A 2-yr, School-Based Resistance Exercise Pilot Program Increases Bone Accrual in Adolescent Girls

The current analysis evaluates cumulative benefits after year two (Y2) of a school-based resistance training intervention.

Adolescent girls were enrolled and measured at the beginning of 6^th grade (baseline, BL) and again at 1^st follow-up (FU1: Y1 end) and 2^nd follow-up (FU2: Y2 end). School gym classes met alternate school days. Site 1 had standard gym classes (CON). Site 2 gym classes included 8-12 minutes of resistance training (INT); INT girls were categorized based on observed participation effort and time (LO, HI). Measurements included: 1) height and weight; 2) questionnaires to assess extracurricular exercise and diet (calcium, vitamin D); 3) dual-energy X-ray absorptiometry (DXA, Lunar Prodigy). Whole body less head (SUB) scans yielded bone mineral content (BMC) and body composition. Lumbar spine (L1-L4) and femoral neck (FN) scans yielded BMC and areal bone mineral density (BMD); radius scans yielded ultradistal and 1/3 BMD. ANCOVA compared group means for percent gains from BL to FU2, accounting for biological maturity, BL height, height change, inter-scan interval, organized activity, calcium and vitamin D.

In 62 girls (21 CON, 41 INT), intention to treat analyses detected INT vs. CON advantages for L1-L4 BMC and BMD (4.1%, 5.6%: p<0.05). HI effort participants (n=19) demonstrated advantages for BMC and BMD at L1-L4 and FN (5.7% to 8.2%, p<0.01) vs. CON.

Over two school years, this resistance intervention yielded lumbar spine advantages; enthusiastic participation (HI) yielded lumbar spine and femoral neck advantages. Further work is warranted to evaluate benefit persistence after intervention cessation.