Table 2.

Intervention Details Described in Line with the TIDIER Framework for Intervention Description^a

1	NAME	Provide the name or a phrase that describes the intervention	Engage-HD Physical Activity intervention	Engage-HD Social Interaction Intervention
2	WHY	Describe any rationale, theory, or goal of the elements essential to the intervention	The Engage-HD Physical Activity intervention specifically focused on developing an individualized lifestyle approach to enhancing physical activity with interpersonal interactions of the physical activity coach underpinned by the concepts of self-determination theory (SDT). The function of the additional intervention components, namely a physical activity workbook and exercise DVD, were to facilitate education, enablement, modeling, and goal setting.	The Engage-HD Social Interaction Intervention was a comparator intervention that provided conversational interaction. This social intervention was developed by our team in order to provide us with a comparator that could help us both control for contact time and account for the potential influence of the interpersonal skills (ie, relatedness) of the coach on any treatment effect while not focusing particularly on the goal setting processes inherent in a physical activity self-management intervention.
3	WHAT	Materials: Describe any physical or informational materials used in the intervention, including those provided to participants or used in intervention delivery or in training of intervention providers. Provide information on where the materials can be accessed (eg, online appendix, URL).	This complex intervention consisted of 3 main elements, namely the Participant/coach interaction (underpinned by SDT), a purpose-developed ENGAGE-HD Workbook and an exercise DVD. The Workbook focused on disease-specific information to facilitate exercise uptake, instructions on use of pedometers, and a goal setting section. The exercise DVD (Move to Exercise) can be accessed online at https://www.youtube.com/channel/UCH7_ed2_mkzXNWPZqVIosw (accessed January 18, 2017).	Conversation cards (with images and text) representing a wide range of topics were used to help direct conversation toward topics of potential interest to the participants during each visit. In the first session, a “getting to know you” conversation took place. Further discussions could focus on a range of topics, including travel, media, food, music and art, entertainment, shopping, animals, science, technology, friends, and socializing.
4		Procedures: Describe each of the procedures, activities, and/or processes used in the intervention, including any enabling or support activities.	Participants enrolled in the ENGAGE-HD physical activity intervention received 6 home visits and interim telephone calls over the course of 14 weeks, during which time they were supported by trained activity coaches to develop an individualized lifestyle approach to enhancing physical activity. During the first face-to-face visit, the coach introduced the participant to the ENGAGE-HD physical activity intervention, the workbook, and the exercise diaries, which participants were asked to complete each week. The initial interactions considered benefits of physical activity and each participant's individual exercise history, as well as setting specific physical activity goals. Further discussion topics on physical activity included implementing a daily activity plan, monitoring exercise intensity, dealing with safety, weather, equipment, and typical barriers (such as time, boredom, lack of equipment, lack of specific knowledge, and support). In the remaining 5 home sessions, the coach continued to support discussions related to the activities in the workbook, and supervised the participant performing components of the Move to Exercise DVD exercise program or other physical activities. Coaches also reviewed exercise diaries completed during the previous week(s). Supportive telephone calls were conducted 3 times over the 14-week period. These calls served to provide encouragement and advice with respect to the promotion of regular physical activity. During the calls, the coach also asked about any falls, health, or medication changes and confirmed the date and time of the next visit.	Participants enrolled in the ENGAGE-HD social interaction intervention received 6 home visits and interim telephone calls over the course of 14 weeks. At each face-to-face visit, the coach engaged with the participant in a talking and communication interaction using purpose-developed conversation cards (with images and text) representing a wide range of topics to help direct conversation toward topics of potential interest to the participants during each visit. Reminder telephone calls were conducted 3 times over the 14-week-period. These calls served to match the contact time provided to the physical intervention group. During the calls, the coach asked about any falls, health, or medication changes and confirmed the date and time of the next visit. At each home visit, the coach also completed a health and falls review with the participant where they were asked about (and recorded any details of) any falls, health professional interaction, or medication changes.
5	WHO PROVIDED	For each category of intervention provider (eg, psychologist, nursing assistant), describe their expertise and background.	Intervention delivery coaches were trained at a total of 8 sites. The coaches delivering the ENGAGE-HD physical activity interventions were either (a) health care professionals (eg, Physical therapists (n = 3), Occupational therapists, or Nurses (n = 4)) with experience of delivering exercise-related activities or with specific experience with HD; or (b) exercise professionals (n = 2). All staff had to meet specific health competencies, namely Skills for Life Competencies, developed by the National Health System (NHS) in the UK. (Competencies can be found at Skills for Life, accessed January 18, 2017: https://tools.skillsforhealth.org.uk/competence/show/html/id/2603/).	Intervention delivery coaches were trained at a total of 8 sites. The coaches delivering the ENGAGE-HD social interaction interventions were either (a) health care professionals (eg, Occupational therapists (n = 1), Nurses (n = 7),) support workers with experience of delivering exercise-related activities (n = 1), researchers with specific experience with HD (n = 1); or (b) exercise professionals (n = 2).
		Describe any training given.	The training model was for a team, including the intervention coordinator, trial chief investigator, and trial manager, to travel to the site location and conduct a 6-hour training session in a small group setting. Coaches at sites received training in both interventions during this 6-hour session. Training for the physical coaches included a 1.5-hour, one-to-one session with either the chief investigator or the intervention coordinator. Both the chief investigator and the intervention coordinator were research physical therapists with extensive experience working with the HD community in both clinical practice and research, who oversaw development of the training materials and ongoing support of the coaching staff. A coach's manual was provided to each coach, and was used as a guide for each of the training sessions. The manual gave an explicit, session-by-session guide, familiarized the coaches with the specific challenges of working with patients with HD, and offered a background to the intervention's SDT framework. In addition to the initial training sessions and coaching manuals, coaches received ongoing support from the intervention coordinator. This support was particularly important in helping guide coaches who have had little or no experience of working with patients with this relatively rare disease. Before each coach visited a participant for the first time, they were able to have a discussion with the intervention coordinator to assist them in interpreting a participant's baseline assessment scores. This allowed them to appropriately anticipate the ability level and potential needs of each participant. After the initial home visits, coaches had a further discussion with the intervention coordinator to develop realistic goals for the participants, based on each participant's particular interests and their current ability levels. Coaches were further encouraged to contact the intervention coordinator if they had any questions about the home visits as the intervention progressed, by either email or video-conferencing.	Training for the social coaches also included a 1.5-hour, one to-one training with the lead intervention coordinator prior to the start of the trial at each site, and the intervention coordinator was available for consultation throughout the trial. A coach's manual was provided to each coach, and was used as a guide for each of the training sessions. The coaching manual gave an explicit, session-by-session guide and familiarized the coaches with the specific challenges of working with patients with HD.
6	HOW	Describe the modes of delivery (eg, face-to-face or by some other mechanism, such as internet or telephone) of the intervention and whether it was provided individually or in a group.	The physical activity sessions were delivered face-to-face. Supportive telephone calls were conducted three times over the 14-week period.	The social interaction sessions were delivered face-to-face. Reminder telephone calls were conducted three times over the 14-week period.
7	WHERE	Describe the type(s) of location(s) where the intervention occurred, including any necessary infrastructure or relevant features	The physical activity sessions were delivered in each participant's home.	The social interaction sessions were delivered in each participant's home.
8	WHEN AND HOW MUCH	Describe the number of times the intervention was delivered and over what period of time, including the number of sessions, their schedule, and their duration, intensity, or dose.	Participants received 6 home visits and 3 interim telephone calls over the course of 14 weeks. Mean face-to-face session duration was 58.3 (8.9) minutes. Mean duration of telephone calls was 10.1 (6.7) minutes.	Participants received 6 home visits and 3 interim telephone calls over the course of 14 weeks. Mean face-to-face session duration was 50.7 (2.7) minutes. Mean duration of telephone calls was 10.7 (6.7) minutes.
9	TAILORING	If the intervention was planned to be personalized, titrated, or adapted, then describe what, why, when, and how.	The intervention was designed to be personalized to each individual by way of specific goal setting. Coaches worked together with participants to address individual barriers and facilitators to meeting goals. Goals were reviewed each session, and the participant and coach worked collaboratively toward meeting the goals. Coaches also provided individualized advice regarding progression of exercise and physical activity.	There was no specific tailoring planned for the social interaction intervention.
10	MODIFICATIONS	If the intervention was modified during the course of the study, describe the changes (what, why, when, and how).	The intervention was not modified during the course of the study.	The intervention was not modified during the course of the study.
11	HOW WELL	Planned: If intervention participation or fidelity was assessed, describe how and by whom, and if any strategies were used	Fidelity was measured by a combination of self-report checklists and independent assessment of the quality of the coaching sessions, based on audio recordings of the third coach home visit. The fidelity of the coach interactions was measured by assessing the extent to which each coach demonstrated efforts to promote autonomy, relatedness, and competence, and a self-assessment completed by the intervention coaches. A set of 10 questions with a mix of rating scales (directly comparable to those scores used to rate fidelity) and free text answers were developed and delivered to the coaches via a web-based survey. The questions covered each coach's views on the training provided, participation in the intervention to SDT, accompanying materials used in the delivery of the intervention, and the intervention in general. Respondents were asked to identify themselves so that their answers could be linked to individual fidelity scores.	Social intervention fidelity was assessed as total time spent in the home during the visit and length of interim telephone calls. This was chosen as the fidelity measure as we were looking to control for any confounds in relation to contact time. As a further evaluation, coaches were asked to record details of the conversations that we used to confirm the focus of discussions (and in particular to establish that the discussions were not related to physical activity).
12		Actual: If intervention participation or fidelity was assessed, describe the extent to which the intervention was delivered as planned.	Mean (SD) interaction time spent in the home for the physical activity intervention across all visits was 58.3 (8.9) minutes. Mean (SD) time spent in discussion across telephone calls was 10.1 (6.7) minutes. Median (range) number of physical activity intervention visits completed were 6 (0-6). The self-report checklists completed by each of the coaches at the first home visit indicated that in 100% of sessions (16/16), coaches introduced the participants to the Physical Activity Workbook, gave the participants the exercise DVD, and discussed the concept of goal setting with the participant. Sessions lasted on average 72.3 minutes. Fidelity scores for coach interactions, based on audio transcripts of the third intervention session, were assessed for 15 of the 16 participants. Overall scores ranged from 7 to 14 out of a possible 16 points, with a mean (SD) score across the coaches of 11.0 (2.4). Coach interactions scored an average of 2.5/4 for autonomy, 3.0/4 for relatedness, 2.7/4 for competence, and 2.8/4 for the overall impression. Self-assessment scores were on average higher than those assigned by the independent rater, namely 3.1/4 for autonomy, 3.3/4 for relatedness, and 3.0/4 for competence.	Mean (SD) interaction time spent in the home for the social intervention across all visits was 50.7 (2.7) minutes. Mean (SD) time spent in discussion across telephone calls was 10.7 (6.7) minutes. Median (range) number of social activity intervention visits were 6 (3-6).