The active and passive grip strength, repeated grip strength, back lift strength, leg press, vertical jump and back extension were measured for 220 boys and 205 girls in the primary school to examine the similarity and difference between back lift strength and grip strength. The results were as follows;
1) The strength of large muscle groups such as back lift strength and leg press in boys were significantly higher than in girls, but no differences were found in the strength of smaller muscle group like a grip strength.
2) Higher increment rate of the passive grip strength to the active strength was found in younger grade of primary school children. They might possess a lower level of contractile force-integrating ability than older ones.
3) No significant differences between boys and girls and among each grade were found in the decrement rate of repeated grip strength and no sigficant relationship between the decrement rate and maximum grip strength.
4) Significant relationship was observed between back lift strength and active or passive grip strength, and the correlation coefficients with the passive strength were lower than the active strength.
5) Significant relationship was observed between back lift strength and vertical jump and back extension in all grade of primary school girls and lower grade of the boys.