Enhancements of Free-Fall Landing on the Trabecular Bone Structure in Tibiae of Growing Female Rats: A Time Course Study

Abstract

The purpose of this study is to investigate the effects of one- and four-week mechanical loading on the bones in young female rats. Seven-week-old female SD rats (n = 40) were randomly assigned into four groups, which were the 1WCON, 1WLAND, 4WCON, and 4WLAND groups (n = 10 for each). Animals of the 1WLAND and 4WLAND groups were respectively subjected to 1- and 4-week free-fall landing program, in which animals were free-fallen from a height of 40 cm for 10 times per day; 5 days per week. The 1WCON and 4WCON groups served as the time-matched control groups. Methods of histomorphometry, tissue geometry, and tissue weight were performed on the animals' femora and tibiae. Two-way (landing × time) ANOVA was used for statistical analysis (α = .05). In the histomorphometric analysis, the landing animals showed significantly higher bone volume ratio (BV/TV, %) and trabecular thickness (Tb. Th, μm). The effect of time was also evident in the bone tissue wet weight (WW) and fat-free dry weight (FFDW), while the landing showed no effects on the WW and the FFDW. Our study preliminarily showed that 1- and 4-week landing training was beneficial on the trabecular structure of the proximal tibia in female rats. Further study would be valuable to investigate related cellular response as well as tissue material properties of the spongy bone in free-fall landing rats.