Biomechanics Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, USA.
Ann Biomed Eng. 2012 May;40(5):1088-101. doi: 10.1007/s10439-011-0481-4. Epub 2011 Dec 21.
Redundancy in the human muscular system makes it challenging to assess age-related changes in muscle mechanical properties in vivo, as ethical considerations prohibit direct muscle force measurement. We overcame this by using a hybrid approach that combined magnetic resonance and ultrasound imaging, dynamometer measurements, muscle modeling, and numerical optimization to obtain subject-specific estimates of the mechanical properties of tibialis anterior, gastrocnemius, and soleus muscles from young and older adults. We hypothesized that older subjects would have lower maximal isometric forces, slower contractile and stiffer elastic characteristics, and that subject-specific muscle properties would give more accurate joint torque predictions compared to generic properties. Unknown muscle model parameters were obtained by minimizing the difference between simulated and actual subject torque-time histories under both isometric and isovelocity conditions. The resulting subject-specific models showed age- and gender-related differences, with older adults displaying reduced maximal isometric forces, slower force-velocity and altered force-length properties and stiffer elasticity. Tibialis anterior was least affected by aging. Subject-specific models gave good predictions of experimental concentric torque-time histories (10-14% error), but were less accurate for eccentric conditions. With generic muscle properties prediction errors were about twice as large. For maximum predictive power, musculoskeletal models should be tailored to individual subjects.
人体肌肉系统的冗余性使得难以在体内评估与年龄相关的肌肉机械特性变化，因为伦理考虑禁止直接测量肌肉力。我们通过使用混合方法克服了这一难题，该方法结合了磁共振和超声成像、测力计测量、肌肉建模和数值优化，从年轻和老年成年人中获得了胫骨前肌、腓肠肌和比目鱼肌的机械特性的特定于个体的估计值。我们假设老年人的最大等长力会更低，收缩和弹性特性更慢更硬，与通用特性相比，特定于个体的肌肉特性将更准确地预测关节扭矩。在等长和等速条件下，通过最小化模拟和实际个体扭矩-时间历史之间的差异来获得未知的肌肉模型参数。所得的特定于个体的模型显示出与年龄和性别相关的差异，老年人的最大等长力降低，力-速度和力-长度特性减慢，弹性变硬。胫骨前肌受老化影响最小。特定于个体的模型很好地预测了实验性向心扭矩-时间历史（误差为 10-14%），但对于离心条件的预测准确性较低。使用通用肌肉特性时，预测误差大约是其两倍。为了获得最大的预测能力，肌肉骨骼模型应根据个体进行定制。
