Simply put, muscle and strength are the capacity of your muscles to lift a certain amount of weight. Though, this called “capacity” is subject to multiple factors, some of which may be improved which would beget your muscles to lift heavier. So, what or those factors, and how to enhance them?

Here’s five scientifically proven factors that have a direct effect on your strength: muscle cross-sectional area, nerve impulses, muscle length, age, gender, energy supply, point of tendon insertion.

Muscle cross-sectional area:

The muscle having bigger cross-section area has more strength because larger muscles have bigger amount of actin and myosin filaments. Muscle and strength can be increased by developing the muscle cross-section, what is called muscle hypertrophy.

One con to keep in mind though is the type of fibers you’ve naturally been given. Depending this fiber breakdown, you’ll be genetically made to be more or less strong and massive.

slow twitch fibers, fast twitch fibers

As you can see above, there are two basic types of fibers. 

The main difference between both is that slow twitch fibers use oxygen in combination with other sources to fuel the muscle whereas fast twitch fibers don’t. Doing so, for an even given space, slow twitch fibers have to leave enough room for both muscle fibers and capillaries which bring oxygen in their blood stream, that’s why it’s called “red fibers”. On the other side, when it comes to slow twitch fibers, the whole space is left to muscle fibers, that’s what gives a whitish color to those fibers.

muscle fibers energetic pathways

At that point, you’ve probably dug it, part of our muscles are made to be strong like our thighs, back or chest, others to be resistant like our traps, forearms or calves.

Fast twitch muscle fibers lead to an increase in muscle size and strength with greater explosive power. To develop those fibers, you want to lift heavy and shortly, meaning sets of 5 to 8 reps at 75%+ 1RM on the “Brzycki scale”.

Now those fibers will get bigger from two ways: myofilaments (actin and myosin) increase, and water and glycogen storage increase. Which leads us to the next factor.

Energy Supply

Glycogen is a form of glucose that’s stored in your muscles and liver. For one molecule of glycogen, the muscle will retain 3 molecules of water. So, if your muscles stock more glycogen, then they will get visually bigger – what we call in the jargon “muscle volume”.

Glycogen is the primary source of fuel during exercise after glucose, and low glycogen levels decrease your ability to gain muscle and strength.

When it comes to fast-twitch fibers, it’s the only chemical source which leads to the mechanical energy that ATP is, and which allows the body to move. So, regarding short and intense efforts that last less than 120 seconds, the muscle uses glucose and glycogen breakdown pathways exclusively to perform the exercise.

lactate cycle

So, once again, the more glucose stock you have, the bigger and stronger you’ll be.

To increase the level of glycogen in your muscle, do at least 100+ reps int total per muscle per workout and go for a high-carb diet, with around 1 to 3 grams of carbs per pound of body weight or more.

If you guys want more details on how to select your carbs read my article “How To Choose Your Carbs?


Muscle density fluctuate depending on age. It increases up to a certain age – about 30 years old –  and then, after a plateau, it decreases overtime as we get older.

muscle mass and strength related to age

This is due to multiple factors in turn, like testosterone decline, muscle stem cells decline, etc…

Muscle and age

To postpone muscle and strength loss, you want to stay active, and outdo yourself regularly. The body is an ever evolving machine, either it progresses or retrogresses, but it never stay still. So, keep exercising at least 3 times a week, even if you feel sick or tired, do what you can but show up at the gym no matter what.

Nerve impulses

Your brain and nervous system have the power to activate more motor units when they need to generate a large amount of force. So, nerve impulses, intensity and the number of motor units determine the muscular strength, since the more muscle fibers stimulated you have, the more strength you’ll develop.

muscle motor unit

Nathaniel Jenkins and his colleagues may have uncovered some answers by measuring how the brain and motor neurons — cells that send electrical signals to muscle — adapt to high- vs. low-load weight training.

Their study suggests that high-load training better conditions the nervous system to transmit electrical signals from the brain to muscles, increasing the force those muscles can produce to a greater extent than does low-load training.

Muscles contract when they receive electrical signals that originate in the brain’s neuron-rich motor cortex. Those signals descend from the cortex to the spinal tract, speeding through the spine while jumping to other motor neurons that then excite muscle fibers.

Long story short, the heavier your push, the more motor-units you focus, and ultimately the more fibers lift the load. Which in the long run will translate in an increase of actin and myosin filaments in more muscle fibers. Doing so, you’ll get bigger and stronger.

Lifting heavy aside, a complementary way to concentrate more motor-unit is to consume pre-workout stimulant like caffeine and taurine. Also, set up a playlist that will get you angry for more iron, like hip-hop or metal (I do both, weird, isn’t?! LoL).

Regarding the 3 following other factors, even though they play a role on muscle and strength levels, you can do nothing about it, so I jotted them down for informational purposes more than anything else.


Men and women have similar tissues but men have bigger muscle size and testosterone/estrogen ratio leading to better strength and muscle density as compared to women.

Muscle and limb length

People with relatively long muscles have greater potential for developing size and strength than person with relatively short muscles. 

Another strength and muscle factor that is naturally determined is limb length. People with short limbs tend to be able to lift more weight because of advantageous leverage factors (arms and legs).

In a nutshell, people with relatively long muscles have greater potential for developing size and strength than persons with relatively short muscles.

Point of Tendon Insertion

Muscle strength is also influenced by the point of tendon insertion. For example, let’s say Jim and John both have the same arm and muscle length. However, Jim’s biceps tendon attaches to his forearm farther from his elbow joint than John’s does. This gives Jim a biomechanical advantage: he is able to lift more weight than John in biceps exercises such as the Biceps Curl.

Alright fit fam, hopefully you’ll learn a bit about your body and how muscle and strength work. I know some section are a bit nerdy and difficult to digest, but I try to make it as easy as possible and practical for you to improve your fit journey out of it. If you guys have any question feel free to shout me an email or hit me on social: @charlyfitlife. See you in the next one!


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