Recovery runs don’t actually accelerate muscle recovery, but they do have other important benefits.
If you asked a stadium-size crowd of other runners to name the most important type of running workout, some would say tempo runs, others would say long runs, and still others would say intervals of one kind or another. None would mention recovery runs. Unless I happened to be in that stadium.
I won’t go quite so far as to say that recovery runs are more important than tempo runs, long runs, and intervals, but I do believe they are no less important. Why? Because recovery runs, if properly integrated into your training regimen, will do just as much to enhance your race performances as any other type of workout. Seriously.
It is widely assumed that the purpose of recovery runs—which we may define as relatively short, slow runs undertaken within a day after a harder run—is to facilitate recovery from preceding hard training. You hear coaches talk about how recovery runs increase blood flow to the legs, clearing away lactic acid, and so forth. 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 actually is relevant to muscle recovery.
In short, recovery runs do not enhance recovery. The real benefit of recovery runs is that they allow you to find the optimal balance between the two factors that have the greatest effect on your fitness and performance: training stress and running volume. Here’s how:
Training stress is what your body experiences in workouts that test the present limits of your running fitness. You can be fairly sure a workout has delivered a training stress when it leaves you severely fatigued or completely exhausted. The two basic categories of workouts that deliver a training stress are high-intensity runs (intervals, tempo runs, hill repeats) and long runs. A training program whose objective is to prepare you for a peak race performance must feature plenty of “key workouts” that challenge your body’s capacity to resist the various causes of high-intensity fatigue (muscular acidosis, etc.) and long-duration fatigue (muscle tissue damage, etc). By exposing your body to fatigue and exhaustion, key workouts stimulate adaptations that enable you to resist fatigue better the next time.
Running volume, on the other hand, has a positive effect on running fitness and performance even in the absence of exhaustive key workouts. In other words, the more running you do (within the limit of what your body can handle before breaking down), the fitter you become, even if you never do any workouts that are especially taxing. The reason is that increases in running economy are very closely correlated with increases in running mileage. Research by Tim Noakes, M.D., and others suggests that while improvement in other performance-related factors such as VO2max ceases before a runner achieves his or her volume limit, running economy continues to improve as running mileage increases, all the way to the limit. For example, if the highest running volume your body can handle is 50 miles per week, you are all but certain to achieve greater running economy at 50 miles per week than at 40 miles per week, even though your VO2max may stop increasing at 40 miles.
You see, running is a bit like juggling. It is a motor skill that requires communication between your brain and your muscles. A great juggler has developed highly refined communication between his brain and muscles during the act of jugging, which enables him to juggle three plates with one hand while blindfolded. A well-trained runner has developed super-efficient communication between her brain and muscles during the act of running, allowing her to run at a high sustained speed with a remarkably low rate of energy expenditure. Sure, the improvements that a runner makes in neuromuscular coordination are less visible than those made by a juggler, but they are no less real.
For both the juggler and the runner, it is time spent simply practicing the relevant action that improves communication between the brain and the muscles. It’s not a matter of testing physiological limits, but of developing a skill through repetition. Thus, the juggler who juggles an hour a day will improve faster than the juggler who juggles five minutes a day, even if the former practices in a dozen separate five-minute sessions and therefore never gets tired. And the same is true for the runner.
Now, training stress—especially key workouts inflicting high-intensity fatigue—and running volume sort of work at cross-purposes. If you go for a bona fide training stress in every workout, you won’t be able to do a huge total amount of running before breaking down. By the same token, if you want to achieve the maximum volume of running, you have to keep the pace slow and avoid single long runs in favor of multiple short runs. But then you won’t get those big fitness boosts that only exhaustive runs can deliver. In other words, you can’t maximize training stress and running volume simultaneously. For the best results, you need to find the optimal balance between these two factors, and that’s where recovery runs come in.
By sprinkling your training regimen with relatively short, easy runs, you can achieve a higher total running volume than you could if you always ran hard. Yet because recovery runs are gentle enough not to create a need for additional recovery, they allow you to perform at a high level in your key workouts and therefore get the most out of them.
I believe that recovery runs also yield improvements in running economy by challenging the neuromuscular system to perform in a pre-fatigued state. Key workouts themselves deliver a training stress that stimulates positive fitness adaptations by forcing a runner to perform beyond the point of initial fatigue. As the motor units that are used preferentially when you run begin to fatigue, other motor units that are less often called upon must be recruited to take up the slack so the athlete can keep running. In general, “slow-twitch” muscle fibers are recruited first and then “fast-twitch” fibers become increasingly active as the slow-twitch fibers wear out. By encountering this challenge, your neuromuscular system is able to find new efficiencies that enable you to run more economically.
Recovery runs, I believe, achieve a similar effect in a slightly different way. In a key workout you experience fatigued running by starting fresh and running hard or far. In a recovery run you start fatigued from your last key workout and therefore experience a healthy dose of fatigued running without having to run hard or far. For this reason, although recovery runs are often referred to as “easy runs”, if they’re planned and executed properly they usually don’t feel very easy. Speaking from personal experience, while my recovery runs are the shortest and slowest runs I do, I still feel rather miserable in many of them because I am already fatigued when I start them. This miserable feeling is, I think, indicative of the fact that the run is accomplishing some real, productive work that will enhance my fitness perhaps almost as much as the key workout that preceded it. Viewed in this way, recovery runs become essentially a way of squeezing more out of your key workouts.