Background and Objective: Osteoporosis is a disease that is spreading as a threat to world health. This study aimed to compare the effect of resistance training, swimming, and combination training patterns on the on mechanical strength of osteoporotic bone tissue of female Wistar rats.
Materials and Methods: The current type of research was experimental and 36 healthy female Wistar rats (6 weeks old) with an average initial weight of 170-190 grams were studied. In order to confirm the induction of osteoporosis in the initial study, 12 were randomly divided into two groups: healthy and alcohol injection. In the main study, the remaining 24 rats were randomly divided into 4 groups (6 rats in each group) after induction of osteoporosis (resistance exercise, swimming exercise, combined exercise and control). Osteoporosis was induced by intraperitoneal injection of 20% ethanol solution and saline at a dose of 3 grams per kilogram of rat body weight, once a day and 4 days a week. Swimming training protocol (12 weeks, 90 minutes per day, 5 days per week) and resistance protocol (12 weeks, 5 days per week and each session including 8 sets with 8 to 12 repetitions of climbing the ladder) were performed. The combined group performed resistance training with progressive overload in 4 sets with 8 to 12 repetitions and swimming training with half the time of the swimming group. After the end of 12 weeks, femur bone samples were taken for densitometry and L5 vertebra and tibia bone to study mechanical resistance indicators. To assess bone strength, a mechanical properties testing machine, the Zwick model, made in Germany, was used. Data were analyzed using SPSS-25 using independent t-tests, one-way analysis of variance and Tukey's at a significance level of less than 0.05 (P<0.05).
Results: The tibia tensile maximum load in swimming, resistance and concurrent training groups was significantly greater than pretest (p=0.000, p=0.004, p=0.03). The L5 maximum load  of resistance and concurrent training groups was significantly greater than pretest (p=0.009 , p=0.001).  the tibia tensile maximum load in concurrent groups was significantly greater than swimming, resistance and control groups (p=0.000, p=0.000, p=0.004 ). The L5 maximum load in concurrent training (p=0.02 , p=0.03) and  resistance group  (p=0.003 , p=0.002) was significantly greater than swimming  and control groups.
Conclusion: It seems that the intervention of swimming and resistance training in a combined model may have a synergistic effect on increasing the mechanical strength of bone in osteoporotic female rats. This model is likely to increase the mechanical strength of bone better than the implementation of swimming or resistance training alone and provide more optimal care against osteoporosis.