The goal of this clinical trial is to evaluate the efficacy of a 12-week digital home-based intervention program, consisting of a tablet-based exercise program with or without personal coaching, to promote physical activity (PA) in older adults after total hip arthroplasty (THA). The main question it aims to answer is:

• Does the combination of the digital exercise program and personal coaching lead to higher PA six months after THA compared to usual care among older adults?

Secondary questions are:

• Does the digital exercise program alone lead to higher PA compared to usual care?
• Does the digital exercise program combined with personal coaching lead to higher PA compared to the exercise program alone?

Participants' PA will be objectively measured with a body-fixed sensor at 1 week before THA (T1), 6 weeks after THA (T2), and 6 months (i.e. after THA (T3). After the postoperative assessment at T2, participants will be randomly assigned to one of three groups:

• 12-week tablet-based exercise program at home with virtual personal coaching for physical activity promotion
• 12-week tablet-based exercise program at home
• Usual care (control group, no additional intervention)

Hip osteoarthritis is common in older adults and is associated with limitations in activities of daily living, mobility, and quality of life. THA effectively reduces pain and improves physical functioning. However, patients often show no or only minimal increase in their typically low preoperative PA after THA. This lack of PA improvements may result from short rehabilitation periods, persistent sedentary habits, and methodological limitations of PA monitoring methods that focus mainly on frequency or temporal parameters (e.g. step count, walking or active durations).

Digital home-based training programs offer an opportunity for patients to continue structured exercises independently and at flexible times, extending postoperative care beyond standard rehabilitation. In addition, personal coaching that applies behavioral change techniques (BCTs) such as goal setting, action planning, self-monitoring with feedback, and barrier identification and management, may help break sedentary habits and promote PA. Recent advances in wearable sensor technology and processing algorithms now also enable a more detailed monitoring of real-world digital mobility outcomes (DMOs), allowing also capturing spatial-related parameters (e.g., walking distance, stride length, gait speed).

The iPATH study is a three-armed, assessor-blinded, randomized, parallel-group clinical trial evaluating the efficacy of two 12-week digital home-based intervention programs to promote PA in 213 older adults after THA:

1. Digital exercise program with personal coaching (Intervention Group 1)
2. Digital exercise program without personal coaching (Intervention Group 2)
3. Usual care (Control Group) - no additional intervention

Outcome assessments are conducted at 1 week preoperatively (T1), 6 weeks postoperatively (T2), and 6 months postoperatively (T3; operationally defined as 26 weeks after THA). Randomization occurs after the T2 assessment, which typically coincides with the end of standard inpatient or outpatient rehabilitation. The digital home-based exercise program in the two intervention arms is based on the Keep-On-Keep-Up (KOKU) app, which includes progressive strength and balance exercises to be performed three times per week. Personal coaching includes three virtual sessions designed to promote PA behavior change using BCTs (goal setting, action planning, self-monitoring and feedback [activity tracker], barrier identification and management). Participants in the control group also receive a tablet but have no access to the KOKU app and do not receive any personal coaching sessions.

The primary outcomes are the mean daily step count (first) and mean daily walking distance (second), derived from a body-fixed sensor attached to the participant's lower back for a maximum measurement period of 7 consecutive days using the newest validated processing alogorithms. Secondary outcomes include additional DMOs (e.g., walking duration, number of walking bouts, walking speed, stride length, cadence), life-space mobility, physical capacity, hip pain and function, psychological and cognitive factors (e.g., concerns about falling, executive functioning), falls, intervention adherence and acceptability, health-related resource use, intervention delivery costs, and safety.

The primary study hypothesis is that the combination of the digital exercise program and personal coaching will lead to higher PA six months after THA compared to usual care. Secondary hypotheses are that (1) the digital exercise program alone will increase PA compared to usual care, and (2) the combination of the digital exercise program and personal coaching will increase PA compared to the digital exercise program alone.

Inclusion Criteria:

• Age ≥65 years
• Coxarthrosis with indication for total hip arthroplasty
• Residence within a radius of ≤50 km from Heidelberg
• Ability to walk ≥10 m (with/without walking aid)
• Access to the internet (Wi-Fi) at home
• Written informed consent

Exclusion Criteria:

• Insufficient German language skills
• Insufficient hearing to communicate via (video) telephone
• Insufficient vision to recognize study materials
• Contralateral coxarthrosis with indication for total hip arthroplasty
• Severe medical condition illnesses that compromise physical fitness (heart failure classified as New York Heart Association [NYHA] class ≥3, heart valve defects associated with syncope, cardiac arrhythmia with dizziness, chronic obstructive pulmonary disease [COPD] with oxygen therapy, cancer with chemotherapy and/or radiation, Parkinson's disease with rollator use [Hoehn & Yahr stage ≥4])
• Living in a nursing home
• Planned major medical procedure within the next 6 months with inpatient hospital stay (e.g., further surgery)
• Simultaneous participation in another competing study
• Cognitive impairment (6-item Cognitive Impairment Test [6CIT] score >7 points)

In line with the principles of open science, anonymized individual participant data from the iPATH trial will be made available to qualified researchers after the primary evaluation has been completed and published. Data will be shared in a format that does not permit identification of individual participants and in full compliance with applicable data protection regulations (e.g., General Data Protection Regulation, EU data protection standards). Access to the data will be provided via a recognized open-access repository and require a formal application with a description of the proposed research project.

Anonymized individual participant data (IPD) will be made available approximately 6 months after publication of the primary evaluation results and will remain accessible without a predefined end date.

The study protocol will be submitted for publication in an open-access, peer-reviewed journal before the last patient is enrolled.

The statistical analysis plan (SAP) will be published alongside the primary evaluation results.

Access will be granted to qualified researchers affiliated with recognized academic or research institutions. A formal application including a research proposal is required, and applicants must agree to a data use agreement ensuring ethical use and compliance with EU data protection regulations. Approved applicants will access the data via the designated open-access repository.

Biostatistician responsible for data analysis remains blinded until the database is locked.