I have a trail 10k planned 8 weeks from now, though I will see how I get on first before I really enter. I'm doing a 5k later that month anyway (Race for Life in Dundee).
I'm basing my training on the '3 times a week for 8 weeks' RW schedule, adding other activities on the other days (cycling, indoor climbing, exercise classes, hillwalking, and rest)
So this morning I did my first speedwork run. I used times instead of distance (easier in the forest), so I planned 4x 80 seconds fast with 3 minutes recovery, running the same stretch back and forth so I could compare runs.
The first one I set off in a nice controlled speed. After 20 seconds I knew it was to fast so I slowed down. Another 20 seconds later and I was struggling to keep moving. After that I set of in a lot slower pace for the other 3 repeats and covered about the same distance at a more even speed.
However, that speed was hardly faster than when I run 10 minute intervals. It's not that I got out of breath, it's more that my legs refused to move and felt like lead. I didn't need the full 3 minutes recovery, even with the slowest jog I was back at my starting point and feeling recovered in 2:30.
Also, afterwards I didn't feel particularly knackered.
Maybe my legs were still tired from the circuit training exercise class on Monday evening. I also realised that most of the exercise I have done in the past years has been endurance. I suppose it will get better if I just keep doing it...