I have a number of athletes who combine running with cycling or swimming, e.g. duathlon and triathlon. Yes you are right, the crazy ones!
I have previously offered them training plans using the old-fashioned coaching method of putting in sessions manually into the diary (or into TrainingPeaks) according to what is approximately correct.
However, I know I can do better than this, and after creating a cycling dynamic planner, I was determined to make one useful for runners.
settings Step 1: User Data
The first step is to input your requirements, namely running training hours (or miles per week), phase of training (build or maintain), preferred days-off and importantly your training style e.g. POLARISED 80:20.

analytics Step 2: Crunch the Data
Next, the algorithm crunches your data, and it does this by working backwards.
What it is trying to do is fit the session duration AND intensity exactly to the hours available. After you specify your training style (e.g. POL80:20, BASE, or PYR), it works out the split of what Z1 (easy), Z2 (medium), and Z3 (hard) sessions to do each day.
Then from your available hours, it works out the duration of each session and finally, using a modification of the Riegel universal pace calculator, it prescribes an appropriate pace.

It will prescribe rest weeks between week 6 and 7 and between weeks 12 and 13. It will also allow a form of periodisation of build or maintain. Build starts easy and adds miles and intensity. Maintain keeps the athletes’ ability more even with only a very slight increase of time.

Bringing it all together from the data entered from the user’s form, the algorithm works out a structured training plan on the fly! It would be almost impossible to work this out manually! The computer is much more accurate than any coach, and it allows very fine-tuning as well as working in miles or km, and hours per week or miles per week… whatever you prefer, it will allow you to hit your targets precisely!

calendar_month Step 3: Format as a Diary
A new feature just added today is a cheat sheet, which means every session is placed into a diary view which can be printed or saved by the runner.

science Step 4: Field Test
With the kind help of the5krunner.com we field-tested this model in about 20 runners of varying abilities. This was very useful, as I tweaked a few “dials” including the pace calculator which was running a little hot!
campaign Step 5: Make it Public
The new running planner can be ordered here: https://shop.cyclingapps.net/ with 50% off using the code “50”.

thumb_up Acknowledgements
Thanks to the5krunner.
