Impact of Physical Activity Interventions on Adolescent Body Composition and Fitness: A Three-Arm Randomized Controlled Trial

Abstract

Background: Adolescent physical inactivity, overweight, and declining fitness represent converging public health crises in Pakistan. Secondary school students in Peshawar, Khyber Pakhtunkhwa, face a distinctive burden: high rates of sedentary behavior driven by examination-focused curricula, absence of structured physical education, gender-based activity restrictions, and nutritionally poor dietary patterns. Physical activity (PA) programs—including structured high-intensity interval training (HIIT) and moderate-intensity continuous PA—offer evidence-based pathways to improving body composition and physical fitness in adolescent populations, but direct evidence from Peshawar's sociocultural and infrastructural context is entirely absent from the literature. Objective: To evaluate the comparative influence of a 12-week High-Intensity Interval Training (HIIT) program and a 12-week Moderate-intensity Physical Activity (MPA) program—relative to a standard physical education control—on body composition (BMI, body fat percentage, waist circumference, lean body mass) and fitness (VO₂max, resting heart rate, muscular endurance, flexibility) in secondary school students in Peshawar District. Methods: A three-arm parallel-group randomized controlled trial was conducted with 120 secondary school students (Grades 7–9, aged 12–16 years) from nine schools across Peshawar District using stratified random sampling (by school type, grade, and sex). Participants were randomly allocated to HIIT (n=40), MPA (n=40), or Control Group (CG; n=40). Both active arms received 12 weeks of supervised, three-sessions-per-week structured PA programs. Primary outcomes included BMI, body fat percentage (bioelectrical impedance analysis), waist circumference, and VO₂max (20-metre shuttle run test); secondary outcomes included resting heart rate, push-up and sit-up endurance, sit-and-reach flexibility, and lean body mass. Assessments occurred at baseline and Week 12. Analyses used one-way ANCOVA with baseline as covariate, mixed-model repeated-measures ANOVA, and Cohen's d effect sizes.  Results: Both active interventions significantly outperformed the Control Group on all body composition and fitness outcomes (all p < .001). HIIT produced significantly greater improvements than MPA on VO₂max (HIIT: +6.56 vs. MPA: +3.70 mL/kg/min; p = .003), body fat percentage (−2.77% vs. −1.57%; p = .001), and push-up endurance (+7.65 vs. +4.77 reps; p = .008). MPA produced significant improvements on all outcomes relative to controls, with large effect sizes (d = 0.94–1.74). Sex-stratified analysis revealed a significant sex × group interaction for body fat percentage (p = .034), with females showing proportionally greater fat reduction in the HIIT condition. School-type subgroup analysis found no significant differential effect across government and private schools (all p > .05) for most outcomes. Conclusions: Both HIIT and moderate-intensity PA programs are highly efficacious for improving body composition and multiple fitness parameters in secondary school students in Peshawar, Pakistan. HIIT demonstrates superior efficacy for cardiorespiratory fitness and body fat reduction. Given Peshawar's resource constraints and gender-access challenges, a hybrid approach—incorporating HIIT principles within culturally adapted, gender-sensitive PE sessions—is recommended for district-wide implementation. These findings provide the first RCT evidence base for PA program design in Peshawar's secondary school system.