Muscles with fast-twitch fibres require longer to heal than slow-twitch because they have mitochondria and endurance-supporting machinery. They are stronger per cross-sectional area, meaning they can take on more damage. They are also less vascularized, meaning poorer nutrient delivery. On top of all of this, they have less myoglobin and other transport proteins to take surface nutrients deep into the belly of the fibre. Given fast-twitch muscles are usually more substantial, the recovery process is time-consuming. However, even larger quad muscles take longer than the hamstrings because the former are predominately slow while the latter is fast.