Thanks a lot El G, theres mountain of information there - really appreciate iti nearly deleted this answer a few times, i dont really think i should be too proscriptive but i cant think of another useful way to answer the question. but there is more than one way to skin a cat. this is far from the only answer
it depends on how you run them.
You're probably at the point where you need to be running with a bit more intent. When i was training for tri's i found that swimming or biking the next day after a hard session manageable on the body but i was younger then.
Plodding 10k easy from here won't get you the improvement you're looking for. Its never the distance that's the issue its the speed. The general fitness you'll gain from more volume overall might but you need to start some controlled quicker running.
The aim is to go comfortably hard.
Never to overdo it and burn the candle at both ends.
If the 5k PR + 5k works, grand but i reckon its a big injury risk if you do it weekly.
Presumably you run it hard and you accumulate lactic, then keep going after a bit chances are you'll break down quickly enough and your legs will be trashed for Sunday.
Are you familar with Jack Daniels (the coach not the whiskey), he proscribed paces based on assumed VO2 max from distance races. Called Vdot. They are not a holy grail but a decent starting point for most runners.
V.O2 Running Calculator
An easy-to-use training platform for athletes and coaches, including the science and formulas of legendary coach Dr. Jack Daniels.vdoto2.com
Next week or the week after take your park run seriously.
Get a good 20 min warm up. Do a few strides beforehand, no pints the night before and properly race your Park Run this will get you a recent 5k time for current fitness.
Plug this into your calculator (by all means run another 5 but really you should be too bait to want to do any more than shuffle a bit) and you'll get a VDOT.
This will give you training paces and race projections. The one you need most is your threshold pace. i.e. the pace you can run where your body is generating latic and clearing it without it going exponential.
Your 1:51:10 ish marathon is about a VDOT of 40. this projects to a 50min ish 10k so reasonably good for you (but needs to be tested in the park run, do not use these paces here they are a guide only).
Training paces give Marathon Pace of 5:28 per km. Threshold pace of 5:07 mins per km. I think Daniels is a bit ambitious for his T pace so say 5:10 or so.
I would use these as the basis for your running and let the swim/bike be your easy session.
so your Tues 10k, can be
20min E warm up, 10 min T, 3 mins Rest x2, 20 min Cooldown. You'd be lookng to build this up to about 40mins over time split basically any way you want between 4 and 20 mins with decent recovery.
I like 8-10 4 min reps for this, or 5x8mins etc with 1min recovery for both.
Sat Session would be a touch slower and a bit longer between T and M pace maybe 5:15 or 5:20 or so. Err on the side of caution
20 min E warm up, 20 min steady, 5 mins E, 10 mins steady, 20 mins Easy. Build up to about an hour of work. over time by adding 5 mins either side of the rest. This might end up being your long run and you reover on the bike on a sunday. if its part of park run grand as long as you have pace disipline.
The idea will always be that you feel you are going too slow by rep 1 and are feeling it by the last min of the last rep but could keep going. you are looking to achieve a state not a pace so if you need to run your 20min sets 10 secs slower than your 1k reps thats okay but always be cautious. Some days you'll feel like shit and go slower. thats okay.
Some days you'll feel great, resist the urge to push it. Anyone can do it once. the aim is to get on the bike the next day and the pool the day.after and another session the next day or whatever.
Repeat your park run time trial every 8 weeks or so and update your paces.
I hope this helps and is clear and not nonsense
I need to read through it a few times and figure out how it would work.. theres a load of terminology there I am completely unfamiliar with as I'm a turn up and do it type rather than getting deep into reading or theory stuff.
I was laughing at your point about no drinking the night before the Park Run to set the line in the sand.. I doubt I have ever run it without a good gulp of wine the night before as it unfortunately follows the end of the week at work and me chilling out!
Right now I'm running 10kms around the 50-51 minute mark, thats simply taking off with no plan in mind and just looking to run at what i would consider a steady pace which tends to be 5:06 more often than not
I hear what you're saying about the park run - the one last week the first 5km was average 4:35-4:40/km, the next 5km was 4:40-4:55/km so I could see how that could cause issue now that I read what you are saying about lactic build up. I could definitely feel it in my legs on Sunday on the cycle, but I went over Howth, turned, and then went back over it the opposite direction so didn't make it easy on myself
