OBJECTIVES The purpose of this study was to investigate the weight loss and isotonic core exercise on oswestry disability index (ODI), trunk extensor and flexor muscle strength in obese middle-aged women with chronic low back pain.METHODS Eighteen obese middle-aged woman with chronic low back pain were randomly assigned into weight loss + core exercise group (WL+CE, n=6), core exercise group (CE, n=6), and control group (CON, n=6). The weight loss goal was set at approximately 0.5-1 kg per week, and core exercises were conducted for 60 minutes, three times a week, for 8 weeks. Body composition (weight, % body fat, muscle mass, WHR), ODI, trunk extensor and flexor muscle strength were measured before, 4 weeks, and 8 weeks after core exercise.RESULTS WHR and ODI significantly decreased at 4 and 8 weeks of exercise in both the WL+CE and CE groups compared to before exercise (p<.05, respectively). Trunk extensor muscle strength significant increased at 8 weeks after exercise compared to before exercise at 146°, 158°, 170°, and 182° in the WL+CE (p<.05, respectively), and significant increased at 8 weeks after exercise compared to before exercise at 146° and 158° in the CE (p<.05, respectively). Trunk flexor muscle strength was a significant increase at 8 weeks after exercise compared to before exercise at 146°, 158°, and 182° in the WL+CE (p<.05, respectively), and significant increase at 8 weeks after exercise compared to before exercise at 110°, 134°, 146°, and 170° in the CE (p<.05, respectively).CONCLUSIONS The results of this study suggest that weight loss and core exercise improve WHR, ODI, and trunk extensor and flexor muscle strength in obese middle-aged women with chronic low back pain.