Designing a physical activity service, leading it and judging whether it worked are core competencies for a sport and exercise medicine (SEM) clinician working beyond individual patients, and they are examined because so many services are built on enthusiasm rather than method. The recurring failure is a scheme that is popular, well liked by staff and participants, and entirely unable to demonstrate that it changed anything, because no baseline was captured, no comparison existed and the only data collected were attendance figures. This page covers how to build a service on identified need, how to evaluate it properly, and what leading one involves in practice.
How is a service designed?
A defensible service starts with need rather than with an idea. Needs assessment establishes who is inactive in this population, which groups are least served, what the barriers are locally and what already exists, drawing on routine data, local surveys and the people the service intends to reach. Outcomes come next and must be specified before anything is built, because a service designed to increase activity looks different from one designed to reduce isolation or to improve a clinical measure. A programme theory or logic model then sits between need and design, setting out how the proposed components are expected to produce the intended outcomes and what assumptions must hold for that to happen. The intervention is designed around recognised behaviour change techniques rather than assembled from available facilities, and it is piloted to test specific feasibility uncertainties such as recruitment, acceptability, delivery fidelity, data collection and progression criteria, rather than simply run as a smaller version of the full programme.
Service development runs as a cycle from needs assessment through outcome definition, design, piloting, delivery and evaluation, with findings feeding back into need. The evaluation must be designed before delivery begins.
Several design decisions determine whether a service will reach the people it is meant to. Referral routes shape who arrives, so a scheme reachable only through general practice will miss those who do not attend. Cost, transport, timing and setting all filter participants, and a service delivered in a leisure centre at midday reaches a very different population from one delivered in a community hall in the evening. Staff mix matters, both for competence and for whether participants feel the service is for people like them. Recruitment, retention and the transition after the programme are all common failure points, and building in follow-up contact, gradual progression and a planned handover into ongoing community activity addresses the most common reason schemes fail to produce lasting change. Leading such a service means governance as well as design: clear clinical accountability, agreed inclusion and exclusion criteria, staff training and supervision, incident reporting, data protection, and a plan for sustainability beyond the initial funding period.
How is a service evaluated?
Evaluation has three components and confusing them is the commonest error. Process evaluation asks whether the service was delivered as intended, and covers reach, fidelity, the dose delivered and the dose received, adaptations made during delivery, participant experience, context and the mechanisms through which the service is expected to work, alongside referrals, uptake, completion and dropout. Outcome evaluation asks whether the intended outcomes changed, which requires a baseline measure and a defined follow-up point; a comparison group is not strictly needed to document change, but it is needed to claim credibly that the service caused it. Economic evaluation asks whether the benefit justified the cost, and while it is not essential for every small service evaluation, it is usually decisive for commissioning and scaling. Attendance is one process measure, but attendance alone does not provide a complete process evaluation and says nothing about effectiveness or value for money. The methodological framework most often cited for this work is the guidance on developing and evaluating complex interventions, which emphasises context, programme theory, stakeholder involvement, identifying key uncertainties, refinement, economic considerations and implementation, and treats these services as complex because they have multiple interacting components and depend heavily on context.
Evaluation has three distinct components: process asks whether the service was delivered as intended, outcome asks whether the intended outcomes changed, and economic asks whether the benefit justified the cost. Attendance alone is only one process measure.
The practical difficulties are worth anticipating. Selection bias is pervasive, because people who accept a referral and attend differ systematically from those who do not, so before-and-after comparisons in completers flatter the service. Regression to the mean affects any service recruiting people at their worst. Loss to follow-up is typically substantial and non-random, since those who dropped out are also least likely to return a questionnaire, and analysing only completers converts a modest effect into an impressive one. Where individual randomisation is impractical, consider cluster randomisation or a stepped-wedge trial, in which the order in which clusters receive the service is commonly randomised, where research approvals are appropriate. Non-randomised alternatives include a controlled interrupted time series, difference-in-differences, and carefully matched comparison areas. Note that introducing random allocation or additional research procedures may convert a service evaluation into research, which then requires the relevant sponsorship and approvals. Reporting should be honest about all of this, because a service evaluation that overstates its effect makes the next commissioning decision worse rather than better. A minimum evaluation dataset should also capture adverse events, unintended consequences, equity of reach and outcomes, and data completeness. Finally, evaluation findings should feed back into the design cycle rather than being filed, which is the difference between a service that improves and one that simply continues.
Exam Tips
•Start from needs assessment, define outcomes, then set out a programme theory explaining how components produce outcomes and what assumptions must hold, before designing around behaviour change techniques.
•Referral routes, cost, transport, timing, setting and staff mix all determine who actually reaches the service.
•Recruitment, retention and the transition after the programme are all common failure points, so plan follow-up contact and a handover into ongoing activity.
•Evaluation has three parts: process, covering reach, fidelity, dose, adaptations, experience and context; outcome, requiring baseline and follow-up, with a comparison group needed to claim causation; and economic, usually decisive for commissioning.
•Attendance is a process measure only: it does not establish outcomes, effectiveness or value for money, and completer-only analysis inflates apparent effect through selection, regression to the mean and non-random loss to follow-up.
•Where individual randomisation is impractical, consider cluster randomisation or a stepped-wedge trial, which commonly randomises the order clusters receive the service, or non-randomised options such as controlled interrupted time series, difference-in-differences or matched comparison areas.