According to this video (sorry for the poor reference but it represents my level of understanding in physiology), muscle grow as a consequence of repairing micro-lesions.

How are these micro-lesions sensed in order to activate protein synthesis? What are the key molecules that trigger myosin synthesis and muscle growth?

  • $\begingroup$ It's not so much due to muscle damage, but due to certain proteins being released from the Z-disks of the sarcomeres which initiate certain signaling cascades involved in muscle proteins. Moreover, during exercise there is a certain amount of metabolic stress which activates other pathways also involved in muscle protein synthesis. I suggest you read up on the STARS pathway (link.springer.com/article/10.1007/s00424-014-1475-5) and mTORC1 regulation. $\endgroup$
    – pbond
    Jul 24, 2015 at 13:55

1 Answer 1


During exercise muscles are put under stress which eventually causes micro tears in the muscle fibres.

These micro tears put pressure on the nerve endings which causes the pain. The body will then repair the tears during rest and recovery using proteins and sufficient fuel. The muscle will then become slightly bigger and stronger.

Energy systems used to repair these lesions are the following

There are three different types of energy systems:

  • Phosphocreatine
  • Lactic Acid
  • -Aerobic

    1.Phosphocreatine Energy System

The ATP-PC system lasts for 8-10 seconds. During the ATP-PC system a phosphate breaks off of the ATP to form ADP and a lot of energy. ADP will then bind with another free phosphate to form ATP. The ATP-PC system is an anaerobic energy system as it dose not use oxygen.

  1. Lactic Acid Energy System

Glucose is broken down sustain performance for a longer amount of time than the ATP-PC system.However this system does not use oxygen so is not suited for events over 90 seconds. When the ATP-PC system starts to fade the process of anaerobic glycolysis begins. Glycogen is stored in the liver and is broken down without the presence of oxygen. This produces lactic acid which limits energy production.

  1. Aerobic Energy system

The aerobic energy system is constantly being used in your body to supply the muscles with energy. In sport the aerobic energy system is used for events that last anything over 90 seconds. The aerobic system can be used constantly but only if there is a constant supply of glycogen and fatty acids. The aerobic system uses oxygen, glucose and fatty acids to yield large amounts of ATP. The system takes place within the mitochondria and produces two bi-products, carbon dioxide and water.

  • $\begingroup$ These are some generalizations, I beleive the aa which is responsible for protein synthesis is BCAA leucine. $\endgroup$
    – Macedon93
    Sep 25, 2014 at 18:49
  • $\begingroup$ Thank you. I am no so interested in "where does the energy allowing muscle work come from?" but I am interested in "the key molecules that directly trigger the synthesis of new myosin proteins?" Sorry if my question was a bit unclear. $\endgroup$
    – Sulawesi
    Sep 30, 2014 at 16:19
  • $\begingroup$ You summarized the three main energy systems (why?) and gave no explanation of the actual mechanism. This does not answer the question at all. $\endgroup$
    – pbond
    Jul 24, 2015 at 13:56

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