Sprint animation script help fix please?

I want to play an animation playing when Shift is being hold, and when you release it. The animation stops. How do I add it in here, and also the script only works in studio, but not in roblox client. z_z Help fix! Take a look below.

if script.Parent.Name == "PlayerGui" then
	local mouse = game.Players.LocalPlayer:GetMouse()
	local running = false
	local gui = script.sprntGui.Frame
	energy = 100
	mouse.KeyDown:connect(function (key) -- Run function
		key = string.lower(key)
		if string.byte(key) == 48 then
			running = true
			local keyConnection = mouse.KeyUp:connect(function (key)
				if string.byte(key) == 48 then
					running = false
				end
			end)
			for i = 1,5 do
				game.Workspace.CurrentCamera.FieldOfView = (70+(i*2))
				wait()
			end
			game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 30
			repeat 
				wait() 
				if energy ~= 20 then
					gui.Size = gui.Size-UDim2.new(0,5,0,0) energy = energy-1
				else
					running = false
				end
			until 
				running == false
				
			keyConnection:disconnect()
			game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16
			for i = 1,5 do
				game.Workspace.CurrentCamera.FieldOfView = (80-(i*2))
				wait()
			end
			coroutine.resume(coroutine.create(function()
				repeat 
					wait() if energy ~= 100 then gui.Size = gui.Size+UDim2.new(0,5,0,0) energy = energy+1 end
				until
					running == true
			end))
		end
	end)
else
	print("YOU MUST PUT THIS INSIDE STARTGUI")
end