adjust speed doesnt seem to be working for me at all?

hi sorry if this is a dumb question but when i use adjust speed it doesnt seem to work

local slam = hum:LoadAnimation(Anims.slam)
slam:Play()
    while hum.FloorMaterial == Enum.Material.Air do
        wait()  
        slam:AdjustSpeed(0)
        print(hum.FloorMaterial)
    end

it prints the floor material but the animation isnt freezing there arent any errors