While I was on the bike I was thinking about how at its simplest form there are only three types of race specific workouts. Meaning workouts designed to prepare you for a specific race distance and time. Certainly there are many other types of workouts designed to make internal changes to the bodies physiology that will result in better racing capabilities but in terms of that last part of the puzzle you really have three options.
Option 1 is to run the distance and try to run it faster each time you repeat the workout. IE today I ran 5k in 16:00. I want to run it in 15:00. So in a week or so I will run it again and try to run a little faster than 16:00. I personally find this kind of workout very hard to improve on. In fact I essentially don't do anything like this anymore. I tend to increase distance at the same pace then when I have managed to go further at the same pace I come back down in distance and then increase the pace. So if I had run the 5k in 16:00 I would go and run 6k in 19:12 and 7k in 22:24 and so on until I had run 8 or 10k at 3:12 a kilometer and then I would come back to the 5k and try and run 3 to 5 seconds per K faster. Still for myself and I'm sure many others this was the first type of workouts I attempted and it seemed the most obvious plan to get better. It just didn't work as well as it seemed it should.
Option 2 is to run the pace you want to run and try to increase the distance in an attempt to build up to the desired race distance. With the same goal of 15:00 let us say we can run a mile in 4:48. So in a week or two we try to run 2k in 6:00 then 2400 in 7:12 and so on. This generally works really well for me in tempo workouts. IE lactate threshold pace and slower. Sometimes I hit a wall and have to do some other workouts to make a jump in fitness but very often I can make a lot of progress with this approach. I have much less success with this approach in the more lactic acid limited distances and paces. So If I am trying to run that 15:00 5k this type of workout quickly becomes a no improvement game.
Options 3 is the interval option. At it's simplest level the specific interval workout involves running something close to the total volume of the goal race at about the goal race pace. This is the most common type of workout in running. The results vary greatly but when this is done correctly they can be quite profound. I think the greatest key to real success is that you should be reducing the rest and extending the distance of the intervals no increase the pace. So if the goal is that 5k in 15minutes and you can do 25x200m in 36 with 100 jog rests the goal should be to do 300's in 54 then 400's in 72 and so on always with the short rest. OR if you can do 3x mile in 4:48 but you need 5mins rest. To continue to do the 3xmile at 4:48 but each time try to reduce the rest until you can manage the workout with only a short jog rest. Most likely you use some combination of these two.
The biggest mistake I have made in intervals in my time as a runner and probably the most common mistake I see in runners workouts is to try and do the workouts faster. I am talking about specific workouts here. An example. My senior year in high school I entered spring track with a 9:57 2 mile personal best. I desperately wanted to be a sub 9:00 2 miler. Very early in the season I did a workout of 8x400m at around 68 seconds with a 400 meter walk/jog break. Now we can discuss the over ambitiousness of the goal another time and certianly if I was coaching myself in the same spot now I would have pushed for a goal time of no faster than 9:20 for that season but I digress. On that day I did 3200m of work in just about 9:04. I repeated this workout with similar rest a handful of times over the spring, sometimes the rest would be standing while a teammate ran a hard 400 as we did them relay style. Sometimes I would walk or slowly jog the 400. By the end of the season my last hard workout I ran 8x400 and averaged just over 60 seconds. To this day that is the fastest set of 400's I have ever done. My flat out PB is 58.8. So 3200m of work in right about 8:00. That is an improvement of 1:04 for 3200 meters. In other words that was the exact amount of improvement I was looking for to become a sub 9:00 two miler. However I only lowered my 2 mile race best to 9:47. An improvement of 10 seconds.
What had happened? I had taught myself to get very good at intervals. I was recovering better and better between very hard efforts. So that I could improve the quality of those efforts. However I was not getting much better at running the specific pace I wished to hold for 2 miles without any breaks. To be clear no single type of training was going to get me under 9:00 that spring. That was out of my reach at that time but I am certain given the extreme improvement of my intervals that spring that I could have run in the 9:20's. If I had set out to run my 2 mile workouts at the same pace, 68 to 70 seconds but reduced the rest each time out until I was doing a 100m jog. I could also have increase the distance and perhaps done something like 4x800 with 200 jog rests at the same pace. This would take similar or less improvement as I showed in the intervals I did but would have provided the type of improvement I needed to race better. I have done workouts like 4x800 with 200 jog and 8x400 with 100m jog many times in the years since and I never fail to race within a few seconds of the total time of those intervals.
Anyway that is what was rolling through my head as I spun away today. Nothing new, nothing shocking but good thoughts all the same.