How Lifting Weights Builds Muscle

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When looking at how lifting weights builds muscle, we need to first look at a biological process called muscle hypertrophy. Muscular hypertrophy is the body’s way of repairing damaged muscle tissue after injury or intense exercise. It is this re-fusing of these fibers during periods of rest after intensive resistance training that causes the muscles  to grow in size over time.

The process I have just described is very much a summarized version of what happens when muscles grow in size as a result of effective resistance training. There are actually many more factors which determine to what extent our muscles grow after weight training. In the rest of this article I will go into more detail about the processes involved, and I will give you some tips on how you can use this knowledge to really get the most from your training regime and diet plan.

how lifting weights builds muscle

In order to continue to build muscle, you need to keep challenging your muscles over time. Seeing as your muscles get stronger the more times they repair and continue to grow, the heavier you will need to lift in order to continue to get stronger and build more muscle. This is called progressive overload and it is very important if you want to continue to make progress.

It is widely thought that muscle hypertrophy causes muscles to grow not though increasing the number of muscle fibers, but actually by increasing the mass and cylindrical size of each of the individual fibers as they tear and fuse back together during the healing process. It is the mechanoreceptors that are located near the membrane of each individual that detect the strain and damage to these muscle fibers and signal to body to begin the process of muscular hypertrophy.

There are 4 factors that affect the extent to which the muscles experience mechanical load during a contraction. This then also affects to what extent muscle hypertrophy and muscle growth takes place during recovery.


These four factors are;

  1. 1The size principle
  2. 2The force-velocity relationship
  3. 3The length-tension relationship
  4. 4Fatigue

The size principle

The size principle refers to the size of the motor units that are used to contract groups of muscle fibers during movement and exercise etc. Larger motor units are able to contract a larger group of muscle fibers (many thousands) at one time thus allowing a greater amount of muscle hypertrophy to occur during recovery. Also, the particular type of muscle fibers that the high threshold motor units recruit are naturally more susceptible to this muscle repair and growth process.

The size of motor units used can depend largely on the type of exercise performed. For example, aerobic exercise such as running or swimming does not stimulate the larger motor units, whilst heavy weight/resistance training does which therefore leads to greater muscle growth over time.

The force-velocity relationship

This refers to the speed in which the muscle fibers contract and relax during lifting (concentric) and lowering (eccentric concentric movement) of weights. It is now thought that slower muscle contractions and extensions actually creates a greater force within the muscle fibers and therefore increases the amount of hypertrophy and muscular growth that takes place.

A fast speed repetition of an exercise causes the thick mysoin and the thin actin filaments within the muscle fibers to just slide past one another. However, slower repetitions of an exercise allows more bridges (links) to be formed between the mysoins and actins which in turn causes greater tension and force in each muscle fiber. This leads to greater hypertrophy and muscular growth.

The above facts shows us my the technique of lengthening the Time Under Tension (TUT) when weight training is so important for effective muscle building. Rushing repetitions of exercises does very little for effective muscle building.

Negative repetitions in which you lift the weight at normal speed but then lower the weight slowly over 5-10 seconds is the most effective way of producing the greatest force and tension within the muscles. This is because the cross-bridge links between the mysoins and actins appear to be stronger during the lowering of weights.

The length-tension relationship

The length-tension relationship states that more force and tension is produced in the muscle fibers when they are at certain lengths, which then creates greater hypertrophy and muscle growth. In order to create the most force and tension in a muscle, you need to actively lengthen the muscle significantly beyond their passive length tension point which is the position of the muscle where it is just resting in its natural position. 

​When you contract the muscle fully, your muscle fibers will also reach a peak in force and tension that can be produced. Clench your fist as tight as you can and you will feel this in action.

In essence, for optimal muscle hypertrophy and muscle growth, you need to ensure you actively lengthen your muscle during the concentric movement, and you also need to sufficiently contract your muscles at the peak of the eccentric concentric movement. It is the extreme lengthening and contracting of muscles that causes the greatest muscle growth (i.e. performing a full range of motion during exercise)

If you are a bit of a science lover and would like to learn in a bit more depth about the length-tension relationship in muscles, then I highly suggest that you watch the short video below by Professor Roofs MD.


Fatigue is the final factor I am going to talk about when it comes to looking at the variables involved when applying force and mechanical tension on muscles.

When it comes to muscles, fatigue is the decreasing ability to produce force and therefore tension in that particular muscle due to exercise or exertion.

​Fatigue of the central nervous system (central fatigue) and fatigue of the muscle tissue itself (peripheral fatigue) both contribute to this decreasing ability to produce muscular force as exercise of that muscle continues.

Peripheral fatigue increases the amount of mechanical load that muscle fibres experience as the muscle’s fatigue levels increase. This means that as the muscle tires completely, training with a lighter weight will cause a similar amount of tension and hypertrophy in the muscle, as to what was being experienced originally with the heavier weight. This practice is known as drop sets.

​ As we a have already established, fatigue is important for muscle growth. Therefore it is important to train to failure on each set of exercises. This means lifting the weight until you can not physically perform another single repetition.

​However, how do we take advantage of  fatigued muscle that has been training to failure fully in order to increase hypertrophy and muscle growth.

​The answer is in drop sets. This means that once you are struggling to perform the required amount of repetitions per set on one particular weight, it is then very advantageous to lower the weight you are lifting so that you can perform the required amount of repetitions again. Do this until muscular failure and drop the weight again.

​In doing this you really fatigue the muscle effectively which will enhance your muscle building results.

There is another biological process that is responsible for muscle growth which occurs alongside muscle hypertrophy. Both of these process can be optimized and enhanced through our lifestyle choices which we will come onto in a bit. ​

​First though; what other process is responsible for muscular repair and growth?…

The Role of Protein Synthesis in Muscle Building

Protein synthesis is a vital biological process in the body in which new blocks of protein are produced in order to build new muscle. Protein synthesis works in a synergistic way and in tandem with muscular hypertrophy in order to build new muscle as a result of intense exercise and optimal diet with sufficient protein consumption.

Think of protein synthesis as the factory that makes the bricks; and think of muscular hypertrophy as the builders who take those bricks and builds a new house out of them.

​This clever biological process can only take place in an efficient way if follow factors are taken care of through our lifestyle choices. 

​Some of there factors are;

  • Weight/resistance training (to failure in order to tear the muscle fibers​)
  • Diet (particularly protein consumption)
  • ​Rest and recovery (Giving the body time after an intense workout to build and repair new muscle tissue  to through the process of muscular hypertrophy)

This is how muscle growth as a result of weight training, diet and recovery works.

​And below is a study that illustrates this point.

how lifting weights builds muscle


The study shown above illustrates how using weight training to damage muscle fibers on a microscopic level really does increase muscle size and strength.

However, What is also clear is that training to failure with weights in of itself is not enough to stimulate significant muscle growth. In order for protein synthesis to be at an optimal state, we must ensure we consume the required amount of protein alongside a healthy balanced diet with sufficient caloric daily intake in order to promote muscle growth. 

So in order to build muscle effectively from weight training, we must ensure that we train to total failure of the muscle. You need to perform as many repetitions as you can until you can not do a another one at all. This will ensure that you sufficiently cause small micro tears to happen in the muscle tissue which will in turn cause the muscle to rebuild and grow effectively.

It is also best to train the larger muscle groups such as chest and legs, rather than small singular muscles such as biceps and triceps. This will not only mean that you damage more muscle tissue in one go, but your body will burn more calories and therefore body fat in the recovery time after the workout.

I am not going to go into more details about workout techniques here. I have written a very in depth article already on this website which not only goes into how to perform strength exercises for optimal muscle growth, but also goes into how to calculate your daily caloric requirements as well.

You can go HERE in order to ready the informative article (opens the article which is on this website but in a new window).

For some people, the idea of working out in the gym or anywhere in public is not their idea of fun, and I can absolutely understand these worries.

Therefore, you can read my article HERE, which will talk you through how to effectively get your resistance workout in, without leaving the house. (Again, the article is on this website but will open in a new window for you)

When it comes to supplementation for enhanced muscle growth, the fitness industry has not done its consumers any favors. In all honesty, many supplements are a complete waste of money.

​However, there are a handful of products which can actually assist your body with the muscle building processes we have already discussed earlier. For example, whey protein will help provide the building blocks for protein synthesis and muscle growth. 

Creatine can also help the body produce the required high intensity energy required for you to perform heavy and intense workout sessions. Creatine improves your body’s production and utilization of ATP (Adenosine triphosphate). ATP is a form of energy stored in your cells which is used for contracting your muscles during exercise and daily activity.

The two above mentioned supplements can actually assist you quite well when trying to build muscle. As already mentioned, your weight lifting and diet must be on point first. These supplements are not magic. However, they can certainly make your life easier when it comes to your ongoing quest for muscles! 

​I wrote a very in depth review on the top 4 best supplements in a blog post on this website. You can go HERE and check it out if you so wish (again, this review is on this website but opens in a new window).

This review will help you find out which supplement and which brand is best for you without you inadvertently throwing wasting your hard earned money! 


So there you have it!

When looking at how lifting weights builds muscle, we just need to look at the scientific facts that I have already mentioned in this article, and then use that information and put it into good use. This will allow you to optimize your workout and training plan in order to get the best results when it comes to building muscle. 

We now know that it is the hypertrophy and repair of the muscles as a result of microscopic damage through intense resistance training to failure that causes the greatest muscle growth. Combine this with an optimal diet for protein synthesis and hypertrophy to occur and you are on to a winner.

So, here is how to put this information into practice for yourself. I have already gone through these points throughout the article, but below I will give the most important takeaway points in the most simplistic way.

  • Train heavy with weights to complete muscular failure. Perform repetitions until you can not perform any more.
  • Perform negative repetitions slowly to increase the time under tension of the muscles. Try 2 seconds lifting the weight and 6 seconds lowering the weight.
  • Make sure you use a full range of motion while performing the exercise. Fully lengthen and fully contract the muscle on each repetition.
  • When you can not perform the required amount of repetitions per set for a particular exercise, lower the weight you are using and continue to performs as close as you can to the required amount of repetitions until you hit muscular failure again. This is called a drop set.
  • Make sure you consume a healthy and clean diet with the required amount of calories and protein required for your body to build muscle. Check out the other articles that I have linked to in this article for more information regarding this.

Well there you have it! I hope you have found this article both informative and useful. If you enjoyed the content and you feel like you gained a lot from it, then you can join our newsletter below. This way you will always be notified when we release new articles, and you will have access to content that is not release to anyone else publicly.

I wish you all the best with your health and fitness journey!

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