High-impact exercise in rats prior to and during suspension can prevent bone loss

Abstract

High-impact exercise has been considered an important method for treating bone loss in osteopenic experimental models. In this study, we investigated the effects of osteopenia caused by inactivity in femora and tibiae of rats subjected to jump training using the rat tail suspension model. Eight-week-old female Wistar rats were divided into five groups (n=10 each group): jump training for 2 weeks before suspension and training during 3 weeks of suspension; jump training for 2 weeks before suspension; jump training only during suspension; suspension without any training; and a control group. The exercise protocol consisted of 20 jumps/day, 5 days/week, with a jump height of 40 cm. The bone mineral density of the femora and tibiae was measured by double energy X-ray absorptiometry and the same bones were evaluated by mechanical tests. Bone microarchitecture was evaluated by scanning electron microscopy. One-way ANOVA was used to compare groups. Significance was determined as P<0.05. Regarding bone mineral density, mechanical properties and bone microarchitecture, the beneficial effects were greater in the bones of animals subjected to pre-suspension training and subsequently to training during suspension, compared with the bones of animals subjected to pre-suspension training or to training during suspension. Our results indicate that a period of high impact exercise prior to tail suspension in rats can prevent the installation of osteopenia if there is also training during the tail suspension.

Figure 1. Experimental design. Rats were divided into 5 groups (n=10) as follows: T/ST: jump training before suspension and training during suspension; T/S: jump training before suspension; U/ST: training only during suspension; U/S: suspension without any training, and U/U: untrained and unrestricted in regular cages.

Figure 2. Schematic drawing of the rat tail suspension model.

Figure 3. Mechanical testing. A, flexo-compression test of the femora and B, 3-point bending flexural test of the tibiae.

Figure 4. Preparation and analysis by scanning electron microscopy.

Figure 5. BMD (bone mineral density; g/cm²) of the experimental groups. T/ST: trained/suspended+trained rats; T/S: trained/suspended rats; U/ST: untrained/suspended+trained rats; U/S: untrained/suspended rats; U/U: untrained/unrestricted. Results are reported as mean and 95%CI for n=10 rats per group.

Figure 6. Mechanical properties of the femora (left panel) and tibiae (right panel). T/ST: trained/suspended+trained rats; T/S: trained/suspended rats; U/ST: untrained/suspended+trained rats; U/S: untrained/suspended rats; U/U: untrained/unrestricted. L_max: maximum load (N); St: stiffness (N/mm). Results are reported as mean and 95%CI for n=10 rats per group.

Figure 7. Scanning electron microscopy showing comparative bone micro-architecture. Arrows indicate trabecular space. T/ST: trained/suspended+trained rats; T/S: trained/suspended rats; U/ST: untrained/suspended+trained rats; U/S: untrained/suspended rats; U/U: untrained/unrestricted.