Why does increasing training pace lead to poor race times?

When an organism breaks down and then recovers it's stronger after the recovery than it was before. All training is based on this idea of breaking down and then recovering. As long as you're doing those things you should be getting faster.

But the recovery needs to be complete. If you break an organism down and then break it down again after it's only partially recovered it probably has not gotten stronger than it was before its breakdown so it's not going to strengthen as much as if the recovery was complete.

Harder running breaks you down more than easier running does. The two need to stand in balance to each other. Not enough stressful running and you get lesser breakdown and are not as strong upon recovery. Too much hard running and not enough recovery and you'll wear yourself down and get slower. If you're running harder and getting faster you've found the right balance. If you're running harder and getting slower or stagnating you're probably running too hard too often.

There are loads of threads here about the physiological benefits of volume training but I don't really mess with physiology much. Volume training improves your circulatory system and prepares you better for hard running. Imagine two people of identical age and physical abilities and background except that one has been running ten miles a day for a year and the other has just been really active and athletic but has done very little running. Now they're going to go to a track and see who can run the most 400s at 70 seconds with a 200 jog as recovery. Which one is your money on? Mine is on the ten mile a day guy even if he's a bit slower in an all out 400 than the non-runner because the ten mile days have given him a much higher level of running fitness.

I don't think anybody 'understands' how volume can make a runner faster, where 'understand' means 'be able to explain physical cause and effect.' It really does work, though, at least for most runners, and certainly myself and every runner I've known personally.

For a 16min 5k runner make sure you're doing at least 80miles a week. Average that for a few months and then see how you're doing.

My lame 800m PR came at the end of XC, at the start of the rest week following a season with 100+ mile weeks, and numerous weeks in the mid 80s. Our coach who was a high mileage advocate had us run an 800m time trial - boom, PR. He had us run a hard 800 to prove a point, which he proved quite nicely. Several other people ran PBs or near all time bests in this little outing.

You would think race-specific paces would help but I guess that's what the whole "strenth=speed" mantra tries to counter with.