Activation of mTOR signaling in young and old human skeletal muscle in response to combined resistance exercise and whey protein ingestion
 
 
Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Year: 2012
Volume: 37
Page numbers: 21-30

Summary of background and research design:

Background: Aging is associated with a decline in muscle mass presumably due to a hampered ability of the muscle to respond to anabolic stimuli, such as resistance exercise or dietary protein. It is thought that down–regulation of the mTOR biochemical signaling pathway is responsible for this phenomenon. Whey protein contains a substantial amount of essential amino acids, which are thought to stimulate protein synthesis of enzymes in the mTOR pathway.

Hypothesis: A combination of resistance training and a whey protein post–exercise supplement will be more effective than exercise alone in stimulating the mTOR pathway in younger and older people.

Subjects:
“Younger”– 16 healthy men, age 18–25 y
“Older”– 15 healthy men, age 60–75 y

Experimental Design: randomized, double–blinded, repeated measures

Treatments: Whey protein (27 g) or a placebo (artificial color and flavor, no protein)

Protocol: Before and after a 12 wk resistance training period, an acute resistance exercise trial was performed. The whey protein or placebo was ingested immediately after each exercise session during the training period. A fasting, resting muscle biopsy was acquired, then participants performed 3 sets of 8 reps of single–legged knee extensions at 60°/sec with 2 min in between sets. Biopsies were acquired from both the exercising leg and the resting leg 2 hrs later.
       For resistance exercise training, the participants completed 12 wks of training, supervised by a certified trainer. The training was 3 days per week. The routine included a light warm–up then resistance training– leg press, bench press, seated row, leg extension, dumb–bell shoulder press, and sit–ups. The amount of weight was adjusted appropriately throughout the 12 wks to maximize muscle growth and minimize injury.
       Muscle tissue was analyzed for proteins in the mTOR pathway, mRNA levels for the respective proteins, and the phosphorylation state of various proteins in the pathways, which suggests if the proteins are “on” or “off”.
 

Summary of research findings:
  • Energy intake did not vary between treatment groups within each age category. However, men in the supplement group exhibited a larger daily intake of protein early in the study than those in the placebo group.
  • All groups displayed gains in muscle strength as a result of the training program with no difference between the whey and placebo groups. However, the young participants in the whey group exhibited a significant increase in eccentric strength compared to their counterparts in the placebo group.
  • The phosphorylation states of many proteins in the mTOR pathway were affected by the combination of exercise and whey protein supplementation in both age groups, indicating that muscle protein synthesis was more active with protein supplementation and exercise vs. exercise alone. There were some effects in the placebo group as well, but the effects were more numerous and dramatic in the whey protein group compared to the placebo group.
  • For example, the mTOR complex exhibited a greater level of phosphorylation in young men, but only when they consumed the whey protein with exercise. Also, 4E–BP1 showed a greater level of phosphorylation after exercise (indicator that protein synthesis can move forward), but only in the older participants who consumed whey protein.

Key practice applications: Nutrition, training status, and age can affect the muscle’s response to acute exercise. However, it appears that a 12 wk, routine, resistance exercise program can be equally effective in older or younger men. As long as they are consuming adequate protein and other nutrient requirements, the ingestion of protein postexercise did not appear to be critical for long term strength gains. With that said, whey protein consumed immediately after exercise led to a more activated mTOR signaling pathway which could enhance recovery and/or have effects that were not able to be observed in this study.

Key search terms for this article (5-7 terms): elderly, older, protein, whey, timing, resistance training program, protein synthesis, mTOR

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