Muscle as an endocrine organ

Exercise can protect the body from a myriad number of disease states, from Type-2 Diabetes Mellitus to hypertension, cardiovascular disease and even dementia and cancer. Mental health states like depression also benefit from regular exercise. 

The finding that Interleukin-6 (IL-6) a chemical produced by the muscle during exercise can stimulate the liver to release glucose was the first time muscle was seen as an endocrine (hormone-releasing) organ. When IL-6 is produced by immune system cells or visceral fat, it is pro-inflammatory, i.e. it stimulates inflammation in the organs and tissues where it is produced. When produced by immune system cells or visceral fat, it is called a 'cytokine', but when the muscle produces it, it is called a 'myokine'. Interestingly, as a myokine, IL-6 is anti-inflammatory - it decreases the inflammatory cascade in tissues. So this molecule is either Jekyll or Hyde depending on its origin. 

Over the past decade, 100's of myokines have been discovered 

Extracellular Vesicles - EVs 

The Myokine Biology unit at the Garvan Institue in Australia has discovered the amazing way exercised muscle communicates with cells both near and far through both paracrine (nearby) and endocrine (far) cellular chemical signalling. 

These EVs carry numerous compounds that include but are not limited to a large array of proteins, lipids, myokines, DNA, RNA. 

These vesicles preferentially target the liver which is understandable as the liver has a large reserve of glycogen that can be converted to glucose during exercise and out of a possible 20,000 protein-coding genes in human cells, 60% of these are expressed in the liver. 

Exercise requires an optimal intake of nutrient resources

It is important to remember that muscle can only produce effective EVs and stimulate muscle growth if you provide your body with an adequate intake of nutrients. 

Exercise is s double-edged sword as it can be tremendously beneficial in terms of health and disease outcomes but it can also be damaging not only in terms of injury caused by poor form or excessive exercise but also through the Triage mechanism where a deficiency of a micronutrient or amino acid needed for cellular signalling or muscle growth will result in major organ systems being cannibalised to provide these nutrients.

Organs and bone are large reservoirs of protein, minerals and other micronutrients like vitamins. Over time, organs can diminish in size affecting function and bones can become weaker (osteopenia or osteoporosis).

So exercising without a solid dietary foundation or indeed not supplementing with protein or essential amino acids (EAAs) in the peri-exercise period is folly.  

References: 

1. Whitham, M., et al. (2018). "Extracellular Vesicles Provide a Means for Tissue Crosstalk during Exercise." Cell Metabolism 27(1): 237-251. e234.
2. FEBBRAIO, M. and B. PEDERSEN (2002). "Muscle-derived interleukin-6: mechanisms for activation and possible biological roles." The FASEB Journal 16(11): 1335.
3. Petersen, A. and B. Pedersen (2005). "The anti-inflammatory effect of exercise." Journal of Applied Physiology 98(4): 1154.

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