what up with stamina drain

it was on second half of extra time i put 4new fresh players from bench and they run slow as team instat to be fress and fast like what happen with this drain stamnina from banch people i keep them specific for that reason to have good stamina players but nothing they move so slow it was in tone with team like fix this issue way stamina drain affect players from banch ???? when i just introducem on pitch your game is make no sens