protected void CheckPowerUpExpiration(GameTime gameTime)
 {
     // Is a power-up active?
     if (powerUpExpiration > 0)
     {
         // Decrement power-up timer
         powerUpExpiration -= gameTime.ElapsedGameTime.Milliseconds;
         if (powerUpExpiration <= 0)
         {
             // If power-up timer has expired, end all power-ups
             powerUpExpiration = 0;
             player.ResetScale();
             player.ResetSpeed();
         }
     }
 }