Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Open Access

Peer-reviewed

Research Article

Examining dose-response of an outdoor walk group program in the Getting Older Adults Outdoors (GO-OUT) trial

Abstract

Objective

The Getting Older Adults Outdoors (GO-OUT) randomized trial showed that a 10-week outdoor walk group (OWG) program was not superior to 10 weekly phone reminders in increasing physical and mental health; however, OWG attendance varied. This study examined whether dose-response relationships existed between OWG attendance and improvement in physical and mental health among older adults with mobility limitations.

Methods

We analyzed data from 76 OWG participants with pre- and post-intervention scores on at least one of seven measures of health outcomes (walking endurance, comfortable and fast walking speed, balance, lower extremity strength, walking self-efficacy, and emotional well-being). Participants were classified as attending 0–9, 10–15, and 16–20 OWG sessions based on attendance tertiles. We adjusted for participant sex and study site in regression analyses.

Results

Among the 76 participants, mean age was 74.9 ± 6.6 years and 72% were female. Compared to those attending 0–9 OWG sessions, participants attending 16–20 sessions exhibited a 56.3-meter greater improvement in walking endurance (95% CI: 17.3, 95.4, p = 0.005); 0.15-meter/second greater improvement in comfortable walking speed (95% CI: 0.01, 0.29, p = 0.034); and 0.18-meter/second greater improvement in fast walking speed (95% CI: 0.03, 0.34, p = 0.020). Higher attendance was associated with greater odds of improvement in comfortable walking speed (OR = 7.1; 95% CI: 1.1, 57.8, p = 0.047) and fast walking speed (OR = 10.1, 95% CI: 1.8, 72.0, p = 0.014). No significant dose-response relationships for the remaining outcomes were observed.

Conclusions

Higher attendance in a park-based, supervised, task-oriented and progressive OWG program is associated with greater improvement in walking endurance and walking speed among older adults with mobility limitations. Attendance likely impacted walking capacity and not balance, lower extremity strength, walking self-efficacy or emotional well-being due to task-specificity of training. This study highlights the importance of attendance when designing and implementing OWG programs to enhance walking endurance and speed among older adults.

Citation: Su T-T, Barclay R, Moineddin R, Salbach NM (2025) Examining dose-response of an outdoor walk group program in the Getting Older Adults Outdoors (GO-OUT) trial. PLoS ONE 20(3): e0309933. https://doi.org/10.1371/journal.pone.0309933

Editor: Matteo Vandoni, University of Pavia, ITALY

Received: August 20, 2024; Accepted: January 22, 2025; Published: March 13, 2025

Copyright: © 2025 Su et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Data cannot be made publicly available due to ethical and legal restrictions. Specifically, permission for public data sharing was not obtained from the Research Ethics Boards at the University of Alberta, University of Manitoba, University of Toronto, or McGill University, nor was consent for public access obtained from participants. However, data are available upon reasonable request and subject to review by the appropriate Research Ethics Board. Requests for access to the data can be directed to the corresponding author or the Health Sciences Research Ethics Board at the University of Toronto (ethics.review@utoronto.ca).

Funding: This work was supported by the Canadian Institutes of Health Research (grant number 376439). NMS holds the Toronto Rehabilitation Institute Chair at the University of Toronto.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Walking in outdoor natural environments plays a critical role in supporting the health and well-being of older adults. An accumulating body of evidence has shown that outdoor walking is associated with a wide array of health benefits. These benefits include improved physical activity and fitness [1,2], better cognitive and mental functioning [3,4], increased energy and greater feelings of revitalization [5]. In addition, exposure to natural environments has been linked to a decreased incidence of chronic health conditions such as diabetes, stroke, coronary heart disease, and all-cause mortality [6,7]. The combination of physical activity and natural environments makes outdoor walking an ideal and promising strategy for health promotion among older adults.

Although walking outdoors is a preferred mode of physical activity [5], a recent systematic review and meta-analysis found no significant difference between outdoor community ambulation and other comparison interventions (e.g., standard care or educational lectures) in improving older adults’ walking endurance and depression [8]. While the limited number of studies included and quality of evidence partly account for this phenomenon [8], attendance may play a major role in shaping the overall effects of outdoor walking. In particular, previous studies have shown that attendance, defined as the number or proportion of sessions attended, can fluctuate between 58% and 77% among older adults participating in exercise interventions [9–14]. Attendance in exercise programs is of special importance for older adults with mobility limitations, as research indicates that poor attendance or non-attendance are significant risk factors for adverse outcomes such as more frequent falls and increased utilization of healthcare resources [9,15]. Given that attendance levels can affect the total amount of training and environmental stimuli received, it is important to understand whether and how the effects of outdoor walking may vary depending on participants’ attendance to the interventions.

The Getting Older Adults Outdoors (GO-OUT) study [16] provides a basis for examining the impact of outdoor walking attendance on older adults’ health. The GO-OUT trial is a randomized controlled trial designed to evaluate the effects of a park-based, task-oriented walking program on walking activity and capacity among older adults with mobility limitations [16]. One group participated in a 1-day educational workshop plus a 10-week outdoor walk group (OWG) program, while the other group completed the same workshop and received a weekly telephone reminder for 10 weeks. Despite participants providing positive feedback on the OWG program [17], our quantitative analyses revealed no significant difference between the two groups in changes in minutes walked outdoors; health promoting behaviors, or successful aging pre- to post-intervention [18]. The OWG only led to greater improvement in walking capacity through walking self-efficacy compared to the weekly reminders group [18]. As noted in the process evaluation of the GO-OUT trial [19], the observed lack of effects may be attributed to varying levels of attendance within the OWG, as mean attendance ranged from 43.8% to 84.9% across the study sites.

To better understand the benefits of outdoor walking interventions and inform their implementation in community settings, the objective of this study was to explore whether a dose-response relationship existed between attendance in the OWG program and improvement in physical and mental health among older adults with mobility limitations. We focused on seven physical and mental health outcomes measured in the GO-OUT trial: walking endurance, comfortable and fast walking speed, balance, lower extremity strength, walking self-efficacy, and emotional well-being. These outcomes were investigated as they are essential for promoting healthy aging and improving health-related quality of life in older adult populations, making them key indicators for evaluating the benefits of the OWG program [17,20,21]. Knowledge derived from the present study will not only help to equip clinical practitioners with evidence-based recommendations but also inform marketing strategies to motivate older adults to engage with community-based exercise programs.

Methods

Study design

The GO-OUT randomized controlled trial was conducted in four urban cities in Canada (Edmonton, Winnipeg, Toronto and Montreal), and was registered on ClinicalTrials.gov (registration number: NCT03292510). A detailed study protocol for the GO-OUT trial has been reported [16]. Between February 20, 2018 and May 15, 2019, the GO-OUT trial enrolled 190 older adults with mobility limitations. Upon enrollment, participants attended a 1-day educational workshop designed to enhance knowledge and skills to engage in outdoor walking and prevent falls. After the workshop, participants were stratified by study site and participant type (enrolled as an individual or a dyad) and randomized into either the 10-week OWG program (n = 98) or the 10-week weekly reminders group (n = 92) [18]. Outcome evaluations were conducted at baseline, 3 months, 5.5 months, and 12 months. This study focused on the dose-response relationship between attendance in the OWG and improvement in health. Therefore, we limited our analytic sample to participants who were randomly assigned to the OWG program, remained in the study at the 3-month follow-up, and did not have missing data on all seven health outcomes at that time (n = 76). Health sciences research ethics boards at the University of Toronto, University of Manitoba, University of Alberta, and McGill University approved the trial protocol and participants provided written informed consent prior to baseline assessment. The research ethics board at the University of Toronto approved this analysis.

Participants

Individuals were considered eligible for the trial if they were adults aged 65 years and older, living independently in the community, who self-reported difficulty walking outdoors but affirmed the capacity to walk at least one block (50m) with or without a walking aid, expressed willingness to sign a liability waiver or obtain physician clearance for exercise, exhibited mental competency (scoring at least 18 out of 22 on the Mini-Mental State Exam telephone version), were available to participate in the workshop and at least 5 weeks of the OWG program, and were able to speak and understand English. Individuals were excluded if they met the physical activity recommendation of 150 minutes per week, were receiving rehabilitation to improve walking, or at high risk for falls according to the American Geriatrics Society/British Geriatrics Society criteria [18]. We recruited by advertising with local newspapers, radio stations, senior’s centres, residences, and charities.

Intervention: Outdoor walk group program

Based on a conceptual framework of community mobility [22], the OWG program was designed to enhance older adults’ competency in multiple dimensions of mobility such as walking distance, walking speed, postural transitions, and external physical load, within an outdoor environment [16]. The program involved attending two 1-hour sessions of group-based outdoor walking in large parks each week for a duration of 10 weeks (maximum of 20 sessions). The OWG program was progressive, task-specific, and implemented during summer months (June–August). Each session consisted of a 10-minute warm up, a distance walk, practice of a specific outdoor walking skill, a second distance walk, and a 10-minute cool down. Each OWG had a leader (physiotherapist or kinesiologist), who was authorized to adjust the program’s difficulty to ensure an optimal level of challenge for the participants [19]. Leaders were supported by additional trained staff to ensure a 1:3 ratio of OWG facilitators (leader/assistant) to participants. The 10-week duration of the OWG program is aligned with extant literature, which indicates that most group-based walking interventions for older adults range from 2 to 3 months [23]. After each OWG session, group leaders completed standardized forms to document implementation of session activities and participant attendance [19]. For the analysis of this study, participants were grouped into three categories based on attendance tertiles, which reflected the tri-modal distribution of attendance in the OWG program. The first, second, and third tertiles corresponded to participants attending 0–9, 10–15, and 16–20 total OWG sessions, respectively.

Data collection

Information on individual characteristics was collected at baseline [16]. Participants self-reported their age (years), sex (male vs. female), highest level of education, and use of walking aids. The Charlson Comorbidity Index [24] was used to assess participants’ diagnosis of 18 comorbidities such as diabetes, hypertension, cancer, and heart diseases at baseline. The final weighted score ranges from 0 to 39, with higher scores indicating the presence of greater and more severe comorbidities.

Performance-based measures

Walking endurance was assessed using the 6-minute walk test [25]. Participants received instructions to walk as far as possible in six minutes by walking back and forth along a straight, 30-meter walkway. Participants were asked to complete the test using their assistive devices and corrective eyewear as applicable. The maximum distance walked within six minutes was documented in meters. The 6-minute walk test demonstrates excellent test-retest reliability (intra-class correlation coefficient (ICC) = 0.95) and is considered a valid test of physical functioning and endurance among older adults [26,27].

Walking speed was assessed using the 10-meter walk test [28]. Participants were instructed to walk over a 14-meter walkway twice, once at a comfortable and once at a fast pace. Participants were asked to use their usual assistive devices and corrective eyewear to complete the test as applicable. The time taken to walk the central 10 meters was documented in seconds and used to calculate comfortable and fast walking speed (meter/second; m/s). The 10-meter walk test demonstrates excellent test-test reliability (ICCs = 0.96–0.98) and is recommended for clinical assessment of walking speed among older adults [29,30].

Balance was evaluated using the Mini Balance Evaluation System test (mini-BESTest) [31]. The mini-BESTest is a 14-item test developed to assess four balance domains [32]. Scores for anticipatory postural adjustments, reactive postural control, and sensory orientation range from 0 to 6, whereas the score for dynamic gait ranges from 0 to 10. Higher scores indicate greater balance in the respective subsystem. A total summed score, ranging from 0 to 28, is calculated to measure overall balance function. The mini-BESTest demonstrates good to excellent reliability (ICC > 0.90). Evidence of construct validity has been reported [31,33].

Lower extremity strength was measured using the 30-second sit-to-stand test [34]. Participants were instructed to sit in the middle of the chair, place arms folded across the chest, keep their feet placed on the floor, and repeat rising to a full standing position and sitting back down. The number of stands completed in 30 seconds was documented. The 30-second sit-to-stand test has shown excellent test-retest reliability (ICC = 0.95) and validity among community-dwelling older adults [34,35].

Self-report questionnaires

Walking self-efficacy was evaluated using the ambulatory self-confidence questionnaire [36]. A total of 22 items are used to measure how confident participants are in their ability to walk in different environmental situations. Participants rated their responses to each item on a 10-point scale (0, not at all confident to 10, extremely confident). The total score is calculated as the mean of item scores and ranges from 0 to 10, with higher scores indicating greater confidence with walking ability. The ambulatory self-confidence questionnaire demonstrates excellent internal consistency (Cronbach’s α = 0.95) and test-retest reliability (ICC = 0.92) among community-dwelling older adults [36].

Emotional well-being was evaluated using the emotional well-being scale of the RAND 36-Item Health Survey (RAND-36) [37]. Participants answered five questions on their emotions and experiences over the past four weeks. Total scores range from 0 to 100, with higher scores indicating better emotional well-being. The RAND-36 Health Survey was adapted from the instruments administered in the Medical Outcome Study [37], and its emotional well-being scale has demonstrated internal consistency and reliability (Cronbach’s α = 0.90).

Statistical analysis

Descriptive statistics were computed to describe participant characteristics and measures of physical and mental health at baseline in each attendance tertile groups (i.e., attended 0–9, 10–15, and 16–20 sessions). The tertile-based approach was adopted to account for the tri-modal distribution of OWG attendance observed in the GO-OUT trial. This approach enables clearer comparisons across low, moderate, and high levels of program engagement that could otherwise be obscured by using raw attendance data. We conducted nonparametric Kruskal-Wallis and chi-squared tests to compare differences in baseline characteristics and health outcome measures between attendance tertile groups. Wilcoxon signed-rank tests were used to examine changes in health outcomes from baseline to 3 months for each tertile group.

To examine potential forms of dose-response relationships between attendance and health improvement among older adults participating in the OWG program, we applied three established methodologies from the health sciences literature. These approaches, measuring the extent of improvement [38], the odds of improvement [39], and the overall count of health outcome improvements [40], have been used in similar studies focusing on older adults and other populations. Extent of improvement: First, we calculated an absolute change score on each measure of the seven health outcomes (walking endurance, comfortable and fast walking speed, balance, lower extremity strength, walking self-efficacy, and emotional well-being) from baseline to 3 months, where a positive change score indicates an improvement in the respective outcome. We employed linear regression models, using change scores as the dependent variable, and regressed them against the three attendance tertile groups. This allowed us to investigate whether higher attendance was associated with a greater extent of improvement in physical and mental health. A total of seven regression models were tested, with each focusing on a specific health outcome. We reported Hedges’ g effect sizes to provide insights into the magnitude of the dose-response relationship tested, with values of 0.15, 0.40, 0.75 representing small, medium, and large effects [41]. Odds of improvement: Second, we created a binary response variable to represent improvement (yes for change score > 0; no for change score ≤ 0) in each of the seven health outcomes. Separate logistic regression models were implemented to compare the odds of experiencing improvement in each health outcome across the three attendance groups. Overall count of improvement in health: Third, an overall count of improved health outcomes was created for each participant. A score of 0 suggests no improvement was found, while a score of 7 indicates improvement in all seven physical and mental health outcomes. A Poisson regression model was used to assess whether the number of improved health outcomes increased as a function of attendance in the OWG program. All models were adjusted for participant sex and study site, which were the two characteristics that differed across the attendance groups.

Recognizing that our analytic sample was restricted to 76 out of 98 OWG participants who remained in the study at 3 months and had data available for one or more of the seven health outcomes, we followed established procedure and employed the two-stage Heckman correction [42–44] to account for the impact of missing data and potential selection bias. Specifically, we first computed the inverse Mills ratio based on the full sample of older adults who were assigned to the OWG (n = 98) using a probit model. This ratio was then included in the regression models as an explanatory variable to adjust for non-selection hazards [42]. We conducted sensitivity analysis to compare findings with and without the Heckman correction. A two-tailed p-value less than 0.05 was considered statistically significant. All statistical analyses were performed using R software (Version 4.0.5).

Results

Descriptive statistics

Among the 98 older adults randomized to the OWG program, 78 remained in the study at the 3-month follow-up (79.6%). Among these, 2 participants had missing data on all seven health outcomes at the 3-month evaluation and were excluded from the analysis. Table 1 presents baseline participant characteristics and scores on measures of health outcomes for the entire sample and by level of outdoor walk group attendance of the 76 older adults included in the dose-response analysis. Mean±standard deviation age was 74.9 ± 6.6 years, and 72% of the participants were female. Prior to the OWG program, the mean distance that participants achieved on the 6-minute walk test was 363.2 ± 92.7 meters. The average walking speed was 1.09 ± 0.24 m/s at a comfortable pace and 1.43 ± 0.31 m/s at a fast pace. The mean score of mini-BESTest, 30-second sit-to-stand test, ambulatory self-confidence questionnaire, and RAND-36 emotional well-being scale, was 20.6 ± 4.7 (out of 28), 8.1 ± 3.5, 7.9 ± 1.6 (out of 10), and 77.1 ± 16.5 (out of 100), respectively. Upon closer examination of the three attendance tertile groups, participants from site 2 (56%) and site 4 (53%) attended 16 or more OWG sessions more frequently than those from site 1 (17%) and site 3 (17%) (p = 0.017). Fifty-seven percent of the 21 male participants but only 29% of the 55 female participants attended 16 or more OWG sessions (p = 0.006). For physical performance, participants who attended 0–9 OWG sessions showed a trend toward greater baseline walking endurance (p = 0.067) and had significantly faster baseline walking speed (p = 0.030) compared to those attending a greater number of sessions. Remaining baseline individual and clinical characteristics did not differ across the three attendance tertile groups. S1 Table shows that the baseline characteristics of OWG participants who remained in the GO-OUT study at 3 months (n = 78) compared to those who withdrew (n = 20) were similar with one exception: compared to participants who withdrew, individuals remaining in the study reported higher average emotional well-being at baseline (p = 0.032).

thumbnail
Download:
Table 1. Participant characteristics and scores on health outcome measures at baseline by level of outdoor walk group attendance.

https://doi.org/10.1371/journal.pone.0309933.t001

Mean change in scores on physical and mental health outcome measures by outdoor walk group attendance

Table 2 presents the scores at baseline and 3 months, and change in score from baseline to 3 months, on seven physical and mental health outcome measures, stratified by OWG attendance tertile groups. After the 10-week OWG program, participants in all three attendance groups demonstrated significant improvement in 6-minute walk test performance, with improvements ranging from 15.7 meters to 37.3 meters. The second (10–15 sessions) and third (16–20 sessions) tertile groups also showed significant improvements in the 10-meter walk test at a comfortable and fast pace. On the 30-second sit-to-stand test, participants in the first (0–9 sessions) and third (16–20 sessions) tertile groups performed approximately one additional stand from baseline to 3 months. No significant changes were observed on measures of walking self-efficacy, balance or emotional well-being in any of the OWG attendance tertile groups.

thumbnail
Download:
Table 2. Change in score on seven health outcome measures from baseline to 3 months by level of outdoor walk group attendance.

https://doi.org/10.1371/journal.pone.0309933.t002

Influence of outdoor walk group attendance on the extent of improvement in health

The associations between attendance in the OWG program and extent of improvement in the seven physical and mental health outcomes are summarized in Table 3. Compared to those who attended 0–9 OWG sessions (1st tertile), participants who attended 16–20 sessions (3rd tertile) exhibited, on average, a 56.33-meter greater improvement in the 6-minute walk test performance from baseline to 3 months that was statistically significant (95% CI: 17.29, 95.36, p = 0.005). Participants attending 16–20 sessions achieved on average, a 28.28-meter greater improvement in the 6-minute walk test performance from baseline to 3 months than those who attended 10–15 sessions, but this difference was not statistically significant (b = 28.28, 95% CI: −0.26, 56.82, p = 0.052). The effect sizes of the dose-response relationships observed were small in magnitude (Hedges’ g range: 0.23–0.36; see S2 Table).

thumbnail
Download:
Table 3. Associations between outdoor walk group attendance and the extent of improvement in health outcome measures from baseline to 3 months.

https://doi.org/10.1371/journal.pone.0309933.t003

Participants attending 10–15 OWG sessions exhibited a significantly greater extent of improvement in fast walking speed compared to those with 0–9 sessions (b = 0.14, 95% CI: 0.01, 0.28, p = 0.040). Similarly, those attending 16–20 sessions demonstrated significantly greater improvements in both comfortable walking speed (b = 0.15, 95% CI: 0.01, 0.29, p = 0.034) and fast walking speed (b = 0.18, 95% CI: 0.03, 0.34, p = 0.020) compared to participants with 0–9 sessions. The effects observed were medium to strong in magnitude (Hedges’ g range: 0.49–0.80). There were no significant relationships found between attendance and absolute changes in measures of balance, lower extremity strength, walking self-efficacy, and emotional well-being. Fig 1 presents results without covariate adjustment.

thumbnail
Download:
Fig 1. Changes in measures of physical and mental health from baseline to 3 months across three outdoor walk group attendance groups.

Note: The 1st tertile group attended 0–9 sessions; the 2nd tertile group attended 10–15 sessions; the 3rd tertile group attended 16–20 sessions. Dots above the horizontal dashed line indicate an improvement (change score > 0) in the respective health outcome measure from baseline to 3 months.

https://doi.org/10.1371/journal.pone.0309933.g001

Influence of outdoor walk group program attendance on the odds of improvement in health

Table 4 presents the associations between OWG attendance and the odds of experiencing an improvement in health. Results from the adjusted logistic regression models showed that compared to those attending only 0–9 OWG sessions, the odds of experiencing an improvement in comfortable walking speed from baseline to 3 months tended to be about 7 times larger among participants who attended 16–20 OWG sessions (Odds ratio [OR] = 7.06, 95% CI: 1.13, 57.83, p = 0.047). The odds of experiencing an improvement in fast walking speed were 10 times greater among participants who attended 16–20 OWG sessions than those attending 0–9 sessions (OR = 10.06, 95% CI: 1.75, 72.00, p = 0.014) and 3 times larger than those attending 10–15 sessions but this comparison was not statistically significant (OR = 3.19, 95% CI: 0.82, 12.50, p = 0.095). Likewise, participants attending 10–15 OWG sessions tended to have higher odds of improvement in walking self-efficacy, as measured by the ambulatory self-confidence questionnaire, compared to those attending 0–9 sessions but this comparison was not statistically significant (OR = 3.88, 95% CI: 0.94, 17.43, p = 0.066). The unadjusted percentages of participants experiencing an improvement in health across the three attendance tertile groups are presented in S1 Fig.

thumbnail
Download:
Table 4. Associations between outdoor walk group attendance and the odds of experiencing improvement in health outcome measures from baseline to 3 months.

https://doi.org/10.1371/journal.pone.0309933.t004

Influence of outdoor walk group program attendance on the number of health outcomes improved

Table 5 presents results from the Poisson regression model of the relationship between OWG program attendance and the overall count of improved health outcomes from baseline to 3 months. The total number of improvements on the measures of seven health outcomes increased with the number of OWG sessions attended: 4.00 ± 1.46 for 0–9 sessions, 4.03 ± 1.69 for 10–15 sessions, and 4.43 ± 1.50 for 16–20 sessions; the differences across tertile groups, however, were not statistically significant. Analyses conducted with and without the Heckman correction yielded similar results. The findings from the models without the correction are presented in S3–S5 Tables.

thumbnail
Download:
Table 5. Associations between outdoor walk group attendance and the total count of improvement on health outcome measures from baseline to 3 months.

https://doi.org/10.1371/journal.pone.0309933.t005

Discussion

This study investigated potential dose-response relationships between attendance in an OWG program and improvement on measures of seven physical and mental health outcomes among community-dwelling older adults with mobility limitations. Results showed that, compared to participants with lower attendance levels, those with higher attendance exhibited greater improvement in walking endurance, comfortable walking speed, and fast walking speed, from baseline to post-intervention. Moreover, participants with higher attendance had an increased odds of experiencing improvement in comfortable and fast walking speed.

Overall, our findings align with the existing body of literature documenting the health benefits of walking interventions [4,23,45–47]. For example, a recent systematic review and meta-analysis of nine randomized controlled trials reported that walking-only interventions significantly improved walking endurance and health-related quality of life among community-dwelling older adults [47]. Our study extends this body of work by focusing on a park-based, supervised, task-oriented and progressive OWG program and exploring the role of session attendance in driving improvements in older adults’ health. We found that participants who attended 16–20 park-based walking sessions demonstrated a 56.3-meter greater improvement in walking endurance, as measured by the 6-minute walk test, compared to those who attended only 0–9 sessions. Our findings are consistent with prior work reported by Dondzila et al. [48], showing a gradual improvement in 6-minute walk test performance as older adults increased their walking activity from 2,500 to 7,500 steps per day. Notably, participants in our study who were in the high attendance tertile (16–20 sessions) showed a mean improvement of 37.3 meters in 6-minute walk test performance from baseline to 3 months, which exceeds the minimal clinically important difference (MCID) of 30.5 meters [49]. In contrast, participants in the lower attendance tertiles (0–15 sessions) did not achieve improvements that surpassed the MCID. Our study presents preliminary evidence suggesting that participating in 16 or more sessions of a park-based OWG program over a period of 10 weeks may be needed to provide sufficient training for achieving improvements in walking endurance among older adults with mobility limitations.

Our study is among the first to identify dose-response relationships between attendance in OWG sessions and improvements in both comfortable and fast walking speed within a community setting. Although evidence directly examining this relationship remains limited, previous research has explored related concepts [50–53]. For instance, a recent randomized controlled trial led by Klassen and colleagues [51] showed that acute stroke patients receiving high-dose exercise interventions (40 sessions) in an indoor hospital setting exhibited significant improvements in walking speed compared to those receiving standard stroke care, while no such improvements were observed among those with low-dose interventions (20 sessions). Similarly, a meta-analysis involving 2,054 community-dwelling older adults suggested that high-dose therapeutic exercise interventions, defined as three 60-minute sessions per week, had a significant positive impact on improving walking speed, whereas low-dose interventions did not yield similar effects [52]. It is worth noting that participants in our study who attended 16–20 OWG sessions demonstrated an average improvement of 0.12 ± 0.17 m/s in comfortable walking speed and 0.13 ± 0.16 m/s in fast walking speed from baseline to 3 months. The mean improvement in comfortable walking speed surpasses the minimum MCID value of 0.10 m/s identified in prior studies involving diverse patient populations, including older adults with stroke, hip fracture, and multiple sclerosis [54]. Moreover, the extent of change in fast walking speed among participants attending 16–20 OWG sessions also exceeds the minimum MCID value of 0.12 m/s reported in a recent systematic review involving community-dwelling older adults [55]. These findings underscore that greater participation in an outdoor walk group program is associated with not only statistically significant, but also clinically meaningful, improvements in walking capacities.

To delve deeper into the impact of attendance in the OWG program, our study expanded its scope beyond merely measuring changes in health. We incorporated two additional approaches to operationalize dose-response and investigate how attendance would affect both the odds and overall count of improvements in health. Through this approach, we identified emerging evidence suggesting that, although not statistically significant, attending a greater number of OWG sessions may positively influence older adults’ walking self-efficacy. As a range of methodological approaches have been developed to examine dose-response relationships across fields of health sciences [38–40], further research utilizing distinct operational definitions of response is warranted to evaluate the potential benefits of outdoor walking interventions on health of older adults.

Contrary to expectations, our analysis revealed no significant dose-response relationship between attendance in the OWG program and improvement in balance, lower extremity strength, and emotional well-being. Several factors may shed light on these findings. First and foremost, the OWG program focused primarily on task-specific training designed to enhance older adults’ competency and skills in outdoor ambulation, including walking, turning, and stepping sideways [16]. Task-specificity of training may help to explain why we observed associations between attendance and improvements in walking capacity, but not in other general health outcomes. Given the focus of our intervention on walking distance, with two distance walks completed each session [19], it is not surprising that associations between attendance and improvements in walking endurance and speed were observed. Second, a meta-analysis including 1,252 participants across 10 studies demonstrated a U-shaped relationship between nature-based exercise and mental health [56]. They found that the largest benefits of nature and green exercise on mental health, measured by self-esteem and total mood disturbance, were observed at the shortest duration of 5 minutes per day. These benefits diminished as the duration increased to 10–60 min and half-day sessions but rose again for the whole day duration. This phenomenon may partly explain the lack of clear dose-response relationship between OWG attendance and emotional well-being in our study. Interestingly, an experimental study conducted by Li and colleagues showed contrasting effects of outdoor walking based on timing and location [57]. They found that while walking in an urban environment during nighttime was associated with positive effects on blood pressure, emotions and moods among middle-aged and older adults, walking in the same environment during daytime had negative effects on health potentially due to urban stressors such as noise, crowding, and air pollution. As our OWG program was administered in parks within four large Canadian cities during the day, it is possible that the timing and location of the walks, and the need to obtain transportation to parks, may have influenced the observed outcomes. Taken together, these insights highlight the complexity of designing and implementing outdoor walking interventions for older adults, suggesting the need to leverage an integrated paradigm that accounts for the diverse individual, environmental, and contextual factors involved in these initiatives [20].

This study possesses numerous strengths. Our OWG program is among the first that incorporates task-specific training of outdoor activities targeted towards enhancing community mobility skills among older adults [8]. In addition, our study spanned four major cities across Canada, which strengthens the external validity of our findings and allows generalization to similar urban environments. Furthermore, the inclusion of a broad range of outcome measures and operational definitions of response contributes to a better understanding of the impact of outdoor walking interventions on older adults’ health. However, findings should be interpreted within the context of their limitations. For example, although we observed gradients in the association between OWG attendance and total count of improved health outcomes, the lack of significance may result from limited sample size compared to prior studies involving outdoor community ambulation interventions among older adults [8]. Importantly, our study targeted older adults with mobility limitations. Even though participants self-reported difficulty walking outdoors, their baseline comfortable (1.09 ± 0.24 m/s) and fast walking speed (1.43 ± 0.31 m/s) were mostly above the average requirements for community ambulation (0.44 to 1.32m/s) [58]. This discrepancy suggests that our sample may have included individuals who possessed relatively higher functional capacity, potentially limiting the generalizability of findings to older adults with more severe mobility impairments. We also noted that attendance levels varied widely across the four study sites. Our planned process evaluation documented several reasons for non-attendance, including illness, vacation, transportation difficulties, and other commitments [18,19]. To improve participation, attention should be given to developing strategies that address both individual and structural barriers and promote consistent engagement among older adults across diverse urban settings [11–13,59]. Collectively, our study offers practical implications for the design, implementation, and promotion of community-based exercise interventions aimed at supporting the health of older adults [60,61]. From a design perspective, our findings underscore the necessity of tailoring programs to meet the needs, abilities, and preferences of older adults to maximize their engagement. From a promotional standpoint, healthcare providers and program developers may leverage the insights from this study to emphasize the importance of consistent attendance as a key factor in achieving meaningful improvements in walking capacity. Building on these findings, future research could explore the impact of attendance in different settings, such as long-term care facilities or through hybrid models that combine outdoor walking with online support. In parallel, investigating how attendance interacts with other dose parameters, such as walking intensity, frequency, and duration, represents another critical avenue for future research.

In conclusion, this study highlights the positive impact of attendance in a park-based, supervised, task-oriented and progressive OWG program on improving walking endurance, comfortable walking speed, and fast walking speed among older adults with mobility limitations. Our findings reinforce the importance of continued clinical and research endeavors to support participation and engagement in outdoor walking programs. Ultimately, these efforts will allow us to translate volume into value, enhancing the health and well-being for older adults.

Supporting information

S1 Fig. Raw percentage of participants who experienced improvement in physical and mental health outcomes from baseline to 3 months across three outdoor walk group tertile attendance groups.

https://doi.org/10.1371/journal.pone.0309933.s001

(PDF)

S1 Table. Comparison of baseline characteristics between outdoor walk group participants who remained in the GO-OUT study and those who had withdrawn at 3 months.

https://doi.org/10.1371/journal.pone.0309933.s002

(PDF)

S2 Table. Size of the effect of outdoor walk group attendance on the extent of improvement on health outcome measures from baseline to 3 months.

https://doi.org/10.1371/journal.pone.0309933.s003

(PDF)

S3 Table. Associations between outdoor walk group attendance and the extent of improvement on health outcome measures from baseline to 3 months (without the Heckman correction).

https://doi.org/10.1371/journal.pone.0309933.s004

(PDF)

S4 Table. Associations between outdoor walk group attendance and the odds of experiencing improvement on health outcome measures from baseline to 3 months (without the Heckman correction).

https://doi.org/10.1371/journal.pone.0309933.s005

(PDF)

S5 Table. Associations between outdoor walk group attendance and total count of health outcomes with improved scores from baseline to 3 months (without the Heckman correction).

https://doi.org/10.1371/journal.pone.0309933.s006

(PDF)

References

  1. 1. Jacobs JM, Cohen A, Hammerman-Rozenberg R, Azoulay D, Maaravi Y, Stessman J. Going outdoors daily predicts long-term functional and health benefits among ambulatory older people. J Aging Health. 2008;20(3):259–72. pmid:18332184
  2. 2. Fritschi JO, Brown WJ, Laukkanen R, van Uffelen JGZ. The effects of pole walking on health in adults: a systematic review. Scand J Med Sci Sports. 2012;22(5):e70–8. pmid:22734947
  3. 3. Fujita K, Fujiwara Y, Chaves PHM, Motohashi Y, Shinkai S. Frequency of going outdoors as a good predictors for incident disability of physical function as well as disability recovery in community-dwelling older adults in rural Japan. J Epidemiol. 2006;16(6):261–70. pmid:17085876
  4. 4. Hanson S, Jones A. Is there evidence that walking groups have health benefits? A systematic review and meta-analysis. Br J Sports Med. 2015;49(11):710–5. pmid:25601182
  5. 5. Thompson Coon J, Boddy K, Stein K, Whear R, Barton J, Depledge MH. Does participating in physical activity in outdoor natural environments have a greater effect on physical and mental wellbeing than physical activity indoors? A systematic review. Environ Sci Technol. 2011;45(5):1761–72. pmid:21291246
  6. 6. Twohig-Bennett C, Jones A. The health benefits of the great outdoors: a systematic review and meta-analysis of greenspace exposure and health outcomes. Environ Res. 2018;166:628–37. pmid:29982151
  7. 7. Gascon M, Triguero-Mas M, Martínez D, Dadvand P, Rojas-Rueda D, Plasència A, et al. Residential green spaces and mortality: a systematic review. Environ Int. 2016;86:60–7. pmid:26540085
  8. 8. Bhatia D, Salbach NM, Akinrolie O, Alsbury-Nealy K, dos Santos RB, Eftekhar P, et al. Outdoor community ambulation interventions to improve physical and mental health in older adults: a systematic review and meta-analysis. J Aging Phys Act. 2022;30(6):1061–74. pmid:35418512
  9. 9. Hawley-Hague H, Horne M, Skelton DA, Todd C. Review of how we should define (and measure) adherence in studies examining older adults’ participation in exercise classes. BMJ Open. 2016;6(6):e011560. pmid:27338884
  10. 10. Hawley-Hague H, Horne M, Campbell M, Demack S, Skelton DA, Todd C. Multiple levels of influence on older adults’ attendance and adherence to community exercise classes. Gerontologist. 2014;54(4):599–610. pmid:23899623
  11. 11. Rivera-Torres S, Fahey TD, Rivera MA. Adherence to exercise programs in older adults: informative report. Gerontol Geriatr Med. 2019;5:2333721418823604. pmid:30733977
  12. 12. Picorelli AMA, Pereira LSM, Pereira DS, Felício D, Sherrington C. Adherence to exercise programs for older people is influenced by program characteristics and personal factors: a systematic review. J Physiother. 2014;60(3):151–6. pmid:25092418
  13. 13. Davila VS, Conroy DE, Danilovich MK. Factors that influence walking intervention adherence for older adults living in retirement communities. J Aging Phys Act. 2021;30(1):65–72. pmid:34384049
  14. 14. Pavey T, Taylor A, Hillsdon M, Fox K, Campbell J, Foster C, et al. Levels and predictors of exercise referral scheme uptake and adherence: a systematic review. J Epidemiol Community Health. 2012;66(8):737–44. pmid:22493474
  15. 15. Mikolaizak AS, Lord SR, Tiedemann A, Simpson P, Caplan G, Bendall JC, et al. Adherence to a multifactorial fall prevention program following paramedic care: predictors and impact on falls and health service use. Results from an RCT a priori subgroup analysis. Australas J Ageing. 2018;37(1):54–61. pmid:29139599
  16. 16. Salbach NM, Barclay R, Webber SC, Jones CA, Mayo NE, Lix LM, et al. A theory-based, task-oriented, outdoor walking programme for older adults with difficulty walking outdoors: protocol for the Getting Older Adults Outdoors (GO-OUT) randomised controlled trial. BMJ Open. 2019;9:e029393. pmid:31005945
  17. 17. Kokorelias KM, Ripat J, Barclay R, Jones A, Mayo NE, Grant T, et al. A park-based group mobility program for older adults with difficulty walking outdoors: a qualitative process evaluation of the Getting Older Adults Outdoors (GO-OUT) randomized controlled trial. BMC Geriatr. 2025;25:16.
  18. 18. Salbach NM, Mayo NE, Webber SC, Jones CA, Lix LM, Ripat J, et al. Short-term effects of a park-based group mobility program on increasing outdoor walking in older adults with difficulty walking outdoors: the Getting Older Adults Outdoors (GO-OUT) randomized controlled trial. BMC Geriatr. 2024;24:740. pmid:39243012
  19. 19. Barclay R, Webber SC, Hahn F, Jones CA, Mayo NE, Sivakumaran S, et al. A park-based group mobility program for older adults with difficulty walking outdoors: a quantitative process evaluation of the Getting Older Adults Outdoors (GO-OUT) randomized controlled trial. BMC Geriatr. 2023;23:833. pmid:38082248
  20. 20. Liu Y, Salbach NM, Webber SC, Barclay R. Individual and environmental variables related to outdoor walking among older adults: verifying a model to guide the design of interventions targeting outdoor walking. PLoS One. 2024;19(1):e0296216. pmid:38198462
  21. 21. Simonsick EM, Newman AB, Visser M, Goodpaster B, Kritchevsky SB, Rubin S, et al.; Health, Aging and Body Composition Study. Mobility limitation in self-described well-functioning older adults: importance of endurance walk testing. J Gerontol A Biol Sci Med Sci. 2008;63(8):841–7. pmid:18772472
  22. 22. Patla AE, Shumway-Cook A. Dimensions of mobility: defining the complexity and difficulty associated with community mobility. J Aging Phys Act. 1999;7(1):7–19.
  23. 23. Kassavou A, Turner A, French DP. Do interventions to promote walking in groups increase physical activity? A meta-analysis. Int J Behav Nutr Phys Act. 2013;10:18. pmid:23388115
  24. 24. Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: Development and validation. J Chronic Dis. 1987;40(5):373–83. pmid:3558716
  25. 25. Holland AE, Spruit MA, Troosters T, Puhan MA, Pepin V, Saey D, et al. An official European Respiratory Society/American Thoracic Society technical standard: field walking tests in chronic respiratory disease. Eur Respir J. 2014;44(6):1428–46. pmid:25359355
  26. 26. Steffen TM, Hacker TA, Mollinger L. Age- and gender-related test performance in community-dwelling elderly people: Six-Minute Walk Test, Berg Balance Scale, Timed Up & Go Test, and gait speeds. Phys Ther. 2002;82(2):128–37. pmid:11856064
  27. 27. Rikli RE, Jones CJ. The reliability and validity of a 6-Minute Walk Test as a measure of physical endurance in older adults. J Aging Phys Act. 1998;6(4):363–75.
  28. 28. Perera S, Mody SH, Woodman RC, Studenski SA. Meaningful change and responsiveness in common physical performance measures in older adults. J Am Geriatr Soc. 2006;54(5):743–9. pmid:16696738
  29. 29. Peters DM, Fritz SL, Krotish DE. Assessing the reliability and validity of a shorter walk test compared with the 10-Meter Walk Test for measurements of gait speed in healthy, older adults. J Geriatr Phys Ther. 2013;36(1):24–30. pmid:22415358
  30. 30. Kim H, Park I, Lee H, Lee O. The reliability and validity of gait speed with different walking pace and distances against general health, physical function, and chronic disease in aged adults. J Exerc Nutrition Biochem. 2016;20(3):46–50. pmid:27757387
  31. 31. Horak FB, Wrisley DM, Frank J. The balance evaluation systems test (BESTest) to differentiate balance deficits. Phys Ther. 2009;89(5):484–98. pmid:19329772
  32. 32. Franchignoni F, Horak F, Godi M, Nardone A, Giordano A. Using psychometric techniques to improve the Balance Evaluation System’s Test: the mini-BESTest. J Rehabil Med. 2010;42(4):323–31. pmid:20461334
  33. 33. Godi M, Franchignoni F, Caligari M, Giordano A, Turcato AM, Nardone A. Comparison of reliability, validity, and responsiveness of the mini-BESTest and Berg Balance Scale in patients with balance disorders. Phys Ther. 2013;93(2):158–67. pmid:23023812
  34. 34. Rikli RE, Jones CJ. Development and validation of a functional fitness test for community-residing older adults. J Aging Phys Act. 1999;7(2):129–61.
  35. 35. Jones CJ, Rikli RE, Beam WC. A 30-s chair-stand test as a measure of lower body strength in community-residing older adults. Res Q Exerc Sport. 1999;70(2):113–9. pmid:10380242
  36. 36. Asano M, Miller WC, Eng JJ. Development and psychometric properties of the ambulatory self-confidence questionnaire. Gerontology. 2007;53(6):373–81. pmid:17622732
  37. 37. Hays RD, Sherbourne CD, Mazel RM. The RAND 36-item health survey 1.0. Health Econ. 1993;2(3):217–27. pmid:8275167
  38. 38. Zheng P, Pleuss JD, Turner DS, Ducharme SW, Aguiar EJ. Dose–response association between physical activity (daily mims, peak 30-minute mims) and cognitive function among older adults: NHANES 2011–2014. J Gerontol A Biol Sci Med Sci. 2023;78(2):286–91. pmid:35512348
  39. 39. Kline CE, Sui X, Hall MH, Youngstedt SD, Blair SN, Earnest CP, et al. Dose–response effects of exercise training on the subjective sleep quality of postmenopausal women: exploratory analyses of a randomised controlled trial. BMJ Open. 2012;2(4):e001044. pmid:22798253
  40. 40. Maloney A, Simonsson USH, Schaddelee M. D optimal designs for three Poisson dose–response models. J Pharmacokinet Pharmacodyn. 2013;40(2):201–11. pmid:23420229
  41. 41. Brydges CR. Effect size guidelines, sample size calculations, and statistical power in gerontology. Innov. Aging. 2019;3(4):igz036. pmid:31528719
  42. 42. Heckman JJ. Sample selection bias as a specification error. Econometrica. 1979;47(1):153–61.
  43. 43. Koné S, Bonfoh B, Dao D, Koné I, Fink G. Heckman-type selection models to obtain unbiased estimates with missing measures outcome: theoretical considerations and an application to missing birth weight data. BMC Med Res Methodol. 2019;19(1):231. pmid:31815610
  44. 44. Muñoz J, Hufstedler H, Gustafson P, Bärnighausen T, De Jong VMT, Debray TPA. Dealing with missing data using the Heckman selection model: methods primer for epidemiologists. Int J Epidemiol. 2023;52(1):5–13. pmid:36610459
  45. 45. Kalu ME, Dal Bello-Haas V, Hadjistavropoulos T, Thorpe L, Griffin M, Ploeg J, et al. The effects of a walking intervention on gait parameters in older adults residing in long-term care: a randomized controlled trial. J Nutr Health Aging. 2021;25(9):1099–105. pmid:34725668
  46. 46. MacRae PG, Asplund LA, Schnelle JF, Ouslander JG, Abrahamse A, Morris C. A walking program for nursing home residents: effects on walk endurance, physical activity, mobility, and quality of life. J Am Geriatr Soc. 1996;44(2):175–80. pmid:8576508
  47. 47. Ishigaki T, Misu S, Miyashita T, Matsumoto D, Kamiya M, Okamae A, et al. Effects of walking-only intervention on physical function, fall-related outcomes, and health-related quality of life in community-dwelling older adults: a systematic review and meta-analysis. J Aging Phys Act. 2024 [cited 18 Nov 2024. ];33(1):71–83.
  48. 48. Dondzila CJ, Gennuso KP, Swartz AM, Tarima S, Lenz EK, Stein SS, et al. Dose-response walking activity and physical function in older adults. J Aging Phys Act. 2015;23(2):194–9. pmid:24812209
  49. 49. Bohannon RW, Crouch R. Minimal clinically important difference for change in 6-minute walk test distance of adults with pathology: a systematic review. J Eval Clin Pract. 2017;23(2):377–81. pmid:27592691
  50. 50. Li P-S, Hsieh C-J, Tallutondok EB, Peng H-J. The dose-response efficacy of physical training on frailty status and physical performance in community-dwelling elderly: a systematic review and meta-analysis of randomized controlled trials. Healthcare (Basel). 2022;10(3):586. pmid:35327063
  51. 51. Klassen TD, Dukelow SP, Bayley MT, Benavente O, Hill MD, Krassioukov A, et al. Higher doses improve walking recovery during stroke inpatient rehabilitation. Stroke. 2020;51(9):2639–48. pmid:32811378
  52. 52. Lopopolo RB, Greco M, Sullivan D, Craik RL, Mangione KK. Effect of therapeutic exercise on gait speed in community-dwelling elderly people: a meta-analysis. Phys Ther. 2006;86(4):520–40. pmid:16579669
  53. 53. Kaushal N, Langlois F, Desjardins-Crépeau L, Hagger MS, Bherer L. Investigating dose–response effects of multimodal exercise programs on health-related quality of life in older adults. Clin Interv Aging. 2019;14:209–17. pmid:30774322
  54. 54. Bohannon RW, Glenney SS. Minimal clinically important difference for change in comfortable gait speed of adults with pathology: a systematic review. J Eval Clin Pract. 2014;20(4):295–300. pmid:24798823
  55. 55. Mehdipour A, Malouka S, Beauchamp M, Richardson J, Kuspinar A. Measurement properties of the usual and fast gait speed tests in community-dwelling older adults: a COSMIN-based systematic review. Age Ageing. 2024;53(3):afae055. pmid:38517125
  56. 56. Barton J, Pretty J. What is the best dose of nature and green exercise for improving mental health? A multi-study analysis. Environ Sci Technol. 2010;44(10):3947–55. pmid:20337470
  57. 57. Li H, Liu H, Yang Z, Bi S, Cao Y, Zhang G. The effects of green and urban walking in different time frames on physio-psychological responses of middle-aged and older people in Chengdu, China. Int J Environ Res Public Health. 2021;18(1):90.
  58. 58. Salbach NM, O’Brien K, Brooks D, Irvin E, Martino R, Takhar P, et al. Speed and distance requirements for community ambulation: a systematic review. Arch Phys Med Rehabil. 2014;95(1):117–28.e11. pmid:23820298
  59. 59. Vseteckova J, Dadova K, Gracia R, Ryan G, Borgstrom E, Abington J, et al. Barriers and facilitators to adherence to walking group exercise in older people living with dementia in the community: a systematic review. Eur Rev Aging Phys Act. 2020;17:15. pmid:32973961
  60. 60. Aravind G, Bashir K, Cameron JI, Howe J-A, Jaglal SB, Bayley MT, et al. Community-based exercise programs incorporating healthcare-community partnerships to improve function post-stroke: feasibility of a 2-group randomized controlled trial. Pilot Feasibility Stud. 2022;8:88. pmid:35459194
  61. 61. Alsbury-Nealy K, Colquhoun H, Jaglal SB, Munce S, Salbach NM. Referrals from healthcare professionals to community-based exercise programs targeting people with balance and mobility limitations: an interviewer-administered survey. Physiother Canada. 2023;e20220069.