Does muscle turn to fat?


If you’re a recreational gym goer or just a curious beginner interested in building muscle you may have come across this question before;

“When you do a lot of training, like weight lifting and build muscle, if you stop, will your muscle turn to fat?”

In simple terms – no it does not, and never will. Let me explain…

What is muscle made of?

All tissues in our body are made up of cells; skin, hair, nails, bones, muscle, fat, organs and blood, are all cells will different functions. A skin cell has the job of repairing and growing skin. A muscle cell has the job of growing and performing the functions of a muscle. A fat cell again is a very different type of cell to muscle. When people say “muscle turns to fat”, this is vey wrong and impossible because the cells can’t magically convert into something it’s not. It would be like saying apples turn to oranges in summer, which we know doesn’t happen.

Muscle cells are very metabolically active, in other words they use a lot of energy to stay alive. The primary job of skeletal muscle is to move limbs, to walk, run, swim or do anything that is active. The muscle is attached to bones, the muscle contracts and pulls on bones to create movement.

What happens to skeletal muscle when you start exercising?

Lets starting from the beginning; imagine you have never exercised before. Lets call this a “detrained state”. When you’re detrained, your body will only hold the amount of muscle bulk you need to perform the activities of daily life. This means, if you watch TV and sit for long periods of time and don’t do much, your muscles will be very small and weak to match the level of activity you’re doing.

Like wise, if you have a job as a stonemason or furniture removalist, you’re probably going to have a larger amount of muscle in your arms to help you do your job easily. For example, larger shoulder and bicep muscles to help you lift heavy pieces of stone or furniture.

In contrast, muscle is very metabolically active. It burns up a lot of energy in evolution terms this can be a disadvantage. It means you need to eat more (or forage for more food, if you’re a cave man) to maintain that metabolic rate and muscle size.

When you go to the gym and lift weights, you’re training your muscles to adapt to that level of work. Your muscles get bigger to help you lift more weight more efficiently next time. This process is called remodelling you’re creating an environment to induce the growth in muscle size. Muscle cells rarely grow in number (hyperplasia), they grow in size which is called hypertrophy. How much hypertrophy you achieve through weight training is dependant on your genetics, age, and diet.

As soon as you stop weight training or any form of exercise, your body begins to reduce the size of your muscles so you don’t need to waste energy on muscle you’re not using.

It’s not that your muscle is turning to fat when you stop exercising, it’s that they’re reducing in size because your not using them and you are gaining body fat, your fat cells are getting larger. You’re experiencing a change in body composition, which is the change of the ratio of fat to muscle.

How do you gain fat mass?

We are all born with a designated number of fat cells. Fat cells are very unique in that they can grow or swell in size (hypertrophy), holding on to more fat and they can grow in number (hyperplasia). Reference- Hypertrophy and/or Hyperplasia : Dynamics of Adipose Tissue.

Typically, when you over eat chronically for days in a row the body starts to store the extra energy you eat as fat, in fat cells. If you continue to over eat, this process will continue to happen until your fat cells become so large and swollen they start to bud off into new fat cells. Yes, your fat cells begin to multiply.

In contrast, when you lose weight, your fat cells shrink in size. The only bad thing is you can’t get rid off the extra fat cells you have accumulated. The problem with fat cells is they aren’t metabolically beneficial. They don’t use up a lot of energy to stay alive. It’s also interesting to note fat cells also secrete hormones that regulate hunger and inflammation such as leptin, C-reactive protein and IL-6. Scientists believe the hormone secretion may be one of the contributing reasons it’s so hard for a majority of the population to keep weight off.

How long does it take to lose muscle?

The body is breaking down and rebuilding tissue all the time. In as little as 4-5 days you will notice a decrease in muscle strength and after 4-6 weeks there will be a loss in muscle size from inactivity. After only two weeks of detraining you will feel a drop in cardiovascular fitness. The reduction in fitness will be compounded if you lose muscle from lack of activity and gain body fat from overeating.

Over this time you may lose visible tone and not be able to lift the normal weight you usually do at the gym. You might also feel out of breath walking up hill or climbing stairs. You might feel sluggish, lethargic and tired from inactivity and a reduction in fitness. If you’re a real exercise addict you might feel a drop in motivation and drive to workout.

What’s the best way to start exercising again after a break?

When you start exercising you will be very sore for a number of days with delayed onset muscle soreness (DOMS). You will also notice that you can’t just pick up where you left off. For most people it will be starting back at square one with rebuilding strength and fitness.

My best tip to reduce the amount of DOMS and weakness you experience is to not stop exercising in the first place! Even if you only mange 15-20min of exercise each day this is enough to maintain your gains. It’s easier to stick to a routine in a maintenance program, than to start again. Make exercise the way you socialise with friends, try car-pooling to the gym to keep accountable to your friends and your workout.


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