It is a well known fact that a proper resistance training program stimulates muscle protein synthesis. How does various nutrients and hormones combined with exercise affect net muscle protein balance? In this installment of The Practical Scientist we will look at Human Muscle Protein Synthesis After Physical Activity and Feeding by Benjamin F. Miller to answer some of these questions. This paper will help readers make wise choices regarding nutrition and take advantage of the anabolic stimuli caused by resistance training.

Key points from Human Muscle Protein Synthesis After Physical Activity and Feeding. Benjamin F. Miller.

The increase in protein synthesis after feeding is a systemic transient storage phenomenon, whereas physical exercise stimulates a local long term adaptive response. Providing nutrition after physical activity takes advantage of the anabolic signaling pathways that the physical activity has initiated by providing amino acid building blocks and energy for protein synthesis.

Physical activity has triggered an adaptive response to which the nutrition provides the necessary building blocks for an optimal response (my comment: No matter what you tell some trainees they can’t seen to get it through their head that training alone is not sufficient to optimize gains in skeletal muscle tissue.) In other words, nutrition is necessary to take advantage of an adaptive environment created by exercise.

Just as adipose is the storage depot of excess free fatty acids and muscle and liver glycogen are the storage site of glucose (my comment: kidney contains small amounts of glycogen), skeletal muscle can be viewed as the storage depot of amino acids. As mentioned by Wolfe, skeletal muscle protein is the only AA reserve in the body capable of significant losses without compromising the ability to sustain life. In the fasted state, skeletal muscle protein breakdown increases to sustain the free AA pool (my comment: excerpt from Protein Essentials by Jamie Hale- The free amino acids are located mainly in the cytosol (aqueous part of cytoplasm) and circulating blood. To keep the pool adequately supplied, it is important to consume a sufficient quantity of indispensable amino acids daily. Amino acids released by the breakdown of dietary or tissue protein, synthesized de novo, or mixed with other free amino acids distributed throughout the body make up the amino acid pool. The pool provides amino acids for protein synthesis and oxidation and contains about 100 grams of amino acids. It is small in comparison with the amount of total protein stored in the body (about 12 kg in a 70 kg man). The free pool is approximately 1 percent of the size of the amino acids stored in tissue. The free pool of amino acids is important for protein metabolism for various reasons. It provides a link between dietary and body protein, as they both contribute to it. The free pool is also involved with protein turnover. It has also been noted that concentrations of certain amino acids in the pool, particularly glutamine, are directly correlated with muscle protein synthesis. Approximately 60 percent of the amino acid pool is compromised by glutamine). Conversely, when fed, AA stimulate muscle protein synthesis to maintain AA stores during subsequent fasts.

A flooding dose of essential amino acids stimulated the fractional synthesis rates of skeletal muscle protein when simultaneously measured by the continuous infusion technique. However, when nonessential AA were used as a flood, FSR was not increased (my comment: the body makes a sufficient quantity of nonessential amino acids to support needs from metabolic intermediates and other amino acids, including more in the diet does not further enhance MPS). The stimulation of muscle protein synthesis by EAA is an interesting display of human design. Because EAA by definition can only come from the diet, the increased concentration of EAA indicates that a meal has been consumed. The signaling of a consumed meal would not work with NEAA because the concentrations of NEAA can change in the absence of a meal through transamination (my comment: transamination- The reaction between an amino acid and an -keto acid through which the amino group is transferred from the former to the latter; in certain cases the reaction may be between an amino acid and an aldehyde).