Stress Similarity and the Biomechanics of Terrestrial Locomotion in Mammals

动物用四肢来产生和传递与运动和支撑重力有关的力。这些力对肌肉和骨骼设计的进化以及这些组织对机械载荷变化的适应性反应都有重要影响。反过来，对运动支持的机械要求影响动物在运动活动中消耗的能量，并决定其性能的极限。通过比较大小差别很大的物种的运动机制，Biewener博士试图建立一般的原则，来解释自然选择是如何支持陆生哺乳动物有效地承受重力负荷的。其中一种策略似乎是肢体姿势的有规律的大小依赖变化。通过采取更直立的姿势，大型动物在跑步时降低了必须通过肌肉和骨骼传递的力量。这种力量的减少抵消了大型动物由于组织的面积和体积缩放而导致的支撑体重能力的下降。这种机械约束的基础是要求运动应力（单位面积的力）作用于骨骼和肌肉组织，使其保持在每个组织强度的安全范围内。这些组织的“安全系数”似乎大约是它们强度的三分之一。本研究对骨和肌肉适应生理需求变化的功能机制和能力具有重要的应用意义。这在与运动相关的体能训练、残障性身体损伤恢复的物理治疗方案、克服运动缺陷的外科肌肉/肌腱移植策略以及评估与年龄相关的骨质流失有关的体育锻炼的重要性方面都很重要。

Animals use their limbs to generate and transmit forces associated with movement and suppport against the force of gravity. These forces are an important influence both on the evolution of muscle and bone design, as well as on the adaptive response of these tissues to changes in mechanical loading. Mechanical requirements for locomotor support, in turn, affect the energy expended by an animal during locomotor activity and dictate the limits of its performance. By comparing the mechanics of locomotion of broadly differing sized species, Dr. Biewener seeks to establish general principles that govern how natural selection has favored strategies for effective support of gravitational loads in terrestrial mammals. One such strategy appears to be regular size-dependent change in limb posture. By adopting a more upright posture, larger animals lower the forces that must be transmitted by their muscles and bones when running. This decrease in force offsets the diminished ability of larger animals to support their weight due to the effect of size on the area to volume scaling of their tissues. Underlying this mechanical constraint is the requirement that locomotor stresses (force per unit area) acting in bone and muscle tissue be kept within a safe fraction of each tissue's strength. The "safety factor" of these tissues appears to be roughly one-third of their strength. This research has applied significance relating to the functional mechanism and capacity of bone and muscle to respond adaptively to changes in physical requirements. This is important in terms of physical training associated with sports-related activity, physical therapy programs for recovery from disabling physical injury, for surgical muscle/tendon transplantation strategies to overcome motor deficits, as well as for evaluating the importance of physical exercise in relation to age-related bone loss.