More cold water on low heart rate training: The effect of slow running is not associated with training myocardial contractility

I want to throw this out there, as I also read a lot of the work from Couzens/Byrn/et al and I think their research and work on aerobic training is great. That said, there is a very important caveat to all of their research and principles:

They are triathletes and most of their work is with and designed for Ironman Triathletes. These guys on race day have to swim several miles, immediately bike 112 miles, then immediately run a full marathon. Most take 12-15 hours or more to finish an Ironman. This is obviously magnitudes beyond what even a marathoner has to do, and so the specific training and development they need to undertake will differ accordingly.

I do agree with Couzens that most recreational athletes should do most of their work in Z1, with a limited stimulus in Z2 and above, at least until they get comfortable enough with running regularly that they can easily recover between workouts.

However, his training recommendations stem from the Ironman's need to move for 12-15 consecutive hours on raceday. A marathoner who is only going to move for 2.5, 3.5, 5.5 hours probably won't need to train that much, let alone a road or track runner who is only going to race hard for a few minutes.

Their recommendations to do a lot of Z1 comes from the reality that someone moving for 12-15 hours on race day probably needs to spend most of that time in Z1 or Z2 to avoid dropping dead. If most of your racing is going to be done during shorter periods in higher zones, then you probably should focus your run-specific training around working in those higher zones.

All this said, I'm not against runners doing a lot of Z1 cross training or Z2 easy running (I realize for most it's very hard to run for long in Z1) as base training, with maybe a fast workout every week or two to maintain that ability. I think you'd burn out going harder than that more often for an extended period of time and the harder workouts are best done as a training block several weeks before your race(s).

P.S. This quote from the thread

I can't remember the sources he got it from, but Jeff Gaudette did find that there are minimum thresholds to spur optimal capillary development (60% of VO2max), myoglobin content (63%) and mitochondrial development (70%), and 60% VO2max for most corresponds to a heart rate of around 65-66% of max. So I would say that's probably a good bottom end for Z1, and many other coaches and writers seem to generally agree with that.

Stroke volume is relative to blood volume. The important question that everyone seems to be missing is how variable blood volume is on training and racing? In other words, how does plasma shift affect your performance?

21 years posting here and still the question is ignored, because mainstream 'exercise physiology' doesn't recognise something so obvious.

I don't know about Garmin but Polar Vantage V2 and V3 claim their running power is estimated using only sensors in the watch. My guess is its an accelerometer that measures how forcefully your arm swing is, since that's proportional to leg extension.