Influence of Amino Acids, Dietary Protein, and Physical Activity on Muscle Mass Development in Humans

Abstract

Ingestion of protein is crucial for maintenance of a variety of body functions and within the scope of this review we will specifically focus on the regulation of skeletal muscle mass. A quantitative limitation exists as to how much muscle protein the body can synthesize in response to protein intake. Ingestion of excess protein exerts an unwanted load to the body and therefore, it is important to find the least amount of protein that provides the maximal hypertrophic stimulus. Hence, research has focused on revealing the relationship between protein intake (dose) and its resulting stimulation of muscle protein synthesis (response). In addition to the protein amount, the protein digestibility and, hence, the availability of its constituent amino acids is decisive for the response. In this regard, recent studies have provided in-depth knowledge about the time-course of the muscle protein synthetic response dependent on the characteristics of the protein ingested. The effect of protein intake on muscle protein accretion can further be stimulated by prior exercise training. In the ageing population, physical training may counteract the development of “anabolic resistance” and restore the beneficial effect of protein feeding. Presently, our knowledge is based on measures obtained in standardized experimental settings or during long-term intervention periods. However, to improve coherence between these types of data and to further improve our knowledge of the effects of protein ingestion, other investigative approaches than those presently used are requested.

Effects of Postexercise Protein Intake on Muscle Mass and Strength During Resistance Training: Is There an Optimal Ratio Between Fast and Slow Proteins?

“…Previous studies clearly suggested that fast-digested and slow-digested proteins have synergistic effects on muscle anabolism (Dideriksen et al, 2013;Boirie et al, 1997).…”

Glutamine metabolism in advanced age

“…[69][70][71][72] Because protein ingestion is crucial for the maintenance of a variety of body functions, the requirements of protein in the elderly are a major factor in maintaining skeletal muscle mass; the amount of protein ingested that induces maximal muscle protein synthesis must be higher in elderly than in young individuals in order to combat anabolic resistance in the elderly. 5,[73][74][75][76][77] Dysregulation of autophagy [78][79][80] contributes notably to aging. Autophagy, a lysosomal process involved in the maintenance of cellular homeostasis, is inhibited by the insulin-amino acid-mTOR signaling pathway that controls both protein synthesis and longevity (see next paragraph).…”

Effect of Physical and Flexibility Exercise on Plasma Levels of Some Liver Enzymes and Biomolecules of Young Nigerian Adults

“…However, while the decrease in the male participants was statistically significant, the decrease in the female participants was not statistically significant. A plausible reason for this decrease in total protein value has been suggested [21][22][23], to be due to increased demand of glucogenic amino acids for the generation of energy leading to increased degradation of proteins. A similar result was obtained for plasma albumin.…”