Feasibility of ‘Muscle Movers’: a teacher-delivered program to support children’s participation in muscle-strengthening physical activity

Background: Muscle-strengthening activity (MSA) is beneficial for school-aged children, but most school-based MSA interventions have been delivered by external specialists or research staff, limiting scalability. We aimed to assess the feasibility of a teacher-delivered MSA intervention for children in advance of a future efficacy trial. Methods: We conducted a single-group feasibility trial with two Stage 2 (i.e. grade 3–4) classes from one primary school in New South Wales, Australia. The 6-week Muscle Movers intervention included (i) enhanced PE lessons focused on foundational MSA skills (1 × 45 min/week), (ii) classroom energiser breaks (2 × 5 min/week), and (iii) active homework tasks (1 × 10 min/week). We assessed acceptability, implementation, adaptation, and practicality using survey and interview methods. We also assessed pre–post change in children’s perceived strength, upper-body muscular endurance, and lower-body muscular power. Data were analysed in SPSS (V.25) using descriptive statistics and paired-samples t-tests, with Cohen’s d as a measure of effect size. Results: Two female teachers (31 and 59 years) and 30 students (mean [SD] = 9.8 [0.6] years; 40% female) were enrolled. Acceptability was high for teachers (mean [SD] = 5.0 [0.0] out of 5) and students (mean [SD] = 4.1 [1.0] out of 5). Teachers implemented all PE lessons and more than double the intended energiser breaks (mean [SD] = 5.5 [2.1] per week). Conversely, homework task assignment (mean [SD] = 5.0 [1.4]) and completion (mean [SD] = 2.5 [0.7]) were lower than intended. Teachers reported high confidence to deliver the program and viewed it as practical and adaptable. We found a moderate increase in children’s push-up performance (mean [95%CI] = 2.2 repetitions [0.7 to 3.8]; d = 0.61), but no meaningful changes in perceived strength (mean [95%CI] = 0.1 units [- 0.1 to 0.4]; d = 0.22) or standing long jump (mean [95%CI] = - 1.4 cm [- 7.4 to 4.7]; d = - 0.09). Conclusions: Muscle Movers was feasible for classroom teachers to implement in a primary school setting. The observed improvement in students’ upper-body muscular endurance should be confirmed using an appropriately powered randomised controlled trial. Trial registration: Retrospectively registered with the Australian and New Zealand Clinical Trials Registry (ACTRN12625000703404).