Can't change movement speed after adding a sprint system

So im trying to make a sprinting system, and i added a check so that the character can't sprint backwards, only forward, and i think i did it, but the problem now is that i can't seem to change the movement speed for other things, like waking for example, weirdly, changing the movement speed worked before i added the sprinting check, but now it doesn't work. [https://imgur.com/a/qy3e26P](https://imgur.com/a/qy3e26P)