Csapo Robert, Malis Vadim, Sinha Usha, Du Jiang, Sinha Shantanu
Department of Radiology, University of California, San Diego, CA, USA.
BMC Musculoskelet Disord. 2014 Jun 17;15:209. doi: 10.1186/1471-2474-15-209.
In human skeletal muscles, the aging process causes a decrease of contractile and a concomitant increase of intramuscular adipose (IMAT) and connective (IMCT) tissues. The accumulation of non-contractile tissues may contribute to the significant loss of intrinsic muscle strength typically observed at older age but their in vivo quantification is challenging. The purpose of this study was to establish MR imaging-based methods to quantify the relative amounts of IMCT, IMAT and contractile tissues in young and older human cohorts, and investigate their roles in determining age-associated changes in skeletal muscle strength.
Five young (31.6 ± 7.0 yrs) and five older (83.4 ± 3.2 yrs) Japanese women were subject to a detailed MR imaging protocol, including Fast Gradient Echo, Quantitative Fat/Water (IDEAL) and Ultra-short Echo Time (UTE) sequences, to determine contractile muscle tissue and IMAT within the entire Triceps Surae complex, and IMCT within both heads of the Gastrocnemius muscle. Specific force was calculated as the ratio of isometric plantarflexor force and the physiological cross-sectional area of the Triceps Surae complex.
In the older cohort, total Triceps Surae volume was smaller by 17.5%, while the relative amounts of Triceps Surae IMAT and Gastrocnemius IMCT were larger by 55.1% and 48.9%, respectively. Differences of 38.6% and 42.1% in plantarflexor force and specific force were observed. After subtraction of IMAT and IMCT from total muscle volume, differences in intrinsic strength decreased to 29.6%.
Our data establishes that aging causes significant changes in skeletal muscle composition, with marked increases in non-contractile tissues. Such quantification of the remodeling process is likely to be of functional and clinical importance in elucidating the causes of the disproportionate age-associated decrease of force compared to that of muscle volume.
在人类骨骼肌中，衰老过程会导致收缩功能下降，同时肌肉内脂肪（IMAT）和结缔组织（IMCT）增多。非收缩性组织的积累可能是导致老年人肌肉固有力量显著丧失的原因，但对其进行体内定量分析具有挑战性。本研究的目的是建立基于磁共振成像的方法，以量化年轻和老年人群中IMCT、IMAT和收缩性组织的相对含量，并研究它们在确定与年龄相关的骨骼肌力量变化中的作用。
对五名年轻（31.6±7.0岁）和五名老年（83.4±3.2岁）日本女性进行详细的磁共振成像检查，包括快速梯度回波、定量脂肪/水（IDEAL）和超短回波时间（UTE）序列，以确定整个小腿三头肌复合体中的收缩性肌肉组织和IMAT，以及腓肠肌两头中的IMCT。比肌力计算为等长跖屈力与小腿三头肌复合体生理横截面积的比值。
在老年组中，小腿三头肌总体积减少了17.5%，而小腿三头肌IMAT和腓肠肌IMCT的相对含量分别增加了55.1%和48.9%。跖屈力和比肌力分别有38.6%和42.1%的差异。从总肌肉体积中减去IMAT和IMCT后，固有力量差异降至29.6%。
我们的数据表明，衰老会导致骨骼肌组成发生显著变化，非收缩性组织明显增加。这种对重塑过程的量化可能在阐明与年龄相关的力量下降与肌肉体积下降不成比例的原因方面具有功能和临床意义。
