Department of Nutrition and Metabolism.
Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX.
J Nutr. 2018 Jun 1;148(6):900-909. doi: 10.1093/jn/nxy064.
The muscle protein anabolic response to contraction and feeding may be blunted in older adults. Acute bouts of exercise can improve the ability of amino acids to stimulate muscle protein synthesis (MPS) by activating mechanistic target of rapamycin complex 1 (mTORC1) signaling, but it is not known whether exercise training may improve muscle sensitivity to amino acid availability.
The aim of this study was to determine if muscle protein anabolism is resistant to essential amino acids (EAAs) and whether resistance exercise training (RET) improves muscle sensitivity to EAA in healthy older adults.
In a longitudinal study, 19 healthy older adults [mean ± SD age: 71 ± 4 y body mass index (kg/m2): 28 ± 3] were trained for 12 wk with a whole-body program of progressive RET (60-75% 1-repetition maximum). Body composition, strength, and metabolic health were measured pre- and posttraining. We also performed stable isotope infusion experiments with muscle biopsies pre- and posttraining to measure MPS and markers of amino acid sensing in the basal state and in response to 6.8 g of EAA ingestion.
RET increased muscle strength by 16%, lean mass by 2%, and muscle cross-sectional area by 27% in healthy older adults (P < 0.05). MPS and mTORC1 signaling (i.e., phosphorylation status of protein kinase B, 4E binding protein 1, 70-kDa S6 protein kinase, and ribosomal protein S6) increased after EAA ingestion (P < 0.05) pre- and posttraining. RET increased basal MPS by 36% (P < 0.05); however, RET did not affect the response of MPS and mTORC1 signaling to EAA ingestion.
RET increases strength and basal MPS, promoting hypertrophy in healthy older adults. In these subjects, a small dose of EAAs stimulates muscle mTORC1 signaling and MPS, and this response to EAAs does not improve after RET. Our data indicate that anabolic resistance to amino acids may not be a problem in healthy older adults. This trial was registered at www.clinicaltrials.gov as NCT02999802.
收缩和进食引起的肌肉蛋白合成反应可能在老年人中减弱。急性运动可以通过激活雷帕霉素靶蛋白复合物 1（mTORC1）信号来提高氨基酸刺激肌肉蛋白合成（MPS）的能力，但运动训练是否能提高肌肉对氨基酸可用性的敏感性尚不清楚。
本研究旨在确定肌肉蛋白合成是否对必需氨基酸（EAA）有抗性，以及阻力运动训练（RET）是否能改善健康老年人对 EAA 的肌肉敏感性。
在一项纵向研究中，19 名健康老年人[平均年龄±标准差（y）：71±4；体重指数（kg/m2）：28±3]接受了 12 周的全身渐进性 RET（60-75% 1 次重复最大值）训练。在训练前后测量身体成分、力量和代谢健康状况。我们还在训练前后进行了稳定同位素输注实验，用肌肉活检测量 MPS 和氨基酸感应标志物在基础状态和 6.8g EAA 摄入后的反应。
RET 使健康老年人的肌肉力量增加 16%，瘦体重增加 2%，肌肉横截面积增加 27%（P<0.05）。MPS 和 mTORC1 信号（即蛋白激酶 B 的磷酸化状态、4E 结合蛋白 1、70kDa S6 蛋白激酶和核糖体蛋白 S6）在 EAA 摄入前后均增加（P<0.05）。RET 使基础 MPS 增加 36%（P<0.05）；然而，RET 并没有影响 MPS 和 mTORC1 信号对 EAA 摄入的反应。
RET 增加了力量和基础 MPS，促进了健康老年人的肌肉肥大。在这些受试者中，小剂量的 EAA 刺激肌肉 mTORC1 信号和 MPS，而这种对 EAA 的反应在 RET 后并没有改善。我们的数据表明，氨基酸的合成抵抗可能不是健康老年人的问题。这项试验在 www.clinicaltrials.gov 上注册为 NCT02999802。
