Slow-SPEED UK is an 18-month randomised, double-blind feasibility trial evaluating the delivery, adherence, and acceptability of a digitally supported physical activity programme in community-dwelling adults aged 40 and over with objectively confirmed hyposmia (reduced sense of smell) and low baseline physical activity.

Participants are randomly assigned 1:1 to either a full-dose activity-support programme (targeting a 100% increase in daily step count) or a very low-dose active control (targeting a 10% increase). Both arms are delivered via a smartphone application linked to a wearable activity monitor (Fitbit Charge 6), with personalised weekly goals expressed as relative percentages to maintain blinding. The study is not designed to test clinical efficacy.

Slow-SPEED UK is an 18-month, randomised, double-blind, parallel-group feasibility trial evaluating the feasibility, acceptability, and safety of a digitally supported physical activity programme in community-dwelling adults aged 40 and over with objectively confirmed hyposmia (reduced sense of smell) and low baseline physical activity. The study is not designed or powered to assess clinical efficacy or disease outcomes.

Participants are identified through two routes: the PREDICT-PD research platform at Queen Mary University of London, and the Smell and Taste Clinic at James Paget University Hospital NHS Foundation Trust. Potential participants undergo telephone pre-screening followed by confirmatory olfactory testing using the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Those scoring at or below the 15th percentile for age and sex are classified as hyposmic. Eligible individuals then enter a 4-week run-in period during which habitual daily step count is measured using a Fitbit Charge 6. Only those averaging fewer than 7,000 steps per day over at least 21 valid days proceed to randomisation. If recruitment falls below 70% of target after the first two months, and subject to Sponsor approval and REC amendment, the eligibility threshold may be broadened to fewer than 10,000 steps per day.

Eligible participants are randomly assigned 1:1 to one of two arms using sequentially numbered opaque sealed envelopes, stratified by age, sex, baseline activity level, and severity of smell loss. Double-blinding is maintained by presenting all activity goals within the smartphone application as relative percentage targets rather than absolute step values, ensuring neither participants nor investigators are aware of group allocation during the study period.

Both arms use the Slow-SPEED smartphone application integrated with the Fitbit Charge 6 wearable activity tracker. The intervention arm targets a progressive increase in daily step count up to 100% above individual baseline, with weekly goals increasing by 5% increments. The active control arm targets a 10% increase above baseline, with weekly goals increasing by 0.5% increments. Both arms use the same application structure, automated feedback, goal progression algorithm, and motivational features, including gamification, visualised progress, and optional non-directive motivational prompts. All participants also complete assessments using the Roche Mobile Application V2 (remote motor tasks performed every 6 weeks throughout the study period) and wear an Axivity AX6 accelerometer for 7-day bursts at baseline, 9 months, and 18 months.

Assessments are conducted at three time points: baseline (in-person), 9 months (remote), and 18 months (in-person). Baseline and 18-month in-person visits include olfactory testing (UPSIT), blood pressure measurement using standard sphygmomanometry, clinical motor assessment (MDS-UPDRS Part III), digital motor tasks (BRAIN test, Digital Finger Tapping, Manus Neurodynamica digital pen, NeuroClues eye-tracking), and a structured battery of questionnaires covering physical activity (LAPAQ), mood and anxiety (HADS), sleep quality (PSQI), quality of life, autonomic symptoms (SCOPA-AUT), and cognitive screening (MoCA). The 9-month remote assessment includes questionnaires and remote digital task completion. Physical activity is measured continuously throughout the study period via the Fitbit Charge 6.

The primary endpoint is the change in average daily step count from baseline (weeks 0-4) to the final four weeks of the 18-month study period, analysed descriptively as a measure of engagement and sustainability. Secondary endpoints include change in moderate-to-vigorous physical activity (MVPA), wearable-derived digital mobility and gait measures, motor and non-motor assessments, and participant-reported outcomes including health-related quality of life and usability of the digital tools.

The primary objective is to evaluate feasibility, defined by recruitment rate, retention, adherence to the intervention, engagement with digital tools, completeness of outcome data, and safety over 18 months. Secondary objectives are descriptive and exploratory. All analyses follow the intention-to-treat principle and emphasise estimation with 95% confidence intervals rather than hypothesis testing. Results will be used to inform the design and operational parameters of a future definitive trial.

Inclusion criteria

• Age ≥ 40 years
• Objective hyposmia, defined as scoring below the 15th percentile (adjusted for age/sex) on UPSIT
• Ability and willingness to provide written informed consent
• Proficiency in written and spoken English sufficient to complete study procedures.
• Willingness and ability to attend baseline (in-person), 9-month (remote), and 18-month (in-person) assessments.
• Access to telephone or internet for interim communication. Specifically, in possession of a suitable smartphone (screen size minimum 4.6 inch; Android version 9 or iOS version 15 or newer).
• Physical activity threshold: During the 4-week eligibility run-in, the mean daily step count must be <7,000 steps/day, calculated over ≥21 valid days (a valid day = ≥10 hours wear time or ≥1,000 steps). If recruitment after the first 2 months is <60-70% of target, and subject to TSC/Sponsor approval and REC amendment, eligibility may be broadened to <10,000 steps/day (i.e. participants averaging 7,000-9,999 steps/day become eligible).

Exclusion criteria

• Clinical diagnosis of PD, dementia, or other neurodegenerative conditions
• Severe or unstable medical or psychiatric illness likely to impair participation
• Use of agents known to alter olfaction (e.g. intranasal zinc, chronic corticosteroids)
• Current enrolment in an interventional study within the past 3 months (standard research retention guidance).
• Inability to complete study procedures in English, per investigator assessment
• Unable to give consent
• Participants not living independently in the community. Participants in nursing homes, hospitalised persons on in a non-institutionalised setting are excluded.
• Subject's personal smartphone is Fitbit-incompatible i.e. Huawei P8 Lite; Huawei P9 Lite; Xiaomi Mi 6; Huawei P20 Lite
• Activity level above threshold during eligibility run-in: mean daily step count ≥7,000 steps/day (or ≥10,000 steps/day if the broadened threshold is activated).

Blinding is maintained by presenting all activity goals within the Slow-SPEED smartphone application as relative percentage targets rather than absolute step values. Everyone involved remains unaware of group allocation throughout the 18-month study period. The use of an active control arm receiving a minimum activity target through the same digital platform, with identical application structure, contact frequency, and user experience across both arms, further supports blinding by minimising differences in participant experience between groups. Allocation concealment is achieved through sequentially numbered, opaque, sealed envelopes. To assess the integrity of blinding, participants will be asked at study completion to indicate which group they believe they were allocated to.