Study design
This study is a single-blind three-arm parallel RCT approved by the Research Ethics Committee of Hong Kong Baptist University (ID:REC/21/22/0281) and registered in the ClinicalTrials.gov (NCT06190327). This protocol follows the standardized guidelines proposed by the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT). Participants will be recruited from community senior service centers in Hong Kong, where all older adults are community-dwelling residents. All eligible participants will be randomly assigned into three groups: (a) IG-1: the blended indoor and outdoor MSE intervention group; (b) IG-2: indoor-only MSE intervention group; (c): CG: control group, using the random function available in Excel software, in a ratio of 1:1:1. Assessments will be conducted at pre-intervention (T1: immediately after the eligibility assessment), post-intervention (T2: immediately after 16-week intervention), 3-month follow up (T3: 3 month after intervention the end of the intervention). Assignments will be blinded to the assessors until all tests are finished.
Study population
Older adults will be involved in this study if they: 1) are aged 60-74 years living in the community. 2) no contraindications for physical exercise (e.g., physical disability, unstable cardiovascular diseases, etc.). 3) scoring 5-15 using 15-item Geriatric Depression Scale (GDS-15) [32] (i.e., mild, moderate, and severe level of depressive symptoms). 4) able to communicate in Cantonese. Participants will be excluded if they: 1) suffer from cognitive impairment identified by the Chinese version of the Mini-Mental Status Examination (MMSE) (i.e., score < 24) [33]; 2) fail to pass the Physical Activity Readiness Questionnaire for Everyone (PAR-Q+) screening or without the physician’s approval for the readiness of participation in the moderate-intensity exercise. 3) have history of a clinical diagnosis of depression and receiving relevant treatment. 4) are attending other health projects related to physical exercise.
Sample size was calculated by G*Power software (version 3.1.9.6) with MANOVA with repeated measures. Based on the previous meta-analysis examine the effect of exercise intervention on people with non-clinical depressive symptoms (Cohen's d=0.34) [34] and a study compared the effect of the combined exercise (aerobic + resistance) on depression for postmenopausal women in outdoor setting to it conducted in indoor setting (Cohen's d=0.44) [35], an average small effect size (Cohen’s d) of 0.34 is used in the present study to achieve adequate power. Assuming a statistical power (1-β) of 80%, α of 0.05, and approximately 20% dropout rate, a total of 129 participants (43 in each arm) will be required to achieve a robust evaluation of treatment effects.
Participants will be recruited from community senior service centers in Hong Kong. Advertisement of this program will be distributed by the manager of the senior center to all senior members via social media (e.g. WhatsApp groups, Facebook), seniors' group meetings, and bulletin boards. If interested, potential participants will be able to register their details.
After registration, the GDS-15 with Chinese version [32] will be adopted to screen out those with depressive symptoms. Participants who score less than five will be excluded. If participants suffer from cognitive impairment identified by MMSE [33] screening with the score less than 24, will also be excluded. Moreover, if participants answer “yes” to any of the items of PAR-Q+ screening, they will be required to obtain medical approval from their general practitioner before involving in this exercise program.
Eligible participants will attend the baseline assessment (T1) at community senior service centers close to their area of residence. Investigator will introduce the study procedures individually to them, and all questions will be clarified. And then, they will be asked to sign an informed consent form before the commencement of the intervention, and authorize the research team to anonymously record, analyze, and use their data for academic purposes. Figure 1 shows the flowchart of participants from recruitment and allocation in this study.
Intervention
There will be four steps at the preparation stage of intervention development. Step 1: a steering group, consisting of key stakeholders who are involved in this program (i.e., elderly participants, manager of senior service center, exercise coach, and research team members), will be formed to develop intervention content, optimize the intervention components, to identify the facilitators and barriers for the intervention implementation, and to formulate strategies for maintaining participants’ engagement and adherence. Step 2: a one-month pilot study for blended indoor and outdoor MSE intervention group (IG-1) will be implemented to test and optimize the strategies and relevant materials. Participant recruitment, instruments, data collection, adaptability and feasibility of the intervention will be sufficiently considered in the pilot study. Step 3: a comprehensive plan of the intervention implementation will be established to guarantee the safety, effectiveness, supportiveness and enjoyment of the intervention implementation. An operational manual will also be constructed in this step. Step 4: an evaluation plan for the effectiveness of intervention implementation will be developed. Any amendments will be made if necessary.
In addition, a briefing session will be provided for all eligible participants in senior service centers, participants will receive detailed information about the exercise program in which they are enrolled (e.g., study procedure, schedule). Furthermore, another briefing session with a mock test for student helpers (major in sport science) also will be arranged one to two weeks before the pre-test to introduce the details of data collection and intervention implementation.
Intervention settings
Participants in 16-week blended indoor and outdoor MSE intervention group (IG-1) will engage in one indoor exercise session and one outdoor session in each week, while those who are randomly assigned to 16-week indoor-only MSE intervention group (IG-2) will engage in two indoor exercise sessions in each week. Regarding the intervention setting, the indoor exercise session will be conducted in the activity room of the government sports center, which is around 150 square meters in size (see Picture 1). The outdoor exercise session will be held in an urban park namely Kowloon Park, which has outdoor facilities including a jogging track, a large open space with seats around and loggia. All these outdoor facilities are in the green natural environment (see Picture 2 to Picture 4).
Exercise prescription
Based on the British National Institute for Health and Care Excellence guidelines [36] and previous studies [34, 37], effective exercise training programs for older adults with depressive symptoms are generally 10-16 weeks with 2-3 sessions/week (≥ 45 min/session). Thus, this study will adopt a modest dose of intervention, including 16 weeks with 2 sessions/week (90 minutes/session). As the exercise mode of this study will be MSE combining aerobic, muscular strength and balance trainings, each 90-min session will consist of 10-min warm-up, 30-min aerobic training, 20-min muscular strength training, 20-min postural balance training, and 10-min cool-down. Both two intervention groups (IG-1 & IG-2) will be delivered safely and effectively by qualified coach recommended by the Physical Fitness Association of Hong Kong, China (PFA) with professional monitoring.
According to the guidelines introduced by “ACSM’s Exercise for Older Adults” [38] and advice of PFA, the prescription of exercise programs for the two intervention groups will be formed (as shown in Table 1). First, a 10-min warm up (e.g. light walking and stretching) will be conducted. During the aerobic training, session 1/week of two intervention groups will conduct dancing via using chairs and towel, while session 2/week of two intervention groups will conduct walking (IG-1: outdoor walking in urban park, IG-2: indoor walking). As for the muscular strength training, weights (resistance) will be derived from participants’ own bodies, resistance band (15 pounds & 25 pounds), and adjustable ankle weights (0.5kg, 1kg, 2kg). The intensity of both aerobic training and muscular strength training will be light to somewhat hard (The rate of perceived exertion (RPE) 11 to 13, using the Cantonese version) [39]. Each participant will be required to report their RPEs during the aerobic and muscular strength training sessions. During postural balance training, there will be no restricted intensity, but the difficulty level of exercise will be increased from performing balance exercise without equipment (week 1-6) to with equipment (25cm Yoga mini balls) (week 7-16). Adjustment of training intensity and difficulty will be made in accordance with individual’s fitness level, and adaptability of the training. To ensure the safety and effectiveness of this exercise program, each intervention group will be separated into two sub-groups, with maximum 22 participants in each sub-group. It means that 2 sub-groups of 2 intervention groups will be conducted in separate timeslots but taught by the same coach at the same venue to ensure both sub-groups will receive similar teaching and learning quality. Participants in both two intervention groups will not be required to change their usual care pathways (e.g., medication use), and all interventions will be delivered while maintaining their original lifestyles.
In order to strengthen the CN of IG-1 participants during the outdoor exercise session at Kowloon Park, the following strategies will be employed. During the 10-min warm up, the coach will lead participants executing light walking and stretching while guiding them to focus on their sensory experience during the exercise. Such as looking at the green vegetation around themselves and the sunlight falling through the gaps in the leaves (visual sense), listening to the birds singing from nature and the wind rustling through the leaves (auditory sense), smelling the fresh air mixed with grass and soil (olfactory sense), and feeling the touch of the breeze on the skin (tactile sense).
During the aerobic training section, IG-1 participants will engage in a 30-minute nature walking along a trail surrounded by greenery. The walking route will circle an artificial lake and pass through some gentle ascents and descents in the terrain. During the nature walking, the coach will guild participants to interact with nature, including touching leaves and flowers and listening the sound of waterfalls and birds to deepen the immersion in the natural environment.
During the muscular strength training and balance training, sounds from nature will be used as background music, and participants’ auditory senses will be stimulated and reinforced. The coach will ask all participants a question “When you perform the exercise, do you hear the birds singing from nature and the wind rustling through the leaves?” during strength training section and balance training section, respectively. All participants will be asked to report their answers (“Yes” or “No”) to the student helper. If participant’s answer is “No”, the student helper will remind the participant to focus on his/her auditory senses in the natural environment.
Lastly, during the 10-minute cool down at the end of the outdoor MSE session, in addition to stretching, the coach will guide the participants to close their eyes with mind-body breathing to reflect on what they just have seen and felt during the exercise session in natural environment, such as the smell of soil and vegetation, the sound of waterfall, the feeling of touching the leaves and the color of flowers. By implementing these strategies, a stronger connection with nature can be promoted among participants in IG-1.
Safety considerations and adverse events for two exercise groups
During outdoor exercise session, if it rains and the rainfall is light or intermittent, participants can walk on the jogging track holding an umbrella and perform muscular strength and balance trainings in the open space of the park with loggia (see Picture 4). In case of the extreme weather conditions, such as yellow rainstorm warning or above issued by the Observatory, and extreme heat (above 30°C), the outdoor exercise session may be notified of cancellation in advance or rescheduled if deemed unsafe by the tutor. All outdoor sessions will be scheduled in the morning to avoid stronger sunlight and uncomfortable temperatures. Moreover, the researchers or coach will encourage and remind participants the night before each outdoor session to bring their plenty of water, towels, hat, sunglasses, and an alternative clothing.
In response to sports injuries during indoor and outdoor exercise sessions, the first aid box will be prepared on-site. In addition, the coach and student helpers (major in sport science) who involving in this study all have first-aid certificates and equipped with knowledges and skills about sports injury prevention and preliminary treatment. They are capable to handle any sports injury issue among participants during this time. All adverse events reported by the participant will be recorded.
Control group
Participants randomly allocated to the CG will not receive any intervention during the whole program (16-week treatment and 3-month follow-up), and they will be required to maintain their current lifestyles. To monitor the control condition, participants will need to keep diaries to record their daily physical exercise, mood, medicines used, illness and participation in other health-related activities. The research assistant will biweekly give telephone calls to the participants to check their diaries and identify if they change their lifestyles or experience adverse events.
Participant retention strategies
Several effective strategies will be adopted for participant retention based on previous studies on depression treatment for older adults [40]. 1) emphasizing study benefits and promote positive attitudes for participating in this program (e.g., expected health outcomes, free tests of physical fitness). The results of each assessment will be compiled into a health report to be provided as feedback to the participants; 2) designing the intervention components according to the Safety, Supportive, Active, and Enjoyable principles (e.g., group-based, diverse exercise mode, utility of music and equipment); 3) applying several behavioral change techniques that facilitate the maintenance of participation during the intervention implementation (e.g., positive persuasion, social support, verbal encouragement, message reminder prior to the intervention session); and 4) providing financial incentives for completing all measurements of outcomes (HK$300 supermarket coupons for each participant). The retention strategies will be discussed with all relevant stakeholders who are the members of the steering group. Amendments will be made if necessary.
Outcome evaluation of the intervention
Data collection for all tests will be done by the researchers. All participants will be informed that the data obtained during the program will be stored in a computer and will be treated confidentially. Identification code will be used to identify each participant. Data entry will be handled by two other researchers in the research team. For this protocol, Data monitoring committee (DMC) is not needed as it is a low-risk study with short intervention duration.
Primary outcome
Depressive symptoms: The Chinese version of the 15-item Geriatric Depression Scale (GDS-15) [32] will be used to measure subjective depression levels. The GDS-15, as an effective measure of depressive symptoms in older adults, has been shown to have good reliability and validity in Chinese older adults [32, 41]. Answers will be given on a yes/no scale. Sample items will include “Are you basically satisfied with your life?” and “Do you prefer to stay at home, rather than going out and doing things?” in past week. The total score ranges from 0 to 15, where 0-4 = normal, 5-8 = mild depressive symptoms, 9-11 = moderate depressive symptoms and 12-15 = severe depressive symptoms. Assessments will be conducted at T1, T2 and T3.
Secondary outcomes
Salivary cortisol: Salivary cortisol will be measured as a biomarker for depressive symptoms. All participants will be provided with two salivate tubes and asked to collect the saliva samples (2-3ml) at awakening, and 30 min after awakening respectively on the next day. Participants will be instructed to rinse their mouth with normal saline but abstain from eating, drinking, or brushing their teeth prior to saliva collection. Participants will use passive drool method to collect saliva naturally in the mouth for 60 seconds before dribbling the saliva into containers. Following the collection of samples, participants will be instructed to record the exact time of collection on the label and freeze the salivate tubes in their home refrigerator (0-4 ℃) to keep the salivary cortisol stable until transport to the research lab. All the uncentrifuged saliva samples will then be transported and stored at -20℃ until analyses. Saliva will be assayed for cortisol (μg/dL) concentrations by a registered laboratory using a Salimetric high sensitivity ELISA kit [42]. The inter assay coefficients of variation (based on low- and high-control samples) is set at 5% for cortisol. Assessments will be conducted at T1, T2 and T3.
Physical fitness: Physical fitness will be assessed using the Senior Fitness Test (SFT) Manual [43], which includes body mass index (BMI), 30s chair stand, 30s arm curl, 2min step test, chair sit-and-reach test, back scratch test and 8ft up-and-go test, to measure muscular strength, aerobic endurance, flexibility, agility and dynamic balance for older adults. This validated instrument is reliable with an intra-class correlation coefficient (ICC) ranged from 0.8 to 0.98. Assessments will be conducted at T1, T2 and T3.
Physical activity enjoyment: The Chinese version of the 8-item physical activity enjoyment scale (PACES) [44] will be adopted to measure participant’s enjoyment level after engaging in blended indoor and outdoor MSE program. This scale has revealed strong internal consistency and reliability among Hong Kong older adults (Cronbach's alpha=0.92). It will be scored by 7 bipolar rating, from one extreme to the other extreme, for example, from “it’s very pleasant” to “it’s very unpleasant”. Assessments will be conducted at T1, T2 and T3.
Connectedness to nature (CN) (mediator): CN will be measured using the 14-item connectedness to nature scale with Chinese version [45] to assess the sense of belonging to the natural world. The original scale was developed by Mayer & Frantz [46] with sound reliability (Cronbach's alpha=0.84). This five-point scale, ranging from 1 “strongly disagree” to 5 “strongly agree”. Sample items will include “I often feel like I am only a small part of the natural world around me, and that I am no more important than the grass on the ground or the birds in the trees”. Assessments will be conducted at T1, T2 and T3.
Loneliness (covariate): Loneliness will be measured by using the 6-item De Jong Gierveld Loneliness Scale with Chinese version [47]. This scale has been shown a sound reliability and validity for older adults in Hong Kong (Cronbach's alpha=0.76) [47]. Item 1 to item 3 as negatively worded items will be measured “emotional loneliness”, answer “yes” will score 1, answer “more or less” will score 1, answer “no” will score 0. Item 4 to item 6 as positively worded items will be used to assessed “social loneliness”, answer “yes” will score 0, answer “more or less” will score 1, answer “no” will score 1. Sample items will include “I experience a general sense of emptiness”, and “There are many people I can trust completely”. Assessments will be conducted at T1.
Sociodemographic characteristics include name, mobile number, gender, age, educational level, household income, marital status, number of children and living status, will be collected at T1.
Process evaluation of the intervention
Process evaluation will be used to understand and evaluate implementation and participants’ viewpoints of the acceptability of the intervention components and outcome measures. A comprehensive framework for designing and reporting process evaluation of RCTs will be employed [48], which including the changes of outcome variables, the safety, acceptability and satisfactory of intervention implementation. Upon completion of the last intervention session of the 16-week period, participants in two intervention groups will be asked to complete the Questionnaire of Process Evaluation and the Exercise Acceptability Questionnaire. The quality and data review for auditing trial conduct will conduct every 6 months by sponsor with a review of all source documents and a review of data entry.
Statistical analysis
SPSS 29.0 and Mplus 7 will be employed for data analysis. Diagnostic tests (e.g., outlier detection and distribution examination) will be conducted for all data prior to the main analysis. Skewed data of continuous variables will be log-transformed or replaced with median values prior to the data analyses. Missing data (missing at random) will be addressed with multiple imputation approach with chained equations, except for the dropouts (attrition under 30%) that will be imputed with the last observed values. Sensitivity testing (per-protocol analysis) will be employed to detect the impact of missing data and attrition. Intention-to-treat principles will be used for the primary analysis.
Independent samples t tests, F tests, and Chi square tests will be applied to compare the baseline characteristics before the intervention (T1). A series of generalized linear mixed models will be employed to evaluate the intervention effects on outcome measures, with time, groups, and their interaction as fixed effects with individuals as random effects. The baseline values will be controlled for all analyses. In addition, structural equation modeling will be employed to analyze mediating effects (CN) of intervention effectiveness, using the 95% bias-corrected bootstrap approach (5000 resamples). The significance level will be set as 95% (two-tailed). The results will be reported following the guide of CONSORT checklist.
Pilot study
A 4-week pilot study of the blended indoor and outdoor MSE program will be conducted to test the adaptability and feasibility of the intervention as well as the data collection instruments in older adults. 12 participants will be recruited from one community elderly center in Hong Kong. They will be asked to complete all measurements (questionnaires, fitness test and saliva collection) and a 4-week blended indoor and outdoor MSE course. The 4-week pilot study (1 indoor MSE session + 1 outdoor MSE session per week) will include all the movements of three components of MSE in the main intervention but shrink the week duration compared to the main intervention. The detailed exercise content of the pilot study can be found in Table 2. Amendments will be made where necessary. The participants in the pilot study will not be involved in the main study.
Time schedule of the study
The proposed study will be completed in 24 months, as shown in Figure 2 (additional file 1).