Everything you read about training tells you: Resting is just as important as training.

I understand that if I train to much I get a negative training result. But do we really have to rest like running one day and taking a day off? How is that different from just running every day but half the distance?

I'm interested in the biological or biomechanical background for the need of actual rest periods. Or references that demonstrate that training less intense with out rest days is ok too.

I'm primary interested in running, but kind a hope the same principles apply for all kinds of training.

This question: Importance of Rest Days is similar yet different. It's answers don't talk about what is actually happening inside the body and cells, except for some "supercompensation" handwaving.

  • 1
    Resting is not 100% necessary, especially when doing submaximal efforts. I don't have time today, but I will write up an answer in the next couple.
    – JohnP
    Aug 25, 2014 at 21:51
  • Rest days? This is why we sleep! Rest days for most people who talk about them are just another excuse not to train/exercise hard. It's another excuse for not doing what needs to be done. Eat right, sleep long, train hard!
    – R-Dub
    Aug 26, 2014 at 6:44
  • @Matt Chan I tried to clarify why I don't think this is a duplicate. Care to explain, why you think my explanation is not sufficient? Aug 26, 2014 at 12:20
  • I'll reopen it and hopefully there will be detailed answers for it.
    – user241
    Aug 27, 2014 at 2:29
  • @JohnP I hope you still remember your plans to post an answer? Sep 5, 2014 at 13:51

1 Answer 1


We are training to produce adaptations, and through those adaptations we become more capable. There are a lot of different adaptations that happen as a result of training; for example, in aerobic training the heart's stroke volume increases and Haemoglobin levels in blood rise. In muscular training, muscle fibers get stronger. In the case of muscles, working them hard breaks down muscles - that is why we get sore - and we need rest so that there is time for them to rebuild.

For aerobic training it's more complex. The response of our bodies - how much we improve - is related to how hard we work out (often known as "training stress"). But how hard we work out depends upon how well-rested we are.

If we run every day, we will become good at running every day - our bodies will adapt quite well - but we will never be fully rested, so we will be limited on the amount of stress we put on our bodies. On the other hand, if we run every other day, we will be more rested and therefore be able to put more training stress on our system, leading to more improvement during our next rest day. Another way to look at it is that your body adapts to the peak effort that you using during training, not the total amount of effort.

This is the whole principle behind High-Intensity training, or interval training. It works very well, but only if you have enough time between interval sessions so that you can recover enough. If you don't recover enough, you won't be able to increase your peak effort in future workouts.

If you want more information on specific adaptations, a search of "physiological adaptations to exercise" should find you good info. A search on "science of interval training" (or hit training) should find good info there.

The key to recovery days is that you aren't putting additional training stress on your system, as that will compromise your recovery. In general, active recovery - working out lightly - is superior to pure rest, as long as you work out very lightly.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.