From this NTY article Why Trainers Say, 'Slow Down':
"Of the tens of thousands of Americans who pay as much as $180 to register for marathons, as many as 25% fail to make it to the race. Injury, illness and loss of motivation as a result of overtraining are major reasons for this."
"No matter how conclusively science may prove the value of rest and recovery, the culture of endurance sports lionizes those who seemingly never rest."
"The body responds beautifully to the right schedule of training stresses," Lynn Bjorklund, who in 1981 set the still-standing female course record for the Pikes Peak Marathon, wrote in an email. "However, too much stress and not enough nutrition or recovery pushes your body toward injury and illness. You need to stay in that zone of just enough, and that takes a very high tuned and honest appraisal of yourself."
The operative words in that last quote are “Just enough”. Paraphrasing Arthur Jones: The proper amount of exercise is the amount that produces the best result; any amount beyond that point is at best a waste of time and at worst injurious.
According to a Runner’s World article 70 percent of runners have an injury in a year of running. Instead of seeing how much exercise you can withstand find that amount that is just enough to produce the best result.
People often hit a plateau in their training, and they try to overcome that plateau by training more - that is most often a mistake. By training too often you ruin two workouts. The first workout that stimulated change is worthless if you do not give your body a chance to recover. The second workout is worthless as well as you cannot give your best effort if you are not 100 percent.
While running can be done on a daily basis strength increases occur exercising as little as once or twice a week if it's the right exercise program. The personal trainers at New Orleans Personal Trainers and at Austin Personal Training have devised a program where the goal is not to see how much exercise you can withstand; the goal is to produce the most results in minimal time. They can guide you through a personal training program that will enable you to get more out of less time exercising and keep improving.