Fartlek Pain!!

So ive been doing around 3 -4 mile runs for a few weeks now with a 5k race done in 26 mins and onto a 10k race next month before the half marathon in October.

I've been going ok with a bit of soreness in the legs and knees but nothing major and a bit of a cough this week which is annoying. Anyway im desperate to increase my speed as I still feel quite sluggish when running. Today I decided to do an hours run with a 10 min walm up followed by fartlkek training. I was going to do 10 min walm up then 4 mins quick, 1 min slow and carry that on for 40 mins. I was going ok but even at just 10km an hour i was finding it tough. Then i decided 4 mins of "sprinting" each time was too much so I did one min on one min off.

Anyway I had to cut my run short after 40 mins and 3 miles as I felt my right hip almost lock up and a fairly sharp pain in my right glute. Im really frustrated as Im worried I just wont get the speed, any thoughts?

Im 11 and a half stone, a bit overweight and 29 soon, i dont seem to be losing weight yet either which is annoying!!!

4 mins of sprinting does sound too much, I would say if you havent done interval training before start with something like inserting 6 to 8 x 30secs fast, 1 min slow into your normal run.

As i understand it, Fartlek and Interval training are slightly different.

this is a Fartlek training session designed for a cross country runner (nicked from Wikipedia), but you should tailor for your particular discipline.

• Warm up: easy running for 5 to 10 minutes.
• Steady, hard speed for 1.5–2.5 kilometres (0.93–1.6 mi); like a long repetition.
• Recovery: rapid walking for about 5 minutes.
• Start of speed work: easy running interspersed with sprints of about 50–60 metres (160–200 ft), repeated until a little tired.
• Easy running with three or four "quick steps" now and then (simulating suddenly speeding up to avoid being overtaken by another runner).
• Full speed uphill for 175–200 metres (574–660 ft).
• Fast pace for 1 minute.
• The whole routine is then repeated until the total time prescribed on the training schedule has elapsed.

I think you might be being a bit over-optimistic about your rate of progress.  I wouldn't worry about speed sessions etc yet, wait until you've been running for six months plus and are comfortable with completing a 10k race distance.  If you've only been running a few weeks, your body is busy trying to adapt to the demands of running without adding the extra overhead of increasing pace.  As your just starting out you should see some improvement in pace through steady state running, so there's no need to force it with specific speed sessions. 

If your runs are currently 3 to 4 miles, trying to incorporate sprints into a run of this length is going to hurt.  Have a look at the various training plans on this site and you'll see that speed sessions are normally around 50% of the distance covered by the weekly run.