Power Geoffrey A, Minozzo Fábio C, Spendiff Sally, Filion Marie-Eve, Konokhova Yana, Purves-Smith Maddy F, Pion Charlotte, Aubertin-Leheudre Mylène, Morais José A, Herzog Walter, Hepple Russell T, Taivassalo Tanja, Rassier Dilson E
Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, Ontario, Canada; Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada;
Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada; The Muscle Physiology and Biophysics Laboratory, McGill University, Montreal, Quebec, Canada;
Am J Physiol Cell Physiol. 2016 Feb 15;310(4):C318-27. doi: 10.1152/ajpcell.00289.2015. Epub 2015 Dec 2.
Normal adult aging is associated with impaired muscle contractile function; however, to what extent cross-bridge kinetics are altered in aging muscle is not clear. We used a slacken restretch maneuver on single muscle fiber segments biopsied from the vastus lateralis of young adults (∼23 yr), older nonathlete (NA) adults (∼80 yr), and age-matched world class masters athletes (MA; ∼80 yr) to assess the rate of force redevelopment (ktr) and cross-bridge kinetics. A post hoc analysis was performed, and only the mechanical properties of "slow type" fibers based on unloaded shortening velocity (Vo) measurements are reported. The MA and NA were ∼54 and 43% weaker, respectively, for specific force compared with young. Similarly, when force was normalized to cross-sectional area determined via the fiber shape angularity data, both old groups did not differ, and the MA and NA were ∼43 and 48% weaker, respectively, compared with young (P < 0.05). Vo for both MA and NA old groups was 62 and 46% slower, respectively, compared with young. Both MA and NA adults had approximately two times slower values for ktr compared with young. The slower Vo in both old groups relative to young, coupled with a similarly reduced ktr, suggests impaired cross-bridge kinetics are responsible for impaired single fiber contractile properties with aging. These results challenge the widely accepted resilience of slow type fibers to cellular aging.
正常成年人的衰老与肌肉收缩功能受损有关；然而，衰老肌肉中横桥动力学的改变程度尚不清楚。我们对从年轻成年人（约23岁）、老年非运动员（NA）成年人（约80岁）和年龄匹配的世界级大师级运动员（MA；约80岁）的股外侧肌活检获取的单根肌纤维节段进行了松弛后再拉伸操作，以评估力量重新发展的速率（ktr）和横桥动力学。进行了事后分析，并且仅报告了基于无负荷缩短速度（Vo）测量的“慢肌纤维类型”的力学特性。与年轻人相比，MA和NA的比力分别弱约54%和43%。同样，当将力量标准化为通过纤维形状角度数据确定的横截面积时，两个老年组没有差异，并且与年轻人相比，MA和NA分别弱约43%和48%（P<0.05）。与年轻人相比，MA和NA老年组的Vo分别慢62%和46%。与年轻人相比，MA和NA成年人的ktr值均慢约两倍。相对于年轻人，两个老年组较慢的Vo，再加上同样降低的ktr，表明横桥动力学受损是衰老导致单根肌纤维收缩特性受损的原因。这些结果挑战了人们广泛接受的慢肌纤维对细胞衰老具有弹性的观点。
