Slow twitch muscle fiber
Slow twitch muscle fibers are rich in capillaries and can therefore obtain more blood, and consequently oxygen, than other muscle fibers. These muscle fibers are able to resist fatigue for large periods of time. Slow twitch muscle are good for endurance, but cannot provide as much force as other types of muscle fibers. Endurance athletes, such as marathon runners, have predominantly slow twitch muscle fibers. These fibers are dense and hard, but not big on volume. While slow twitch muscle fibers help to burn fat more efficiently, they are not what you need if you want strength and voluminization.
Fast twitch muscle fiber
Fast twitch muscle fibers provide explosive power, but they also fatigue quickly. These kinds of muscle fibers will give you strength, but not much endurance. These fibers rely on creatine phosphate and glucose for energy, and are bigger in size as compared to slow twitch muscle fibers. Those looking for maximum muscular gains should try to develop more of these fast twitch muscle fibers as opposed to slow twitch muscle fibers. There are two types of fast twitch muscle fibers—Type A and Type B. Type A fibers provide more strength than Type B fibers, but also tire more easily.
Great! So how does this help me? Well for starters, all human beings have all three types of muscle fibers. Your genes determine the ratio in which these fibers are distributed. Those who have a larger proportion of slow twitch muscle fibers will find it harder to pack on muscle, but will also do better at endurance sports, and vice versa. However, this does not mean that you are stuck with what you were born with. Muscle fiber also develops based on your diet and the activity that you perform. Even if you have more of slow twitch muscle fiber, with dedication, perseverance, and a proper diet, even you can become a he-man; the only difference is that you will have to work at it a bit harder as compared to someone who has more of fast twitch muscle fiber in his body.
