Switching a foundation run for a bike

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    Hi all,

    Doing marathon L1, like everyone else, loving it, enjoying the miles and variety, especially as I’ve been working from the book for the last 3 years.

    I am beginning to miss my bike though. How much damage would I be doing to my progress if I switch one of the midweek foundation runs for a turbo session with similar aerobic objective and training stress score? Would it help if I jumped off for a 10min brick run afterwards?


    Matt Fitzgerald

    Little to no damage. There’s research to back that up, and my own extensive cross-training experience does as well. It could even be a net positive if you are at all prone to niggles during marathon training.


    As written in the book, everybody after 35 should benefit from it. 3 runs/week minimum and the rest complement with cross sessions.

    @Matt: that gives you 6 days/week (3 runs + 3 cross sessions) spicing up with core and strength will give you the most gains, not compromising running performance and minimizing the risks that come with age and (run)training?

    The older we (I) get the more I feel my body loves/needs mixing it up. I do every run in a different pair of shoes (in a rotation of 3) and feel that’s a good thing.


    Thanks so much both!! Great to hear 😀


    You hit a nerve! Tying all of this to aging is simply wrong.

    I will agree that there are undeniable aspects to aging, but too often people jump to conclusions that are more appropriately assigned to training and nutrition errors.

    Five years ago, just shy of my 70th birthday I took on a personal project to explore the impacts on my life attributable to aging. The paradigm I chose was: confirm (through research), consider (reasoning), and conclude. I did this with running and daily solving of rated chess problems.

    I chose 80/20 running plans because they are balanced, addressing the three physical adaptations of aerobic, anaerobic, and lactate processes. I found it useful to include strength and mobility work, but I wouldn’t conclude I need more or less than a youth training at the same levels I do. Yes, I did slow down compared to my abilities as a youth, but I improved over the past five years. I would argue that my reduced ability is attributable to a lower maximum heart rate only.

    Similarly, solving chess problems I found no decrease in the time it takes to solve problems of the same rating, and no decrease in my estimated ratings solving problems. If anything, my strength stayed the same only because I made no attempts to improve by solving more difficult problems. (I need to fix that).

    My conclusion is that attributing problems to aging is just an abdication and denying yourself the opportunity to be at your best. KEEP LEARNING!

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