In every training plan there is at least one rest day, it is very important to take one day off of training. According to Ed Eyestone (from Runner’s World), rest lets your body adapt to the work and improve. A day off every seven to 14 days prevents overuse injuries, restores glycogen stores, prevents mental burnout.
Rest days are the second most important part of marathon training; according to Dr. Scaff “the whole purpose of training is to break the body down so that it will rebuild itself stronger than before. It’s when you fail to allow time for the rebuilding phase that problems occur”. For novices, it is recommended two nonconsecutive days a week of complete rest – days when you don’t work out at all!
For intermediate and advanced runners may do some jogging or stretching on one or both rest days; but even elite athletes must take rest days. If you need an additional rest day, take it.
Strength training is also very important, to keep our body strong and injury free. Fit two days of strength training in your program, just leave a day of ‘no strength training’ between them and make sure you still keep at least 1or 2 days of ‘total rest’ per week.
Partially taken from “How to gain more by running less”, “Complete book of running”, “Beginner Triathlete”