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.
Objective
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.
Methods
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.
Results
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.
Conclusion
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.
Key Words
aging
anabolic resistance
resistance training
muscle protein synthesis
mTOR
Abbreviations
CSA
cross-sectional area
EAA
essential amino acid
FSR
fractional synthetic rate
LAMP2
lysosome-associated membrane protein 2
MPS
muscle protein synthesis
mTOR
mammalian/mechanistic target of rapamycin
mTORC1
mechanistic target of rapamycin complex 1
OGTT
oral-glucose-tolerance test
RET
resistance exercise training
S6K1
70-kDa S6 protein kinase
UTMB
University of Texas Medical Branch at Galveston
1-RM
1-repetition maximum
4E-BP1
4E binding protein 1.
Cited by (0)
Supported by NIH/National Institute on Aging grants R56 AG051267 and P30 AG024832 and NIH/National Center for Advancing Translational Sciences grant UL1 TR001439.