As a competitor runner I usually run 5k and 10k races. For the last 6 months I've been cutting back on my weekly mileage of 40 miles a week
and long runs of 10 miles, to focus more on speed intervals and tempo runs. About 2 months ago I did manage to break my PR of 5k cross country during a traing run by 25sec., but seem to have reached a wall on any futher improvement dispite the added intensity of runs and increased intervals. A club I belong to had a 30k race about two weeks ago and I decided to enter just for fun. I finished the race better than expected and felt fine other than some tightness in my calves. The following week during my 400m interval training I noticed my inteval times had improved by an average of 7 seconds by the same effort.
During my weely 5 mile run I ran a whole 2 minutes faster with less effort. I have always been told that runnning long makes you slower, but it seems to have improved my speed. Any thoughts :o to maybe why and if someone else has had the same experience?. :o

Anyone has some good website on running techniques?

I am refering to how you position yourself when running and the most economical way to run...

I can't answer for other runners but tight muscles never make me faster. My stride lengh decreases and I run much slower. There is some evidence that when you sometimes run longer than you are use too, your
your body searches for help from fast twich muscle fibers when your slow twitch fatique. therefore in theory helping you run faster. When I ran the intervals I had no soreness or tightness at all.