Whenever we train the body has to go through a process of recovery. How long it takes depends on how hard you worked and how long it lasted. You could be able to run again later in the day after a genuinely easy run whereas a full-on marathon takes the better part of a month to recover from.
While I don’t pretend to understand all the details, the recovery process broadly breaks into four areas:
If it lasts long enough even the easiest-paced run will eventually lead you to run out of fuel. If you’re very well-trained you may be able to get by on fats but for most runners it’s their glycogen stores (sugar-based fuel) which needs to be replenished.
Usually eating some carbohydrates e.g. a banana, sandwich, cereal, bagel on arriving home helps the refuelling. The body is geared towards restocking its fuel supplies within an hour of finishing exercise. After this it will take longer to fully effect. There is a loading rate of how quickly the body can convert food into glycogen and for the hardest training athletes it’s slower than they can use it up! But, for the average runner, just eating sensibly after a run should be enough.
The process of training is all about putting the body under stress so that it has to repair stronger. The harder you train or race, the more muscle fibres are torn apart to be rebuilt. Anyone who has done a hard race or a big interval session knows about the aches and pains it leads to.
Often training hard doesn’t express itself as soreness for long, certainly later in the day or a struggle on the next day’s run but not for days on end. Yet a good Threshold run can take 4-5 days to recover from, speedwork 10-14 days. As I say, there may not be any obvious aches or pains but if you’re attentive to your running you can find there’s something missing for a while. By then it’s certainly not a case of being underfuelled, it’s just waiting for the muscles to repair and other adaptations to take place.
Ramped up sympathetic nervous system
High levels of anaerobic training and the waste products it creates can lead the body to rev up the sympathetic nervous system – it’s the equivalent of being in ‘fight or flight’. You can have trouble sleeping, concentrating, feel thirsty or hungry without realising why. The body shifts from being in a mildly alkaline state to a mildly acidic one and takes time to recover back.
Neuromuscular connections are simply how the brain communicates with the body. Some of it is conscious like putting out your hand, others of it is automatic like breathing.
Whenever you train, the brain and the central nervous system has to rewire itself to integrate the changes. For example, if you do balance on one leg, the brain has to figure out and store the new ‘motor programmes’ that enable you to learn to balance better. Likewise if you run quicker the brain stores new ‘motor programmes’ detailing which muscles fire, what sequence they fire in and how strongly. This is, of course, a simple overview with much more deeper ‘programming’ going on as the heart speeds up to pump more blood, sweat rates improve, lungs breath deeper among many more.
There’s an overlap between this point and the previous one. If you train very hard, especially in ways you haven’t done before, there’s more for the brain and sympathetic nervous system to reprogram and adapt to. If you do too much then you feel tired and overloaded until it calms down. This is one of the reasons why sprinters don’t do too much sprint training in each session.
Most of the effects of training are recovered from within a day or two of the training session. This is typically why we only train hard 2-3 times each week – taking at least one easy day in between. A good recovery run shouldn’t be using up any significant fuel stores and because it’s low-intensity it won’t do much, if any, muscle damage. The “hard-easy” combination is a simple rule of thumb because people know they can’t train hard every day.
Of course how much time you actually need to recover depends on how hard and how long you trained for. JackD estimates you need one day of recovery per mile of racing. That fits with the traditional advice that you need a month to recover from a marathon. In my experience a 10K (6.22 miles) takes a week to fully recover from. Muscle damage is the thing that takes longest to recover from which is why we never push training sessions all-out but leave it for race day.
Ultimately when you’re in the middle of a training plan, it’s a collection of workouts, easy run and long runs which each overlaps with the others and from which you’ve rarely fully recovered. This is why a good taper into a race boosts your racing ability. You finally give the body enough time to recover from all the different workouts and be at its peak!