Randomized Controlled Study of Effects of Sudden Impact Loading on Rat Femur

Abstract

Physical loading creating high peak strains on the skeleton at high strain rates is suggested to be the most effective type of activity in terms of bone mineral acquisition. This study assessed the effects of sudden impact loading on mineral and mechanical bone properties in 13-week-old Sprague-Dawley rats. The rats were randomly assigned as sedentary controls (SED, n ‫؍‬ 10), control animals receiving low-intensity exercise (EX, n ‫؍‬ 15), and experimental animals receiving low-intensity exercise combined with sudden impact-loading (EX ؉ IMP, n ‫؍‬ 15). In the EX group, the rats walked in a walking mill at a speed of 10 cm/s for 20 minutes/day, 5 days/week for 9 weeks. In the EX ؉ IMP group, the program was identical to the EX group except for the additional sudden impacts administered to their skeleton during the walking exercise. At the start, there were 50 impacts per session, after which their number was gradually increased to 200 impacts per session by week 6 and then kept constant until the end of the experiment, week 9. These horizontally and vertically directed body impacts were produced by a custom-made walking mill equipped with computer-controlled high-pressure air cylinders. After sacrifice, both femora of each rat were removed and their dimensions, bone mineral content (BMC) by dual-energy X-ray absorptiometry, and mechanical properties by femoral shaft three-point bending and femoral neck compression were determined. The cortical wall thickness increased significantly in the EX and EX ؉ IMP groups as compared with SEDs (؉7.6%, p ‫؍‬ 0.049 and ؉10%, p ‫؍‬ 0.020, respectively). The EX ؉ IMP group showed ؉9.0% ( p ‫؍‬ 0.046) higher cross-sectional moment of inertia values than the EX group. No significant intergroup differences were seen in the BMC values, while the breaking load of the femoral shaft (EX ؉ IMP vs. SED ؉8.8%, p ‫؍‬ 0.047) and femoral neck (EX ؉ IMP vs. SED ؉14.1%, p ‫؍‬ 0.013) was significantly enhanced by the impact loading. In conclusion, this study indicates that mechanical loading can substantially improve the mechanical characteristics of a rat femur without simultaneous gain in its mineral mass. If this is true in humans too, our finding gives an interesting perspective to the numerous longitudinal exercise studies (of women) in which the exercise-induced gains in bone mass and density have remained mild to moderate

Increased density and periosteal expansion of the tibia in young adult men following short-term arduous training

“…The findings from animal models are corroborated, to a certain extent, in human studies that report increased areal bone mineral density following high impact exercise [14][15][16][17] Areal BMD is not a suitable surrogate measure of bone strength with exercise interventions [18] since animal studies report large changes in bone strength despite only modest changes in density [1,19]. This is supported in cross-sectional studies of athletes using peripheral Quantitative Computed Tomography (pQCT), which describe a thicker cortex in the playing arm of tennis players [20], the tibia of triple jumpers [21] and in athletes from impact sports [22] compared with matched controls, with little or no differences in density [23].…”

Exercise-induced bone gain is due to enlargement in bone size without a change in volumetric bone density: a peripheral quantitative computed tomography study of the upper arms of male tennis players

“…21,32 However, the effects of loading on the true volumetric density of bone as well as bone geometry have remained largely unknown because of the lack of reliable and safe measurement techniques. Recently, several pQCT devices have been introduced for examining peripheral bone sites with a significantly lower radiation dose than with conventional CT equipment.…”

Paricalcitol [19-Nor-1,25-(OH)2D2] in the Treatment of Experimental Renal Bone Disease

“…(12) Biomechanical testing A Lloyd material testing device (LR5K; J.J. Lloyd Instruments, Southampton, UK) was used for the anteroposterior three-point bending of the right femoral shafts and compression of the right femoral necks. (13,14) For the threepoint bending, the femora were placed on their posterior surface on the supports of the apparatus. The first support was placed just distal to the trochanter minor and the second just proximal to the condyles of femur.…”

“…(14) After the three-point bending of the femoral shaft, the proximal part of each specimen was collected and used for femoral neck compression test according to a previously described protocol. (13,14) The proximal half of each femur was mounted in a fixation device, (15) and the specimen was placed under the testing device, and a vertical load was applied to the top of the femoral head using a brass crossbar until failure of the femoral neck. The breaking load (F max ) was determined from the load deformation curve.…”