What happens to our muscle cells with endurance training versus strength training? Cell signalling simplified


Our muscle cells are constantly adapting and changing to the exercise we do or do not do over time.  They behave in what is called a plastic manner, meaning that they can be modified or changed.  This is what enables us to adapt to our training.

If the training is guided properly and fatigue and recovery are taken into consideration we get better at a task over time.  Research over the last few years has started to highlight how the training we do allows our bodies to adapt to the training.  I want to introduce you to a concept called cell signalling. Let me explain.

Through endurance training our stores of glucose within the muscle cells and liver (glycogen) will reduce over time.  Traditionally this form of training is at a lower intensity and for a longer duration, which over time reduces our stores of glycogen and raises a product in the cells called AMP.  AMP concentrations are gradually raised as when your muscle contract they use a product called ATP which is then converted to AMP to provide energy to the muscle cell.  If this occurs over a long duration the concentration of AMP can rise.  The raised levels of AMP and lowered level of glycogen turns on the machinery to stimulate the development of a structure in the cell that is called mitochondria.  These mitochondria are the energy factories that provide the majority of the ATP for muscle contractions to occur repetitively at a low intensity.  So, if there are more mitochondria in the muscle cell, the availability of ATP increases, which enables the muscle to continue contracting for longer, hence raising your endurance capacity. 




If we look at strength training this acts through very different cell signalling pathways.  If appropriate training is provided it activates a pathway that leads to raised levels of mTOR.  mTOR has been shown to increase protein synthesis inside the muscle cell.  This in turn leads to the muscle adapting to the resistance training by adding more muscle to its structure. 



So, lets talk about a few practical considerations to consider based on this information:

  1. As these are separate pathways it is not smart or wise to do strength training at the same time as endurance training as you will mute the potential gains of each pathway.  Ask yourself what your goal is prior to the session to gain strength or improve endurance? I recommend to allow a few meals between sessions to replace lost energy stores and/or if possible do an endurance session on a separate day to a strength session.
  2. If the volume of your resistance training is too much and you do not replace the lost glycogen stores as you train you will suppress your mTOR response.  Glycogen loss is linked to high intensity exercise.  So, if you do resistance training with only water you may need to consider this. 
  3. The availability of amino acids ( building blocks of protein) assists the muscle cells to enhance mTOR function, especially the availability of the amino acid leucine (more on this in another post).  So this makes sense, if you have the building blocks of protein available it will allow proteins to be made.
  4. If endurance training occurs too soon after a resistance training session, the mTOR response will be suppressed, leading to reduced protein synthesis and suppressed muscle growth and strength gains.  This works in the opposite direction as well.
  5. To enhance your adaptation to resistance training it is wise to maintain your glycogen stores during the session and to ensure that you have a protein rich meal/shake within 20-30 minutes of finishing the session that has a reasonably decent concentration of leucine (2-3g out of 20-25g total).  Remember that carbohydrate ingestion post work out is also important to promote insulin release, glycogen replacement and to enhance protein synthesis and recovery.    
Jess Knollmeyer