Okay. For some rather arcane legal reasons I had to go back to my hometown for a week and was nowhere near a computer. Let me try and catch up with what has been going on. (Did a search to see if my name had come up recently).
RunForTheSON,
You have been doing well. As you have noted the 10k was relatively easy (indicating your aerobic system is beginning to get well trained). It was not a hang-on affair from 4 miles onwards. You ran at 6.20m/m (39.20)
You then jumped into a 5k and barely broke 19 mins and were disappointed with the time. Now someone who runs 10k at 6.20m/m, should expect to run 5k no better than 15-20 secs per mile faster (better runners may only be 12 secs/mile faster).
So, someone who ran 6.20 for 10k should expect to run ~6.05m/m for 5k (18.51). Presumably around where you finished. So your 5k was where your 10k predicted.
I am hopefully going to get into this in more detail in another thread to Joe Blow, but all this training you have been doing is just base training, it has not been designed to get you into 5k (or 10k) race shape.
So, see yourself as having just completed phase 1. Distance is not a problem now, you can run a long run of 18 miles and 10 miles at a good lick, (note that a 17.30 5k guy thought 10m in 65.00 was tough, showing that he is not well-trained aerobically. You know it isn?t tough if you are trained right). But you are not race fast.
After base training, you must then move into phase 2. Which will involve 3 things. (First begin by deciding what you are training towards; mile PR, 5k PR, marathon PR, because that will decide what you are about to do).
In phase 2 you must think like this. 3 things to do each week:
1. Do some work at race pace
2. Do some work faster than race pace
3. Protect the LT you have already built up
So, let?s say you wish to go for a 5k PR (or age PR). You need to start doing some running each week at 5k pace. Here you might begin with 1k repeats (with slightly less than equal time recovery). Soon as you can, increase them to 1200s and even 1600s. If you can run 4 x 1 mile at 5k race pace with 2.00-2.30 recovery you can put them together in a race.
Do some faster work. This can be at 1500m (short intervals of 200-400m) to 3k pace (longer intervals 600-800m).
Be careful. You are not trying to hammer these. No crawling off the track.
At first, the 1500s can be run in sets of 3-4 with 60-75 secs recovery and five mins jog between sets.
The 600-800s should have equal time slow jog recovery. Run a max of 3-4k at this pace.
(Take 3k pace as 5k pace minus 15 secs mile, and 1500m pace as 5k pace minus 25 secs mile.)
Finally, protect that LT. Here you can either do a straight run of 4-5 miles at 5k pace + 25 secs. Or a 10 mile run at marathon pace (5k + 40 secs). Some runners like a progression run of 8 miles, like 4 miles at M-pace winding up to 4 miles of 5k+25 pace. This has not to be a race. This is not a session to be improved each week. But as the 5k and 10k race paces improve (and they will), you can slowly improve the LT pace.
All else easy running. If aiming for 5-10k, your longest run might be an easy 90 mins on Thurs. (With Tue, Fri and Sun as "work" days).
Notice that training this way you get fitter for distance first (ie: aerobically fit). You would do well in a 10 mile or half marathon race before you would do well in a 5k (as you found out).
I would suggest you move into phase 2 for 3-6 weeks. As always you should see a change in 3 weeks, and a definite improvement (and better racing) in 6 weeks.
Be careful/honest of the paces you choose. From now on always work off of race times (although a HRM is handy for easy running to make sure it is easy).. And if the paces become easier (in the short and long intervals), do not move up the speed, but shorten the recovery. Do not move up the training speeds until you race faster times. Things may come and things may go but race times never lie.