I started using MAF running in mid-September, when I weighed in at around 225 and when I was woefully out of shape. When I did run and when I was in shape, I typically did 10 minute miles on a five mile run.
Since September, I've been putting the miles in--usually 10-12 a week, up until fairly recently when I began splitting my run efforts with cycling efforts. In late November, I did a MAF test using a high school track. My MAF HR is 130ish, for what it's worth. Splits were as follows:
Warm Up: 13:40 at 120bpm
Mile 1: 12:38
Mile 2: 13:13 (+ :35)
Mile 3: 13:26 (+ :13)
Mile 4: 13:49 (+ :23)
Mile 5: 14:23 (+ :34)
Today I did another one, and got pretty miserable results.
Warm Up mile: 14:18 (120 bpm)
Mile 1: 14:00
Mile 2: 14:54 (+ :54)
Mile 3: 15:24 (+ :30)
I also weigh 200 now, so you would think I would be faster.
In late December I got a subscription to Zwift and started riding at my MAF heart rate in the trainer. I think that the reason I am slower now (at least for today) is simple fatigue. I did 90 minutes on the bike yesterday, after doing three days last week of running/riding. Incidentally, the run was on a hilly course and my first mile was 13:06, for what that's worth.
Anyway, I felt a little discouraged at seeing 15:24 on my third mile split, so I decided that rather than run two more plodding miles for a comparison that I knew would be bad, instead I would take off and run at a strong training pace. I probably ran a little harder than I should have, and I didn't walk at all (I used to be a Galloway guy), but the fourth mile was a surprisingly comfortable 8:19. My heart rate was in the high 160s the entire time, which is normal for me on long runs and rides where I'm actually pushing myself.
So anyway, for all you slow clydesdales out there, this method does get results. You just don't see them unless you're actively looking.
One more thing of interest. I've found that music can influence my heart beat by a point or two. I also have noticed on Zwift that when I'm "climbing" my heart rate is higher per watt than when I'm coasting, even though I'm not really doing either--I'm just stationary in the trainer pedaling away. There's a mental aspect to all this that I wish I was better at.
From my experience, I have good days and then I have bad days. I wouldn't worry about this last MAF test at all. The fact you were able to crank out an 8:19 mile and still feel good is more telling to me. I would stick to the low HR training. It took me a LONG time to see any tangible results. And there are always ups and downs.
The comment on the music is absolutely true. If I'm on an easy run and I'm listening to talk radio and then switch to music, my HR might increase by up to 10 bpm. Not even exaggerating. If I imagine myself in a race, the same thing can happen where my bpm will go up by about 10 bpm without changing pace. It does settle after a few minutes though. I wouldn't sweat any of that. I certainly don't and continue to play music for motivation and think about my races.
Good luck!
Welp, tomorrow I'm back to MAF style running. But tonight I went ahead and ran at a typical training pace. Heart rate stayed at 160, and I did five miles in 50 minutes. I also ran on a lot of hills, so I'm pretty happy with the results I got.
I'll say again, in September I did three miles at an average pace of 11:41, and it almost killed me. So I decided to try the low intensity running (MAF), and have done that since. I have never felt like I put forth any effort, but today I did what I used to do when I was in shape and it wasn't that difficult.
I'm sold.
Test again. If the regression is still there, then that means your aerobic system is not developing due to either not enough volume, too much volume, or there's something else (like mental stress) affecting you.
Try to keep the same course for your test runs. TM is great if you have one.
Often, one can see the regression in non-MAF test runs as well. Runs done on the same course with the same HR plan. How have those runs been? Did you notice any change in pace at the same HR when you added the cycling? Have you felt more tired and stressed? Are you feeling good?