Differences In Femur And Lumbar Vertebra Adaptations To Running And Swimming In Wistar Rat Models

Bone tissue adaptations to exercise are specific of the type of mechanical loading profile and, therefore, differ between different physical activities. PURPOSE: Our objective was to compare the long-term adaptive response of the femur and lumbar vertebra to running (weight-bearing activity; WB) and swimming (non-weight bearing activity; nWB) in young male Wistar rats. METHODS: Rats (n = 20, 3 months; 323 ± 20 g) were randomized into: i) WB (n = 10) housed in cages with running wheel or ii) nWB (n = 10) submitted to a swimming protocol, 2 h/day, 5d/week, for eight months. Body weight (BW), food intake and running wheel distance were recorded. At sacrifice, gastrocnemius and soleus muscles were removed and weighted. Lumbar vertebrae (L4-L5) and femur were also removed and analysed through micro-computed tomography and histology to determine microarchitecture, geometry and cellular density. Groups were compared by independent samples t-test. RESULTS: WB group ran approximately 9 km/week in the activity wheel. WB group presented higher BW (533.7 ± 48.1 vs 477.3 ± 47.7 g; p = .02) and pooled muscle mass (6.54 ± 0.47 vs 5.98 ± 0.32 g; p < .01) compared to nWB group despite food intake being similar between groups. At the femur, WB group displayed higher trabecular (0.435 ± 0.00 vs0.425 ± 0.01 g/cm3; p = .036) and cortical (1.469 ± 0.03 vs 1.437 ± 0.02 g/cm3; p = .019) volumetric bone mineral density, as well as higher cortical thickness (0.654 ± 0.03 vs 0.587 ± 0.03 mm; p = .001) and lower cortical porosity (3.26 ± 0.7 vs4.19 ± 0.35%; p < .01) compared to nWB group. Nonetheless, at the lumbar vertebra, it was the nWB group that displayed a lower trabecular separation (0.091 ± 0.0 vs 0.080 ± 0.0; p < .01) and higher trabecular connectivity (487.7 ± 151.0 vs1051.4 ± 370.0; p < 0.001) compared to the WB group. No differences were observed between groups or anatomical regions regarding osteocyte or osteoclast density. CONCLUSION: Site-dependent responses to different types of exercise were observed, with running being more effective to improve muscle mass and femur bone quality, whereas swimming was associated with positive effects mostly on the lumbar vertebra. CIAFEL is funded by FCT grant UID/DTP/00617/2020; ITR is funded by FCT grant LA/P/0064/2020. LF and AB are supported by FCT grants SFRH/BD/145211/2019 and MTS/SAS/0077/2020, respectively. Experiments were supported by FCT grant PTDC/SAU-DES/4113/2020