A
question on Rose's blog got me wondering about the science of recovery runs. As usual, I don't have time for proper science, so I consulted Google instead.
There are a
number of opinions out there.
This one is particularly interesting:
"The truth is that lactic acid levels return to normal within an hour after even the most brutal workouts. Nor does lactic acid cause muscle fatigue in the first place. Nor is there any evidence that the sort of light activity that a recovery run entails promotes muscle tissue repair, glycogen replenishment or any other physiological response that is actually relevant to muscle recovery.
In short, recovery runs do not enhance recovery. Nevertheless, recovery runs are almost universally practiced by top runners. That wouldn't be the case if this type of workout weren't beneficial. So what is the real benefit of recovery runs? The real benefit of recovery runs is that they increase your fitness--perhaps almost as much as longer, faster runs do--by challenging you to run in a pre-fatigued state (i.e. a state of lingering fatigue from previous training.)
There is evidence that fitness adaptations occur not so much in proportion to how much time you spend exercising but rather in proportion to how much time you spend exercising beyond the point of initial fatigue in workouts. So-called key workouts (runs that are challenging in their pace or duration) boost fitness by taking your body well beyond the point of initial fatigue.
Recovery workouts, on the other hand, are performed entirely in a fatigued state, and therefore also boost fitness despite being shorter and/or slower than key workouts.
[...]
Additional research has shown that when athletes begin a workout with energy-depleted muscle fibers and lingering muscle damage from previous training, the brain alters the muscle recruitment patterns used to produce movement. Essentially, the brain tries to avoid using the worn-out muscle fibers and instead involves fresher muscle fibers that are less worn out precisely because they are less preferred under normal conditions. "
Interesting stuff. I think we often use the throwaway term "recovery run" (and also banter about lactic acid) without really knowing what they mean.
Incidentally, I love the Copenhagen study described in the link. I imagine some poor bastard running round in circles at the end of it...
At the end of the day though, this part is all I need to know:
If you run just three times per week, each run should be a "key workout" followed by a day off. Sorted.
