Fast Running Blog

I was wondering how much time people would expect their 5k time to increase by, if they ran one in a a period of time when they are training for halfs and marathons?
Example: my PB of 18:22 when I started training for 10k/5k earlier this year
Now when training for a half marathon/early marathon training I have run 18:52 and 18:53 (footing was not good) in recent months.

So a loss of around 30secs or so.

And how do people avoid losing leg speed when marathon training, for example through experience I find if I don't keep in touch with 5k pace at least every other week I start feeling sluggish and find it hard to achieve paces that come pretty easily when I do keep in touch with 5k pace.

I'm new to running (running for less than 2 years), so I may not represent most on the thread.  My pr for a 5k is 19:09.  I've not run many and my only 5k's have been raced on very hilly courses.  This pr happened when I was averaging 60-70 mpw.  When getting up in the 80's to 90's, mile repeats (6min miles) become much more difficult for me (6:10 becomes more managable...thus translates to 30 seconds over 3 miles).  Most of my year round training has been in preparation for a marathon.  Although I have never run a 5k when my mileage has been low, I can definitely run much faster on 40-50 mile weeks.  This may change over the next few years as my body adjusts to the mileage.  My marathon pr went from 4:12 in May '08 to 3:09 in October '09. 

My opinion...

Although there are some people that set their 5k PR off relatively low mileage with lots of speedwork, there are lots of people who actually run their best 5k times during marathon training.  This includes myself- I just broke my old 5k PR from high school by 25 seconds at a low-key, untapered 4th of July race this summer, with minimal speedwork.  The high mileage of marathon training is actually quite conducive to setting PR's at shorter distances.  My marathon training includes some speedwork (I did 1 mile repeats a number of times, and 1000m repeats once), but I was never pounding out 400m repeats.  Yet breaking my old 5k PR was relatively easy. 

Overall, I don't think you need to expect your 5k time to get worse during marathon training.  If it does, all you have to do is add 2-4 weeks of focused speedwork to your marathon mileage and you will likely be running faster than ever.  If you are running slower, it is likely due to missing that small amount of speedwork, plus perhaps some residual fatigue from your training.

It depends on what is limiting your 5 K performance. If it is aerobic fitness, marathon training will help you smash your 5 K PR. Otherwise, you will lose about 30 seconds.

400 meter repeats have helped me maintain 5 K speed while training for the marathon in the past.