Stress Similarity and the Biomechanics of Terrestrial Locomotion in Mammals

动物用四肢来产生和传递与运动相关的力量，并支持抵抗重力的力量。这些力对肌肉和骨骼设计的演变以及这些组织对机械负荷变化的适应性反应都是重要的影响。运动支撑的机械要求反过来又会影响动物在运动活动中消耗的能量，并决定其表现的极限。通过比较体型大相径庭的物种的运动机制，比温纳试图建立一般原则，指导自然选择如何有利于陆地哺乳动物有效支持重力负荷的策略。一种这样的策略似乎是四肢姿势的定期大小变化。通过采取更直立的姿势，较大的动物可以降低跑步时肌肉和骨骼必须传递的力量。这种力量的减少抵消了大型动物支持其体重的能力的减弱，这是由于大小对其组织的面积和体积比例的影响。在这种机械约束的基础上，要求作用于骨骼和肌肉组织的运动应力(单位面积的力)保持在每个组织强度的安全分数内。这些组织的“安全系数”似乎约为其强度的三分之一。这项研究对骨骼和肌肉对身体需求变化的适应能力和作用机制具有应用意义。这对于与运动相关的活动相关的体育训练、从致残的身体损伤中恢复的物理治疗计划、克服运动缺陷的外科肌肉/肌腱移植策略以及评估体育锻炼对于与年龄相关的骨丢失的重要性而言都是重要的。

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.