**Background:** Many people do not regularly participate in physical activity, which may negatively impact their health. Current guidelines focus on weekly accumulation of at least 150 minutes of moderate to vigorous intensity physical activity (MVPA), often promoted as 30 minutes on at least five days per week. An alternative 'whole day' approach called Snacktivity™ encourages small, frequent 2–5 minute 'snacks' of MVPA throughout the day to accumulate the same weekly total. This approach may address common barriers such as lack of time and may help build confidence and habit formation. The primary aim of this feasibility trial is to assess the feasibility and acceptability of the Snacktivity™ intervention and trial methods to inform a subsequent phase III randomised trial.
**Methods:** This is a two-arm, multi-centre, individually randomised controlled feasibility trial aiming to recruit 80 inactive adults (aged ≥18 years) from health and community settings and social media in the East and West Midlands, UK. Participants are randomised 1:1 to receive either the Snacktivity™ intervention or usual care for 12 weeks. The Snacktivity™ intervention includes a brief consultation (approximately 5–7 minutes) delivered by healthcare providers or researchers, a Fitbit Versa 2 physical activity monitor, and a smartphone app (SnackApp™) that provides self-monitoring, prompts, goal setting, and feedback. The usual care group receives standard physical activity advice (150 minutes of MVPA per week) and a leaflet. The primary outcome is feasibility and acceptability, assessed by recruitment rate (target 80 participants over 5 months), Snacktivity™ adherence (≥4 bouts of MVPA lasting ≥2 minutes on average each day over 12 weeks, assessed by Fitbit), physical activity adherence (≥105 minutes MVPA per week on average), and attrition rate. Pre-specified traffic light progression criteria are defined: green (recruitment ≥80%, Snacktivity™ adherence ≥65%, physical activity adherence ≥60%, attrition <21%), amber (50–79%, 45–64%, 45–59%, 21–35%), and red (<50%, <45%, <45%, >35%). Secondary outcomes include MVPA, total physical activity, sedentary time, sleep, weight, waist circumference, blood pressure, depression/anxiety (Hospital Anxiety and Depression Scale), physical activity enjoyment, exercise self-efficacy, and habit strength. Data are collected at baseline and 12-week follow-up. A nested qualitative study will conduct semi-structured interviews with 20–25 participants and 12–15 healthcare providers to explore experiences and refine the intervention.
**Key Results:** The trial has so far recruited 72 participants who have completed their baseline assessment, and follow-up is ongoing. Recruitment to the qualitative study is ongoing and expected to be completed in February 2023. The paper reports no final results as it is a protocol.
**Clinical Implications:** If the feasibility criteria are met, a phase III trial will evaluate the clinical and cost-effectiveness of Snacktivity™ for increasing physical activity. Snacktivity™ offers a potentially scalable, time-efficient approach that could be integrated into routine healthcare consultations and daily life, addressing the common barrier of lack of time. It also encourages breaking up sedentary time, which may have additional health benefits. The findings will inform whether this alternative method of promoting physical activity is acceptable and feasible for the public and healthcare providers.