When I was 26 (I'm 33 now) I submitted a question about sprinting to Charlie Francis, possibly the best sprint coach to ever live. Well funny thing is I was an Tom Furman's site and saw a collection of Q and A's with Charlie Francis that he has posted. I was shocked to find my question and his answer in there. It only took 7 years for me to get the answer. Here is my question that I gave him and the following is his answer. But you know what? I am still pumped to have this answer because it does answer some questions for me as I head off to the track to sprint right after I post this! God bless Charlie Francis!
Sprinting, Rapid Improvements, and Those Wacky East Germans
Q: I'm a 26 year old 100m sprinter who's been sprinting on and off since my junior year in high school. In the college program I attended my times were worse than in high school and I attribute it to the buffoon type of aerobic training my coach insisted I do. Well, years have passed and since having read your material I sprinted my PR of 10.72 (electronic- previous best was 11.00) with very poor strength levels. My goal is to get down to 10.4 this upcoming track season. Is this level of rapid improvement possible in one year? 10.72 felt like I was floating; it was the easiest race I've run. Have you ever seen anyone drop their 100m time by 4/10's of seconds?
A: That's a lot of time to drop all at once, especially as you've already dropped 3/10's in the last year! I'd suggest that you put some of the time planning on hold and concentrate on getting the best training program in place that you can. Relax and let the results come to you.
Your comment about your 10.72 race illustrates what I mean. The best races always feel easy! Don't put pressure on yourself. I'm not sure what sort of aerobic training you did before, but I've always had a significant aerobic component in my running programs (about 35% anaerobic, 65% aerobic). These runs act as an "active recovery," enhancing blood flow and increasing capillary density (the enhanced microscopic network slows down the flow of blood past the cells, allowing more time for complete nutrient transfer).
The other poorly understood, but even more important benefit, is the increased ability of the body to generate more heat around the muscle motor neurons. Increased heat around the neurons lowers electrical resistance, allowing more current to pass. This permits more muscle fiber to act as fast twitch fiber!
The East Germans understood the role of additional heat when an extensive review of world record performances revealed how often the record setter was at the early stages of a cold and running a fever when the record was set. (Later into the cold, the adverse effects outweigh the benefits, of course.) This led the East Germans to experiment with de-natured viruses to generate a slight fever immediately prior to a world record attempt!
The warning here is that these "tempo" runs must not interfere in any way with the quality of the high-speed runs. This means that aerobic interval runs must not exceed 75% of your best possible speed. If your best time for the 200 meters is 21 seconds, then your interval 200 meter runs must be slower than 28 seconds! Additionally, your last interval must be as fast as your first. If you have any problem doing that, you're going too fast!