We have long known that our bodies react to stress by becoming fatigued, then adapting during rest to better handle that stress. In sports we use training to apply stress (i.e. workload), and then allow the athlete to recover and repair to an augmented state so the body can handle a higher stress or workload. Applying too much stress to an athlete will cause them to go over the edge of no return and become over-trained. Over-training is technically defined as a loss of external function or decreasing performance with increased training. Basically if your training a lot but seeing performance going down, then you probably are over-training.
So how much is enough and what is too much? That is a good question and that is specific to the athlete. Typically, I have found that most athletes with a decent training base can handle 2 – 3 fairly long, hard training days with minimal risk. These can typically be up to double the normal distance of the average training day for the athlete. As the “crash” training gets longer it does increase the risk of over-training. Typically, I do not advise athletes going over 4 days of “crash” training since that drastically increases the risk of over-training and I have seen diminishing returns from long over-load cycles. Make sure you are recovering about the same number of days as your “crash” training. The recovery period should include some easy spins as well.
Of course there is some risk to this type of training. Connective tissue overuse injuries are the biggest risk. It is important during these over load phases to pay close attention to your joints and understand the pain from suffering from long miles and the pain from a more serious inflammation. Staying on top of hydration and fueling will also help this training be more successful. A good goal is to drink at least 20 oz of water, although this will vary greatly by athlete and weather, and taking in around 250 calories per hour.
Do work and enjoy the suffering!