Three female aerobic dance instructors and 4 female participants were subjected to this study in order to evaluate the floor reaction force during aerobic dance exercise. The typical steps of low-impact and high-impact exercise (walking, hell-touch, lunge, running, hopping and skipping) were examined on Kistler force platform.
　The peak floor reaction force of "lunge" as low-impact step was 3.2 BW for one leg and that was greater than 2.4 BW of "hopping" as high-impact. This results showed that the peak reaction force of some "low-impact" steps might exceed that of the "high-impact" instantaneously.
　From the survey of aerobic dance instructors by questionnaire, 61 out of 126 (48.4%) had experience of pain in lower extremity or back (spinal) due to aerobic dance exercise. The rate of injuries obtained in this study was lower than those of the similar studies made in 1985, 1986 and 1988. However the problem of overuse or overwork still existed, for 76.8% of the injuries were considered to be chronic. On the other hand, there was no significant relationship between the occurrence of injuries and the amount of exercise or the distribution of low and high-impact phases in one workout.
　In the light of these findings, it could be said that in order to prevent the injuries due to aerobic dance exercise, in addition to the amount of exercise and the distribution of low and high-impact exercise, duration permitted for each step based on its intensity (floor reaction force) must be taken into consideration.

DESCENTE SPORTS SCIENCE Vol.13/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE