Why are rest days important?
When the weather permits, I jog (or otherwise work-out) every day, but people often tell me I should not, because rest days are important. What is the rationale behind this?
Evidence shows that more than 5 days a week training increases your risk of musculoskeletal injury.
Rest is physically necessary so that the muscles can repair, rebuild and strengthen -- continuous training can actually weaken it. Without sufficient time to repair, the body will continue to breakdown from intensive exercise.
Overtraining often occurs from a lack of recovery time. Some signs of overtraining are feeling of general malaise, staleness, depression, decreased sports performance and increased risk of injury.
This image from pponline.co.uk explains why you need some rest.
Making sure to workout when you're muscles are slightly stronger than before your workout will allow you to literally built up your muscles:
Without rest, you will build muscle mass quicker than your supporting organs can build and adjust to enable their proper use. At that point, you will hit a plateau which you will be unable to cross. However, this does not hold true for aerobic exercise, where the Mayo Clinic suggests 30 minutes daily. This is more for muscle building and strength training.
It has everything to do with the person. Top athletes train every day, and a lot of hours. Usually, they have spent some years making the body able to withstand a lot of training.
I was the fastest running youth in Norway some years back in 60-200m, and trained about 20 hours a week in the weeks with the most load. That was when between the age of 15 and 18. I had no problems with injuries, but again, this is often individually.
If someone wants to train everyday, like I do, the trick is to have a lot variation in the training. One simple example, just to easily show what I mean is this:
Monday: Running Tuesday: Upper body weightlifting Wednesday: Lower body weightlifting Thursday: Mobility and stretching Friday: Running ...
Supercompensation would be some of the explanation if the goal is to get in better shape.
As I understand it: When the body rests it creates more muscle mass than what was actually destroyed during the exercise.
I assume this depends on person, as well as speed and duration of the exercise.
Personally, after running few days in a row I get muscles tired: it feels like your legs are filled with lead. Not something you want before a big college competition.
But if you notice no changes in your body, I daresay it's ok. Walking is also an exercise and we do it daily without a problem.