Author(s): GAO, Y., CAO, M., SHAO, S., Institution: SHENZHEN UNIVERSITY, Country: CHINA, Abstract-ID: 1393

INTRODUCTION:
Adolescent obesity is associated with early cardiometabolic risk and impaired physical fitness. High-intensity interval-based exercise is time-efficient and potentially scalable in school settings; however, the minimal effective weekly frequency of non-running, low-equipment high-intensity training (HIT) remains unclear. Direct head-to-head comparisons of different weekly frequencies within controlled school-based programs are limited. This pilot randomized trial examined dose-response patterns across weekly HIT frequencies in adolescents with obesity.
METHODS:
Thirty-one Chinese adolescents with obesity (11–13 years) were randomly allocated to low (1 session/week; n=10), moderate (2 sessions/week; n=10), or high (3 sessions/week; n=11) frequency school-based HIT for 12 weeks. Sessions were delivered within regular physical education classes and comprised three circuits of six bodyweight exercises (30 s work, 30 s recovery per station), targeting 80–90% age-predicted HRmax. Primary outcomes were BMI z-score and waist circumference. Secondary outcomes included fat mass, fat-free mass, bone mineral density (BMD), fasting glucose and lipid profile, directly measured VO2max (COSMED K5), blood pressure, and handgrip strength. Linear mixed models and ANCOVA on change scores were applied.
RESULTS:
All 31 participants (24 boys; mean age 12.8 ± 0.4 years) completed the intervention with >90% attendance and no exercise-related adverse events. Improvements in adiposity outcomes showed a graded pattern from low to high frequency, including reductions in body weight (-1.05, -2.14, -4.02 kg), BMI (-0.54, -1.26, -2.33 kg/m2), and BMI z-score (-0.10, -0.25, -0.52). Relative handgrip strength increased more markedly at higher weekly frequencies. Directly measured VO2max improved in all groups, with numerically greater gains at higher frequencies. Diastolic blood pressure showed a favorable trend with increasing weekly dose. BMD increased over time (0.06–0.08 g/cm2; time effect p=0.001) with similar gains across frequencies. Metabolic markers (HOMA-IR and triglycerides) improved modestly.
CONCLUSION:
A brief, school-feasible, non-running HIT program performed 1–3 times per week appears safe and beneficial for adolescents with obesity. Once-weekly HIT may yield meaningful improvements in adiposity and fitness, while higher weekly frequencies may provide additional benefits in central adiposity and aerobic capacity. These findings support flexible frequency prescriptions within constrained physical education time.