Explanation for the choice of comparators

The ED program will serve as an attention control group to reduce for unknown and known confounding factors such as the effects of attention and social interactions on health outcomes. Social interactions have known gender differences, with women benefitting from social engagement more than men [14]. The ED program will utilize the same participant schedule in frequency and duration of contact as the HC to isolate the specific effects of HC on physical activity.

Intervention description Health coaching (HC) intervention

The HC intervention will be delivered over 26 weeks using a Brief Action Planning (BAP) framework to promote PA [15]. Brief Action Planning is grounded in the practice of motivational interviewing and uses evidence-based constructs from the behavior change literature: self-efficacy and action planning [15]. The primary behavior change techniques used are as follows: (1) goal-setting, (2) action planning, (3) self-monitoring, and (4) feedback. Health coaches will facilitate goal-setting and action planning with participants. Participants will utilize daily PA diaries to enable self-monitoring, and the HC will provide feedback on progress toward individualized PA goals and strategies.

The HC intervention will be delivered by exercise professionals (e.g., kinesiologists) with ≥ 1 year of experience working with older adults or clinical populations. All HC will be trained and certified in BAP training by the Centre for Collaboration, Motivation and Innovation [16]. Our HC protocol enables a standardized delivery with an intra-cluster correlation coefficient (ICC) of 0.00071 observed in a previous RCT by a study co-investigator, across 4 BAP trained coaches in adults with knee osteoarthritis [17].

Delivery

Participants in the HC intervention will have an initial one-hour session in-person with their coach, who will conduct a brief physical assessment and work with the participant to establish a plan to accomplish their PA goals. Using BAP principles [15], coaches will guide participants to (1) set an activity goal, (2) develop an action plan, (3) identify barriers and solutions, and then (4) rate their confidence in the plan. Coaches will utilize SMART (specific, measurable, attainable, relevant, time-bound) goal setting principles [18, 19]. Once participants have established a goal and plan, they will be asked to rate their confidence in executing the plan on a scale of 0 to 10, with 10 indicating very confident. Collaborative problem solving will occur until the confidence rating reaches ≥ 7/10.

During the initial HC visit, coaches will guide participants to create a plan to increase their participation in MVPA by 50 min per week in 5-, 7-, and 10-min bouts of exercise. Participants will be oriented to various modes of physical activity to increase their MVPA through activities like walking or stationary cycling. The research team will also provide participants with exercise sessions of 5-, 7-, and 10-min durations that will be available as videos and hardcopy manuals. Coaches will teach participants to self-monitor their intensity of PA utilizing the 20-point Borg Rating of Perceived Exertion (RPE). Participants will aim to do moderate to vigorous physical activity with an RPE of 13–14 (“somewhat hard”) on the Borg scale. After the initial HC session, participants will receive 8 × 20-min sessions via zoom or phone calls over the 26-week RCT (Table 1). During these sessions, coaches will continue to help participants set and modify their own exercise goals to gradually increase PA time and intensity and work with participants to create action plans to achieve these goals.

Table 1 Overview of HC group

The fidelity of the HC program will be independently assessed using a multidimensional approach. Audio recordings will be obtained to assess HC delivery and will be rated by an independent coder, not involved in the delivery of the HC intervention, utilizing the Conventry, Aberdeen, & London – Refined (CALO-RE) taxonomy [20]. Informed by Cucciare and colleagues protocol [21], we will analyze recordings from the 1st, 5th (middle), and 10th (last) participant assigned to each coach.

Health education (ED) program

The ED program will consist of group education sessions delivered in person with an option for people to attend via zoom or phone call. The frequency and duration of ED sessions will be delivered in a manner identical to the HC program, with one initial hour-long session followed by 8 × 20-min education sessions. The initial education topic will be an interactive session on falls prevention. The other education topics will include the following: (1) goal-setting, (2) nutrition, (3) sleep, and (4) mindfulness.

Criteria for discontinuing or modifying allocated interventions

Participants will have the goal of increasing PA by 50 min per week, in small doses of 5-, 7-, and 10-min bouts as they choose. In this sense, participants exercise dose will be primarily self-limited based on personal goals and tolerance, with study personnel serving to guide and assist with modification as necessary. Participants who experience falls or report any serious adverse events related or unrelated to the study may require modification of physical activity or require additional medical clearance from the study or their family physician prior to returning to the intervention.

Strategies to improve adherence to interventions

HC participants will manually track their weekly PA in a physical log. Health coaches will actively work with participants to help them adjust and modify their action plan to meet their PA goals.

To minimize attrition within the ED group, participants will receive a 1-h HC session and 2 follow-up HC phone calls upon completing the 52-week assessment. At this time, participants will receive access to the exercise intervention videos and manuals.

Relevant concomitant care permitted or prohibited during the trial

All participants will seek health care as usual, without any care being prohibited throughout trial. Health care utilization will be assessed via monthly self-report diaries and questionnaires assessed every 3 months throughout the trial duration.

Provisions for post-trial care

There are no provisions for ancillary and post-trial care. Medical expenses due to care sought for study or non-study-related adverse events will be paid by participant’s usual medical services plan.

Outcomes Descriptors

We will collect information on key descriptors including general health, biological sex, current medication use, education, and socioeconomic status via interview and questionnaires. Resting vital signs, heart rate and blood pressure, will be measured with an automatic sphygmomanometer, the Omron HEM-775 in a seated position prior to physical assessments. Body mass index will be calculated as mass in kg/height in m [2]. Comorbidity with physical function will be determined by the Function Comorbidity Index [22]. Functional status will be assessed using the Lawton-Brody Instrumental Activities of Daily Living (IADL) Scale [23]. Gender-related characteristics will be assessed using questionnaires about gender identity (Gender Identity Scale) [24] and institutional gender (income, education level). The Gender Identity Scale offers three gender identities: female/woman/girl, male/man/boy, and other gender(s) [24].

All outcomes will be assessed at baseline, 13 weeks (mid-point), 26 weeks (final), and 52 weeks (follow-up). The following secondary outcomes will also be collected midway through the follow-up period at 39 weeks via phone call: fatigue, community mobility, mood, health-related quality of life, and sleep.

Primary outcomeMobility

The primary outcome is mobility, measured by the SPPB. The SPPB is a standardized measure of lower extremity physical performance that includes standing balance, walking, and sit-to-stand [25]. Each component is rated out of 4 points, for a maximum score of 12 points, with higher scores indicating better performance. A low score of 9 or less on the SPPB is a risk factor for institutionalization, morbidity, mortality, and disability in non-disabled older adults [26]. Specifically, scores of 9 or less on the SPPB are predictive of MMD [27].

Secondary outcomesPhysical activity

Average daily MVPA and sedentary time will be measured using the SenseWear Mini, a research-grade multimodal sensor. The SenseWear Mini integrates tri-axial accelerometer data, physiological sensor data, and personal demographic information to provide valid and reliable estimates of steps and energy expenditure in metabolic equivalent of task (MET) [28, 29]. We will calculate MVPA as the average daily minutes spent with an energy expenditure of ≥ 3 MET, the lower bound of MVPA. Sedentary time will be defined as the average daily minutes spent with an energy expenditure of ≤ 1.5 MET during waking hours. Participants will wear the device around their non-dominant upper arm for 9 days at baseline and 3 and 6 months. Data from the last 7 days of wear will be utilized for analysis to minimize potential effects of the device temporarily increasing their PA levels [30]. An alternative tri-axial accelerometer-based wearable may be used for those who experience contact dermatitis with the SenseWear Mini.

The Community Health Activities Model Program for Seniors (CHAMPS) Physical Activity Questionnaire for Older Adults will be used as a paper and pencil measure of physical activity. The CHAMPS is a 41-item questionnaire assessing weekly frequency and duration of physical activities relevant for older adults [31].

Gait speed

Gait speed in m/s will be assessed during two trials of the 4-m walk performed during the SPPB assessment.

400-m walk

Participant’s capacity to perform the 400-m walk overtime will be assessed by whether participants can complete the 400-m in ≤ 15 min and will be recorded as “yes” or “no.” Capacity to complete the 400-m walk is a major risk factor for major mobility disability. During the 400-m walk, participants will be asked to walk 10 laps (out and back) on a 20-m course at their usual pace [32]. Participants will be able to use a cane, but no further physical assistance or walking aid will be permitted. If needed, they may stop for a standing rest of up to 1 min during the test. During the 400-m walk participants heart rate will be continuously measured using a wearable device.

Cognitive function

We will use a battery of standardized neuropsychological tests to assess multiple cognitive domains. The National Institutes of Health (NIH) Toolbox Cognition battery [33, 34] is a comprehensive computerized neuropsychological test battery with normative values. We will use the following assessments from the NIH Toolbox: (1) Dimensional Card Sorting to measure set shifting, (2) Flanker Inhibitory Control and Attention Test to measure response inhibition and attention, (3) List Sorting Working Memory Test to measure working memory, and (4) Picture Sequence Memory Test to measure episodic memory. Additionally, we will use the following paper and pen neuropsychological assessments: (1) 13-item Alzheimer's Disease Assessment Scale-Cogniive (ADAS-Cog), [35, 36] (2) Trail Making Test Parts A and B (B-A; set shifting), [37] (3) Digit Span Forward and Backward (working memory), [38] (4) Rey Auditory Verbal Learning Test (verbal memory), [37] (5) the Digit Symbol Substitution Test (processing speed), [39] (6) Stroop Colour Word Test (response inhibition), [40] (7) Category Fluency, (8) Clock Drawing, and (9) MoCA [41]. The paper and pen neuropsychological battery will allow us to calculate the ADAS-Cog-Plus [35].

Fatigue

The 9-item Fatigue Severity Scale [42] will be used to assess how fatigue interferes with certain activities and its severity.

Strength

Dominant quadriceps strength in kilograms will be measured with a standardized strain gauge. Dominant grip strength in Newtons will be measured using a digital Jamar isometric hand dynamometer. Participants will perform three trials each for quadriceps and grip strength assessments.

Functional and community mobility

Participants will perform two trials of the Timed Up-and-Go Test to assess functional mobility [43]. Community mobility will be assessed using the Life Space Questionnaire [44].

Mood

We will use the Centre for Epidemiological Studies Depression Scale, a commonly used screening tool for depressive symptoms [45].

Health-related quality of life

A self-report questionnaire, the EuroQol EQ-5 Domain (5D)-5 Level (5L) (EQ-5D-5L), will be utilized to assess health-related quality of life [46,47,48]. The EQ-5D-5L is a preference-based utility measure incorporating five domains of health: mobility, self-care, usual activity, pain, and anxiety/depression. Higher scores indicate a greater severity of problems within the domain. We have used the EQ-5D previously for a cost-utility analyses in older adults with mobility limitations [9, 49]. It calculates health state utility values that can provide weightings for quality-adjusted life years (QALYs). Canadian conversion tariffs will be used to estimate health state utility values [47].

Sleep

Objective sleep duration and sleep efficiency will be measured using the SenseWear Mini [50]. Sleep quality will be assessed using the 19-item Pittsburgh Sleep Quality Index [51], a commonly used subjective sleep questionnaire. Participants will also keep a self-report sleep diary which will be used to confirm sleep windows calculated from the SenseWear Mini. The STOP-Bang questionnaire will be used to screen for risk of obstructive sleep apnea at baseline [52].

Falls

Falls will be prospectively documented by all participants on a monthly basis via calendars provided by the research team. Participants will be asked to report any falls directly to the research team after they occur. We will complete a follow-up falls interview over the phone to obtain information regarding the fall and determine if any adjustments to the study protocol and interventions are required.

Health resource utilization (HRU)

Cost data will be collected monthly via HRU diaries, and these self-report cost diaries will be confirmed during in person assessments or via telephone calls every 3 months using the HRU questionnaire [53], which is based on validated cost questionnaires [54,55,56]. The HRU questionnaire is utilized to collect specific details on (1) health professional visits; (2) hospital, rehabilitation facility, and inpatient clinic visits; (3) laboratory procedures or investigations; and (4) medications. Using a fully allocated hospital cost model (for in-patient costs) and the British Columbia provincial guide to medical fees (for outpatient costs), we will assign health care resource utilization on a per participant basis. Evidence from a systematic review of 15 studies demonstrates good agreement between self-reported questionnaires on resources utilization and administrative data [57].

Intervention adherence

Adherence to the intervention will be measured as session attendance (HC and ED groups). Session attendance will be recorded by health coaches and education session leaders and will be estimated as the percentage of total sessions attended.

Participant timeline

Participant enrolment began July 2023 and the first participant was randomized September 5, 2023. We expect participant recruitment, assessments, and follow-up visits to be completed by October 2026. Participants will undergo a phone screening to determine preliminary eligibility. If appropriate, participants will be invited for an in-person screening. Within 1 month of the in-person screening, participants will complete the remainder of the baseline assessments and will be randomized to either the HC or ED group. Participants will partake in intervention procedures for 26 weeks. Upon completing the intervention, participants will be followed for another 26 weeks. Upon the final follow-up assessment at 52 weeks, participants in the ED group will receive an initial HC visit followed by 2 additional HC calls and receive access to exercise-related materials. The participant timeline of assessments is shown in Table 2.

Table 2 Participant timeline of assessmentsSample size

The sample size for this study is 290 participants, based on SPPB data published in the LIFE study that examined changes in SPPB scores based on changes in MVPA [6]. At 6 months, those in the highest quartile of MVPA change (i.e., > 43 min per week) experienced a mean improvement (calculated as 6 months minus baseline) of 1.21 in SPPB score with a SD = 0.98. A 0.5 difference in SPPB score is considered a clinically meaningful change [58]. Assuming at least 90% of our HC participants will increase their participation in MVPA by at least 50 min per week, and splitting the remaining 10% of HC participants equally among the 3rd quartile in MVPA change (mean SPPB change = 1.16) and the 2nd quartile in MVPA change (mean SPPB change = 0.89), we anticipate a mean SPPB improvement of 0.90 × 1.21 + 0.05 × 1.16 + 0.05 × 0.89 = 1.19 in the HC group. For the ED group, we assume the mean SPPB change will be similar to what was observed in the LIFE study control group [6]; we calculated this value to be 0.84 from the published data. Thus, the effect size for the SPPB outcome is (1.19 − 0.84)/0.98 = 0.36.

Using a two-tailed test alpha = 0.05, our estimated effect size requires a sample size of 246 participants (123 per group) in order to achieve 80% power, assuming the outcomes for all participants are independent. In principle, this sample size should be adjusted by a design effect (DE) to account for the nesting of participants within coaches in the HC arm and nesting of participants within cohorts in the ED arm. However, as noted in the description of the HC intervention, the ICC in a previous study was found to be only 0.0007 [17]. Together with an expected 15 participants per coach, the DE is only 1 + (15 − 1) × 0.007 = 1.01 which implies a negligible impact on the required sample size. No data are available on the ICC within ED groups, but we expect it to be low enough to also have negligible impact. Allowing for a 15% dropout rate leads to the sample size of 290 participants (i.e., 145/group).

Recruitment

We will recruit participants from 2 committed clinics: (1) Vancouver General Hospital (VGH) Falls Prevention Clinic and (2) VGH Geriatric Internal Medicine Teaching Clinic. Additionally, we will recruit participants through word of mouth, public talks, and advertisements place in community centers and newspapers. We have an established track record of recruiting older adults, including those with mobility limitations, for behavioral RCTs.