Background Effective strategies to combat childhood obesity are challenging, especially among South Asian girls. We conducted a pilot cluster trial of a school-based physical activity programme among preadolescent girls to determine the feasibility (recruitment, retention and implementation) of the programme and influence on blood pressure (BP) and body mass index (BMI).

Methods This two-arm parallel cluster intervention trial was conducted in four similar all-girls public sector schools in Karachi over a 20-week period. All girls aged 9–11 years were included. Intervention was a physical activity programme of 30 min duration four times a week. Primary outcome was to assess the feasibility of the physical activity programme defined as recruitment and retention >70% and treatment fidelity of >80% of physical activity programme. Secondary outcomes were changes in systolic BP (SBP), diastolic BP (DBP) and BMI from baseline to follow-up.

Results A total of 360 participants were invited to participate, 280 girls met eligibility criteria, and were recruited; 131 (77%) in the intervention group and 146 (87%) in control group. At follow-up, the overall retention of participants was 222 (79.2%); 105 (80.1%) in the intervention group and 117 (78.5%) in the control group. The difference in mean change from baseline to follow-up in SBP, DBP and BMI score was 1.9 mm Hg, 0.7 mm Hg and 0.55 kg/m² between intervention and control arms, respectively.

Conclusions A school-based physical activity programme in a public sector girls school of urban Pakistan is feasible. There was a favourable trend in BP and BMI at follow-up. (Clinical trial ID NCT 00533819).