I am an elite cat rider, and i am constantly in a cycle of gradual training overload, followed by rest. I try and get total weekly durations over a 4 week block of, for example, 18, 20, 26 then 8 - so you take yourself to being totally shagged, and then recover - then repeat. With timing of races it isn't always easy to stick to a schedule, but if you try and work the rest / easy days into the schedule before important / tough races it works well.
Previosu years I have had to work full time, and have trained lower duration / higher intensity - this year was my first experiment with a massive LSD base over the winter. Apart from a handful of training races, and a classic in Belgium I have only done one L4 training session and one SST since end of season 2007. No L5 yet and not a single sprint in training.
Sure - the first races were strange, but I am feeling / noticing that a massive base of around 320 hours of L2 has given me the engine to rapidly improve the intensity that I can generate when it is required, the duration that I can sustain that intensity for, and reduce the time required to recover from that effort afterwards, plus increasing the ability to repeat it many times.
I believe that the massive amount of riding i have completed pre season has improved the ability of my body to deliver blood and oxygen to my leg muscles - I have seen considerable vascularization (almost brusing around veins), my resting HR dropped 6 beats, my body fat % is reduced, and my muscle mass is bigger. The downsides have been 3 x feverish colds in 3 months, mouth ulcers and hugely increased spending on food!
I did not notice such improvements when training only SST and L4 in the preseason.
The proof of the pudding will be if I continue to improve as the season develops with my new training, as in previous years, sure, in March I have been ready to go hard, and not surprised by intensity, but last year I noticed little or no improvement from March to september - only an increase in fatigue and frustration. now I feel that each weekend I am going faster, and going further.
Right now I am saying that this justifies for me a 20hr week average for upper level racing.