Why Muscles Get Stronger Whilst You Get Leaner

To know why your muscles get stronger whilst you get leaner it’s important to know more about muscles themselves. I’ll explain to you the basic science behind muscle growth. But understand this first misconception, if you’re a female reading. It’s not just males that need muscle growth, strong muscles are just as important for females looking to get leaner as well.

Did you know that muscles are made of up of three kinds of muscles fibres?

There are slow twitch muscle fibres (Type I) and fast twitch muscles fibres, which are split into Type IIa and Type IIb. Genetics usually determine the amount of each muscle fibres you have. Hence why some people may be good at some activities and other may not be as good.

All those types of muscles exist in our body, and those fibres can usually also be conditioned for specific activities.

Slow twitch muscles are the ones used mainly for endurance type sports or exercise like marathons, or slow steady state cardio. You’ll notice that long distance runners generally are not that muscular to look at. However that does not mean that they’re not strong. It means that they’re composed of slower twitch muscle fibres which are great for long endurance type activities, rather than strength based exercise.

Fast twitch are the opposite to slow twitch. Type IIa fast twitch fibres are capable of exerting more strength and force, however they tire quicker then slow twitch. Type IIb fibres are capable of even more force than Type IIa, and tire even quicker. An example of mostly fast twitch muscle fibres being used would be with resistance training/weight lifting.

For example, let’s compare a 100 meter sprinters physique to a long distance runner. The sprinter would need more power in a short burst of time, hence why they look more muscular. Fast twitch, but burn out quicker. They have developed more Type II fibres, but would not be able to maintain their run as long as a long distance marathon runner with their Type I fibres. Slow twitching, but last longer.

It’s important to work on the strength of all muscles. However if you want bigger leaner muscles you need to concentrate on building both your Type IIa and Type IIb, more than you would your slow twitch fibres, Using a solid resistance training program consistently will also give you a leaner look as you reduce body fat and increase your lean muscle. Hence the absolute necessity for both male and females to participate in strength training.

Another Misconception …

How muscles get bigger is by doing “more work” at the gym and really killing yourself. This might be true for the experienced body builder who has now conditioned genetics. But initially the would have started with …

Less is more

For the everyday person you really should be thinking about the quality of your workouts and not the quantity of sets and reps. That is, weights training times of between 20-45 minutes, if you’re not at athlete level just yet.

Muscles get bigger and leaner outside the gym, when they get the appropriate nutrition and rest. In the gym they just get damaged, in a good way know as micro-tears to the muscle fibres. When you’re at rest they can recover and repair and get stronger.

The Result …

Whilst your muscles get stronger you have more of a chance of reducing your body fat percentage and fat cells around the muscles. This is because the food you consume is used more to maintain or build new muscle rather than get stored in your fat cells and those calories under utilized.

For the “everyday” body builder (and we can all choose to be), a general weights training plan is enough to see you progress and get stronger and leaner. You can get a fantastic and simple resistance training program which we can prescribe. All bodies are NOT created equal, so you’re best off getting a consultation with a coach. There are many variables to training when it comes to building lean muscle, and losing the fat so why not get a health and fitness professional to help you along the way.


As a Trainer and Coach for over 10 years now, I've helped many people reach their goals as well as achieve my own including having lost 35kg. I'm my very own guinea pig when it come to achieving a fitter, healthier life and now I'm here to help you. Start by signing up to the Really Really Fit newsletter, Free Book and Video training that will change your mindset and life.

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