How Do Muscles Grow?

how do muscles grow

How does a muscle grow?

For a muscle to grow, the body needs to undergo a process called muscle protein synthesis (MPS). MPS is the driving force for muscular adaptations and hypertrophy and is largely regulated by training stimulus and nutrition. Muscle growth occurs when the rates of MPS are higher than the rates of muscle protein breakdown (MPB). MPB occurs when MPS rates are lower than the rates of breakdown. MPS occurs on a cellular level when mTORC1 is stimulated by amino acids, glucose, insulin, anabolic hormones, and hypertrophic training stimuli (Proud, 2009). mTORC1 functions to activate the steps involved with mRNA translation, which is responsible for encoding ribosomal proteins and elongation factors (Proud, 2009). These amino acids and growth stimuli provide the precursors and substrates for muscle protein synthesis and enhance protein accumulation (Proud, 2009). The amino acid leucine plays a very important role in the signaling of mTORC1 as it acts to suppress muscle protein breakdown and is one of the main stimulating factors in initiating the mTORC1 pathway (Proud, 2009). The overall consensus from the literature is that muscle protein synthesis is triggered and regulated via the mTORC1 pathway and/or IGF-1 and is induced by amino acid absorption, hypertrophic exercise stimuli, or both combined. 

What is muscle protein breakdown and how does it happen?

MPB is the opposite effect of MPS and occurs at higher rates than protein synthesis in a fasted state or in the presence of certain diseases such as sarcopenia, sepsis, cachexia, and chronic kidney disease (Gordon et al., 2013). MPB is most commonly caused by IGF-1/insulin resistance, malnutrition, and/or physical inactivity (Gordon et al., 2013). Muscle protein breakdown aside from disease or malnutrition is a natural process the body goes through in its regulation of protein accumulation and degradation. In a fasted state or post-training, muscle protein breakdown rates are higher than baseline due to inadequate nutritional substrates to trigger mTORC1 or IGF-1. For physique athletes in a dieting phase, rates of muscle protein breakdown are higher due to being in a caloric deficit (Helms et al., 2014). 

Finding a positive protein balance to build muscle

The net difference between muscle protein synthesis and muscle protein breakdown is what determines whether muscle tissue is increasing, decreasing, or being maintained (Karagounis et al., 2018). After training or after an overnight fast, the body is in a negative protein balance meaning there are not enough amino acids in the system to stimulate muscle protein synthesis. Muscle hypertrophy occurs when the body is in a positive protein balance which can be induced by the ingestion of food containing essential amino acids or a protein supplement. If your goal is to build muscle then it is advantageous for you to be in a positive protein balance as frequently as possible. This will allow you to reap the muscle-building benefits of muscle protein synthesis and avoid excessive muscle protein breakdown. According to Schoenfeld & Aragon (2018), four protein feedings per day of 0.4-0.5g/kg/meal have been seen to be the optimal dose and feeding frequency to maximize muscle building. Areta et al., (2013) found that 20-25g of protein per meal is the optimal dose of protein to facilitate muscle protein synthesis and utilization of amino acids. The study also highlighted that 20g of protein ingested every three hours post-training is the optimal frequency and dose to maximize muscle building.

How to optimize protein intake for muscle building

After a bout of resistance training, studies have found that there is an optimal window of anabolism that needs to be taken advantage of to elicit the greatest anabolic response with a protein feeding. Bohe et al. (2001) presented that the so-called ‘anabolic window’ post-exercise lasts for approximately two hours. Contrary to that, MacDougall et al. (1995) found that the positive effects of exercise-induced muscle protein synthesis last for up to 24 hours in trained subjects and up to 48 hours in untrained subjects. Regardless of timing, ensuring adequate consumption of protein and carbohydrates during these recovery windows is shown to have favorable results to elicit higher amounts of muscle protein synthesis resulting in higher overall muscle mass. Dreyer et al. (2008) state that ingestion of essential amino acids and carbohydrates after a bout of resistance training enhances activation of the mTORC1 signaling pathway and elevates rates of muscle protein synthesis one to two hours after training. These rates remain elevated by 50% four hours post-training and 109% twenty-four hours after training with regular protein feedings (MacDougall et al., 1995). For leaner individuals, evidence suggests that their recommended intake of protein is even higher than those with more body fat (Hall, 2007).

Overall, consuming 20-30g of protein four times a day and optimizing your protein intake post-training is the best way to ensure you are building muscle and reaping the benefits of your hard work in the gym. One scoop of Glow Protein contains 27g of highly bioavailable protein and is a super convenient way to get in your protein after a workout. Check out our full line of Glow Protein here!