Muscles type I
Type I muscles work for endurance effort.
There are many different kinds of sports, exercises or routines that can be used to burn more calories, which is ultimately necessary for fat loss. While calorie deficits do not necessarily require exercise, a good workout will slightly improve your metabolism (development of more muscle cells, a stronger heart) and it will help burn more calories.
All of the types of exercise you can choose from can be broken down into two categories: slow and fast movement.
Slow movement implicates type I muscle cells (red muscle cells).
Biological characteristics of red muscle cells and their importance for fat loss.
Red muscle cells do not have the same characteristics as their fast counterpart. They have a different mechanical structure and, more importantly, they process energy differently. Red muscle cells get the energy from the bloodstream for immediate use. They do not store much. This means that if you use them for long stretches of time (endurance sports such as jogging), they will need the bloodstream to constantly supply them with energy substrate.
If you run for an hour, the ability to regulate blood sugar using just glucagon and the glycogen in the liver will be insufficient. Glycogen storage in the liver would deplete dangerously and when it runs out, you would be unable to continue running and urgently need to eat carbohydrates to prevent your system from shutting down. Thankfully, a mechanism that shuts down the use of glucose and shifts your red muscle cells to a different source of energy kicks in gradually from the moment you start running (or practicing any kind of low to medium intensity effort).
That different source of energy is no other than fat (fatty acids that were released in the bloodstream by the adrenaline that was secreted as a result of physical effort). The mechanism that shifts from using glucose to using only fatty acids is called the Pasteur effect.
The fatty acids in the bloodstream are absorbed by your muscle cells, and enter the Krebs cycle in the mitochondria (a very important detail) where they will be catabolized into sugar, and ultimately ATP.
Does this mean that endurance effort is the ony way to burn fat?
No.
It is the only way to burn fat as a direct result of exercising. There is a very big difference.
Only cells that have mitochondria can use fatty acids for energy. Red muscle cells have plenty. White muscle cells, however, have very few. That means they are practically incapable of burning fat directly. But what counts isn’t the ability to burn fat directly. What counts is the ability to burn calories. White muscle cells can burn calories as well, and leave it to other cells to burn fat while they burn glucose.
This may all seem like plain trivia, but it isn’t. What makes these details extremely important is that each individual has a different proportion of red and white mucle cells. That means that each individual’s strategy for using exercise to enhance fat loss will depend on whether they have a red or white muscle cell predominance. At first, your efforts will concentrate on best using what you have available. If you want to become athletic, you will later aim for good balance between the two by developping the muscle type that you are lacking.
People that struggle with weight typically have a white muscle cell predominance. In some cases there are so few red muscle cells that the overall number of mitochondria in the body is so low that fat loss is made very difficult, or slow. In that case ketosis happens frequently (fatty acids are catabolized in the liver, which is dangerous). Medical supervision is especially required in those cases, and some development of red muscle cells through endurance training will be required before the body can become efficient enough for fat loss to occur.
This may be one cause for fat loss being difficult. There can be others, such as dehydration, lack of oxygen, poor lymphatic and blood circulation and resistance to insulin (glucose and fatty acids have a hard time entering your body’s cells). How to lose weight thus depends on individual characteristics, that lead to different fat loss strategies and a more or less important need for medical supervision.