Sprint drains/regens too fast when shift is spammed?

I made a server-sided sprint that goes like this:

[1] - Gets input from the client when the player presses shift and passes it to the server.

[2] - The server places players into a table when input is begun and takes them out when the input is ended.

[3] - Runs a loop that repeats until they are put into/taken out of the table which subtracts/adds a set amount of stamina.

The problem is that when someone presses shift really fast, it regens/drains really fast as well. This would lead to players being able to just shift spam in order to get back to the max stamina after they run out.

(Ex. https://gyazo.com/3dc28ed6e0f9c5193d6477de1a9370af.gif)

Any ideas on what the problem could be?

Server

local PlayerService, RepStorage, RunService = game:GetService('Players'), game:GetService('ReplicatedStorage'), game:GetService('RunService')   ;
local Module = require(RepStorage:WaitForChild('Modules'):FindFirstChild('MechanicsModule'))    ;
local Events = RepStorage.RemoteEvents  ;   local Sprint, UpdateStamina = Events.Sprint, Events.StaminaUpdate   ;
local MaxStamina = Module.MaxStamina    ;   local SprintCost, SprintModifier, SprintRegen = Module.SprintCost, Module.SprintModifier, Module.SprintRegen    ;
local NormalSpeed = Module.NormalSpeed  ;   local SprintSpeed = Module.SprintSpeed  ;   local WaitTime = .01    ;

local SprintingPlayers = {} ;

function isPlayerInTable(Player)
    for Index, Value in pairs(SprintingPlayers) do
        if Player.Name == Value then
            return true
        end
    end
end

function Sprinting(Stamina, Player, Humanoid)
    for i, SprintingPlayer in pairs(SprintingPlayers) do
        if isPlayerInTable(Player) ~= true then print'no sprint' return end
        repeat
            if Module.IsMoving(Humanoid) and isPlayerInTable(Player) then
                if Stamina.Value >= SprintCost then
                    Stamina.Value = Stamina.Value - SprintCost  ;   Humanoid.WalkSpeed = SprintSpeed    ;   wait(WaitTime)  ;
                else
                    Humanoid.WalkSpeed = NormalSpeed    ;   wait(WaitTime)  ;
                end
            elseif not Module.IsMoving(Humanoid) and isPlayerInTable(Player) then
                if Stamina.Value < MaxStamina then
                    Stamina.Value = Stamina.Value + SprintRegen ;   Humanoid.WalkSpeed = NormalSpeed    ;   wait(WaitTime)  ;
                end
            end
            wait()  ;
        until not isPlayerInTable(Player) or Humanoid:GetState() == Enum.HumanoidStateType.Dead 
    end
end

function NotSprinting(Stamina, Player, Humanoid)
    if #SprintingPlayers > 0 then
        for i, SprintingPlayer in pairs(SprintingPlayers) do
            if not isPlayerInTable(Player) then
                repeat
                    if Stamina.Value < MaxStamina then
                        Stamina.Value = Stamina.Value + SprintRegen ;   Humanoid.WalkSpeed = NormalSpeed    ;   wait(WaitTime)  ;
                    elseif Stamina.Value > MaxStamina then
                        Stamina.Value = MaxStamina
                    end
                    wait()  ;
                until isPlayerInTable(Player) or Humanoid:GetState() == Enum.HumanoidStateType.Dead     
            end
        end
    elseif #SprintingPlayers <= 0 and not isPlayerInTable(Player) then
        repeat
            if Stamina.Value < MaxStamina then
                Stamina.Value = Stamina.Value + SprintRegen ;   Humanoid.WalkSpeed = NormalSpeed    ;   wait(WaitTime)  ;
            elseif Stamina.Value > MaxStamina then
                Stamina.Value = MaxStamina
            end
            wait()  ;
        until isPlayerInTable(Player) or Humanoid:GetState() == Enum.HumanoidStateType.Dead
    end
end

function AddToTable(Stamina, Player, Humanoid)
    if not isPlayerInTable(Player) then 
        table.insert(SprintingPlayers, Player.Name) 
        Sprinting(Stamina, Player, Humanoid)    
    end
end

function RemoveFromTable(Stamina, Player, Humanoid)
    if #SprintingPlayers > 0 then
        for Index, Value in pairs(SprintingPlayers) do
            if Value == Player.Name then
                table.remove(SprintingPlayers, Index)   ;
                NotSprinting(Stamina, Player, Humanoid) ;   
            end
        end
    else
        NotSprinting(Stamina, Player, Humanoid) ;   
    end
end

PlayerService.PlayerAdded:Connect(function(Player)
    Player.CharacterAdded:Connect(function(Character)
        local Root = Character:WaitForChild('HumanoidRootPart') or Character:FindFirstChild('HumanoidRootPart') ;
        local Stamina = Instance.new('IntValue', Root)  ;
        Stamina.Name = 'Stamina'    ;   Stamina.Value = MaxStamina  ;

        Stamina.Changed:Connect(function(Property)
            UpdateStamina:FireClient(Player, Stamina.Value, MaxStamina)
        end)

    end)
end)

Sprint.OnServerEvent:Connect(function(Player, State, Tick)
    local Character = Player.Character  ;
    local Root = Character:WaitForChild('HumanoidRootPart') or Character:FindFirstChild('HumanoidRootPart') ;
    local Stamina = Root:FindFirstChild('Stamina') or Root:WaitForChild('Stamina')  ;   local Humanoid = Character:FindFirstChild('Humanoid')   ;
    if State then   
        if not isPlayerInTable(Player) then
            AddToTable(Stamina, Player, Humanoid)   ;   
        --  print(Player.Name, 'IS SPRINTING', State)   ;   
        end
    elseif not State then
        if isPlayerInTable(Player) then
            RemoveFromTable(Stamina, Player, Humanoid)
        --  print(Player.Name, 'STOPPED SPRINTING', State)  ;   
        end
    end
end)

Client

InputService.InputBegan:Connect(function(Input, gameProcessed)  
    if not gameProcessed then
        if Input.KeyCode == Enum.KeyCode.LeftShift then
        --  print(Player.Name, 'began sprinting')
            Sprint:FireServer(true)     ;   
        end
    end 
end)

InputService.InputEnded:Connect(function(Input, gameProcessed)  
    if not gameProcessed then
        if Input.KeyCode == Enum.KeyCode.LeftShift then
        --  print(Player.Name, 'stopped sprinting')
            Sprint:FireServer(false)    ;
        end
    end
end)