Muscle Protein Synthesis at Any Age

Whether you’re bodybuilding or strength training, the end goal is to turn on Muscle Protein Synthesis (MPS).
MPS is the process by which muscle repairs and grows. Muscle gets bigger and stronger when it produces more contractile proteins like actin and myosin. Intense training can break those proteins down (Muscle Protein Breakdown, MPB). Thus the equation:
Net MPS = MPS – MPB
The goal of training and dieting is to shift this equation toward more synthesis than breakdown. The molecular switch for turning on MPS is called mammalian target of rapamycin (mTOR). Your training in the gym and food you eat both have the ability to activate mTOR. The actual act of lifting weights and its effect on the cell membranes of muscle also activates mTOR. However, a key activator of mTOR is in the protein we eat.
The amino acid L-leucine has been proven to be the main player in protein for turning on MPS. Not all proteins are created equal: some contain more leucine per gram.
Studies show that gram for gram, whey protein is effective in inducing a larger increase in blood essential amino acids and stimulating MPS post exercise compared to soy.
When you eat, the leucine spike results in the activation of mTOR. When all the other essential amino acids are present, as in drinking whey protein, this activation leads to the production of muscle building proteins. The food you eat also causes insulin release which helps halt the process of MPB. Interestingly, it is the MPB side of the equation that needs the most inhibition to keep your muscle growing.
MPB is initiated by intense training, inflammation, stress, and hormonal imbalances such as elevated cortisol. To boost Net MPS, you must try to keep MPB down.
Insulin production after a meal initiates molecular signals that turn off MPB.
Carbohydrates and proteins like milk derived casein are particularly adept at reducing the activity of cellular machinery of MPB. Deep sleep and its production of growth hormone and IGF-1 helps to limit MPB.
The breakdown product of leucine call beta-hydroxy-beta-methyl-butyric acid or HMB for short is a supplement ingredient that is particularly good at fighting MPB associated with resistance training.
As you get older – which can mean as early as 40 – the equation for Net MPS tends to drift toward MPB. Although the exact reasons for this are multifactorial and complex, science does show that you can fight it.
Science shows that as you age, your muscles become less sensitive to the effects of leucine and insulin.
Interestingly, studies show that it takes a greater leucine spike from a meal to activate mTOR in a 70- year-old than a young adult. This is called “leucine resistance.” 20g of whey protein may optimize mTOR activity in a young adult, but the older individual may require up to 40g to get the same effect. This science shows that it is critical to boost protein in your diet as you age.
Another strategy to enhance MPS with age is to limit the MPB side of the equation. You can do that by using supplements like HMB. In multiple studies, HMB has been shown to reduce MPB in the aging population. By supplementing with 3g of HMB with a leucine rich protein like whey isolates you can optimize muscle health. In summary, keep the math in mind when putting together your training and diet – the harder you live, the faster you fall.
Allow plenty of time in your training schedule for recovery of your muscle.
As you age, that may mean more time between body parts; let the soreness resolve before hitting that part again. Enhance your hormonal milieu by getting more growth hormone producing deep sleep. Use stress management techniques like meditation and yoga. Get more protein per meal and eat meals more regularly. Add HMB, whey protein, and creatine to your supplementation regimen to optimize MPS.


By Dr. Prisk Dr. Victor R. Prisk, MD is a Board-Certified Orthopaedic Surgeon and NPC Welterweight National Champion.