Biewener A A, Bertram J E
Department of Organismal Biology and Anatomy, University of Chicago, IL 60637.
J Exp Biol. 1993 Dec;185:51-69. doi: 10.1242/jeb.185.1.51.
Bones are believed to alter their shape in response to changes in tissue strains produced by physical activity and the goal of this study is to examine whether modeling responses of a growing bone to changes in physical exercise are adjusted to maintain a uniform distribution of functional strains. We test this idea by comparing in vivo strains recorded in the tibiotarsus of white leghorn chicks during 'intensive' treadmill exercise (60% of maximum speed, carrying a weight equal to 20% body weight on the trunk: 60%/L) with strains that had been recorded previously during 'moderate' treadmill exercise (35% of maximum speed, unloaded: 35%/UNL) at similar bone sites. Our hypothesis is that modeling adjustments of bones subjected to the intensive load-carrying exercise should re-establish strains recorded in the bones subjected to moderate exercise. At each exercise level, the animals were exercised for 5 days per week (2500 loading cycles per day) from 2 to 12 weeks of age. As in the moderate exercise group studied earlier, strains measured at six functionally equivalent sites on the tibiotarsus of the 60%/L group were consistently maintained during growth from 4 to 12 weeks of age. In addition, the pattern of strain recorded at these sites was uniformly maintained over the full range of speeds recorded (from 0.48 to 2.70 m s-1 at 12 weeks of age). Peak strains measured at 4 weeks of age in the load-carrying exercise group were initially elevated by 57% overall compared with peak strains recorded in the moderate exercise group. At 8 weeks of age, strain levels in the 60%/L group differed by only 4% overall compared with those recorded in the 35%/UNL group. The nature of strain (tensile versus compressive) and the orientation of principal strain at corresponding sites were also similar in the two groups. At 12 weeks of age, however, bone strain levels in the 60%/L group were again elevated (47% overall) compared with those recorded in the 35%/UNL group, although the general pattern and orientation of strains remained similar. This finding suggests a transient modeling response of the bone to the onset of exercise training, which was lost during subsequent growth, possibly because the normal pattern of functional strain was not altered significantly by the faster load-carrying exercise.
人们认为，骨骼会根据体力活动产生的组织应变变化来改变其形状，本研究的目的是检验生长中的骨骼对体育锻炼变化的塑形反应是否会进行调整，以维持功能应变的均匀分布。我们通过比较白来航鸡胫跗骨在“高强度”跑步机运动（最大速度的60%，躯干负重相当于体重的20%：60%/L）期间记录的体内应变，与之前在类似骨骼部位“中等强度”跑步机运动（最大速度的35%，无负重：35%/UNL）期间记录的应变，来验证这一想法。我们的假设是，承受高强度负重运动的骨骼的塑形调整应能重新建立中等强度运动骨骼中记录的应变。在每个运动水平，动物从2周龄到12周龄每周运动5天（每天2500个加载周期）。与早期研究的中等强度运动组一样，60%/L组胫跗骨六个功能等效部位测量的应变在4周龄到12周龄的生长过程中一直保持稳定。此外，在记录的整个速度范围内（12周龄时从0.48到2.70米/秒），这些部位记录的应变模式也保持一致。负重运动组4周龄时测量的峰值应变最初总体上比中等强度运动组记录的峰值应变高57%。在8周龄时，60%/L组的应变水平与35%/UNL组记录的应变水平总体上仅相差4%。两组相应部位的应变性质（拉伸与压缩）和主应变方向也相似。然而，在12周龄时，60%/L组的骨应变水平与35%/UNL组记录的应变水平相比再次升高（总体上47%），尽管应变的总体模式和方向仍然相似。这一发现表明，骨骼对运动训练开始时存在短暂塑形反应，但在随后的生长过程中消失了，可能是因为更快的负重运动没有显著改变正常的功能应变模式。
