Interval Training

The rule dell'Interval Training is a winner. They say all the gurus and is a proven technique
I often know that during this season (the end) I make the plain and stretch sprint
The sprint for 5 seconds. Max 10 sec and 15
The stretch also a minute

The number of sprints is 10 with 3 minutes of active recovery
The number of stretch is equal to 5 with 3 minutes recovery

I try to express the power in the stretch is 110% VO2max with 100 RPM

I hope to check out help
Daniele

Others will probably have good advice but I like your 2 plain vanilla varieties: the short interval (also known by some as the VO2Max version) and the long, aka threshold interval. There are so may flavors, paradigms, theories, and whatnot, pushing up the ceiling vs. pulling up the ceiling, over unders, yadayadayada, enough to fill a volume the size of War and Peace. Best is just to read as much as you can and play around a little more than that.

For me the long interval is anywhere between 10-20 minutes with 2 or 3 repititions. If doing the shorter version of 10-12 minutes (some say 12 minutes is the shortest these should be), I usually do 3 reps with half the length of the interval as a rest period. 10 minute effort, and I'll rest for 5 minutes. For the 20 minute effort (which I usually evolve to a month or so after doing the 10 minute ones) I'll repeat twice and rest for 10 minutes between. Intensity is slightly higher than tempo, but slightly lower than time trial pace, for me around 80-85% MaxHR. These efforts really help bump up sustainable speed and are good for the long term evolution of cycling strength.

The short interval is 4-6 repititions of a 3-4 minute effort, with an equal amount of rest between, at around 88-92% of maxHR. If using perceived effort, pretty much a 9.5 on a scale of 1-10. Some folks do multiple sets of these with a larger rest period between each set. At the end of the effort, you should be spent, but not so spent that you cannot complete the full set. Huge anerobic, and yes aerobic gains too, are made from these but the real beauty of these is the intimacy you'll develop with your body and understanding it's limits. After awhile you'll know just how hard you can ride without blowing up. Folks who don't indulge in these usually get dropped in races as they also help improve one's capacity to absorb repeated accelerations. It's important to go into these workouts healthy and well rested, they really beat you up.

When the season is in full swing and I've got a good base (which it sounds like you have!) I generally ride 4-5 days a week where I include one day doing each of the above workouts (earlier in the week so I'm rested for race day), mixed in with a longer 3+ hour ride, a free ride of whatever, and a race day or fast group ride. I might do 2 long interval days instead of the short day, it really depends. There is no hard and fast rule and 5 coaches may have you doing 5 different things. My cadence is generally in the 90-105 RPM range for these workouts - but it's usually always in this range unless I'm sprinting. Do this long enough and eventually your body will adapt and you'll have to mix things up again.

Personally I see little value in the sprint interval for improving "biological" speed, I've always believed this is genetically set. The value of the 8 to 15 second sprinting interval for me is to improve sprinting technique, which CAN improve sprinting speed dramatically.

Hope this helps.