… ‘fast-twitch’ or type II muscle fibers are less efficient at using energy to produce force (as when you climb stairs or lift weights) than are ‘slow-twitch’ (type I) muscle fibers. In other words, they burn more calories when generating a given level of force.
If you want to stay lean all your life, then your best bet may be to perform exercise that increases the size of your fast-twitch fibers. This will allow you to burn more calories 24 hours a day, 7 days a week.
A few facts:
-FT fibers are more easily hypetrophied than slow twitch fibers. More muscle=more calories burned
FT fibers are used mainly in anaerobic training like sprinting and lifting-very few calories are burned during the training itself, but there is an afterburn effect. The opposite is true for endurance training
-There is no way around calories in vs calories out.
*In my opinion the key to being “lean” is to get some sort of exercise daily and eat properly. It doesn’t matter if you are FT or ST dominant if you eat more calories than your using you will gain weight. If you have more muscle mass you will be able to eat more calories. However when/if you quit training and lose the muscle , you may get fat because you won’t burn nearly as many calories as before and will probably eat the same way. So after retiring from sports an athlete can’t just rest on his fast twictch ass, eat whatever he wants and expect no to get fat.