Effect of physical activity before pregnancy on fetuses of mice exercised forcibly during pregnancy

Colony‐bred ICR‐JCL female mice were subjected to physical training by imposing a daily routine of running 6 days a week for 4 weeks from the 6th‐9th weeks of age. These and nontrained females were mated and some from both groups were forced to exercise (running for 30 min/day) on the 9th‐16th days of gestation. Pregnant mice were killed on the 19th day of gestation. The fetuses of females exercised during midpregnancy showed increased mortality, slight decrease in body weight, and some delayed ossification, but no malformations. Training before pregnancy was effective in decreasing the fetal mortality in the females exercised during midpregnancy.