Tim asks: I need to run my first 25 kilometres for my marathon training on the same day as a very popular 10K in my area. I really enjoy this race and have run it several years in a row. Can I do both or should I focus on one thing?
Yes, you can do both. When something like this pops up in your training schedule, many runners deal with it by incorporating the 10K into the long run. That said, understand that you should not be “racing” the 10K.
Because of the length of this training run and because it’s your first time running that distance, you should pace yourself conservatively during the 10K portion and run it no faster than your goal marathon race pace.
The focus of this training run is two-fold: completing your longest training run to date and practicing your goal marathon race pace for 10 kilometres in the midst of a long run. This is not a day for personal records, so focus on completing the mileage and enjoying the social atmosphere of race day. (It will really help during that middle portion of the long run.)
I suggest running 13 kilometres before the race at a very easy, comfortable pace. Time it just right so you finish the 13 kilometres and arrive at the start line with very little wait time. You want just enough time to get some water and/or nutrition, use the bathroom, and line up.
Then, run the 10K at your desired goal marathon race pace. This will be a great way to practice pacing for your marathon, and it will still be a challenging workout given the total distance of your run. When you cross the finish line, get water, take some nutrition if needed, and continue running the remainder of your mileage—about 2.8 kilometres, at a very easy pace for a cooldown.
Just keep your goals and intentions straight. This workout makes a nice change of pace (literally) for your long run and gives you the enjoyable atmosphere of a race.