Strength classes fill up — but almost nobody checks if people keep lifting

Guidelines ask adults to do muscle-strengthening activity on at least two days a week, and few people meet that target. That gap makes the design of real-world programmes — in gyms, community settings and workplaces — a public health question rather than just a training one. If we want more of the population lifting, we need to know which promotional approaches actually change behaviour and which merely fill a class for a few weeks. This review set out to audit what the intervention literature can currently tell us.

The authors conducted a pre-registered systematic review of studies reporting behavioural outcomes from 'real-life' interventions promoting muscle-strengthening exercise in healthy, community-dwelling adults. Study selection, data extraction and quality assessment were completed, and the behaviour change techniques used in each intervention were coded. Sixty-nine unique studies were included, ranging from 10 to 3507 participants, of which 36 were randomised controlled trials. Study quality was graded, producing five strong, 12 moderate and 52 weak ratings. Session attendance and any measure of actual engagement in strength exercise were extracted alongside health outcomes.

Participation looked healthy on the surface: of the 54 studies reporting session attendance, rates ranged from 10 to 100%, and only seven fell below 60%. But just nine studies assessed and reported whether participants were genuinely engaging in muscle-strengthening exercise. Among the randomised trials, 70.0% showed an improvement in functional performance. There was moderate evidence of no change in blood pressure or body mass index, and conflicting evidence for other outcomes. The commonest behaviour change techniques were instruction on how to perform the behaviour (91.3%), behavioural practice or rehearsal (76.8%) and demonstration of the behaviour (76.8%).

This complicates the assumption that we already know how to get people strength training. Attendance data suggest people will turn up when a programme is offered, which is encouraging, but attendance is not the same construct as sustained behaviour, and the review shows the field has rarely measured the latter. The null findings for blood pressure and BMI temper expectations that short promotional programmes will shift those particular markers. The authors conclude the evidence base is too weak, and too thinly reported, to say which promotion strategies work best.

The useful signal here is that most randomised trials of these programmes improved functional performance, which is the kind of everyday capability strength work is supposed to build. It is also a reason to be sceptical of claims that a particular scheme 'gets people lifting', because that outcome is almost never measured. If you are choosing a programme, attendance figures tell you people showed up, not that they kept training afterwards. And short strength-promotion programmes should not be expected to move blood pressure or BMI on their own.