The principle of training reversibility states that a stop or decline in training will stop or decline the training effect. It is also true that when you start or increase training will increase the training effect. I'm a big proponent of simple ideas, but this sounds too simplistic. But it is a start in my quest to answer the question of how long can you maintain the the training effect and how long should I rest before get out of shape? It turns out that the answer to this question is different for endurance athletes and speed power athletes.
There is a minimum amount of training that needs to be done in order to maintain the skills, strength, and stamina gained from a training block. One marker endurance athletes use to track their training is VO2 max which is the body's ability to take in and utilize oxygen. Several studies indicate the following drop of VO2 max
The specific cause of this decline seems to be primarily caused by three factors.
These three factors effect mitochondrial ATP production and cellular activity ultimately decreasing performance.
Persistent training is necessary to maintain high levels of aerobic capacity and muscles oxidative potential, so timing detraining for endurance athletes can be balancing act.
Speed Power Athletes
Gains made from strength training can be maintained longer. During the first two weeks of no training, studies have shown that your strength levels will be maintained or show no significant loss. In fact, your anaerobic potential and maximal short term power output can be maintained for up to 7 weeks without significant deterioration. So, technically your sprint speed may not significantly deteriorate for seven weeks. So, why is it that you don't feel as fast or performa as well in speed power activities after a seven week layoff?
What does deteriorate is your ability to apply this strength for the same length of time and with the same efficiency. The technical skill of sprinting or performing your sport has been developed throughout the training block. Movement patterns and nerve to muscle connections have been ingrained. It is these pattens and channels that deteriorate during a layoff. Also, the length of time that you can apply maintained strength declines because of the three factors above.
Because it is not the loss of strength that causes a decline in performance after a layoff, speed power athletes have more flexibility over endurance athletes when timing layoffs. The fact that layoffs from training only significantly effect neurological factors means training round injuries is possible. Speed power athletes can come back to similar performance abilities after an injury or layoff by continuing to train the neurological pathways of their skill. Mentally rehearsing perfect form and going through the motions slowly and deliberately will keep your skills from deteriorating.