In answer to the first question, here are all the individual improvements (or, in some cases, worsening) of performance. HIT is high-intensity, HVT is high-volume; the shaded area represents the typical variability in the measurement, so changes of less than about one percent aren’t significant:
As expected, wide variation. On average, the high-intensity group clearly outperforms the high-volume group, even though they ran less (39 km per week compared to 47 km per week). This doesn’t necessarily mean that intensity is “better” than volume, of course; to maximise performance, you need both intensity and volume, so it’s a question of finding the right balance, not choosing one or the other.
With that in mind, the more important question was whether any parameters could predict individual responses. An interesting pattern turned up relating to resting heart-rate variability (a measure of how much the time between successive heart beats varies), measured for four-hour periods on at least two successive nights. While there’s been quite a bit of discussion lately about using HRV to monitor postworkout recovery, this was different: using HRV measured before the training period started, in an attempt to predict how people would respond to different types of training.
Here’s how the results broke down for those with below-average and above-average HRV:
For the high-volume group, those with low HRV responded best; for the high-intensity group, it was the other way around. The paper discusses in general terms why this might make sense. There’s some evidence that having high HRV indicates a greater ability to handle increased training stress, so you’re a good candidate to benefit from more intensity. Having low HRV might indicate that you’re already pushing close to what your body can tolerate, so you’re better off with the milder stimulus of higher volume.
It’s also interesting to wonder whether high or low resting HRV, in this context, represents an innate (presumably genetic) quality in these athletes, so that those who respond best to volume will always respond best to volume. Or is it a marker of, say, fitness? Is it possible that low-HRV athletes benefit from volume, but if they stick with that program for a year, their HRV will increase and then they’ll be in a position to benefit more from increased intensity? Lots of open questions to ponder.
In reality, I don’t think we should put too much weight on these specific findings for now, given that it’s a small preliminary study. But it points to an interesting direction for new studies: instead of trying to figure out which training techniques are “best,” trying to figure out who benefits most from different types of training, and how to figure out what category you’re in. For now, the best approach is still the old-school way: try different workouts and training plans… and see which ones make you race fastest.