In my last blog I detailed the plethora of benefits related to having more muscle mass. In this blog I will go further into the science of the muscle building process alongside some practical takeaways to apply to your own training. 


The process of increasing muscle size is called muscular hypertrophy. It is often believed that this process is activated by simply inducing micro-damage in the muscle fibres via exercise which subsequently repair stronger than before. While this is not necessarily false, there is a lot more to it – in some cases reducing muscle damage is actually more beneficial to overall muscle growth.  


Let’s explore. 


Muscular hypertrophy involves three primary mechanisms, one of which is muscle micro-damage as outlined above, but this is seen as a potentially lessor contributing mechanism. The two more dominant mechanisms are mechanical tension and metabolic stress, which both play a big role when considering resistance program design.  


Mechanical tension, which is generated when muscle fibres are stretched or contracted during resistance training, is particularly important for triggering the cellular signalling pathways that promote muscle growth. This process, called mechanotransduction, involves the conversion of mechanical stimuli into biochemical signals that regulate gene expression and cellular function. In other words, the mechanical stimulus triggers muscle growth. This is thought to be the primary mechanism for muscle growth – the muscles adapt to the force it is exposed to.  


The next mechanism to consider is metabolic stress, which refers to the accumulation of metabolites in the muscle during resistance training, such as lactate and hydrogen ions. This leads to an increase in cell swelling, which can trigger anabolic signalling pathways that promote muscle growth.  


Metabolic stress is often felt as muscle heaviness or tightness during exercise and is particularly pronounced more towards the end of the set. This accumulation inhibits the muscle’s contractile ability to some degree, or in other words contributes to fatigue. This fatigue somewhat recovers during the rest period, however if a large amount of metabolic stress occurs, it will likely need a much longer period of rest to see full recovery of muscle function – 24 to 48 hours.  


Considering the fatigue state of a muscle is very important during training: too much metabolic stress too early in a session may result in suboptimal training. It is often thought that the optimal way to build muscle is to overwhelm the target tissue and take it to complete fatigue on each set. Anyone that resistance trains would tell you that after a set of taking the muscle to full exhaustion, the next set is somewhat lackluster. This becomes a problem in the context of a full session – 2 or 3 sets may be a very effective stimulus, but beyond this, the muscle may be too fatigued to generate sufficient mechanical tension which results in training in a sort of in-between state where low tension is achieved while racking up fatigue in the muscle.  


Think of it this way – imagine Joe can bench press 100kg for 10 reps which is his point of complete fatigue. His next set he may be able to achieve approximately 7 repetitions due to fatigue. On a third set he may only achieve 5 repetitions. So overall he has achieved 22 repetitions of 100kg bench press with a high degree of metabolic stress, meaning his ability to perform his next exercise is significantly impacted.  


Take the same example but imagine he stops a few repetitions shy of complete failure, say 8 reps. After sufficient rest it is likely that he will hit 8 reps a further 2 times, leading to a total of 24 reps rather than 22. It is also likely that he is less fatigued given his appropriate pacing of reps, so he will be able to lift better for his next exercise i.e more mechanical tension. In this example, Joe has generated more mechanical tension with far less fatigue. Of course, everyone is different and the numbers above may differ depending on rest periods, training age and genetics. The logic still stands – excessive fatigue = muscular impairment = reduced ability to produce mechanical tension. In some cases this can be a negative trade off and may result in less muscular hypertrophy.  


The final mechanism is muscle damage, a breakdown of muscle fibres during resistance training. This damage triggers an inflammatory response, which stimulates satellite cells to repair and rebuild the damaged muscle fibres. Muscle damage can be increased by performing exercises that emphasize the eccentric phase, such as slow and controlled lowering of the weight. Similar to metabolic stress, too much muscle damage may require longer recovery, so it is important to appropriately balance this out. 


This also has implications for individuals who may not be able to tolerate a heavy and fatiguing program, such as older adults, people with a disability or medical condition that makes them prone to fatigue. It is an important message that muscle gains do not solely rely on an insane burn or an overwhelming amount of work. While it is true that a threshold level of mechanical tension and fatigue is required to actually force the body to adapt, this may not be as brutal as is maybe perpetuated by the muscle damage narrative.  

  • Muscular hypertrophy occurs due to many mechanisms, not just simple muscle damage and repair. This has implications for all individuals in different life circumstances. 
  • The way to optimise muscular hypertrophy is a tailored and well-designed program. 
  • Taking your muscles to extreme fatigue at the start of the workout may not be optimal as this compromises the muscle’s ability to generate sufficient mechanical tension throughout the session. It may instead be better to leave 2-3 repetitions in the tank to allow for greater mechanical tension over time. 
  • Metabolic stress and muscle damage do play a role in muscular hypertrophy, however it is important to weigh up the effects of fatigue in the context of the individual. 


Muscle is a very important tissue not just for strength and power, but also for our overall health. Particularly as we get older, increasing or maintaining how much muscle mass we have is vital to our health and wellbeing.  


Some people may have injuries or other physical limitations that limit their capacity for participation in physical activity. In this case, consultation with a health professional can be invaluable to ensure a safe and tailored progression into a program and strategic exercise selection to get the most value out of training. 


At CSSM, we have a fully equipped gym where we can guide and provide an appropriate strengthening plan.  


 Read Hugh’s last blog about muscle mass in adults.

About the author

CSSM physiotherapist Hugh Feary  has previously worked in GP clinics and private practice as well as a variety of local sporting teams including the Fremantle Dockers in the AFLW. 

Hugh enjoys helping others who have any niggles or injuries to modify their program to keep them moving. He does this by empowering them with the information and the tools they need to manage their own health and get back to the things they love to do.




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Krzysztofik, M., Wilk, M., Wojdała, G., & Gołaś, A. (2019). Maximizing muscle hypertrophy: a systematic review of advanced resistance training techniques and methods. International journal of environmental research and public health, 16(24), 4897. 


Schoenfeld BJ. Potential mechanisms for a role of metabolic stress in hypertrophic adaptations to resistance training. Sports Med. 2013 Mar;43(3):179-94. doi: 10.1007/s40279-013-0017-1. PMID: 23338987. 


Schoenfeld, B. J. (2020). Science and development of muscle hypertrophy. Human Kinetics.