Slow twitch VS Fast twitch
Are you more comfortable running long distances, circuit training, or holding planks? OR are you more comfortable with sprints, pushing heavy weight for short duration's? If you answered yes to the first question, chances are slow twitch dominant. You’re probably fast twitch dominant if you answered yes to the second.
We have different types of muscle fiber in the body and they’re classified based on how they produce energy. What’s the difference? Slow will burn out more quickly than fast twitch. These muscles can be trained differently.
Slow twitch uses oxygen to created ATP (adenosine triphosphate) which fuels muscle contraction. This would be considered aerobic. This muscle fiber contains more blood, so they can generate energy longer, but unable to generate a lot of force. Tonic muscles that are responsible for maintaining posture is a good example. Planking, or wall sitting would fall into this category.
Fast twitch muscle uses oxygen to convert glycogen to ATP, which is stored in the muscle. This muscle can generate force but are quicker to fatigue. Fast twitch fiber will be recruited when the force demands are greater than the slow twitch fibers demand. Strength and power training can increase the number on fast twitch muscle fiber. You’ll need to take a longer rest break when working this fiber. ATP is used up quickly and takes longer to recover. Training fast twitch will help you define and increase your size.
Genetics really determines how much of each muscle fiber you possess. However, understanding how the body adapts to exercise can help to develop a program based on your wants and needs.
One other note: Cardio will not devour muscle unless your body is severely stressed or placed in starvation mode. Adding cardio to your weight training program is a valuable tool to help you reach your goals.