Last year, my coach M2 gave me a set of cycling workouts which changed subtly; knowing that I had progressed many years with him, he knew he could increase their difficulty. The rest intervals now had a small but important change: they would be performed at 100RPM.
Now anyone who has tried to spin at 100 RPMs, even at low wattages, knows that it can be a heart rate raising experience. However, I had trained specifically for this. I had spent weekly sessions for years working on improving my ability to cycle at high RPMs. Given Lance Armstrong's success at pedaling at high RPMs, I was determined to do the same. For recovery workouts, I use M2's Pedaling Efficiency workout which is alternating one legged pedaling at 100 RPMs. It became a regular event every week and over a period of months, I could pedal at 100 RPMs through that workout with barely a rise in heart rate, certainly not approaching my lactate threshold heart rate at all.
Throwing 100 RPMs into the rest interval of 30 seconds to 1 minute in between high wattage intervals was scary, but I found that my neural muscular training with that Pedaling Efficiency workout really adapted my nervous system to perform even though the system was tiring. It also meant that in cases where I would raise my effort (ie. sprinting, or passing) that I would not collapse completely after that effort and my RPMs would drop after each of those effort. I could maintain RPMs, shift downward, and maintain my previous speed AND recover energy into my muscles. Before this, I would make the effort and then have to lower RPMs to recover or else my system would just keep rising in effort until I would flame out because I could not recover without the low RPMs. During a race this is really important.
Likewise, I started experimenting with high leg cycle rates in running. I would train weekly on the treadmill and do sessions of super high speed for short intervals. This trained my neuromuscular system to be used to high RPMs and to not easily collapse in the face of heavy or long efforts.
This has manifested itself mainly in hills. You hit the bottom of the hill and attempt to maintain speed up the hill. If the hill is long enough, you may find that by the time you get to the top of the hill you are so tired that you need to slow down your legs' cycle rate in order to gain some rest. This is bad for your speed! As you crest the hill, you have nothing left to surge and accelerate again.
These days I practice relaxing completely BUT maintaining or increasing the cycle rate of my legs. I try to relax the muscles and rest them from the effort of the hill climb and then rest as I tell my legs to spin faster. It's amazing that one can train for this; it really helps in not slowing down or collapsing entirely as you crest a hill and then move to the downhill on the other side where you want to keep higher RPMs to keep yourself moving down the hill. Thus, the rest interval happens during the crest and on the downhill.
I attribute this ability to high RPM training on the treadmill, using neuromuscular training intervals to train my nervous system to operate even in conditions of high effort. I also practice this when I'm out during a run through rolling hills; at every crest of a hill, I relax completely to rest but keep my legs' cycle rate high, or try to even cycle them faster. I don't want the nerves to stop firing when fatigued; I want to them to keep going even though my muscles are tired.
Again, the value of neuromuscular training is revealed. Whether on the bike or on the run, training your body to rest while maintaining high RPMs is a valuable tactic to being fast.