Aerobic Endurance Training Does Not Protect Bone Against Poorly Controlled Type 1 Diabetes in Young Adult Rats

Streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM) decreases trabecular bone volume and bone strength in rodents. The current study investigated the potential protective effects of aerobic endurance training (AET) on bone in STZ-induced T1DM young adult rats. Sixty-four 8-week-old male Sprague-Dawley rats were randomly divided into 4 groups of 16: control non-T1DM sedentary (CS) and exercised (CX), T1DM sedentary (DS) and exercised (DX). Blood glucose was maintained at 9-15 mmol/L using subcutaneously implanted insulin pellets (Linplant, Linshin Canada, Inc.). AET was performed at ~75-85% VO_2max for 1 h/day, 5 day/week for 10 weeks. Areal and volumetric bone mineral density (aBMD and vBMD; excised femur) were measured using dual-energy X-ray absorptiometry (DXA; QDR 4500A) and micro computed tomography (μCT; Aloka). Bone strength was tested using a 3-point bending test (Instron 5544 Load Frame). Two-way ANOVA was used to test for T1DM and exercise differences followed by Tukey's HSD tests for interaction effects; significance was set at P < 0.05. T1DM had lower body weight (18.0%), aBMD (8.6%), cortical vBMD (1.6%), trabecular vBMD (2.1%), maximum load at break (22.2%), and increased elastic modulus (11.3%) vs. control (P < 0.001). Exercise in T1DM further decreased body weight (4.7%) vs. sedentary (P = 0.043) and maximum extension during the bending test that demonstrated DX was increased (7.3%) vs. CX (P = 0.033). There were no other beneficial effects of exercise on bone. These results suggest that 10 weeks of AET in rats do not have protective effects on bone in the short term and that T1DM rats have compromised bone health.