During 2008-2009, I didn't see a significant improvement in my shorter race times. I set some major half marathon PRs, but the 5K-10K didn't budge much. (And I'm not even going to get into my back luck with marathons and lack of PRs there. . . )
In 2010, I experienced a major spike in my fitness level.
5K: New PR by 1:01 (from a 7:31 pace to 7:11 pace)
5 Mile: New PR by 2:30 (from a 7:56 pace to a 7:26 pace)
I also set a new 10K PR, but the jump there isn't as significant because the course was insanely hilly.
While there are many factors that I believe contributed to this, there is one key type of training that I think has made the most impact: interval training using a heart rate monitor to dictate the pace/effort.
In the summer of 2009, I had a few meetings with a running coach. She taught me about heart rate zones and suggested that I get a V02 Max test to determine my optimal training zones. Since then, I've based almost every training run on my heart rate. During one of our sessions, I told her that I couldn't get my heart rate high enough (zone 5b) for V02 Max improvement. I had been doing classic 400m and 800m intervals and my heart rate wouldn't get high enough for the training stimulus I needed.
She then gave me a workout that I have sworn by ever since. 3 minutes hard, 3 minutes recovery. It's that simple. She told me to start with 4 sets and that I could work myself up to 6 sets during a training cycle. She told me that my heart rate should reach zone 5b (187-189) during the second interval and all subsequent intervals, but that it probably wouldn't get up there on the first one. It took me a few tries to get this workout right. This was before I had access to a track, so I ran them on a running trail that was on a slight incline/decline. The first time, I did the first two sets too fast and ended up not being able to do the last two at enough effort. My coach told me that it was okay to walk during the 3-minute recovery jogs. She said that in order to get your HR high enough, you need to have enough recovery time to be able to get the speed you need. 3 minutes is also the magic number for the amount of time during the interval. With less time, then your HR isn't in the zone for long enough. With more time--- well-- I couldn't imagine keeping it up for more than 3 minutes!
I've been incorporating this workout into my training regularly for over a year now. Depending on where I am in my training, I will do 4, 5 or 6 sets. I almost always do them on a track, except for this week when the winds were sustained at 20 mph, so I did the treadmill. The distance usually ends up being about 0.45 mile and the pace is around 6:35-6:40 (when I started with this workout it was 6:55). This is much faster than 5K pace, which is what a lot of prescribed programs suggest for interval pace. It's extremely tough and I have to use all my mental strength to push through them. But knowing that my heart rate needs to be at 187-189 for the workout to be effective motivates me to keep the speed up and not stop. The splits of a workout from Sept. 22 can be seen here.
Endurance is my natural strength and I have always struggled to get my shorter race times to match up with the "equivalent" of their long distance counterparts (apparently this is true of only 10% of runners). But now I think that I am about equal in both speed and endurance, thanks to these 3-minute intervals.
Note: I highly recommend programming this workout into a Garmin using Garmin Training Center. The 3-minute segments are pre-loaded so that you hear a beep when it's time to start and stop the interval. Heart Rate, speed and distance for each interval is recorded without having to press any buttons. And trust me, 100% of the focus needs to be on keeping the effort level up- not fooling around with a timing device!