Runners around the world widely assume that the purpose of recovery runs which are relatively short and slow runs undertaken within 24 to 36 hours post a longer or harder run is to facilitate recovery from preceding hard training. A lot of times we hear from runners talking about how recovery runs increase blood flow to the legs, clearing away lactic acid and so forth.
The reality is that lactic acid returns to their normal levels within a few hours and also does not cause muscle fatigue in the first place. Neither there is any evidence that shows a recovery run brings about muscle tissue repair, glycogen replenishment that is actually relevant to muscle recovery.
In general, recovery runs should be the easiest training day of the week, other than rest days.
What are the real benefits of Recovery Run? If your goal is to increase your running endurance levels then shorter and slow runs are for you as they challenge your muscles which are already fatigue from previous training also known as pre-fatigued state. But this causes micro-trauma to your muscles i.e break down of your healthy muscle tissue. To make it simple evidence shows that endurance adaptations occurs higher in runners who spend time exercising beyond the point of initial fatigue level.
So are recovery runs required? Research shows there is no need to push your body just after 24 hours of your previous long run. Furthermore, when a runner or an athlete begins a workout with energy-depleted muscle fibers and lingering muscle damage from previous training, the brain alters the muscle recovery patterns causing more damage to the muscles which may lead to an injury.
Recovery is important but not with recovery runs!