"We lose fat only from 45 minutes of exercise" ...I heard that thousand times yet and sincerely I cannot hear it anymore, it's a nonsense !
You know, I'm always looking forward for some informations about the consumption of energy when we're practicing sports. And I just found out some very good ones !!!
- What we know : We know that our body uses sugar (glucose) and fat (fatty acids) as energy source when we run. The sugar delivers 4 Calories per gram and the fat, 9 Calories. Of course our body uses in the same time these two kind of energies.
Then, what we have to understand is that the sugar is easier and faster to oxidize than the fat, then the sugar delivers its energy much more promptly. That's why the sugar is almost the only energy source when we have to run very fast (or when we do a very powerful exercise).
On the other hand the fat is the energy of slowlyness or better, the energy of long duration exercises (like marathon or ironman héhé). Actually, our stocks of fat are almost unlimited. A 70 kg fellow who has a fat percentage of 15% means that he has 10,5 kg of fat in his body. In comparison we have only about 500 gr of sugar stored in our body, 400 gr into our whole muscles and about 100 gr in the liver. The sugar which is into the muscles cannot get out to refuel other muscles or even the nervous system, it's inside then it keeps inside. Plus, 70 % of the blood stream is reserved for our central nervous system and then, it's good to preserve the sugar because we only burn the fat in the presence of sugar. So, no more sugar = no more energy even if you are the most fat guy of the earth ! Of course our body knows how to create sugar without sugar (gluconeogenesis) but it's another tale...
- What we know : We know that our body uses sugar (glucose) and fat (fatty acids) as energy source when we run. The sugar delivers 4 Calories per gram and the fat, 9 Calories. Of course our body uses in the same time these two kind of energies.
Then, what we have to understand is that the sugar is easier and faster to oxidize than the fat, then the sugar delivers its energy much more promptly. That's why the sugar is almost the only energy source when we have to run very fast (or when we do a very powerful exercise).
On the other hand the fat is the energy of slowlyness or better, the energy of long duration exercises (like marathon or ironman héhé). Actually, our stocks of fat are almost unlimited. A 70 kg fellow who has a fat percentage of 15% means that he has 10,5 kg of fat in his body. In comparison we have only about 500 gr of sugar stored in our body, 400 gr into our whole muscles and about 100 gr in the liver. The sugar which is into the muscles cannot get out to refuel other muscles or even the nervous system, it's inside then it keeps inside. Plus, 70 % of the blood stream is reserved for our central nervous system and then, it's good to preserve the sugar because we only burn the fat in the presence of sugar. So, no more sugar = no more energy even if you are the most fat guy of the earth ! Of course our body knows how to create sugar without sugar (gluconeogenesis) but it's another tale...
- How many energy are we using when we're running ?
It's quite simple to figure out. It's 1 Calorie per kilometer and per kg of bodyweight. The speed has a too little effect to be relevant, it's 0,95 to 1,06 Calories from 7,5 km/h to 21km/h. Then I guess it's better to use the average of 1 calorie as a basis.
Ex : I weigh 80 kg. Then when I run a 10 km distance I burn : 1 (Cal) x 80 (kg) x 10 (km) = 800 calories. The problem is I don't know which part of these 800 calories is sugar or is fat...
- Now that we know how to calculate the energy used, we can try to figure out the distribution between the sugar and the fat of this amount of energy ! Then I did a graph that shows us the share of each energy source depending on the time of exercise.
- Now that we know how to calculate the energy used, we can try to figure out the distribution between the sugar and the fat of this amount of energy ! Then I did a graph that shows us the share of each energy source depending on the time of exercise.
(click to enlarge)
As you can see the more your workout lasts the more you will burn fat. Hey! You people who are doing diets, you know now what you have to do... run slowly and longer ;)
Ex : last thursday I ran 21 km. Then I burn, 1(Cal) x80(kg) x 21 (km) = 1680 Calories.
I ran during about 2 hours, then the part of the fat burnt is 31%, then 1680 X 0,31 = 520,8 Calories (of fat). We know that each gram of fat gets 9 Calories, so I burnt an amount of 520,8/9 = 57,87 grams of fat ! Wow ! It's just the amount of butter contained in 2 croissants ! ;)
In conclusion, we do use fat since the beginning of the workout (not only since 45 min of exercise). Of course just a little part of it but even if you run only half a hour you will burn 10% of fat from the whole calories burnt, it's more than nothing. And keep in mind that the more you'll train the more you will able to use fat as source of energy.
Ex : last thursday I ran 21 km. Then I burn, 1(Cal) x80(kg) x 21 (km) = 1680 Calories.
I ran during about 2 hours, then the part of the fat burnt is 31%, then 1680 X 0,31 = 520,8 Calories (of fat). We know that each gram of fat gets 9 Calories, so I burnt an amount of 520,8/9 = 57,87 grams of fat ! Wow ! It's just the amount of butter contained in 2 croissants ! ;)
In conclusion, we do use fat since the beginning of the workout (not only since 45 min of exercise). Of course just a little part of it but even if you run only half a hour you will burn 10% of fat from the whole calories burnt, it's more than nothing. And keep in mind that the more you'll train the more you will able to use fat as source of energy.
Hope you liked this post, for any further informations, any doubts or even to rectify some stuff you can leave a comment.
Keep running...
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