Marathon Training on Foreunner 255

Hi. I’d forget about  Garmin now at this point and ask Chat GPT stating as much information as possible. Weekly volume, recent races, goal time etc. Generally speaking it’s accurate. 

I think you are right, I have been searching different forums and it seems like persisting issue with the watch. Really shame…

I've seen people asking things like that before on message boards, like reddit etc. Even sometimes people have done a long run on purpose themselves because they got anxious, realized they could do it just fine, and then gone back to the Garmin suggestions. In the end it always seems fine, I remember one person who ended up running a marathon something ridiculous like 45 minutes better than their previous best and they never actually did anything huge during the training anyway. So I wouldn't worry, a long run is just running for longer anyway, if you're pacing yourself okay (which the watch will be doing for you) it's no different than a normal run, just longer.

My experience as more of a sprinter type, is that the length of the run makes it completely different. I need to gradually increase the distance to make my muscles robust enough to tolerate it. Practicing energy fueling while you are running is also very relevant for long distances. I would run at least 2/3 of the distance before the actual event, or it will be very painful.

I think in theory long runs are not necessary to prepare your legs for a marathon, but they can highlight other problems.
As an example - when running gets a bit hard, I tend to start looking down. It's not a big problem if I run for an hour, but after 2 hours my neck really starts to hurt. At that point the run is really painful - not because of my legs, but because of my neck. 
So for my next event I know I can't let that happen - since the very first meters I need to make a concious effort to look straight ahead instead of down.
I know it sounds silly, but it's something I wouldn't be aware of without 20+ km runs. It just looks like long runs can highlight issues you wouldn't know existed with shorter runs only.
I guess another common issue would be chafing - I know exactly where to apply vaseline ;)

This is what is in my head, like you don't know what issues might come up until you know. Also you don't know how will you handle energy gels :)

In the settings for suggested workouts, you can choose one or two long run days of your choice. Check if you currently have only one selected, and change it to two runs per week—you should notice a difference. With eight weeks to go, you should definitely be running more than one hour per week; aim for at least two hours per week for long runs.

I highly recommend the Pfitz book advanced Marathon training (don’t be put off by the title or front cover) it’s for mid pack runners all the way to sub elite level. 

I have actually 2 long runs Tuesdays & Saturdays. This Saturday I have 1:01h base run , and then next week Tuesday 40min , so definitely far from long run. But I think at this point I just need to abandon Garmin plan and use alternative.

I wouldn’t class an hour run as a long run. I imagine for a 3:45 marathon runner, that’s around 8K/5M.

I used the suggested workouts last year for the marathon too, and they were useful to see. I like the idea of the threshold and tempo runs, but overall, I felt the plan was light on weekly volume. When I ran around 3:45, I was running about 40 miles/65 km per week.

At this stage, I feel Garmin’s suggested marathon training isn’t as good as we might think. In the future, with AI, it’ll likely be far more useful.