Enhancement of bone quality and longitudinal growth due to free-fall motion in growing rats

Objectives: This study is to investigate the synchronous phenomena between bone quality and longitudinal length in a same subject affected by landing exercise. Physical exercise on the ground induces external loading to human body due to resistance from ground which can activate bone generation or remodeling. Especially, when the impact stimulation is applied to bone, it may improve bone quality and lengthening. Methods: 6-week-old male Wistar rats were randomly allocated to one of two conditions: free fall from 40 cm-height (I40; n = 7), and control (IC; n = 7). The impact stimulations were administered to the free fall groups, 10 times/day, and 5 days/week for 8 weeks. Structural parameters and longitudinal length of tibia were measured to quantitatively evaluate the variation in morphological characteristics and bone length with maturing. Results: The landing impact seems to be commonly effective on the enhancement of bone quality as well as longitudinal growth. However, the extent of enhancement may be more dominant in bone quality than longitudinal growth. On the other hand, the ratio of longitudinal growth seems to be dependent on the duration of stimuli whereas the enhancement of bone quality does not. Conclusions: This study verified that free-falls exercise can be effective on the enhancement of bone qualities and promotion of vertical growth in long bones. We expect that it might be possible for the moderate impact stimulation to be proposed as an aid for prevention of bone loss and promotion of bone lengthening.