The purpose of the current study was to investigate the   effect of 12 weeks of strength training on abdominal strength, explosive power, aerobic endurance and lower back and hamstring flexibility of schoolchildren. subjects  for  this  study were 40 healthy male school children ( age14#1.5 years, height ; 146#5.8 cm, body mass47#4.4kg ) the  foly subjects were randomly assigned in  to two equal groups,STG strength training  group (n=20 ) and CG – control group (n=20). The training  program ‘s  duration was 12  weeks , and  it  consisted  of  own body exercises on circuit based strength training sessions. Abdominal strength- measured through sit ups test  -sit ups completed in the 30 seconds- Explosive power -  standing  Broad Jump test Aerobic  Endurance  -The Cooper Test – test   was used  -lower  back and hamstring Flexibility –sit   and  reach  test.  The   pretest  and  posttest  randomized  control group design was used as an experimental design. selected  criterion variables was statistically analyzed with paired sample  test was used to find out significant   improvement and analysis of covariance (ANCOVA) was used  for significant difference and  all  the  case  0.05 level of  confidence was fixed to test the hypothesis. The Experimental group was  produced favorable change in abdominal strength. Explosive  power , Aerobic endurance  and   lower back & hamstring flexibility due to that effect of 12 weeks of strength exercise    program of school  children. The control group showed no significant change  in  any.

KEY WORDS; An abdominal strength, Explosive power, Aerobic Endurance and lower back and Hamstring Flexibility.