There are two muscle fibre types: “slow-twitch” and “fast twitch” muscle fibres. Most people have an even amount of both, but some may have more of one muscle fibre type than the other.
There are techniques to train each specific muscle type so anyone can increase their speed, no matter what their genetics are.
Exercises to train your slow twitch muscles (suitable for marathon runners) would be long runs and high reps in the gym.
These programs with the exact sets and reps will teach you how to condition your fast twitch muscles (responsible for giving an athlete speed, agility, quickness and power) like the pros. You get immediate access to all programs in the membership area.