The longer I coach, the more convinced I am that for most amateur athletes, workload matters more than distribution of intensity. By this, I mean that in the real world, all the fights on twitter about how much zone 2 is right, polarized vs pyramidal training, or “Is sweet spot a thing” are missing the point. As long as the amount of training stress you’re putting your body under is close to the right amount, you will likely see performance improvements.
The physiological data is fairly clear: for the most part, all intensities train all factors. High intensity training will increase mitochondrial content. Sure, low-intensity training does it better, but not by a lot. Similarly, low intensity training will increase VO2max. Sure, high intensity training does it better, but not by a lot. As you become higher and higher trained, these distinctions matter more, but I’m coming to find that: 1) They matter less than I thought to all but those highest levels, and 2) The levels of athlete to which they matter is higher than I thought. If you’ve trained like an Olympian for five years, it will be hard to get additional VO2max speed without actually doing VO2max speed. At that level it will also be hard to get additional mitochondrial density without a LOT of hours, requiring relatively low intensity training. But until you’re there, I don’t think distribution is the most important factor.
Note that I didn’t say that the distribution doesn’t matter, just that I think workload matters a little more. For example, we can’t get away from the fact that generally performance correlates really well with training volume, and in order to train at high volumes you can’t just go out as hard as you can every day. This necessitates that much of your training be low intensity. And we can’t ignore the fact that generally, in order to get faster, you need to go fast. So we need at least SOME higher intensity work in the plan.
If it’s that simple, then why don’t more people make more gains? Why do plateaus or even losses of fitness occur in amateur athletes if “go out a lot, and get in some hard days” is actually descriptive enough for good training? The rub is in the amount.
One of the more enlightening illustrations of this is in studies of training using heart rate variability (HRV). Researchers continuously find that if you train by HRV you train less and you progress more (Side note: These studies use lab-based ECG-derived HRV data, and not a watch or wrist band, which just don’t work). This suggests that whatever usually limits our workload doesn’t work very well!
Our main challenge is that we can feel the difference between tired and not-tired, but we can’t really feel the difference between not-tired and stronger-than-before. These HRV studies make a lot of sense when you think about the way that most athletes gauge fatigue. If you train, and you get tired, when do you train again? Usually when you feel “not tired,” right? But according to our handy-dandy time-course-of-adaptation figure below, if we train when we feel “not tired” (the end of the recovery period) we’re actually losing out on the vast majority of our adaptations.
This is why we can see athletes train with a “perfect” distribution and not improve, and athletes follow what by any scientifically rigorous standard is a crap plan, and improve. The amount of workload mattered more than the distribution.
