10k to 6k

First time poster.  I've been running for about 4 months and I'm now running 10k at about 1.05 outside and 56 mins on the treadmill 4 times a week.  I only run 10ks.

Yesterday for the first time I went out for a run with some guys from work at lunch the run was 6k.  I found it extremely difficult and I was really hurting (legs, ankles, knees) when I finished.  When I checked my splits they are almost exactly the same as my first 6k in a 10k run?

So... I would like some advice

1. why was it so hard?

2. How can I increase my speed over shorter distances.

Thank you

It was probably nothing to do with the distance and more to do with the time and possibly location.

Did you prepare as you normally would?

Was the terrain the same (more or less hilly)?

As the times were comparable to your normal run i would look to other reasons for the discomfort.

Yes it wasn't like my normal runs, Normally I do some minor stretching then have a walk to warm up before I start running.  Yesterday stretched more and didn't walk. 

The terrain was very different too, many more uneven pavements and stairs (which don't appear at all on my normal routes).

Thanks I feel a little better now.

how were you measuring them.......

Garmin Foreunner watch with GPS

I thought that stretching before running isn't good.cold muscles etc.you should do a walk/ jog for a while and then stretch...could make the difference............lso were you talking etc......the biggest reason is probably the terrain as you have mentioned above..................

More panting than talking, but point taken.  Thank you