Poser
WKR
The beginning of the "cardio zone", which you failed to define, is pretty universally accepted to be 50-60% of one's max heart rate. So let's take '220 - age' for the rough max HR of say a 30 year old...that's about 190 for a max HR...now 50% of 190 is 95...are you saying that ruck training at a HR of 95 is not beneficial nor sustainable? I've taken my HR on multiple heavy pack in/out...its between 90-130 all day...right smack in the middle of ths cadio zone...yet you say maintaining the cardio zone in the mountains is impractical? How so?
Zones are not universal and can vary quite a bit from one individual to the next and A person with significant muscular endurance base can outperform a person with a significant cardio base in a race. For this reason, having a genetic definition of zones is not so practical beyond pointing out that there is a clear delineation between the 2.