Slowing down training runs.....Point of diminishing returns?

I added numbers to your post so I can easily address them.

1. No, not really.  While an open marathon is all about running 26.2 miles as fast as you can, the Ironman marathon is all about running 26.2 miles without slowing down as much as you can.  They are not the same.  I'm a huge proponent of volume when it comes to running.  To be honest, there's almost no point in running fast (whatever that means to each person) in IM training for probably 95% of the AG field at a typical IM.  Run is rarely the limiter in performing well at an IM.  The actual limiters are bike fitness, bike pacing and execution, and swim fitness... and in that order.  Sure, some people are walking the IM marathon because they had less than ideal run training but most people are walking because they were undertrained on the bike, paced the bike like crap, and/or boogered their bike execution, to include nutrition and hydration.

2. Easy runs should be easy.  As in stupid easy.  Read about the polarized training approach, specifically some of Stephen Seiler's work.  The polarized training in a nutshell is everything is either really easy or really hard.  There's pretty much zero threshold training.  So if you're thinking in terms of Zone 1-5, 80% of your training is in Z1, low Z2 and 20% in high Z4, Z5.  There's nothing done in what I'd consider Z2.5 to Z4.5.

3. Depends on how you dice up that 40-50 mpw, how durable/old you are and all that.  40-50 mpw is not too bad if you're running 5-6x per week.  It's an awful lot if you're running 3x per week.  It can be an awful lot no matter the number of runs if you're older, and/or not used to that kind of mileage.  If you can't run 4-6x per week I would not worry about reaching 40-50 mpw.  Doing 45 miles on a typical triathlete training plan of 3 runs per week is probably a recipe for disaster as that's an average of 15 miles per run.  Of course, 40-50 might be a max week and not an average week but the same theory applies.

First time IM'ers stress so much about the run.  It honestly should be the least of your concerns.  You all need to stress about the bike.  For the typical AG'er (those not at the top 5% of their AG), it's almost all about the bike.  The bike sets up your entire day.  It's in and of itself the longest part of the race and sets up the second longest part of the day.  The swim only accounts for about 10% of your time in an IM.  What you do on the bike either accounts for or sets up the other 90%.  All those miles you ran in training means jacksh*t If you're not well trained or haven't executed well on the bike.  The Ironman field is littered with Boston Marathon qualifiers or Kona wannabes who rode their bike like fools and put in 5+ hour marathons.

I did one of my IM's on literally zero run training in the 5 months prior to the race due to injury.  I "ran" a 4:40 for that IM marathon, which certainly wasn't setting the world on fire, but I still outran 2/3rds of the field and I can almost guarantee I had the least amount of run training of the 3000 people out there.  I was just sure that I was in really good swim and bike shape, and executed my pacing and nutrition really well on the bike.

I completely disagree with the bolded part.  He's 52 and doing HIM and IM.  Running fast isn't really something that he needs in his toolbox at the moment.  Consistency, durability, recovery, and volume should be his primary concerns and adding speed work diminishes each and every one of those.

He's not in his 20's or 30's and trying to kill the local short course circuit.

My n=1 experience is similar to above.  I used to pace my longer runs by feel, but based on the VDOT calculator, I was running too fast.  If you haven't done so already, try plugging a recent 5 K or 10 K race time into the calculator to see what your easy pace should be:

VDOT Calculator

I also have the same experience with speedwork.  I'm 45 and in the past few years every time I tried to include speed sessions in my training I would end up with an injury.  Since last fall I decided to ditch the speedwork and only run at an easy pace with 90% on the treadmill.  Although I haven't raced an open 5 K or 10 K in quite awhile, for a few Sprint tris this summer my run split was only a few seconds slower than my PB for an open 5 K.

I did a Sprint Triathlon on literally zero bike and zero swim training in 2008.  I was NOT a triathlete.  I didn't have a bike.  I didn't have access to a pool.  I was a runner through so I did my favorite 12 week 1/2 marathon training plan consisting of 35-45 miles per week to be sure that I was in really good run shape and then bought a swim suit and googles the night before the race and borrow a race bike for the event and road it with platform pedals.  I didn't do the race to be the fastest Triathlete I could be.  I did it to support friends who were doing the race and prepared to be a runner doing a triathlon as a fun cross training day.  My swim pace was 2:17 min/100yd which put me at the back of the pack for a 500 yd pool swim.  My bike pace was around 21 MPH which put me at the front of the pack.  I was the 2nd fastest run time of the entire event (ya... there were only 235 people, but that is still 233 people that I beat on the run and they ALL had better swim and bike fitness than me).  

I realize that there is a huge difference in the training and pacing plans for an Iron distance event and a sprint event, but I learned that if you put in the run training that even if your swim and bike training are sub par that your run fitness will carry you through the run.  I had only run off a bike once in my life before that race (and it was in 2002) so I was in no way prepared for that jello feeling in my legs nor that lactate burn from over doing it on the bike.  My run felt really slow to me and I was sure that I would be middle of the pack competing with seasoned Triathletes that knew how to pace the bike leg and who were used to running off the bike.  My run time was 12% over the open run time I had been doing but when I say how slow Triathletes are at running and what my run ranking was I was really happy with the way things ended.  You always hear people talk about "Swim Fitness", "Bike Fitness", "Run Fitness" but the truth is that you can't separate the three.  You can increase your "fitness" through swimming, cycling, running, core work, weight training, cross fit, etc.  All of it goes into your over all "fitness". Balancing the the type of training you do will help you be more efficient but your "fitness" is either going to be adequate or inadequate.  If you are running 75 miles a week it is probably going to be adequate even if you have zero miles on the bike.  If you are doing 300 mile a week on the bike it is probably going to be adequate even if you have zero miles running, etc. 

I'll offer my .02 in addition to the above as one on the cusp of 50 and training for my third IM.  Never been accused of being fast.   Two years ago I had some shorter races and my coach had me doing some track workouts, resulted in a 10K PR during an Oly race (don't race many standalone runs).

This year, with the benefit of a few years of run training and an MAT practitioner keeping me healthy, I am running 30-35 mpw without injury and without a punishing long long weekend run requiring a longer recovery period (used to get injuries any time I tried to get over 25 mpw).  Running consistently 6 days a week.  Goal has been to end every run as if I could easily run another mile. No speedwork whatsoever save a few :30 pickups during a longer run. 

I've had two longer distance races this year under this protocol, the first one was an almost half at 1-34-10, in which my best run was at a 8:50 pace a couple years ago.  This year I ran an 8:15 pace.  Last month did a swim/run race (with a bike at the front), 18 miles of running over three runs, 4.5 miles, 5.5 miles, 8 miles and 1 mile.  Improved on the 5.5 and 8 mile legs by several minutes. No speedwork.

I'll highlight the above by GMAN, "consistency, durability, recovery and volume."  Taking care of the former will cover the latter.  I've logged my biggest months ever this year volume wise without even thinking about it, just getting the runs in day after day.  30-35 MPW should be more than sufficient to get you successfully thru an IM run (i.e finish), might even finish well if you really work on your pacing 

Last thought, IM marathon is unlike anything you've ever done before.  At mile 8 you're thinking "I could run this pace forever," but by mile 13 you're walking.  The run can unravel on you SUPER fast, and it's not about how fast you can run now, but how fast you can run now and still be running 20 miles later.  If you're running the last 10K of an IM, you're ahead of the vast majority of the field.  But that process goes all the way back to the beginning of the race (i'd argue it goes to the swim, not just the bike).  

ETA BTW, 2 IMs and 15 or so halfs, I have to disagree with the above  ^^ comment that run fitness will get you through run.  In an ironman, run fitness will not get you through if you have little swim or bike fitness (something will always be subpar most likely, we have families and jobs and ....) .  If you are cooked after the swim your day is shot.  If you are cooked after the bike your day is shot.  

"If you are running 75 miles a week it is probably going to be adequate even if you have zero miles on the bike.  If you are doing 300 mile a week on the bike it is probably going to be adequate even if you have zero miles running, etc."   Sorry, that is really bad advice for long course training or racing

No.  Just about everything about that statement is wrong.  "Fitness" is comprised of biomechanical, biochemical, and neuro-muscular components.  This statement only considers the biochemical with a slight nod to biomechanical, and completely ignores neuro-muscular.  This is why periodization (the concept that training should progress from general to specific) and the principle of specificity are crucial to the success of any athlete, but especially multisport endurance athletes in general, and even more so for those racing long course.  At the sprint distance, someone who just wants to finish and have fun can get away with what you suggest, but at the HIM and IM distance, that's a good recipe for implosion.

Chris's and Brian's posts above give pretty good answers.

Originally posted by nc452010 Thanks again for all the input. Really interesting conversation. I'm not sure on crossover fitness, either. But, I keep hearing (from people I know......who should know what they're talking about) that the best way to improve your IM run..........is to bike..... a LOT. I can read between the lines on that one.

You're either misinterpreting what they're saying, or listening to the wrong people.

A high level of bike fitness combined with good pacing is needed to set up the potential for a good run, but it doesn't do anything directly for the ability to run well.

It takes a high level of swim fitness, bike fitness, and run fitness, combined with good pacing through all three legs, to have a good run.  A shortfall in any of those 4 areas will lead to a run fail.  There are no substitutes.

OK my apologies in advance for the threadjack, but based on the bolded statement in Don's post above, I want to throw this out there. 

I have read from the experts and heard on BT that "more time on the bike will improve your run" is one of the big myths of triathlon.  But using an example of a reasonably fit person training for a 5K with 2 training options - (a) run 4 times a week, or (b) run the same 4 times a week plus 3 bike sessions.  I know all the coaches and experts will say that the bike training will not directly translate to running improvements, but this is one of the myths that I struggle to accept. Wouldn't the training plan with the bike sessions lead to a faster 5K time?  Wouldn't they simply have more fitness?  Or does the research show that there is absolutely no benefit to adding in bike sessions when you are training for a running race?  Convince me that this is truly a myth.