 3.0-5.9 METs is moderate-intensity, and at least 6.0 METs is vigorous intensity.⁴⁷ Though, its validity parameters are not in the research and these thresholds are based on absolute intensities which do not take individual characteristics (i.e., age, sex) into consideration.⁴⁸ A likely result of this limitation includes inconsistent examples of light, moderate, and vigorous intensity activities. According to the American College of Sports Medicine (ACSM) METs value table³⁰ which is based off the Physical Activity Guidelines threshold, walking as leisure is categorized as moderate PA. More specifically, “fishing from the riverbank and walking” is measured at 4.0 METs (moderate PA). Mopping the floor is also included as moderate PA at 3.0-3.5 METs, though the 2011 Compendium of Physical Activities⁴⁹ categorizes mopping the floor at a light effort as 2.5 METs, which falls under light PA. It is unclear whether Wu and colleagues utilized any resources, like ACSM or the Compendium of Physical Activities for their examples of activities. Therefore, it is plausible that Wu et al found the positive relationship between moderate-to-vigorous PA and episodic memory if individuals who primarily engage in household PA were categorized as moderate PA; however, depending on which resource is being used, household PA could have also been categorized as light PA. It is imperative for there to be validation studies of these activity thresholds so that associations found between PA and health outcomes are not misconstrued.

Our study did not find a relationship between substituting sedentary behavior with LLPA, HLPA, or moderate-to-vigorous PA and executive functioning. Contrary to our findings, in a cross-sectional study conducted by Wei et al,⁵⁰ replacing sedentary behavior with any PA (i.e., walking, moderate-to-vigorous PA) was associated with better executive functioning. They separated walking and bicycling from moderate-to-vigorous PA, so it is unclear how they classified light PA and thus difficult to compare to our findings. In relation to our HLPA and moderate-to-vigorous PA findings, it is important to emphasize that our participants only engaged in 46 min/day in HLPA and 19 min/day in moderate-to-vigorous PA. As a result, the number of minutes in HLPA and moderate-to-vigorous PA may be insufficient to yield significant associations in executive functioning.

Our findings did not find a relationship between replacing sedentary behavior with LLPA, HLPA, or moderate-to-vigorous PA and working memory. In a study conducted by Gothe et al,⁵¹ there was a positive association between working memory and light PA among older African American adults. Lack of significant associations in our study may be due to our small sample size and warrants investigation with a larger sample size. Nonetheless, it is important to highlight that both Latinos and African Americans engage in high levels of sedentary behavior,⁵² so future studies should continue to explore the potential health benefits of light PA on cognition, given that lighter intensities may be more acceptable among minoritized populations.^5,52

Sensitivity analyses, consisting of combining the LLPA and HLPA variables to represent a total light PA variable within an isotemporal model, were run to better interpret the findings that LLPA, but not HLPA nor moderate-to-vigorous PA were significantly and positively associated with the cognitive outcomes. The analysis revealed that substituting sedentary behavior with total light PA was not significantly associated with any cognitive outcomes. This finding provides rationale for future research to continue to examine the upper and lower thresholds of light PA and associations with cognitive outcomes among sedentary populations. Moderate-to-vigorous PA was also not significantly associated with any cognitive outcomes, except for immediate recall, which assesses episodic memory. In fact, it was negatively associated with immediate recall. Data indicate that many Latinos engage in high levels of occupational PA.⁵³ Though moderate-to-vigorous PA is often associated with leisure PA, it is possible that those engaging in moderate-to-vigorous PA may also consist of time in occupational PA. High levels of occupational PA has been linked to an increased risk of dementia.⁵⁴ As such, this finding warrants further investigation.

Strengths from this study include the demographics of the sample. Current light PA studies focus on older adults, but sedentary middle-aged adults may also prefer lighter intensity activities. Therefore, it is necessary to examine the health benefits middle-aged adults may obtain by participating in light PA. This study population is also Latino and largely non-college educated. Latinos continue to be underrepresented in dementia-related research⁵⁵ despite engaging in high levels of sedentary behavior and experiencing increased risk for cognitive decline, so our study has important implications for addressing disparities in brain health. Finally, this study included several measures to assess each cognitive domain, which allows for a robust exploration of each domain.

There are a few potential limitations of this cross-sectional study. Causal inferences cannot be made between PA intensity and episodic memory. Additionally, there may be a bidirectional association in which participants with better episodic memory may be more likely to meet the PA guidelines. Another limitation is the use of accelerometry thresholds to define light PA. These thresholds make it difficult to categorize specific types of activities, so more research is needed to be able to recommend specific types of activities. Lastly, the sample size of this study was small which makes it harder to generalize the results.

This present study adds to the existing light PA literature. Pursuing the study of light PA, with more of a focus on lower and higher ends of light PA, is needed because these activities may appeal to older adults and are safe for beginning exercisers.

So What?

What is already known on topic?

Engaging in light PA may improve cognitive outcomes among older adults. More specifically, replacing sedentary behavior with equal amounts of light PA has been positively associated with cognition.

What does this article add?

Less is known about the potential benefits of substituting sedentary behavior with light physical activity on episodic memory among middle-aged and minoritized populations. Furthermore, this article examines the potential differential effects of the lower and upper thresholds of light PA on cognition.

What are the implications for health promotion practice or research?

These findings provide support for PA promotion efforts to first focus on replacing sedentary behavior with equal amounts of low-light PA before promoting moderate-to-vigorous PA. Additionally, the results provide evidence for benefits of PA on cognitive outcomes in a racial/ethnic minoritized population that is disproportionately affected by cognitive decline. This has important implications for future physical activity interventions that target Latinos and thus brain health disparities.

Footnotes

Author’s Note

Imani Canton is the first author of the manuscript and Susan Aguiñaga is the senior author. Imani Canton made substantial contributions to the concept and design of the work. All authors contributed substantially to the interpretation of the work. Imani Canton drafted the article, and all authors critically revised the article on its content. All authors approved the final version to be published. The study was approved by the University of Illinois Urbana-Champaign Institutional Review Board. All participants provided informed written consent.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

ORCID iD

Imani Canton

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