Date of Graduation

2007

Document Type

Thesis

Degree Type

MS

Committee Chair

Janet Tou

Abstract

Background: Studies indicate that weight-bearing exercise increases bone mass and bone strength. There are also suggestions that obesity may result in bone loading that increases bone mass and strength. Objective: To investigate the combined effect of exercise and obesity on body mass, bone strength and bone mineral content (BMC) in young Zucker obese fa/fa and lean male rats. Methods: Young (age 6 weeks) obese (fa/fa) and lean male Zucker rats were randomly assigned (n=8-9/group) to either no exercise or treadmill exercise for 9 weeks at a 0% incline. Following the 9-week experiment, both femurs and tibiae were excised and bone morphometry determined. Bone biomechanical strength was assessed by three-point bending test. Total BMC was determined by ashing the whole bone at 600o C. Plasma glucose was determined by glucometer and insulin by radioimmunoassy. One-way Analysis of Variance (ANOVA) was used to determine differences among the treatment groups, and two-way Analysis of Variance (ANOVA) was used to analyze the combination effect of obesity and exercise on BMC and bone strength. Differences were considered significant at p< 0.05. Results: Exercise significantly (p< 0.001) reduced weight gain in the obese but not lean rats. Elevated blood glucose and insulin in obese compared to lean rats was not significantly lowered with the exercise regimen. Results in the bone showed reduced (p< 0.001) longitudinal bone growth, tibial width and bone mass in obese compared to lean rats. However, there was no significant difference in tibial or femoral total BMC or bone strength in the obese compared to lean rats. Exercise had no effect on the bone strength or BMC in either lean or obese rats. Conclusion: Elevated insulin and glucose may be responsible for reduced bone growth in obese rats. Exercising obese rats did not improve bone growth. Exercising did reduce the body weight of obese rats significantly. The absence of effects on the BMC and strength of exercised obese rats may be due to decreased bone loading with weight loss.

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