The time course of changes in bone mass and bone strength induced by the combination of voluntary running exercise and food restriction in young female rats

PURPOSE: This study aimed to determine the time course of changes in bone mass and bone strength induced by the combination of voluntary running exercise and food restriction in young female rats. METHODS: Female Sprague-Dawley rats (aged 7 weeks) were randomly divided into the following three experimental groups after a 1-week acclimatization period: sedentary and ad libitum feeding (SED), voluntary wheel running exercise and ad libitum feeding (EX), and voluntary wheel running and food restriction (EX-FR). Dissections were performed at 2, 4, 8, and 12 weeks. The strength of the femoral mid-shaft was assessed using the three-point bending test. The bone mineral density (BMD) of the tibia was measured using a dual-energy X-ray absorptiometry machine. RESULTS: At 2 weeks, the body weight, abdominal fat weight, and bone weight of the femur in the EX-FR group were significantly lower than those in the SED and EX groups. The BMD of the tibia in the EX-FR group was significantly lower than that in the EX group. At 4 weeks, the bone strength of the femur in the EX-FR group was significantly lower than that in the EX group. At 8 weeks, the bone strength of the femur in the EX-FR group was significantly lower than that in the SED group. CONCLUSION: These findings demonstrate that bone mass is affected earlier than bone strength under energy-deficient exercise conditions, providing important insights into the temporal progression of bone impairment associated with relative energy deficiency.