Incidental Lifestyle Physical Activity and Its Relationships With Overall Frailty and Frailty Domains in Community‐Dwelling Older Japanese

ABSTRACT

Aim

Beyond structured physical activity, emerging evidence suggests the potential health benefits of incidental lifestyle physical activity (ILPA). However, the relationship between ILPA and frailty or frailty domains in older populations remains unclear.

Methods

A total of 15 302 community‐dwelling adults aged 65 years and older in Osaka, Japan, were invited to participate in a mailed survey. The survey included a single‐item question asking about participants' ILPA: “Are you trying to be physically active in your daily life, for example, through housework or transportation?” Frailty outcomes, including overall frailty and frailty domains (physical, nutritional, oral, social, cognitive, and mental), were assessed using the validated Kihon Checklist based on its scoring manual. Logistic regressions were used to investigate associations between ILPA and overall frailty and each frailty domain. Age and sex differences were determined using subgroup analysis and interaction analysis.

Results

The response rate was 49.03%. Logistic regression analyses revealed ILPA is negatively associated with overall frailty and domains including physical, nutritional, oral, social, cognitive, and mental domains of frailty. Most associations were evident regardless of age and sex, while the association between ILPA and the physical domain of frailty was stronger in males (p for interaction = 0.01), while the association with the mental domain of frailty was stronger in females (p for interaction = 0.007).

Conclusions

In community‐dwelling older Japanese adults, ILPA was negatively associated with overall frailty and multiple domains of frailty. While structured physical activity remains critical, the findings underscore the importance of promoting increased ILPA in daily experience.

Most physical activity happened within daily routine, which is called incidental lifestyle physical activities (ILPA). We found negative associations between ILPA and frailty and most frailty domains. The findings suggested ILPA could serve as an additional factor to address frailty and its domains.

1. Introduction

Frailty, which is strongly associated with aging, represents one of the most significant consequences of the global trend of population aging. Physically inactive lifestyles have been consistently linked to an increased risk of frailty and other adverse health outcomes, including reduced physical function, depression, cognitive decline, and poorer oral health [1, 2, 3, 4, 5, 6]. Systematic reviews of randomized control trials suggest that physical activity is the most effective way for preventing frailty and maintaining independence in older adults [7, 8]. Promoting physical activity in daily life among older adults has become a key strategy for long‐term care prevention in Japan. According to the WHO's definition, physical activity includes all movements produced by skeletal muscles that require energy expenditure [9]. There are multiple ways of classifying types of physical activity, and some studies divide physical activity into structured physical activity and incidental lifestyle physical activity (ILPA). While there is no clear definition of ILPA yet, it generally refers to unstructured nonexercise activities such as housework, transportation, or other domestic activities [10, 11]. However, in current interventions and studies, the concept of physical activity primarily emphasizes structured exercises or training programs, which are also seen as lacking appeal for older adults. Age‐related changes in physical, psychological, social, and economic conditions make it challenging for older adults to engage in structured training or exercises. In fact, it has been reported that over 75% of adults' daily physical activity is attributed to incidental lifestyle physical activities (ILPA) [10]. This raises the necessity to understand whether increased ILPA may itself provide measurable health benefits for frailty.

Emerging evidence has highlighted a great public health potential of integrating physical activity into daily life, noting everyday activities such as housework may offer a more practical approach with higher acceptance and adherence among older adults compared to structured exercise [12, 13]. The 2020 WHO Guidelines on physical activity and sedentary behavior emphasize that “all physical activity counts” [14]. Studies have also demonstrated that even small efforts of being physically active are beneficial to health [15]. Existing evidence suggests that even a slight increase in household activities may reduce depression, enhance well‐being, and offset the cardiovascular risks associated with sedentary behavior [16, 17, 18]. Participation in household activities has also been associated with a lower risk of cognitive decline [19]. However, the associations between ILPA and frailty, as well as its subdimensions, remain underexplored.

Systematic reviews have shown that engaging in structured physical activity is one of the effective strategies to improve frailty outcomes [20, 21]. Similarly, cross‐sectional evidence from Japan has reinforced the relationship between sports and reduced risk in multiple frailty domains [1, 22]. However, there are also inconsistent findings which reported no significant association between structured physical activity and reduced risk of frailty [23]. These discrepancies may be attributed to the multidimensionality in physical activity and frailty, and the limited consideration of ILPA. Broadening the scope of what constitutes physical activity—particularly by focusing on lifestyle, routine physical activities—may contribute to a more nuanced understanding of the potential health benefits of increasing physical activity as part of the everyday life experience.

Frailty is a multidimensional syndrome involving a cumulative decline in multiple physiological and psychological systems [24, 25]. In Japan, the national frailty screening tool, the Kihon Checklist (KCL), evaluates frailty across six key domains: Physical, nutritional, oral, social, cognitive, and mental [26, 27]. Investigating the relationships between increasing ILPA and overall frailty—and identifying how this small effort relates to each frailty domain—could significantly enhance our understanding of the mechanisms linking ILPA and frailty.

Thus, the present study aimed to examine the relationships between ILPA and overall frailty, as well as each frailty domain, in community‐dwelling older adults. Additionally, to gain a deeper understanding of the role of ILPA, we also investigated whether sex or age influences the relationships, considering previous studies reported age and sex differences in frailty, household activities, and other lifestyle physical activities [25, 28].

2. Methods

2.1. Study Design and Population

This study was a stand‐alone study. This cross‐sectional survey was conducted on a sample of community‐dwelling older adults aged 65 years and older residing in Osaka, Japan, the country's second‐largest city. The source population (N = 123 954) consists of 56 706 (45.7%) older adults aged 65–74 years and 67 248 (54.3%) individuals aged 75 years and older who were registered in the National Health Insurance Registration System or the Late‐Stage Elderly Medical Care Registration System. A total of 15 302 participants were randomly selected using an age–sex–stratified sampling method from three regions, representing approximately a 10% sampling rate. Each participant was mailed a survey package, which included a self‐administered anonymous paper‐based questionnaire, instructions detailing the survey procedure and ethical considerations, and a prepaid return envelope. Data collection took place from November to December 2022. IRB protocol approval for the study was granted by the Institutional Ethics Committee (Approval No. 22243‐3).

2.2. Independent Variable Assessment: ILPA

The primary independent variable was ILPA. This was assessed with the question: “Are you trying to be physically active in your daily life, for example, through housework or transportation?” The assessment for ILPA was adapted from the National Health and Nutrition Survey [29]. Responses were recorded on a 4‐point scale: “I'm active,” “If I had to say, then I'm active,” “If I had to say, then I'm not active,” and “I'm not active.” For the purposes of analysis, responses were dichotomized into two categories: “yes” (comprising “I'm active” and “If I had to say, then I'm active”) and “no” (comprising “If I had to say, then I'm not active” and “I'm not active”) Although our ILPA measure reflects intention rather than objectively confirmed activity, this aligns with theoretical frameworks like the Theory of Planned Behavior, which posits that intention is a key predictor of future behavior [30]. Perceived effort may signal an internal shift toward health awareness, which has been associated with positive outcomes in prior literature [31].

3. Outcome Variables

The primary outcome variable was frailty status, with secondary outcomes including its domains: physical, nutritional, oral, social, cognitive, and mental [27].

Frailty was assessed using the validated KCL, a nationwide self‐reported screening tool developed by the Ministry of Health, Labour and Welfare, Japan to assess frailty in community‐dwelling older adults. The KCL consists of 25 items, each scored as 0 (positive response) or 1 (negative response). The total score ranges from 0 to 25, with frailty defined as a score of 8 or higher [32]. The cutoff value has been sufficiently validated for identifying frailty and predicting independency or mortality in Japanese community‐dwelling older adults [32, 33]. Participants with missing responses were excluded from scoring.

The KCL also categorizes frailty into the following domains according to its manual [27]:

• Physical domain: Includes five items assessing stair climbing without support, rising from a chair unaided, walking continuously for 15 min, falls in the past year, and fear of falling while walking. A score of 3 or more indicates low physical function.

• Nutritional domain: Includes two items assessing a body mass index (BMI) below 18.5 and unexplained weight loss in the past 6 months. These items were analyzed “underweight” and “unexplained weight loss” separately in this study due to the rarity of participants meeting both criteria simultaneously. Participants who reported weight loss were asked to provide the reasons in an open‐ended question. The research team then reviewed and categorized these responses. Weight loss due to natural decreases, illnesses, and dieting was not applicable for “unexplained weight loss.”

• Oral domain: Includes three items assessing difficulty eating tough foods, choking on liquids, and frequent dry mouth. A score of 2 or more indicates low oral function.

• Social domain: Includes two items assessing weekly outings and reduced outing frequency. A lack of outings more than once a week indicates social isolation.

• Cognitive domain: Includes three items assessing memory loss noticed by others, reliance on looking up phone numbers, and lack of date awareness. A score of 1 or more indicates a risk of cognitive decline.

• Mental domain: Includes five items assessing feelings of fulfillment, joy in activities, difficulty in tasks, helplessness, and unexplained fatigue. A score of 2 or more indicates a risk of depression.

Participants with missing values in any domain were excluded from scoring. The English translations and scoring details for KCL items are presented in Table 1.

TABLE 1.

Definitions and scoring rules for frailty outcomes using the Kihon Checklist (KCL).

KCL items	KCL domains	KCL score
1. Do you go out by bus or train by yourself?		Frailty (range: 0–25, cutoff ≥ 8)
2. Do you go shopping to buy daily necessities by yourself?
3. Do you manage your own deposits and savings at the bank?
4. Do you sometimes visit your friends?
5. Do you turn to your family or friends for advice?
6. Do you normally climb stairs without using a handrail or wall for support?	Low physical function (range: 0–5, cutoff ≥ 3)
7. Do you normally stand up from a chair without any aids?
8. Do you normally walk continuously for 15 min?
9. Have you experienced a fall in the past year?
10. Do you have a fear of falling while walking?
11. Have you lost 2 kg or more in the past 6 months?	Unexplained weight loss
12. Height: cm, weight: kg, BMI: kg/m2 If BMI is less than 18.5, this item is scored.	Underweight
13. Do you have any difficulties eating tough foods compared to 6 months ago?	Low oral function (range: 0–3, cutoff ≥ 2)
14. Have you choked on your tea or soup recently?
15. Do you often experience having a dry mouth?
16. Do you go out at least once a week?	Social isolation (range: 0–2, applicable at not going out more than once a week)
17. Do you go out less frequently compared to last year?
18. Do your family or your friends point out your memory loss?	Cognitive decline risk (range: 0–3, cutoff ≥ 1)
19. Do you make a call by looking up phone numbers?
20. Do you find yourself not knowing today's date?
21. In the last 2 weeks, have you felt a lack of fulfillment in your daily life?	Depression risk (range: 0–5, cutoff ≥ 2)
22. In the last 2 weeks, have you felt a lack of joy when doing the things you used to enjoy?
23. In the last 2 weeks, have you felt difficulty in doing what you could easily do before?
24. In the last 2 weeks, have you felt helpless?
25. In the last 2 weeks, have you felt tired without a reason?

4. Covariates

To reduce the likelihood of confounding, we adjusted a set of covariates in all statistical analyses. These included age, sex (male or female), marital status, subjective economic status, employment, education level, comorbidities, smoking, and social participation. These covariates were determined based on previous studies [34] and univariate analysis (p < 0.1). Marital statuses were categorized as currently married or other (divorced, widowed, or never). Subjective economic status was assessed using a six‐point scale and categorized into “affluent” (responses of somewhat affluent, affluent, or very affluent) and “nonaffluent” (responses of not at all affluent, not affluent, or somewhat not affluent). Employment was defined as having current paid work, either full‐time or part‐time. Education level was categorized into four groups: Elementary/middle school, high school, junior college/technical college, and college or higher. Comorbidities were assessed based on a comprehensive list of age‐related conditions, including cancer, hypertension, diabetes, dyslipidemia, heart diseases, cerebrovascular disease, respiratory disease, hepatic disease, renal disease, musculoskeletal disease, hematologic and immune disease, depression, dementia, Parkinson's disease, injuries, eye diseases, ear diseases, and others. Participants reporting ongoing or residual effects from any of these conditions were classified as having comorbidities. Smoking status was categorized into current smokers and others (ex‐smokers and nonsmokers). Social participation was defined as engagement in activities within social organizations, such as political or local community associations, volunteer groups, reunions, religious groups, sports clubs, hobby‐related clubs, or professional associations, and others.

5. Statistical Analysis

The characteristics of the study sample were summarized using means and standard deviations (SD) for continuous variables and percentages for categorical variables. Differences between participants with and without ILPA were analyzed using the chi‐squared test or Fisher's exact test for categorical variables, and t‐test or Mann–Whitney U test for continuous variables, depending on the data distribution.

Multivariate logistic regression models were employed to evaluate the relationships between the ILPA and various frailty‐related outcomes. Eight separate regression models were constructed, with each model examining one of the following dependent variables: Overall frailty, low physical function, underweight, unexplained weight loss, low oral function, social isolation, cognitive decline risk, and depression risk. ILPA (reference: no) was the primary independent variable in all models.

To estimate potential sex‐specific differences, we conducted separate analyses for males and females, and evaluated interaction effects by incorporating an ILPA × sex interaction term in each frailty outcome model. Subgroup analyses stratified by age groups (64–74 years, 75 years or older) and the interaction term between ILPA and age group were presented in the Supporting Information for no significant effect modification by age was found (Table S1).

Statistical analyses and graphical representations were performed using StataMP 19, and Figure 1 was generated using R version 4.3.2. A two‐tailed significance level of 0.05 was used for all analyses.

FIGURE 1.

Relationships between ILPA and frailty and frailty‐domains. Independent Variable: ILPA (reference: no). Adjusted by age, sex, marriage status, employment, subjective economic status, education level, comorbidities, smoking, and social participation. CI, confidence interval; OR, odds ratio; ILPA, incidental lifestyle physical activity.

6. Results

6.1. Sample Characteristics

A total of 7503 valid questionnaires were collected, yielding a response rate of 49.03%. After excluding individuals requiring moderate‐to‐severe long‐term care and respondents with missing data for selected variables, the final analysis included 5687 participants.

Table 2 provides an overview of the demographics and characteristics of the entire sample, comparing participants with and without the ILPA. The mean age of the participants was 74.60 ± 4.99 years, with 2955 (52.0%) being female. A majority (73.8%) of participants reported having ILPA, with a higher proportion observed among females. Frailty was identified in 23.0% of the analysis sample, and its prevalence was significantly higher among those who did not report ILPA (p < 0.001). The prevalence of frailty domains varied, with social isolation being the least common (2.8%) and depression risk being the most frequent (34.9%).

TABLE 2.

Participant characteristics stratified by ILPA.

		ILPA
	Total	No	Yes
	(N = 5687)	(N = 1491)	(N = 4196)	p
Age, mean (SD), year	74.60 (4.99)	74.09 (4.95)	74.79 (4.99)	< 0.001
Female, n (%)	2955 (52.0%)	670 (44.9%)	2285 (54.5%)	< 0.001
Subjective economic status, affluent, n (%)	3333 (58.6%)	724 (48.6%)	2609 (62.2%)	< 0.001
Education level, n (%)				0.012
Elementary/middle school	677 (11.9%)	188 (12.6%)	489 (11.7%)
High school	2654 (46.7%)	712 (47.8%)	1942 (46.3%)
Junior college/technical college	861 (15.1%)	187 (12.5%)	674 (16.1%)
College or higher	1495 (26.3%)	404 (27.1%)	1091 (26.0%)
Employment, yes, n (%)	1485 (26.1%)	340 (22.8%)	1145 (27.3%)	0.001
Marriage status, currently married, n (%)	4291 (75.5%)	1135 (76.1%)	3156 (75.2%)	0.484
Smoking, yes, n (%)	505 (8.9%)	204 (13.7%)	301 (7.2%)	< 0.001
Social participation, no, n (%)	3220 (56.6%)	655 (43.9%)	2565 (61.1%)	< 0.001
Comorbidities, yes, n (%)	4641 (81.6%)	1304 (87.5%)	3337 (79.5%)	< 0.001
Overall frail, yes, n (%)	1041 (23.0%)	493 (43.9%)	548 (16.1%)	< 0.001
Frailty domains
Low physical function, yes, n (%)	1068 (19.4%)	497 (34.9%)	571 (14.0%)	< 0.001
Underweight (BMI < 18.5), yes, n (%)	466 (8.3%)	116 (7.9%)	350 (8.4%)	0.523
Unexplained weight loss, yes, n (%)	488 (8.7%)	160 (10.8%)	328 (7.9%)	0.001
Low oral function, yes, n (%)	933 (17.3%)	301 (21.5%)	632 (15.8%)	< 0.001
Social isolation, yes, n (%)	155 (2.8%)	93 (6.3%)	62 (1.5%)	< 0.001
Cognitive decline risk, yes, n (%)	1785 (32.3%)	621 (42.9%)	1164 (28.6%)	< 0.001
Depression risk, yes, n (%)	1801 (34.9%)	688 (52.3%)	1113 (28.9%)	< 0.001

Note: p‐values were obtained using the chi‐squared test, Fisher's exact test, t‐test or Mann‐Whitney U test, where appropriate.

Abbreviation: ILPA = incidental lifestyle physical activity.

6.2. Relationships Between ILPA and Frailty/Frailty Domains

The adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) for the relationship between ILPA and frailty outcomes are presented in Figure 1. Using no‐ILPA as the reference group, ILPA was inversely associated with overall frailty (OR = 0.28, 95% CI: 0.24–0.33), low physical function (OR = 0.30, 95% CI: 0.26–0.35), unexplained weight loss (OR = 0.75, 95% CI: 0.61–0.92), low oral function (OR = 0.75, 95% CI: 0.64–0.88), social isolation (OR = 0.30, 95% CI: 0.21–0.42), cognitive decline risk (OR = 0.59, 95% CI: 0.52–0.67), and depression risk (OR = 0.41, 95% CI: 0.36–0.47). Notably, ILPA was not significantly associated with underweight (OR = 1.05, 95% CI: 0.84–1.32).

6.3. Sex‐Specific Differences on Relationships Between ILPA and Frailty/Frailty Domains

Table 3 shows the results of sex‐stratified logistic regression analyses and the effect modification by sex. Consistent relationships were observed between ILPA and overall frailty, low physical function, social isolation, cognitive decline risk, and depression risk in both sexes. Significant associations between ILPA and an underweight status (OR = 0.73, 95% CI: 0.54–0.98), or low oral function (OR = 0.68, 95% CI: 0.54–0.86) were observed in females only. However, no significant sex differences were observed in the associations between ILPA and the overall outcome or its nutritional, oral, social, and cognitive subdomains. Interaction analyses revealed that there was a stronger association between ILPA and low physical function in males (p for interaction = 0.010) while the association between ILPA and depression risk was stronger in females (p for interaction = 0.007), as visualized in Figure 2.

TABLE 3.

Sex differences of the relationships between ILPA (reference: no) and frailty outcomes.

Outcome variables	Subgroups of sex
	Males	Females
	OR (95% CI)	OR (95% CI)	P for interaction
Frail	0.3 (0.24, 0.37)***	0.26 (0.20, 0.32)***	0.501
Low physical function	0.25 (0.20, 0.31)***	0.35 (0.29, 0.43)***	0.01
Underweight (BMI < 18.5)	0.82 (0.56, 1.19)	1.22 (0.91, 1.64)	0.066
Unexplained weight loss	0.79 (0.59, 1.05)	0.73 (0.54, 0.98)*	0.706
Low oral function	0.81 (0.65, 1.02)	0.68 (0.54, 0.86)**	0.382
Social isolation	0.31 (0.19, 0.48)***	0.27 (0.16, 0.46)***	0.604
Cognitive decline risk	0.65 (0.54, 0.77)***	0.53 (0.44, 0.64)***	0.136
Depression risk	0.50 (0.41, 0.60)***	0.33 (0.27, 0.40)***	0.007

Note: Independent Variable: ILPA (reference: no). P for interaction is the p‐value of interaction item of ILPA and sex in each model with each frailty domain as the outcome variable. Adjusted by age, marriage status, employment, subjective economic status, education level, comorbidities, smoking, and social participation.

Abbreviations: CI, confidence interval; OR, odds ratio; ILPA, incidental lifestyle physical activity.

^*** p < 0.001.

^** p < 0.01.

^* p < 0.05.

FIGURE 2.

Interaction effects of ILPA and sex on physical and mental domains of frailty. Predicted probability and 95% CI was shown. ILPA, incidental lifestyle physical activity. p = p‐value. Models were adjusted by age, marriage status, employment, subjective economic status, education level, comorbidities, smoking, and social participation.

7. Discussion

This study systematically examined the relationships between the ILPA and frailty/frailty domains among community‐dwelling older adults in Japan. The findings demonstrate that effort to increase ILPA is negatively associated with overall frailty and most frailty domains, except for nutrition‐related domains (underweight). Furthermore, we found sex‐specific associations between ILPA and the physical domain of frailty or the mental domain of frailty.

7.1. ILPA and Frailty

Physical inactivity or sedentary is associated with the risk of frailty [2]. There is a wealth of evidence illustrating the effectiveness of increased physical activity and reduced sedentary time in mitigating frailty among community‐dwelling older adults [20, 21]. The mechanism is unclear, but increased physical activity is associated with physical, psychological, and social health and contributes to metabolic health and independence [7, 35]. The emerging perspective that physical activity should be integrated into daily routines aligns with the findings of this study [13]. We find ILPA is associated with overall frailty, which is consistent with some studies. Even though there is limited research on the association between ILPA and frailty, some studies supported the potential benefits of ILPA in improving physical and psychological health. Several studies have utilized self‐reported measures of ILPA and observed a higher prevalence of healthy behaviors and lower odds of cardiovascular risk in adults with a higher frequency and greater variety of ILPA [36, 37]. Wearable device‐based studies have illustrated that even a small amount of ILPA like household has a beneficial association with depression, cardiovascular health, and mortality [16, 38]. While our ILPA measure differs in design and precision from device‐based assessments, the observed associations suggest that intentional lifestyle activity may serve as a meaningful proxy for health‐oriented behaviors in older adults. The mechanism of this correlation is unclear; we suggest the cumulative effects of repetitive lifestyle physical activities [39].

However, some other studies also reported inconsistent results. Some studies reported that light ILPA, such as laundry or gardening, are not sufficient to slow frailty progression, especially in those already suffering from frailty [40, 41]. Other studies showed that lifestyle activities like gardening or cleaning are associated with maintaining or improving frailty [1]. A recent study also reported ILPA with an intensity of ≥ 3 metabolic equivalents of task, such as laundry, are beneficial to prevent frailty [42]. These discrepancies may be partially due to the lack of a consistent definition of ILPA. The content and timing of ILPA remain unclear in previous studies. Further quantitative and qualitative research is needed to clarify the role of ILPA in older adults.

7.2. ILPA and Frailty Domains

Our finding is consistent with and extends previous studies. We found only one previous study that examined the relationship between ILPA and part of frailty domains, which found ILPA like gardening, cleaning, and walking is beneficial for physical, social, and psychological domains of frailty [1]. We extended our analysis to systemic domains of frailty and found that ILPA was negatively associated with physical, nutritional, social, cognitive, and mental domains of frailty. This finding aligns with existing evidence suggesting that physical activity reduces systemic oxidative damage and inflammation, enhances muscle quality and metabolic capacity, and mitigates age‐related functional decline [43]. Physical activity is known to exert protective effects on physical functioning in older adults [44]. There is a cross‐sectional study that demonstrated household activities associated with better physical fitness test [28]. There is more high‐quality evidence supporting the protective effect of increased ILPA on depression and cognitive function [16, 19, 45]. It is suggested that ILPA was positively associated with executive function and brain electrical activity [46, 47]. Although we did not find any previous study reporting the relationship between ILPA and oral frailty in older adults, we found a study reporting the positive association between domestic activity and oral function in young adults [48]. Interestingly, no significant association was observed between ILPA and underweight status. We suspect that caloric expenditure caused by ILPA may not be strong enough to influence the result of underweight. A similar finding showed that incidental physical activity was not associated with abdominal obesity [49].

7.3. Sex Differences in the Relationship Between ILPA and Frailty

A novel contribution of this study is the observation of the varying strength of the relationship between ILPA and frailty/frailty domains between the sexes. We found that the males with ILPA have a higher odd of low physical function. The mechanism was unclear, but a previous study also showed that lifestyle physical activities were associated with more physical function test items than females [28]. We hypothesized that older females are more prone to physical function decline than males [50], we also found that the association between ILPA and depression was stronger in females. Similar to this finding, a cohort study reported a lower level of physical activity is associated with a higher risk of depression in females, but not in males [51]. In Japan, approximately 56.2% of older men and 64.5% of older women reported not having regular exercise habits [52]. For older women, this is largely explained by household chores [53]. It has also been reported that approximately 75% of the total physical activity among older women consists of domestic physical activities [28]. In Japan, the gender division of labor remains traditional. Exploring the relationship between ILPA and frailty may provide a new perspective to traditional physical activity strategies, especially for those who are facing barriers to structured physical activities. However, we should notice that older women who undertake more household chores face a higher risk of poor health [54]. In our data, ILPA is a subjective effort to increase physical activity through lifestyle activities. It may be that for women, mental state and intention to increase activity through ILPA are more strongly correlated.

8. Strengths and Limitations

This study has several strengths. First, the large sample size and relatively high response rate enhance the reliability and robustness of the findings. Second, to the best of our knowledge, this is the first study to specifically examine ILPA and their associations with frailty domains among older Japanese adults. This novel focus provides valuable insights into the potential complementary role of ILPA in traditional physical activity‐related frailty prevention and management.

However, the study is not without limitations. The reliance on a self‐administered survey introduces the possibility of bias, as participants may not accurately report their behaviors or intentions. Although the discrepancy between questionnaire measured ILPA and actual ILPA has not yet been evaluated in existing literature, it is suggested that self‐reported data may underestimate or overestimate actual physical activity levels due to recall bias or social desirability bias. We assessed ILPA as a single, global construct, and we did not collect specific components of ILPA, such as types, duration, and intensity of ILPA. Objective measurements along with qualitative data of specific details of ILPA are suggested. Moreover, the use of a single‐term measure of ILPA could be a challenge for validity, although its simplicity offers practicality. There is a lack of a validated questionnaire to assess ILPA, and the development of such assessment tools is suggested for future studies. Also, the ILPA variable used in this study reflects participants' subjective intention or effort to be physically active in daily life; an intention–behavior gap cannot be excluded. Future studies using objective measures of ILPA are needed to confirm these findings. Additionally, the cross‐sectional design prevents us from establishing causal relationships between ILPA and frailty outcomes. There is likely a reverse or bidirectional causality between ILPA and frailty. It is unclear whether individuals are less frail because of ILPA, or whether those who are engaging in ILPA because they are less frail. Longitudinal studies are necessary to confirm these associations and clarify the directionality of these relationships. The generalizability of the findings is also limited. Participants were recruited from a single prefecture in Japan, which may not fully capture regional or cultural variations across the country. Furthermore, as the study population consisted of independent Japanese older adults, it remains unclear whether the results can be extrapolated to other ethnicities or populations with different levels of dependency. Last, frailty in this study was assessed using a multidimensional approach based on the KCL. While this tool is validated for the Japanese population, the results may differ from studies employing alternative frailty measurement instruments. These differences highlight the need for standardized methods to facilitate comparisons across studies and populations.

9. Practical Implications

Despite these limitations, this study still has practical implications for frailty prevention strategies among community‐dwelling older adults. ILPA is practical, inexpensive, and typically self‐initiated; it can be performed within one's daily routine without professional supervision. Given the self‐initiated nature of ILPA, strategies that encourage motivation—such as reinforcing daily routines, peer modeling, or community‐based reinforcement mechanisms—may enhance engagement and sustainability. While most physical activity recommendations are numerical (e.g., step counts, MET, minutes), self‐monitoring and recording could be difficult for older adults due to technology or knowledge barriers. Such behavioral supports for ILPA could serve as feasible complements to structured exercise interventions, particularly for those less inclined to join formal programs.

10. Conclusion

In conclusion, in community‐dwelling older Japanese adults, ILPA was negatively associated with overall frailty and multiple domains including physical, nutritional, oral, social, cognitive, and mental domains of frailty. We found sex‐specific associations between ILPA and the physical or mental domain of frailty. While structured physical activity remains critical, the findings underscore the importance of fostering effort to increase ILPA in daily routine as an additional factor to address frailty and its domains. Further studies are warranted to explore the mechanisms behind these associations and to evaluate how interventions targeting incidental lifestyle physical activities can complement physical activity strategies to improve health outcomes in older adults.

Author Contributions

Conceptualized and designed: Y.L., M.K., Y.A., K.K., and M.K. Data collection and curation: Y.L., M.K., Y.A., H.Y., and M.N. Data management and analysis: Y.L. and K.M. Data interpretation: Y.L., M.K., Y.A., H.Y., M.N., Y.T., L.S., M.M., G.Y., K.K., H.K., and M.K. Original draft: Y.L. Verification and critical feedback: M.K., Y.A., H.Y., M.N., Y.T., L.S., M.M., G.Y., K.K., H.K., and M.K. Funding: Y.L. and M.K. All authors verified the results and revised and finalized the manuscript.

Funding

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant numbers 23K19802 and 23K24672), and the Osaka Prefecture National Health Insurance Health Up Support Project. The funders had no role in the design, execution, analysis/interpretation of data, or writing of the manuscript.

Disclosure

The authors declare no financial or personal conflicts of interest.

Ethics Statement

This study was approved by the Institutional Review Board of Osaka University Hospital (No. 22243‐3). Returning the questionnaire was considered informed consent. No human experiment or use of human tissue was involved in this study.

Supporting information

Table S1: Age differences of the relationships between ILPA (reference: no) and frailty outcomes.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.