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How many carbs do you need to build muscle?

We know that carb is a carb when it comes to fat loss, and that it does not matter if it comes from sugar or a complex carbohydrate source. But how does this affect muscle growth? Are high carb diets better for muscle growth compared to low carb diets?

To understand this, we need to see how your body creates energy and how carbohydrates are used in this process.


All carbohydrate sources. from table sugar to the most complex polysaccharides, are broken down to its simplest form by your body, which is glucose. Glucose is the main energy source that your body primarily uses. Glucose is then converted to pyruvate which can be used in the TCA cycle (aerobic activities) or be converted to lactate (during anaerobic activities). On complete oxidation, around 40% is retained in the form of high energy phosphate bonds ATP. The remaining energy supplies heat to the body.


There are 3 pathways by which your body can obtain ATP.

1. Aerobic system

2. Creatine phosphate system

3. Lactic acid system

The aerobic system

The aerobic system uses the TCA cycle (Krebs cycle) where it can oxidize carbohydrates, fats and some amino acids. During regular daily life activities, this system uses mainly fats for energy (80-90%) while carbohydrates contribute only 5-18% and amino acids 5%.

This system is highly efficient for energy production and is therefore the primary system your body uses. The only limitation is oxygen, which needs to always be available to function properly. This becomes a problem during high intensity activities such as strength exercise, where oxygen requirements go through the roof. This is defined as a percentage of your VO2 max and it depends on your cardiovascular's system ability to deliver blood to exercising muscle. When the energy demand is high, fats cannot be oxidized fast enough, therefore nearly 50% of the energy is produced from carbohydrates. At this point, your body starts using its second energy system.

Creatine phosphate system

When energy demands drastically increase, during a strength exercise, creatine phosphate system kicks in full force rapidly producing ATP to the muscles. Because the muscle cell concentration of creatine phosphate is only 4-5 times greater than that of ATP, most of the energy from this system is depleted in 10-25 seconds of high intensity exercise.

When this happens, the third system kicks in for help.

Lactic acid system

Energy is produced via glycolytic pathway and therefore carbohydrate is the main energy source this time. The system relies on glucose for ATP generation which is also very fast, and it can provide energy for a longer period compared to creatine phosphate system. This system is very important for high intensity exercises that last from 20 to 75 seconds. As the lactate accumulates it lowers the pH of the blood and accumulates fatigue.

The graph below summarizes how your body uses all three systems during the exercise.

Strength training at 80% 1RM can have an energy contribution from aerobic system of up to 40%.

Now that we know that your body has several different ways of creating energy, depending on the requirements, lets see how does your body actually store carbohydrates after you consume them.


Your body tightly regulates the amount of glucose in blood, and there is only a few grams of it at any time. Instead, glucose is stored glycogen. It can be stored in muscle tissue or in liver. When it is needed, the body breaks it down via glycogenesis to turn it back to glucose, which can be used for both aerobic and anaerobic energy systems.

The body stores a lot of glycogen, and it is practically impossible to deplete it with a resistance type workout. A full body workout with 9 different exercises with 3 sets each at 80% 1RM intensity depleted only about a third of total glycogen! There has never been a study that showed a depletion rate of more than 40% with strength training.

On the other hand, endurance training can easily deplete glycogen. A single 90 minute football game can deplete glycogen stores by 90%.

This is good news for anybody who is strictly interested in resistance training. We can clearly see that glycogen is never a problem.

But what if we deplete glycogen stores over time with regular strength training?

A study was performed where subjects did 6 sets of leg extensions at 70% 1RM until failure, after which the did not eat anything afterwards. Within next 6 hours, 75% of the glycogen was restored.

Glycogen stores are highly auto regulated. The more you deplete it, the faster it replenishes itself. The greater the depletion, the more it gets restored for next time. Your glycogen stores can be effectively replenished even without any carbohydrates in your diet. A study was performed where subjects did 6 sets of leg extensions at 70% 1RM until failure, after which the did not eat anything afterwards. Within next 6 hours, 75% of the glycogen was restored.

The way this is possible is that your body can recycle its own lactate via Cori cycle. On top of this, glycerol from fats, and certain amino acids can be converted directly to glucose as well.

So glycogen should never be a problem if you are purely doing strength training.

What about post workout carbs?

Post workout carbs

The myth behind post workout carbs is to stimulate hormone insulin, which in turn helps to rapidly replenish glycogen levels by transporting glucose to muscles. The only problem with this is that it is not necessary for strength trainees, as glycogen levels are never a limiting factor and they get fully replenished with or without carbohydrates within 24 hours.

The second myth about post workout carbs is protein balance. It is believed that consuming post workout carbs, possibly even high glycemic carbs, can help increase insulin levels which can increase protein synthesis. That is one of the main reasons why everyone used dextrose with protein shake after workouts.

The reason why this is completely unnecessary is simple. Protein itself is insulinogenic. Only a 20 g of protein will maximize the effect of insulin in your body. So adding all that extra sugar on top of it is just wasting your calories instead of using them for highly nutritious food instead, which can help you cover all your micronutrients and fiber.

How many carbohydrates do you need?

If you are engaging in endurance type of activities like, bicycling, running, or playing sports, additional carbohydrates are required. The amount that you need to add can be calculated looking at the table below.

Ideally carbohydrates should be consumed after the activity to replenish the glycogen stores that are most likely depleted with this type of activity.

As for the strength training purposes, we saw that our body has several different ways of producing energy for the workout and that it can effectively replenish its glycogen stores even without any carbohydrates in the diet.

What I generally advise to my clients is to optimize their protein and fat intake first, which is 1.8 g per kg of body weight for protein and 20-40% of resting energy expenditure for fats. The rest should be filled with carbs to optimize your muscle growth and strength progression.

Types of carbs are not important for carb purposes as your body breaks them down to its simplest form anyway, but what you need to pay attention to is fiber. This means that your carb sources should be a combination of fruits, whole grans and legumes, as these are rich sources of fiber.

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