The effectiveness and cost effectiveness of Snacktivity™ as an intervention to promote physical activity and health outcomes: a study protocol for a multi-centre randomised controlled trial

Abstract

Background

A novel ‘whole day’ approach that could motivate the public to be more physically active is termed Snacktivity™. Consistent with guidance, the Snacktivity™ approach encourages the public to accumulate ≥ 150 min of physical activity in short 2–5-min ‘activity snacks’ of moderate-vigorous intensity physical activity throughout the day/week. Snacktivity™ also promotes muscle-strengthening activity twice per week. Following completion of research to co-design and develop the Snacktivity™ approach, the aim of this trial is to assess the effectiveness and cost-effectiveness of a Snacktivity™ intervention to increase physical activity and reduce future risk of disease in the population, compared with usual care.

Methods

A multi-centre, two-arm, individually randomised, parallel group, superiority trial, with an economic evaluation, will be conducted in 966 physically inactive adults. Participants will be recruited from National Health Service Trusts and organisations and non-National Health Service settings (e.g. community groups and social media). Participants will be individually randomized (1:1) to the Snacktivity™ intervention group or a usual care comparator group. The Snacktivity intervention involves two main components; a brief 5-min consultation about the principles and purpose of Snacktivity™; and access to technology support (mobile phone app called the SnackApp, linked to a Fitbit activity device (Versa 4)) that through behavioural change techniques promote self-monitoring of physical activity, habit formation, action planning and feedback on the number of activity snacks completed each day. The primary outcome is the difference in average minutes of moderate-vigorous physical activity between the groups at 12-months follow up, measured using a wrist worn accelerometer. Secondary outcomes include accelerometer-assessed average minutes per day of light, moderate, and vigorous intensity physical activity, time sedentary, weight and psychological health outcomes, at 12 month follow-up.

Discussion

Innovative interventions such as Snacktivity™, that aim to support the public to increase their physical activity each day are required. Findings could inform future public health guidance and public health messaging that seeks to raise awareness in the population of the potential benefits of Snacktivity™ for health.

Trial registration

ISRCTN: 12390945. Registered on 22 March, 2024.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-025-09391-8.

Administrative information

Title {1}	The effectiveness and cost effectiveness of Snacktivity™ as an intervention to promote physical activity and health outcomes: a study protocol for a multi-centre randomised controlled trial
Trial registration {2a and 2b}	ISRCTN: 12,390,945. Date of registration: 18/03/2024
Protocol version {3}	Version 5: 22/05/2025
Funding {4}	The trial is funded by the National Institute for Health and Care Research, (Programme Grants for Applied Research). Reference number RP-PG-0618–20008
Author details {5a}	A.J Daley: Centre for Lifestyle Medicine and Behaviour, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom. email: a.daley@lboro.ac.uk R.A Griffin: Birmingham Clinical Trials Unit, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom J.P Sanders: Centre for Lifestyle Medicine and Behaviour, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom C.L Edwardson: Diabetes Research Centre, College of Life Sciences, University of Leicester and Leicester Diabetes Centre, Leicester General Hospital, University Hospitals of Leicester NHS Trust, Leicester, United Kingdom L. Neal: Diabetes Research Centre, College of Life Sciences, University of Leicester and Leicester Diabetes Centre, Leicester General Hospital, University Hospitals of Leicester NHS Trust, Leicester, United Kingdom S. Lee: Centre for Lifestyle Medicine and Behaviour, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom M. Skrybant: School of Health Sciences, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom C.A Moakes: Birmingham Clinical Trials Unit, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom E. Gkini: Birmingham Clinical Trials Unit, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom E. Frew: Health Economics Unit, School of Health Sciences, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom C.J Greaves: School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom K. Gokal: Centre for Lifestyle Medicine and Behaviour, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom S. Tearne: Birmingham Clinical Trials Unit, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom H.M Parretti: Norwich Medical School, Faculty of Medicine and Health, University of East Anglia, Norwich, United Kingdom S.J.H. Biddle: University of Southern Queensland, Springfield, Australia and Faculty of Sport & Health Sciences, University of Jyväskylä, Finland K. Jolly: School of Health Sciences, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom S.M Greenfield: School of Health Sciences, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom R. Maddison: Institute for Physical Activity and Nutrition, Deakin University, Melbourne, Australia D.W Esliger: School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom L.B Sherar: School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom N. Mutrie: Physical Activity for Health Research Centre, University of Edinburgh, Scotland, United Kingdom T. Yates: Diabetes Research Centre, College of Life Sciences, University of Leicester and Leicester Diabetes Centre, Leicester General Hospital, University Hospitals of Leicester NHS Trust., Leicester, United Kingdom N. Ives: Birmingham Clinical Trials Unit, College of Medicine and Health, University of Birmingham, Birmingham, United Kingdom
Name and contact information for the trial sponsor {5b}	Sponsor Dr Christine Burt—Director of Research and Innovation, Birmingham Community Healthcare NHS Foundation Trust Research and Innovation, First Floor, 3 Priestley Wharf, Holt Street, Aston, Birmingham, B7 4BN Co-sponsor Dr Jennifer Johnson—Director of Research & Innovation Loughborough University Research & Innovation Office, Loughborough University, Loughborough, Leicestershire LE11 3TU
Role of sponsor {5c}	The sponsors and funders have not had a role in the study design, and will not have a role in the collection, management, analysis, and interpretation of data, writing of the report or the decision to submit the report for publication, nor will they have any authority over any of these activities

Introduction

Background and rationale {6a}

The population has become less physically active and spend more time sedentary, yet there is compelling evidence that inactivity and high levels of inactive sitting are both independently associated with poorer health and mortality [1–3]. Internationally, guidance states that over a week, the public should achieve ≥ 150-min of moderate-vigorous intensity physical activity (MVPA) [4, 5] and complete muscle strengthening-based activities ≥ twice per week. Updated guidance published in 2019–2020 now recognises the importance to health of physical activity bouts for < 10 min. Correspondingly, the necessity to complete physical activity in bouts of ≥ 10 min was removed from the guidance, which now stipulates that every minute of physical activity is important for health. It is concerning that most adults do not regularly achieve this guidance for physical activity, particularly given the benefits it has to offer to individuals’ physical and mental health [6, 7]. This highlights the importance now of putting in place effective interventions to increase population levels of physical activity. Public Health England have stated that if 1 in 10 adults aged 40–60 years in England achieved just 10-min of brisk walking per day, this action would save the National Health Service (NHS) and taxpayers ~ £310 million per year [8]. Guidance also states that the population should aim to reduce the amount of time spent in sedentary behaviours [5]. Evidence indicates that adults spend approximately 60–70% of their waking hours sedentary [9] and high levels of sedentary time are associated with an increased risk of morbidity and mortality [10–12].

Whilst guidelines for physical activity and sedentary behaviour have been published, guidelines themselves do not change behaviours, it’s having the means and motivation to achieve them that matters to health. The challenge now lies in finding effective ways to promote physical activity in the population. An alternative ‘whole day’ approach that could engage and motivate the public to be regularly physically active and break up sedentary time, is a concept called Snacktivity™ [13]. Snacktivity™ is a novel approach that focuses on encouraging the public to accumulate ≥ 150 min of MVPA per/week and completion of muscle-strengthening activities twice per/week, by promoting frequent ‘activity snacks’. Activity snacks last between 2 to 5 min and include activities such as brisk walking coffee breaks, leg raises during television adverts, using the stairs and not the lift, marching on the spot while waiting for the kettle to boil. Snacktivity™ can be completed throughout the day, and whilst undertaking daily tasks or as part of everyday living. See supplementary file for examples of Snacktivity™. Snacktivity™ does not require any preparation, special equipment or clothing and can be completed in any situation, environment, country or weather conditions. The potential convenience of accumulating Snacktivity™ through activities of daily living makes it accessible to almost everyone. Observational and experimental studies have reported improved cardio-metabolic and aerobic fitness from brief bouts of physical activity, providing the platform to test the usefulness of the approach in real world health settings [14–18].

Justification for the study

Our prior research has shown that the public like the Snacktivity™ approach, find it appealing, and are able to implement activity snacks within their daily lives [19, 20]. Analogous concepts to Snacktivity™ include ‘snackercising’ and vigorous/moderate intermittent lifestyle physical activity (VILPA and MV-ILPA), which the public have also viewed favorably [21]. By focusing on completion of small bouts of physical activity, Snacktivity™ may help to develop people’s confidence to become physically active, and then to maintain participation. Small changes are easier for people to initiate and then maintain than large changes [22], particularly for people who are living with a chronic disease or disability. A common barrier to physical activity is a perceived lack of time [23] and Snacktivity™ directly addresses this barrier as the approach is time-efficient by focusing on encouraging completion of activity snacks that only require a few minutes of time [24]. Simple, brief actions may become habitual more quickly than complex ones, suggesting that integration of small physical activity changes within everyday routines may be a more feasible approach for developing and sustaining physical activity, than trying to achieve large changes [25].

An inverse dose–response relationship is reported between physical activity and all-cause mortality. This relationship is characterised by a steep early slope, meaning the greatest gains in health are experienced when moving people who are sedentary to 2–3 metabolic equivalents (MET)/hours per week (~ 30-min per/week), than from moving more active people to doing marginally more [26, 27]. This means that for inactive people, any increase in physical activity is important [26, 28], providing impetus to investigate the effectiveness of Snacktivity™ in a clinical trial. Snacktivity™ also has the potential to reduce and/or break up prolonged time spent sedentary because the focus is on completing frequent bouts of physical activity across the day. Consistent with the NHS Making Every Contact Count initiative, we have shown that health professionals are able to integrate conversations about Snacktivity™ into routine consultations with patients [29], which could offer a population-based intervention for promoting Snacktivity™.

Objectives {7}

Following completion of studies to co-develop the Snacktivity™ concept, assess methods of trial recruitment, and determine the acceptability of the intervention (including the supporting Snacktivity™ intervention technology), the main objective here is to assess the effectiveness and cost-effectiveness of Snacktivity™ to increase physical activity and reduce future risk of disease in the population, compared with usual care (current guidance for physical activity).

Specific clinical aims and objectives

The primary objective is to assess whether Snacktivity™ increases MVPA at 12 months compared to usual care in adults who do less than the current recommended amount of MVPA per week. The trial aims to assess the effects of a Snacktivity™ intervention on accelerometer assessed average minutes per day of light, moderate and vigorous intensity physical activity, total minutes of physical activity, time sedentary, weight and psychological health outcomes at 3 and 12-month follow-up.

Economic aims and objectives

The aim of the economic analysis is to assess the cost-effectiveness of the Snacktivity™ intervention. It has the following objectives:

• To estimate the cost of the Snacktivity™ intervention to the health service;

• To measure how the Snacktivity™ intervention impacts health care use and levels of productivity;

• To assess whether the Snacktivity™ intervention leads to improved health-related quality of life (HRQOL) and improved wellbeing;

• To estimate the intervention cost-effectiveness in the short term (12 months) and if appropriate, the long term (lifetime).

Trial design {8}

A multi-centre, open-label, two-arm, parallel group, individually randomised trial, with an economic evaluation, to test the superiority of Snacktivity™ compared with usual care (current guidelines for physical activity) will be conducted.

Methods: Participants, interventions and outcomes

Study setting {9}

The study will take place across the United Kingdom (UK) and involve NHS, universities and community health partners. Recruitment will take place from NHS Trusts/settings and non-NHS settings in the UK A list of planned study sites can be found at https://www.birmingham.ac.uk/research/bctu/trials/primary-care/snacktivity. The Snacktivity™ trial and intervention have been purposefully designed to be inclusive and suitable for those living with a disability.

Eligibility criteria {10}

The trial has the following inclusion and exclusion criteria:

Inclusion criteria

• Aged ≥ 18 years

• Completes < 150 min per week of MVPA as assessed by the Physical Activity Vital Sign (PAVS) Questionnaire [30]

• Own a mobile phone capable of hosting apps (e.g. Apple iOS 16.4 + and Android11 +)

• Able to provide informed consent

• Agreement for participants’ health care professional/GP to be notified of involvement in the trial

Exclusion criteria

• Unable to understand English sufficiently to complete the trial assessments

• Women known to be pregnant or breastfeeding

• Inpatient, bedbound or unable to complete physical activity

Who will take informed consent? {26a}

Consent to screening

Potential participants will be asked to provide consent for screening of the trial eligibility. It is expected that most potential participants will complete the consent to screening form and the screening questions via an online link. There will be a brief outline of the trial at the beginning of the screening form, as well as links to the participant information sheet (PIS) and a video summarising the trial that potential participants can view before completing the screening form. Potential participants who complete a paper screening form will be provided with a paper copy of the PIS and a quick response (QR) code which, when scanned, directs them to the trial website for more information.

Consent to the trial

Consent for trial related processes will be obtained before participants join the trial and will be recorded electronically via an online method known as eConsent, completed by participants remotely or by the trial team by telephone/video call. People considered eligible will be invited to take part in the trial. All potential participants will have the opportunity to ask questions and are informed that participation is voluntary and that they will be free to refuse to take part and withdraw from the trial at any time. See supplementary document for a copy of the eConsent form.

Additional consent provisions for collection and use of participant data and biological specimens {26b}

Not applicable as no specimens or samples will be collected.

Interventions

Explanation for the choice of comparators {6b}

Usual care

Prior to, or during the consultation, participants randomised to usual care will be provided with a standard physical activity factsheet. Intervenors (healthcare professionals (HCPs)/researchers) will only discuss (for 1–2 min) the current guidance for physical activity, advising participants to work towards the accumulation of at least 150-min of MVPA per week. In NHS settings, HCPs will discuss this usual care information during routine consultations. For participants recruited via non-NHS settings, a researcher will schedule a video/telephone call with participants to deliver the usual care information. The researcher will mimic the role of a HCP and deliver information as described above.

Intervention description {11a}

Summary and context

Using behavioural change techniques, the Snacktivity™ intervention aims to promote the importance of physical activity through participation in activity snacks, the usefulness of the Snacktivity™ approach, encourage regular self-monitoring of activity snacks to achieve sustained physical activity, goal setting for daily Snacktivity™, as well as promote action planning and implementation strategies. There are two main components within the Snacktivity™ intervention: HCPs (participants recruited via NHS Trusts/settings) or researchers (participants recruited via non-NHS settings) raising and encouraging Snacktivity™ with participants in their consultations; and the promotion of technology to support behaviour change and sustained engagement in activity snacks/physical activity (via the SnackApp mobile phone app and the Fitbit device as described below). The role of the HCP/researcher is to raise the topic of Snacktivity™/physical activity, to signpost participants to the SnackApp for further advice and support, and to encourage participants to use the provided Fitbit device to facilitate their engagement with activity snacks and to obtain feedback on their behaviour. All types of physical activity will be encouraged, and the behavioural goal is for participants to work towards achieving ≥ 150-min of MVPA per week and engage in muscle-strengthening based activityat least twice per week.

The Snacktivity™ intervention is based on self-regulation theory and the habit formation model [31, 32]. Our own work and other studies have shown self-regulation/self-monitoring to be an effective foundation strategy for health behaviour change [33, 34]. Self-monitoring of activity snacks may act as a reward for individuals who control their physical activity behaviour, and are then provided with positive feedback from the monitoring process, thereby enhancing their motivation and reducing the potential for relapse. Frequent monitoring and reflection of Snacktivity™ progress may also improve self-efficacy for participation in both short and longer bouts of physical activity, which could improve other health outcomes, such as weight and mental health [5, 32, 33]. Encouragement of self-monitoring and recording of Snacktivity™/activity is a simple concept for HCPs to advocate as a public health message and simple for people to understand and implement within their lives.

Studies have reported that some groups in society, particularly women, find physical activity difficult to achieve, for example due to cultural or religious reasons, safety concerns, limited mobility, or a lack of time to attend local physical activity opportunities or gyms etc. [35, 36]. As activity snacks can be completed in any environment, including at home, the approach may be acceptable to almost all members of the adult public.

The Snacktivity™ consultation

Intervenors will deliver the Snacktivity™ consultation following a standard protocol. Participants recruited via NHS settings will receive their consultation within a routine health care appointment with the HCP. HCPs can decide when the best time is to raise the topic of Snacktivity™ within the healthcare consultation. If a participant is recruited via a non-NHS setting, a researcher will schedule a video or telephone call with participants to deliver the Snacktivity™ consultation. The researcher will mimic the role of a HCP and will deliver the information following similar processes to HCPs. The Snacktivity™ consultation is intended to be brief and last 5 min.

The HCP/researcher will discuss the purpose of Snacktivity™, the hypothesis underpinning its principals, how it differs from standard physical activity advice, and provide examples of activity snacks. Participants will receive standard guidance about the importance of physical activity and advised to accumulate their physical activity through Snacktivity™. A Snacktivity™ pictureboard illustrating examples of activity snacks will be used to support these conversations. See supplementary file. The role of the HCPs/researchers is also to raise the topic of Snacktivity™/physical activity, to signpost participants to the SnackApp for further advice and support, and to encourage participants to use a provided Fitbit device to facilitate their engagement with completing activity snacks. Intervention participants will be given access to the SnackApp and sent a free of charge Fitbit device once the HCP/researcher has delivered the Snacktivity™ intervention consultation.

SnackApp and Fitbit physical activity device

Given the number of people who are physically inactive in the population we need interventions with high reach, which can be achieved by mobile phone health interventions. Smartphone-based interventions are attractive as most people in the UK own a smartphone [37]. To facilitate habit formation of activity snacks, a mobile phone application called the SnackApp will generate regular reminders and notifications for participants to engage in activity snacks. Self-monitoring may be particularly relevant for developing Snacktivity™ habits because it may be more difficult for people to easily recall how many activity snacks they have achieved each day. The design and content of the SnackApp is based on previous research [29, 38–41]. Some of the principles of existing mobile phone apps and our previous experiences of developing apps for promoting physical activity and lifestyle behaviours have guided the development of the SnackApp [40, 41]. User testing of the SnackApp and Fitbit device suggested that physically inactive adults will engage with the SnackApp, indicating its applicability of use [40].

The key features in the SnackApp are that it automatically calculates daily number of activity snacks/physical activity and provides feedback on inactive time via a Fitbit device (see below for details), provides prompts after prolonged periods of inactivity, encourages regular activity snacks throughout the day, generates individualised motivational push notifications to participants mobile phones based on prior behaviour, encourages goal setting for activity snacks/physical activity and offers individualised feedback related to goal achievement to encourage adherence and facilitate self-efficacy. The SnackApp provides educational content regarding benefits of activity snacks, examples of activity snacks, and a social support forum for the completion of activity snacks. To promote habit formation, participants will be able to plan when and where to perform their activity snacks through an action planning function. Details regarding the specific content and functions of the SnackApp have been described in previous publications [38–40].

The Fitbit device (Versa 4) will display a bespoke Snacktivity™ clock face that provides feedback on the number of steps, activity snacks and active minutes (MVPA) that have been completed by participants so that they can readily see this information at a glance of their device. See supplementary file for illustrations. Participants will be offered remote support from the research team to set-up the Fitbit and SnackApp on their mobile phone.

Training of HCPs/researchers to deliver the Snacktivity™ intervention

An online media-based training module to deliver the intervention has been developed and used in previous research [19, 38–40]. The training module will include information on the importance of adhering to the trial protocol, the research trial procedures, trial design and ways of delivering the Snacktivity™ intervention. The training for intervenors aims to demonstrate different ways in which Snacktivity™ can be promoted within consultations. Intervenors will be trained to promote the rationale for Snacktivity™, the benefits of physical activity for health, give examples of Snacktivity™, and explain implementation plans and action planning. Intervenors will be asked to highlight to participants that Snacktivity™ will work best if they develop habits or routines and ‘what needs to change’ to achieve this. The purpose of the Fitbit device and SnackApp for facilitating self-monitoring of snacks will be discussed and use of this technology will be encouraged. Video clips are included in the training module that show the Snacktivity™ intervention being delivered in practice so that intervenors understand how the intervention might be delivered by them. A Snacktivity™ consultation fidelity checklist will be completed by the HCP/researcher to aid delivery of the intervention and to provide a reminder of areas that must be covered.

Intervention fidelity and process evaluation

With the consent of participants, 10–20% of all Snacktivity™ intervention consultations will be audio-recorded to assess for fidelity using an encrypted Dictaphone or a secure and General Data Protection Regulation (GDPR) compliant online conferencing tool. The recording of consultations will provide the opportunity to assess whether the intervention is being delivered according to the intervention checklist. A range of strategies to reinforce intervention fidelity will be used and include: training HCPs/researchers to deliver the intervention per protocol; explaining the intervention logic model; development and use of a standardised training resource; checks for intervention ‘receipt’ and enactment by checking whether participants attended their consultation; and whether the Fitbit device/SnackApp is activated by participants.

Criteria for discontinuing or modifying allocated interventions {11b}

There are no plans to discontinue the trial or modify the allocated interventions.

Strategies to improve adherence to interventions {11c}

Within the Snacktivity™ intervention, intervenors will promote the importance of physical activity for health, discuss any barriers participants may have to adopting a physically active lifestyle that includes Snacktivity™, and discuss options for action planning to support behaviour change. The SnackApp has functions for self-monitoring of activity snacks, active minutes and steps, goal setting, as well as action planning and personalised feedback on behaviour. Also included is engaging educational content and social support features (i.e. community forum). Push notifications aimed at encouraging regular wear of the Fitbit, motivational messages towards meeting activity snacks goals and educational messages. Monitoring of adherence by participants involves tracking SnackApp usage, and activity snack completion via the SnackApp.

Relevant concomitant care permitted or prohibited during the trial {11d}

This heading is not relevant to the trial.

Provisions for post-trial care {30}

Post trial care will not be offered.

Outcomes {12}

The full schedule of assessments for each outcome or variable of interest are detailed in the supplementary file. The primary outcome is average weekly minutes of MVPA at 12 months measured using the Axivity (AX3) accelerometer. The following secondary outcomes will be assessed using an accelerometer at 3- and 12-months post-randomisation:

• proportion of participants meeting the guidance amount of ≥ 150 min of MVPA per week

• average total minutes of physical activity per day

• average number of minutes of light, moderate and vigorous physical activity per day

• average minutes of MVPA accumulated in bouts lasting ≥ 2, ≥ 5 and ≥ 10-min per day

• average number of MVPA bouts lasting ≥ 2, ≥ 5 and ≥ 10-min per day

• average magnitude of dynamic wrist acceleration per day (as a proxy for total volume of activity)

• average intensity gradient per day (no unit for this variable)

• average minutes of sedentary time per day

• average time (minutes) spent in prolonged (≥ 30 min) sedentary behaviour per day

• average number of prolonged sedentary bouts per day

• average sleep duration (minutes/day) and average sleep efficiency (quality) (%/day)

The following outcomes will also be assessed 3- and 12-months post-randomisation:

• weight (objective (or self-reported if participant is unable to provide objective weight))

• depression/anxiety (Hospital Anxiety and Depression Scale (HADS)) [42]

• quality of life (EQ-5D-5L questionnaire) [43]

• wellbeing (ICECAP-A questionnaire) (to be used in the cost effectiveness analyses) [44]

• self-reported sedentary behaviours (Workforce Sitting Questionnaire (WSQ)) [45]

• sitting (International Physical Activity Questionnaire (IPAQ sitting question only))[46]

• self-efficacy for physical activity (Self-Efficacy for Exercise questionnaire) [47]

• enjoyment of physical activity (Physical Activity Enjoyment Scale (PACES)) [48]

• habitual physical activity (Self-Report Habit Index (intervention group only)) [49]

• participation in activity snacks assessed by Fitbit™ data (intervention group only)

• serious adverse events (SAEs) related to participation in physical activity

Participants’ experiences of the trial will be captured using single item exit questions at 3- and 12-months follow-up.

Snacktivity™ process outcomes (intervention group only)

Questionnaire feedback on the Snacktivity™ intervention will be collected from participants randomised to the intervention group, focusing on the use of the SnackApp and the suggested activity snacks. The Fitbit will provide data across the intervention on the following: steps, distance, bouted active minutes, inactive time, sleep and awake time, wear time, and minutes of light, moderate and vigorous intensity physical activity.

Participant timeline {13}

The trial flow diagram (Fig. 1) outlines participants’ journey through the trial. A schedule of study assessments is detailed n Fig. 2 (SPIRIT participant timeline).

Fig. 1.

Trial flow diagram

Fig. 2.

Participant timeline: Schedule of enrollment, interventions, and assessments

Sample size {14}

The sample size is based on detecting a difference of 30 min in weekly MVPA between the two trial groups (Snacktivity™ and usual care) with a standard deviation (SD) of 120 min. Thirty minutes is considered the minimum clinically important difference and a relatively small standardised effect size (0.25) has been selected to ensure it is consistent with the brief intervention we are proposing. A review of the literature found a wide range of data related to the variability in the SD of MVPA, typically due to the broad and varied inclusion/exclusion criteria used in trials and the diverse samples recruited. Such SD included 83 [50], 102, 128 [51], 108, 144 [52], and 154, 169 [53, 54]. Given this, we have adopted a conservative approach and selected an SD of 120 min to calculate the sample size, whilst acknowledging there will be some degree of variability. A total of 966 participants (90% power) over 16 months are required. It is expected that NHS settings will recruit approximately 35% (n = 338) and non-NHS-settings 65% (n = 628) of the total sample.

Recruitment {15}

Identification

Recruitment will take place from both NHS Trusts/settings and non-NHS settings. NHS settings are defined as any service that is delivered to members of the public by an HCP employed/funded by the NHS, and includes community health services, primary care and general practices, secondary care hospitals). We anticipate NHS Trusts/settings will search their databases using search protocols developed by the lead Clinical Research Network (CRN) and invite potential participants based on eligibility at the pre-screening stage. Potential participants who are aged ≥ 18 years and have a healthcare consultation booked during the recruitment phase of the trial will be invited to take part. Alternatively, HCP’s can ask patients if they would be interested in participating and offer the trial invitation pack in consultations. Non-NHS settings will include recruiting via the National Institute for Health and Care Research (NIHR) Be Part of Research platform, public health organisations and community support groups.

Assignment of interventions: allocation

Sequence generation {16a}

Participants will be randomised at the level of the individual in a 1:1 ratio to receive either the Snacktivity™ intervention or usual care. A minimisation algorithm (with random element) will be used within the randomisation system to ensure balance in the intervention allocations over the following variables: route of recruitment (NHS, Non-NHS), total minutes per week of self-reported physical activity (at baseline assessed using the PAVS) (0–49, 50–99, 100–149 min), age group (18–45, 46 + years old), gender (male, female, prefer not to say). Following randomisation, participants will be informed which group they have been allocated to (by text, email or phone call). Randomisation will be provided by Birmingham Clinical Trials Unit (BCTU) using a secure online system, thereby ensuring allocation concealment. Randomisation can only occur once the baseline questionnaire has been completed and the accelerometer data has been checked for completeness (at least 4 valid days – defined as > 16 h of data per day).

Concealment mechanism {16b}

A central online randomisation system hosted by the trial coordinating centre will ensure concealment of the next treatment allocation. To avoid the possibility of the intervention allocation becoming predictable, a random element will be included in the minimisation algorithm.

Implementation {16c}

The randomisation system will be developed and provided by the trial coordinating centre. Unique log-in usernames and passwords will be provided to those delegated the role of randomising participants. Following randomisation, participants will be informed which group they have been allocated to (by text, email or phone call).

Assignment of interventions: Blinding

Who will be blinded {17a}

As an open trial, participants will not be blinded to the purpose of the trial. Baseline data will be collected before randomisation and follow-up data will be collected remotely with no direct involvement from the research team other than to post the accelerometer and send a link to participants for completion of the study questionnaires. The trial statisticians will not be blinded to group allocation.

Procedure for unblinding if needed {17b}

Not applicable as this is an open trial.

Data collection and management

Plans for assessment and collection of outcomes {18a}

Participants will be sent a link to their email address and/or mobile phone to complete the baseline questionnaire directly into the trial database. A paper copy of the questionnaires can be posted to participants if requested. To assess weight, participants will be asked to upload a picture of themselves standing on their home weighing scales with their weight clearly visible. If participants have difficulty uploading a photograph of their weight (objective reading), we will accept participants entering their weight into the questionnaire without a photo (self-reported reading). The research team will mail the accelerometers directly to participants. Participants will be asked to wear the accelerometer for up to nine days (seven full days plus a partial day, the day before and day after the seven full days) and to complete the accompanying diary (which records the time participants went to sleep and the time they woke up) every day. Participants will post (free of charge) the accelerometer and diary back to the research team, where researchers will check the accelerometer data for completeness. If the accelerometer is received back and the data is invalid (less than 4 valid days), a new accelerometer will be posted to ensure sufficient valid data is obtained. Participants will only be randomised into the trial if they provide valid accelerometer data and complete the study questionnaire. These processes will be repeated for the collection of data at 3- and 12-month follow-up. The study case report forms (CRFs) and study questionnaires are available from the first author on reasonable request.

Plans to promote participant retention and complete follow-up {18b}

Participants will receive a £30 high street shopping voucher (£60 total) once they complete (i.e., provide complete data) follow-up at 3- and 12-months. Participants can withdraw from the intervention but still provide follow-up data. For retention, participants will be contacted by text, email, or telephone call to remind them to complete the questionnaire and return the accelerometer. Questionnaires will be completed online to make data capture easier, and participants will be able to return the accelerometer with ease using any Royal Mail post box.

Data management {19}

Processes will be employed to facilitate the security, accuracy and completeness of the trial data. These processes will be detailed in the trial specific data management plan and include the processes of data entry and self-evident corrections on the trial data. Data entry will be completed by the trial office and participants via a bespoke trial database. The data capture system will conduct automatic range checks for specific data values to ensure high levels of data quality. The trial office will endeavor to obtain any missing questionnaire data by contacting participants. Overdue and missing data will be reviewed every two weeks.

Confidentiality {27}

Personal data and sensitive personal data recorded on all documents will be regarded as strictly confidential and will be handled and stored in accordance with the Data Protection Act 2018 (and subsequent amendments). Participants will only be identified by their unique trial identification number on CRFs and on any correspondence with the trial office. The trial office will maintain the confidentiality of all data and not disclose information by which participants may be identified with any third party.

Plans for collection, laboratory evaluation and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}

Not applicable as no laboratories are involved in the trial and no biological specimens will be collected.

Statistical methods

Statistical methods for primary and secondary outcomes {20a}

A separate Statistical Analysis Plan (SAP) will be produced and will provide a more comprehensive description of the planned statistical analyses. All analyses will be based on the intention to treat principle. For all outcomes, appropriate summary statistics and differences between groups e.g., mean differences, or risks ratios, will be presented, along with corresponding confidence intervals. Where possible intervention effects will be adjusted for the trial minimisation variables (route of recruitment, age, gender, baseline physical activity), and baseline values (where appropriate/available).

Primary outcome

The primary outcome of minutes of MVPA will be expressed as weekly average time and reported by group using means and standard deviations. A mixed-effects repeated measures model will be fitted and results presented as adjusted mean differences and 95% confidence intervals at each time point (3- and 12-months), with 12-months being the primary time point. Time will be included as a categorical (fixed) variable in the model. To allow for a varying treatment effect over time, a time by treatment interaction parameter will be included in the model as standard.

Secondary outcomes

Secondary outcomes of a continuous nature (measured at 3- and 12-months) will be analysed as per the primary outcome. Secondary outcomes which are considered binary (e.g. the proportion of participants meeting the guidance amount of ≥ 150 min of MVPA per week) will be summarised using frequencies and percentages. A regression model will be fitted and results presented as adjusted risk ratios, risk differences and 95% confidence intervals. Secondary outcomes which are collected in the Snacktivity™ group only will be presented using summary statistics.

Cost effectiveness

A separate health economics analysis plan will provide a more comprehensive description of the planned analyses. In brief, the economic analyses will be conducted on an intention to treat basis. The following costs will be collected: intervention-related costs including staff costs for delivering the physical activity advice and App-maintenance costs, participant-recorded health care use including prescription medication, and productivity costs. Wellbeing and HRQOL effects will be measured at baseline, 3- and 12-months using the ICECAP-A, and the EQ-5D-5L, respectively [43, 44]. The incremental costs will then be combined with the incremental outcomes to form a cost-effectiveness analysis (CEA), where the result will be expressed as ‘cost per recommended MVPA per week’ achieved. A cost-utility analysis will combine the costs with outcome to estimate the ‘cost per QALY’. Both the CEA and cost-utility analysis (CUA) will be conducted from a health and social care perspective. In addition, a ‘cost per capability’ achieved will be estimated by combining the costs from a broader perspective (including productivity costs) offset against improvements in wellbeing, measured using the ICECAP-A. The above analyses will be conducted as a within-trial economic evaluation, therefore only using data collected over the 12-month period. All incremental costs and outcomes will be presented as adjusted difference in means with a 95% confidence intervals and p-value. Missing data will be explored and imputed using the most appropriate imputation technique. Sensitivity analysis will be conducted.

If the intervention demonstrates superiority in terms of the primary outcome in comparison to usual care, Markov decision modelling will be used to extrapolate beyond trial findings and will be populated using both data on costs and outcomes within the trial and reviews of previously published studies. The exact nature of the modelling and the health states will be determined using information from a review of previously published modelling studies of interventions to promote physical activity and expert opinion. Model parameters will be sought from the trial and review of previously published studies.

Interim analyses {21b}

No interim analyses are planned.

Methods for additional analyses (e.g. subgroup analyses) {20b}

Subgroup analyses will be performed based on the same variables used in the minimisation algorithm (route of recruitment, total minutes per week of physical activity assessed using the PAVS, age at randomisation and gender) and performed on the primary outcome and the key secondary outcome only (proportion of participants meeting the guidance amount of ≥ 150 min of MVPA per week. Other planned exploratory subgroup analyses will be undertaken for body mass index (BMI) (underweight, healthy weight, overweight, obesity); disability (self-reported as yes, no, prefer not to say); ethnicity; and index of multiple deprivation [55] (divided into quintiles from most to least deprived) for the primary outcome only. The effects of these subgroups will be examined by including an intervention group by subgroup interaction parameter in the regression model, which will be presented alongside the effect estimate and 95% confidence intervals within subgroups.

Methods in analysis to handle protocol non-adherence and any statistical methods to handle missing data {20c}

In the first instance, analysis will be undertaken on received data only with every effort made to follow-up participants to minimise any potential for bias. To examine the possible impact of missing data on the results, and to make sure we are complying with the intention-to-treat principle, sensitivity analysis will be performed on the primary outcome measure [56]. Full details will be included in the SAP, but in summary, missing data will be imputed using multiple imputation.

Plans to give access to the full protocol, participant level-data and statistical code {31c}

The full protocol is available from the Birmingham Clinical Trials Unit. The datasets used and/or analysed during the study can be made available by the last author (NI) upon reasonable request and once the trial has been published. Data transfer will need to occur in agreement with the research collaboration and data transfer guidelines of the Birmingham Clinical Trials Unit and Loughborough University.

Oversight and monitoring

Composition of the coordinating centre and trial steering committee {5d}

A joint independent trial steering and data monitoring committee (TSC/DMC) has been formed to guide and oversee this trial. The TSC/DMC will meet via video call/face-to-face at least twice a year or as required. This is a general population study, the intervention is considered low risk, and no serious adverse events are expected as a result of the intervention. Membership and duties/responsibilities are outlined in the DMC/TSC Terms of Reference.

The trial management group (TMG) includes individuals responsible for the day-to-day management of the trial, including the Chief Investigator (CI), Programme Manager, Trial Statistician(s), Trial Programmer, Trial Manager, Data Manager, Research Associate, Patient/Public Advisory Group (PAG) lead and PAG representatives. The role of the group is to monitor all aspects of the conduct and progress of the trial, ensure that the protocol is adhered to and take appropriate action to safeguard participants and the quality of the trial itself. The TMG will usually meet every month and will monitor participant recruitment. A programme management committee (PMC) will oversee the administration and management of specific aspects of the trial, to include the patient advisory group, procedures related to the accelerometers and distribution of the Fitbit devices, and the financial management of the trial.

Patient and Public Advisory Group (PAG)

This trial is supported by the PAG that consists of eight members of the public from a range of backgrounds with different attitudes towards physical activity. The PAG is facilitated by a Public Involvement Lead and PAG members contributed to the development of the Snacktivity™ intervention through attending quarterly meetings or completing tasks remotely (e.g. providing feedback on public-facing documentation) in earlier work within the overall Snacktivity™ programme of work. PAG members were also represented on the TMG and joint TSC/DMC groups and the authors would like to formally acknowledge these contributions.

Composition of the data monitoring committee, its role and reporting structure {21a}

A joint TSC/DMC has been created to support the trial, which is independent from the sponsor. The TSC/DMC charter is available on request from the first author.

Adverse event reporting and harms {22}

There is no reason to assume that this trial will lead to an excess of adverse events (AEs). The intervention consists of HCPs/researchers promoting short bouts of MVPA within everyday life and use of a commercially available physical activity tracker to monitor activity, along with a mobile app to log movement, none of which are likely to create harm. Furthermore, the promotion of physical activity by HCPs is already part of standard care and has been demonstrated as being low risk for all citizens in England as per the NHS Making Every Contact Count initiative [57]. Therefore, no AEs will be collected for this trial, however, the reporting HCP will still record any relevant events in participants’ medical records in accordance with Good Clinical Practice (GCP) policy (NHS Trusts/settings only). All events which meet the definition of serious will be recorded in the participants notes (except if the participant is recruited from a non-NHS setting), throughout participants’ time in the trial. Participants recruited from non-NHS settings, the trial will identify any potential SAEs from the 3- and 12-month questionnaires and complete the appropriate SAE processes.

Frequency and plans for auditing trial conduct {23}

The investigator will permit trial-related monitoring, audits, ethical review, and regulatory inspection(s) at their site and provide direct access to the investigator site file (ISF). The investigator will comply with these visits and any required follow-up. Sites are also requested to notify the trial office of any relevant inspections or local audits.

Plans for communicating important protocol amendments to relevant parties (e.g. trial participants, ethical committees) {25}

Any modifications to the protocol which may impact the conduct of the study, potential benefit of the patient or may affect patient safety, including changes of study objectives, study design, patient population, sample sizes, study procedures, or significant administrative aspects, will require a formal amendment to the protocol. Such amendments will be agreed upon by Birmingham Community Healthcare NHS Foundation Trust (BCHC) as sponsor, and approved by the Ethics Committee prior to implementation, and notified to the health authorities in accordance with local regulations.

Dissemination plans {31a}

Dissemination will be through culturally adapted co-developed outputs on partner websites, presentations with stakeholders, policy reports, infographics, publications, conferences, public engagement events, adding references to relevant Wikipedia pages and any ideas suggested by our PAG. Results will also be shared with study participants upon request. Authorship will follow the International Committee of Medical Journal Editors (ICMJE) guidelines. Anonymized data and protocols will be shared based on data-sharing agreements.

Discussion

Public health guidance for physical activity now acknowledges the positive contribution that short bouts of physical activity can have for physical and mental health, and that any amount of physical activity is better than none at all [4, 5]. Whilst guidance provides direction on the amount of physical activity that should be completed, they are not designed to motivate and support the public to adhere and integrate physical activity into their lives. Moreover, guidance needs to be translated into messages and interventions that are persuasive, attractive, motivating and habit forming and Snacktivity™ may achieve these outcomes. This change to guidance to remove the necessity for physical activity to be accumulated in bouts of 10 min or more and the inclusion of ‘Every Minute Counts’ for health, has provided opportunities now to develop and test novel and innovative interventions to promote short(er) bouts of physical activity, to reduce future risk of diseases in the population. The findings of this research could influence health policies and clinical guidelines across the world.

Limitations

Several limitations of this study should be acknowledged: The study is limited to physically inactive adults, which restricts the generalizability of findings to other more physically active populations. Although substantial efforts will be made to recruit a diverse sample, this is dependent on those willing to participate. The protocol includes follow-up at 12 months post randomisation, which limits the ability to determine whether the potential benefits of the Snacktivity intervention are maintained over time.

Strengths

The study is based on substantial prior co development research. The trial seeks to recruit participants in a range of health and community settings across the United Kingdom. The primary outcome of physical activity will be assessed by accelerometry. Follow-up will be at 3- and 12-months and a process evaluation study has been included in the protocol. If proven effective, the Snacktivity intervention could become an affordable, accessible option for health services in the Uk and beyond.

Trial status

The trial will follow protocol Version 5 (dated 22/05/2025). Recruitment began in July 2024 and is expected to be completed in November 2025 with follow-up of all participants completed in November 2026.

Abbreviations

AE

Adverse event

ARC

Applied Research Collaboration

BCHC

Birmingham Community Healthcare NHS Foundation Trust

BCTU

Birmingham clinical trials unit

BMI

Body mass index

CEA

Cost-effectiveness analysis

CI

Chief investigator

CRF

Case report form

CRN

Clinical Research Network

CUA

Cost-utility analysis

CVD

Cardiovascular disease

DMC

Data monitoring committee

DMP

Data management plan

GCP

Good clinical practice

GDPR

General data protection regulation

GP

General practitioner

HADS

Hospital Anxiety and Depression Scale

HCP

Health care professional

HRQOL

Health-related quality of life

ICECAP-A

ICECAPability measure for adults

iOS

IPhone operating system

IPAQ

International Physical Activity Questionnaire

ISF

Investigator site file

MET

Metabolic equivalents

MI

Multiple imputation

MV-ILPA

Moderate-to-vigorous intermittent lifestyle physical activity

MVPA

Moderate-vigorous intensity physical activity

NIHR

National Institute for Health and care Research

NHS

National Health Service

PACES

Physical Activity Enjoyment Scale

PAG

Public advisory group

PAVS

Physical Activity Vital Sign

PIS

Participant information sheet

PMC

Programme management committee

QALY

Quality-adjusted life year

QR

Quick response

REC

Research ethics committee

RCT

Randomised controlled trials

SAE

Serious adverse event

SAP

Statistical analysis plan

SD

Standard deviation

TM

Trademark

TMG

Trial management group

TSC

Trial steering committee

UK

United Kingdom

VILPA

Vigorous intermittent lifestyle physical activity

WSQ

Workforce Sitting Questionnaire

Authors’ contributions {31b}

AJD is the chief investigator and developed the original Snacktivity™ idea along with KJ, HP, SJB, CG, DE, TY, CLE, SG, RG, NI, EF, and NM. AJD wrote the initial draft of this manuscript, along with RG, EG, EF and NI. All authors contributed to this publication at a later stage and have read and approved the final version.

Funding {4}

The trial is funded by the National Institute for Health and Care Research (NIHR) (Programme Grants for Applied Research, reference number: RP-PG-0618–20008). AJD and EF are supported by NIHR Research Professorship awards. KJ, MS, and SG are part funded by NIHR Applied Research Collaboration (ARC) West Midlands. This trial is supported by the NIHR Leicester Biomedical Research Centre. MS is also part funded by NIHR Midlands Patient Safety Research Collaboration. This publication presents independent research funded by the NIHR. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR, or the Department of Health and Social Care. The funder had no role in the design of the trial, data collection, analysis, interpretation of data or the writing of the publications arising from the trial.

Data availability {29}

The datasets used and/or analyzed during the current study will be made available from the last author upon reasonable request.

Declarations

Ethics approval and consent to participate {24}

Favorable ethical approval for the trial was granted by the London—Surrey Research Ethics Committee (REC) on 28 March 2024 (REC reference: 24/LO/0186). Written informed consent to participate will be obtained from all participants before they are enrolled in the trial.

Consent for publication {32}

This manuscript does not contain individual personal data from participants.

Competing interests {28}

The authors have no competing interests to declare.