Doubles + LT workout

There are all around many posts in running forum about the "magic" of running doubles...
give a look at there 2 recent threads:
http://www.letsrun.com/forum/flat_read.php?thread=2372073
http://therunzone.com/VB/showthread.php?t=910

since the job was quiet this week, I gave a try and run both Wednesday and Thursday also in the evening on the treadmill, around 35/40 minutes each time.
I slipped on the racing flat and run pretty relaxed with a light stride. The legs get much better after 10/15 minutes, but yesterday I felt anyway already tired in the morning and the evening session was tiring anyway.
Now I have the legs a bit sore, but I guess it takes a while to get used and I must also recognize that compared to my usual weekly mileage of 70/90km this week will lead me to a jump to 120km, so the load increase is a bit rough.
If the work schedule let me do it, I will try to add 1-2 more runs every week and see if there is some benefit for me.

This morning, Long Interval Session on the track (300m)
Purpose: work at LT level, in fractionated way to keep speed a bit higher than a tempo. Target running around 10'21'-10'35", bpm around 175.
Actual: 3x3000m in 10'24" +10'26" + 10'28"(rec: 900m jog 4'30"), with HR around 175-178 (right on target). I was anyway with sore leg at the start and the last interval was tiring, did not run easy anymore (even if the HR was still in range around 178/179).
Tomorrow I definitely deserves a easy run ...