i’ve begun injecting some workouts to help my run speed. anyway i have noticed that my legs have gotten sore in different places from the norm. eg my hip flexors and other muscles on top of my thigh have gotten sore! i have NEVER experienced this before, well not for 4 days after i first noticed it anyway!
it get’s bloody boring just doing the longish stuff (i am training for ironmans)…
Your hip flexors will get sore because you lift your legs more when you run fast (watch any sprinter compared to a marathoner and look at the knee lift). Running fast more often will strengthen your lifting muscles (which is one of the concepts Frank will suggest as a good reason for Powercranks but I think that speedwork tends to strengthen the same muscle groups) and make it easier for you to hold a better run pace.
When I first start hitting the track for speedwork (which I haven’t this year due to a nasty hamstring injury that was caused by going to the track without enough base following another injury … aaarrgh!) I always get sore in my calves and hips for the first few weeks.
Yup, common - a little late in the season maybe though 
At least your base should be fine, but don’t do these workouts often as they are hard on the legs for sure. I’ll do a few in the winter about every other week on a treadmill (yuk) just to keep the feeling and force the 5 min/mile pace that I would not likely be able to do on the roads. Hit the track in late spring after my spring marathon to begin tri season.
i am just entering spring…
Did a hard speed workout last week, 7x1000m and experienced that killer leg ache for the first time all year. We hammered the intervals so I’m not surprised but it’s still been a while. On timing, we’re just picking it up for Worlds/Xterra so depending on what you’re up to it’s definitely not too late:)
Your hip flexors will get sore because you lift your legs more when you run fast (watch any sprinter compared to a marathoner and look at the knee lift). Running fast more often will strengthen your lifting muscles (which is one of the concepts Frank will suggest as a good reason for Powercranks but I think that speedwork tends to strengthen the same muscle groups) and make it easier for you to hold a better run pace.
I think the questions I would ask you is Do you think speed work (say an hour a week’s worth) trains the hip flexors as well as 6-10 hours a week on PowerCranks, and, if so, why? And: Why would an hour a week of speedwork make it easier to hold a better run pace over 5-10 hours of PowerCranks (especially for a marathon where endurance is key)?
Don’t get me wrong, speed work is useful but it is not a very effective way to train the hip flexors for aerobic endurance and, IMHO, cannot match the running speeed benefits received from PowerCranks. And, one more thing, as you found out, speed work is a good way to get injured, which does nothing for speed except, of course, slow one down.