Humanoid.Running is not working right, any other way?

So, what I am trying to do is make a "The Flash" script. So far what it does is, makes a few parts when I move but then stops making parts. I want to continuously place parts as I am moving, it just makes a few.

function showLightning(on,char)
	if on == true then
		local part = Instance.new('Part')
		part.Anchored = true
		part.CanCollide = false
		part.Size = Vector3.new(1,4,3)
		part.BrickColor = BrickColor.new('Bright yellow')
		part.Transparency = .6
		part.CFrame = char.Torso.CFrame * CFrame.new(0,0,3)
		part.Parent = workspace
	else
		print'a'
	end
end

game.Players.PlayerAdded:connect(function(plr)
	plr.CharacterAdded:connect(function(char)
		char:FindFirstChild('Humanoid').Running:connect(function(speed)
			if speed >= 4 then
				showLightning(true, char)
			elseif speed <= 1 then
				showLightning(false, char)
			end
		end)
	end)
end)