Exercise, Amino Acids, and Aging in the Control of Human Muscle Protein Synthesis

Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, TX 77555-1144, USA.
Medicine and science in sports and exercise (Impact Factor: 3.98). 05/2011; 43(12):2249-58. DOI: 10.1249/MSS.0b013e318223b037
Source: PubMed


In this review, we discuss recent research in the field of human skeletal muscle protein metabolism characterizing the acute regulation of mammalian target of rapamycin complex (mTORC) 1 signaling and muscle protein synthesis (MPS) by exercise, amino acid nutrition, and aging. Resistance exercise performed in the fasted state stimulates mixed MPS within 1 h after exercise, which can remain elevated for 48 h. We demonstrate that the activation of mTORC1 signaling (and subsequently enhanced translation initiation) is required for the contraction-induced increase in MPS. In comparison, low-intensity blood flow restriction (BFR) exercise stimulates MPS and mTORC1 signaling to an extent similar to traditional, high-intensity resistance exercise. We also show that mTORC1 signaling is required for the essential amino acid (EAA)-induced increase in MPS. Ingestion of EAAs (or protein) shortly after resistance exercise enhances MPS and mTORC1 signaling compared with resistance exercise or EAAs alone. In older adults, the ability of the skeletal muscle to respond to anabolic stimuli is impaired. For example, in response to an acute bout of resistance exercise, older adults are less able to activate mTORC1 or increase MPS during the first 24 h of postexercise recovery. However, BFR exercise can overcome this impairment. Aging is not associated with a reduced response to EAAs provided the EAA content is sufficient. Therefore, we propose that exercise combined with EAA should be effective not only in improving muscle repair and growth in response to training in athletes, but that strategies such as EAA combined with resistance exercise (or BFR exercise) may be very useful as a countermeasure for sarcopenia and other clinical conditions associated with muscle wasting.

Download full-text


Available from: Christopher S Fry, Oct 14, 2014
    • "Another limitation was the fact that diet was not analysed. Adequate protein intake is necessary for muscle protein synthesis, and inadequate amounts in the diet of participants could have influenced the muscle hypertrophy results (Walker et al., 2011). Lastly, it should be noted that our sample size and lack of a control group may have limited our ability to detect significant changes in some variables. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Elastic band (EB) training is a common form of resistance training used by the elderly, individuals with joint problems or those recovering from injury. EB training performed at low intensities by these populations may have little effect on muscle hypertrophy. However, when combined with blood flow restriction (BFR), low-intensity EB resistance training may result in muscle hypertrophy. Postmenopausal women (61 ± 5 years) were assigned to a moderate-to-high-intensity EB group (MH, n = 8) or a low-intensity EB group combined with BFR (LI-BFR, n = 6). Each group performed seated chest press, seated row and seated shoulder press with EB three times a week for eight weeks. EB colours progressed in each group by having participants maintain a rating of 7–9 on the OMNI Resistance for active muscle (OMNI-RES AM) scale (0–10) throughout training. In the LI-BFR group, BFR pressure progressed during the first 4 weeks of training (80–120 mmHg), after which EB colours were progressed. 1-repetition maximum increased for chest press (P = 0·01), shoulder press (P = 0·02) and seated row (P = 0·01), but no differences were found between groups. Only pectoralis major muscle thickness in the upper body increased (P = 0·04). A trend was found for an increase in total bone-free lean body mass (P = 0·055). The main findings of this study were that moderate-to-high-intensity EB training and low-intensity EB training with BFR resulted in similar increases in strength, total bone-free lean body mass and muscle thickness.
    No preview · Article · Apr 2013 · Clinical Physiology and Functional Imaging
  • Source
    • "Sarcopenia leads to muscle function impairments, physical activity limitations, and restrictions in societal participation. Besides tumor-related hypermetabolism (increased resting energy expenditure, muscle protein catabolism) and inflammation, the balanced process of muscle protein turnover chiefly depends on nutrition and physical activity [48]. Both low-energy input (food intake, mainly low-protein nutrition) and output (physical inactivity, mainly few strength-training-type activities) contribute to progressive muscle wasting. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Timing of exposure to lifestyle factors that influence energy balance may differentially affect colorectal cancer (CRC) risk and prognosis. Caloric restriction in youth and short stature, as markers of early-life exposures, have shown to decrease CRC risk, whereas large body size and low physical activity levels in adulthood are established risk factors for CRC. Regarding prognosis, overweight, sarcopenia, and their co-occurrence (sarcopenic obesity) may negatively influence the health and quality of life of CRC survivors. There is mechanistic support for disruption of the mammalian target of rapamycin (mTOR) pathway as an underlying mechanism possibly driving these associations, because mTOR integrates signals from growth factors, nutrients, mutagens, and hormones to induce cell proliferation, resistance to apoptosis, and autophagy. However, epidemiologic evidence connecting mTOR to energy-balance-related CRC throughout the lifespan is scarce. This perspective proposes how multidimensional molecular epidemiologic studies can shed light on the etiology and prognosis of energy-balance-related CRC.
    Full-text · Article · Mar 2013
  • Source
    • "physical activity and exercise), and 23 nutrition (i.e. AA intake and metabolism) (Abbatecola et al. 2011; Dillon et al. 2010; Horstman 1 et al. 2012; Kimball et al. 2002; Walker et al. 2011; Wall et al. 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Aging is associated with a gradual decline in skeletal muscle mass and strength leading to increased risk for functional impairments. Although basal rates of protein synthesis and degradation are largely unaffected with age, the sensitivity of older muscle cells to the anabolic actions of essential amino acids appears to decline. The major pathway through which essential amino acids induce anabolic responses involves the mammalian target of rapamycin (mTOR) Complex 1, a signaling pathway that is especially sensitive to regulation by the branched chain amino acid leucine. Recent evidence suggests that muscle of older individuals require increasing concentrations of leucine to maintain robust anabolic responses through the mTOR pathway. While the exact mechanisms for the age-related alterations in nutritional signaling through the mTOR pathway remain elusive, there is increasing evidence that decreased sensitivity to insulin action, reductions in endothelial function, and increased oxidative stress may be underlying factors in this decrease in anabolic sensitivity. Ensuring adequate nutrition, including sources of high quality protein, and promoting regular physical activity will remain among the frontline defenses against the onset of sarcopenia in older individuals.
    Full-text · Article · Dec 2012 · Amino Acids
Show more