Differential effect of exercise training duration on bone tissue in male obese rat
Résumé
The association of a well-balanced diet with exercise is a key strategy to treat obesity. Whereas exercise is known to induce beneficial effects on bone, data concerning these effects in a weight loss program in rat are lacking. Because weight loss is linked to a concomitant bone loss, we wondered if exercise training duration may differently affect the bone tissue in such a program. This study aimed to investigate bone responses to two different durations of exercise training combined with a well-balance diet in obese rats. Fifty nine Wistar male rats were previously fed with a high fat/high sucrose diet (HF/HS) for 4 months to induce obesity. A control group (n = 15) was fed with a standard diet (HF/HS vs. Control = T0). Then, all rats were given a well-balanced diet and assigned to 4 different modalities: one month of exercise training (treadmill: 50 min/day, 5 days/week) or sedentarity (T1), two months of exercise or sedentarity (T2). The body composition and BMD were assessed by DXA. Visceral fat mass was weighed and insulin sensitivity was tested. Trabecular micro-architecture of tibia and L2 vertebrae (L2) and the cortical analysis of tibia were performed by 3D microtomography. Osteocalcin and CTX levels were assessed. At T0, the HF/HS diet group had developed a total and abdominal obesity and an impaired glucose tolerance compared with the Control group (p < 0.05). Most of the bone parameters were improved in HF/HS group vs. the Control group: higher total BMC and BMD, lower cortical porosity of tibia and higher Tb.Th of L2 (p < 0.05). One month of exercise (T1) had not affected the body composition and bone parameters except an improvement of insulin sensitivity (p < 0.05) and a tendency to increase BV/TV of tibia (p < 0.06). At T2, the total and fat masses were reduced in exercised group vs. sedentary group (p < 0.01). Regarding the bone parameters, CTX level decreased (p < 0.05), the Tb.Sp of L2 tended to decrease (p < 0.06), the degree of anisotropy (DA) of tibia increased (p < 0.05), and DA of L2 tended to increase (p < 0.06) in exercised group vs. sedentary group. In conclusion, 2 months of exercise had reduced obesity parameters, decreased resorption and improved a part of trabecular parameters of bone tissue whereas 1 month of exercise did not induce such improvement. A two-month program composed of a well balanced diet combined with exercise training is able to treat obesity and to protect bone tissue in male obese rat whereas one month program is not efficient.