Knee osteoarthritis is a common cause of pain and reduced mobility in older adults. Many people have limited access to supervised rehabilitation programs, highlighting the need for simple and safe home-based treatment options.

This study evaluates whether a brief home-based quadriceps isometric exercise program can reduce knee pain in community-dwelling older adults. Participants perform short daily muscle contractions of the thigh muscles for 28 days. In addition, participants are assigned to receive one of four topical formulations (placebo, cannabidiol, arnica, or a combination of cannabidiol and arnica) to explore whether these products modify the exercise response.

The primary outcome is change in knee pain intensity measured using a visual analog scale. Secondary outcomes include adherence and safety. This pilot study aims to assess the feasibility, safety, and preliminary effectiveness of this low-cost and easily accessible strategy to inform future larger clinical trials.

This study is a prospective randomized 4×2 factorial pilot trial conducted in community-dwelling older adults with symptomatic knee osteoarthritis. The purpose is to evaluate the feasibility, safety, and preliminary effectiveness of a brief home-based quadriceps isometric exercise program for short-term pain reduction, and to explore whether topical cannabidiol (CBD), arnica, or their combination modify the exercise response.

Participants are randomly assigned to one of four topical treatment groups (placebo, CBD, arnica, or CBD + arnica) and stratified to either an exercise or no-exercise condition, resulting in eight factorial subgroups. Randomization is computer-generated with allocation concealment using sequentially numbered opaque sealed envelopes.

The intervention period lasts 28 days. Participants allocated to the exercise condition perform daily quadriceps isometric contractions at home consisting of three sets of 10-second near-maximal voluntary contractions with rest intervals, requiring approximately 6 minutes per day. Topical formulations are applied twice daily to the affected knee. Adherence is monitored using daily logs.

The primary outcome is change in knee pain intensity measured using a Visual Analog Scale (VAS) at day 28. Secondary outcomes include feasibility indicators (adherence and retention), safety (adverse events), and exploratory changes in anthropometric and body composition measures.

Analyses are exploratory and include factorial ANCOVA adjusted for baseline values to estimate main effects of exercise and topical treatment, as well as interaction effects. Effect sizes are calculated to aid clinical interpretation.

As a pilot study, results are intended to inform the design and sample size estimation of future adequately powered randomized controlled trials evaluating low-cost, home-based rehabilitation strategies for older adults with knee osteoarthritis.

Inclusion Criteria:

• Adults aged 65 years or older

Clinical diagnosis of chronic knee osteoarthritis according to American College of Rheumatology criteria

Knee pain for ≥3 months

Baseline knee pain intensity ≥4 on a 10-cm Visual Analog Scale (VAS)

Ability to walk independently with or without assistive devices

Ability to understand study procedures and provide written informed consent

Exclusion Criteria:

• Recent knee surgery or intra-articular injection within the last 3 months

Planned knee surgery during the study period

Severe neurological or cardiovascular conditions limiting exercise participation

Skin lesions or hypersensitivity to topical formulations

Current use of topical analgesics on the target knee

Cognitive impairment preventing adherence to the protocol

Participation in another clinical trial within the last 30 days

Individual participant data will not be shared due to institutional privacy policies and protection of patient confidentiality.

Participants were blinded to topical treatment allocation through identical packaging and appearance of formulations. Investigators responsible for data collection were not involved in treatment assignment. Exercise allocation could not be blinded due to the nature of the intervention, and outcomes were self-reported.