We just broke up after seven years . She ' s dealing with tons of work and due to long distance , we barely see each other . We love each other to death , but at the moment , we can ' t be together <| sep |> 1 . Do you build Fast twitching muscle fibers ? Or do they get converted as in your already excisting muscle fibers turn into either slow twitching or fast twitching ? All muscle is either slowtwitch Type 1 or fasttwitch and jackofalltrades Types 2 a and 2 b respectively . That means when someone says build fasttwitch muscle , it ' s really just converting it , as you said , from one type to the other . Sprints , plyos , and Oly lifts are all highly effective at doing this . 2 . How long does it take to build fast twitching muscle fibers , does it take longer than creating muscle with weightlifting or is it the same amount of time ? Muscle is never created when your muscles grow , that ' s exactly what they ' re doing . Growing . New muscle fibers aren ' t being created , simply expanding . But the length of time it would take to convert muscle fibers to different types would vary greatly depending on many different factors . It ' s also important to note that most people have about a 5050 ratio of Type 1 to Type 2 fibers , and most people won ' t be able to change that to more than 6040 , likely with several years of training as well . Even worldclass athletes don ' t get much higher than 70 % of one type of muscle fiber . 3 . Do you supplement these with protein or do they convert like asked before in 1 . ? Making sure you have protein in your diet would be beneficial , if that ' s what you ' re asking ? 4 . Is it better to sprint outdoors than on a treadmill ? Sprinting is sprinting . If you want to do it on a treadmill , I would recommend finding one with a curved running platform . They ' re much better for sprints .