Leg can't seem to take me beyond the 10k mark

I have been running 10ks for the last few years and have recently (last few months) started training for a half marathon ortwo.  I have been doing long runs for a couple of months but can't seem to get to a stage where I feel comfortable after 10k.  

I run 10k in about 44 mins (with a PB of 41) so keep to a 5 mins/KM pace for my halves.  Despite this, my legs seems to get absolutely KO'd after 10-12k and my pace drops significantly.  It's a real intense effort to get through the last 7k or so.  This isn't a one-off and has happened the last 4 or 5 occasions I have run this distance.

I am presuming that the reason for this is due to leg strength.  Does anyone have any advice on how to build this up?  I am thinking squats and cross-training e.g.Spin class but have heard that building leg muscle can have an adverse affect. SO would appreciate advise from you experts!

Thanks in advance!


  • I think you need to just slow down... once you can go further comfortably then worry about speeding up  for a few miles at the end of the long runs, but until you can run longer distances comfortably don't worry at all about speed, just S L O W   D O W N! image 

  • Thanks! Any advice on building relevant leg strength?  I attend a gym a few times a week so doing a spin class would be very easy (in the logistical sense!).

  • hopefully someone that knows will come along, I see lots say how good spin classes are, but then again, you see others say that frankly the only way to improve your leg muscles for running is to run more.

  • Running leg strength - hill sessions.


    However I think that what you are lacking is endurance not strength.  You need to run longer distances at a much slower pace to increase your aerobic adaptation.

    Look at a site such as mcmillanrunning for suggested paces for training paces.

  • MillsyMillsy ✭✭✭
    Some great advice above. Slow the runs down so you can complete the distance.
  • based on the RW training pace calculator your long run pace should be 5:25km!

  • Ok, thanks guys.  So I guess the advice is to consolidate the ability to run at that distance first and not go for a PB.  Thanks again - really appreciate it.



  • Hi guys, 


    A quick note to say thanks for the advice on this.  I followed your advice and ran my first half marathon today at a decent time and without feeling half dead about 10k!  IN fact my final few k were about the same as the rest so there was no tail off at the end.  Thanks!



  • booktrunkbooktrunk ✭✭✭

    Good to hear, well done 

  • Run your runs at a fast, medium or slower pace depending upon the distance of your runs. Your easy runs will be weekly long runs and  slow recovery runs. You fast runs will be intervals and paced runs.3 to 5 days of running per week should see you improve your fitness over time.


  • Hello,sorry for jumping in on this thread,as i am much slower.but much the same question. I currently run 10k about 1hour - 1hour 5 minutes and have entered a half marathon,(quite a long way off) and i am currently upping my mileage. my last run was 7.9 miles in 1 hour 20 mins.What would be the best pace for my long slow run at the weekend ?

  • Bill this is the calculator to use, but don't worry if your easy runs are done a bit slower.


  • for slower runners.a good guide is at a pace you can still chat  image  .but you can look at the calculator for a guide pace


  • Thanks,will have a look.

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