The logical question that arises from that is: How close does one have to be to LT2 in order to benefit, and how quickly do those benefits drop off below/fatigue rise above?
Does training at LT2 minus 10% lose all of the benefit? What about LT2 minus 5%? +/-5% seems like an educated guessable target based on FTP and 1hr running paces.
Does training at LT2 plus 10% incur so much fatigue that it’s basically useless? Again, LT2 plus 5% seems like an achievable guess based on common indicators.
I will of course be interested to see if Phil has a response for this, but based on what I’ve gathered, working between LT1 (LT in Phil’s book) and LT2 (~CP in Phil’s book) is pretty similar no matter where you are in that range. VO2 slow component is present and you won’t hit VO2max. The main difference will just be how much duration you can do for a workout. More, longer intervals at the lower end and fewer, shorter intervals at the higher end. With that in mind, I don’t think LT2 - 10% is that big of a deal. Just do another interval or up the intensity a little if it is still too easy towards the end of your planned workout.
I think LT2 (or certainly CP) + 10% would be a significantly different stimulus. You’re past any kind of physiological steady state. You’ll know because you will not be able to do something like 2x20 minutes at this intensity.
To me it comes down to having a decent understanding of what is going on in your body, a sense of what some reasonable workout designs are, and then just trying it out and adjusting if the workout is too hard or too easy. The testing to find some specific number is interesting to me because I like data and tracking progress, but it isn’t really all that necessary.
In agreement with the sliding scale, and the need to extend workout nearer LT1 and shorten workouts nearer LT2. I suppose the devil is in the details with this. If the sliding scale is linear, we would expect similar stimulus from 10 @ LT1, 20 @ LT2, and 15 @ halfway in between. But if it’s exponential, as suggested by the lactate charts, the midpoint for “iso-stimulus” reps is more like 13.
The biggest headache with figuring out this type of training is that contrary to your last paragraph, these workout designs seem (and coaches affirm) easier than what most athletes would self-select. If literature is anything to be believed, a 20hr/wk athlete should be doing something like 45-90 minutes near LT2 4 times per week, plus races or short intervals on another day. That’s a ton of volume at “threshold”, so having the target off by a few percent could leave a lot on the table.
It seems, based on replies and some more literature, going over LT2 has a pretty steep drop off in total effect (by way of not being able to do as much), and going under LT2 has a drop off in effect as well, but somewhat lower. The game would then be maximizing training by getting as close as you can to LT2 for as long as you can without going over.
It’s not linear. It’s not as simple as tss might have you believe. Even if tss is the same for a vo2 max workout and a z2 workout the stimulus and physical adaptations are very different. You can’t really compare them in any sensible way.
45-90mins near LT2 is not a lot. The classic threshold cycling workout is 2*20mins. For running lactate threshold tends to be something in the ball park of 10km race pace. Should easily be able to accumulate 45-90mins around LT2 with 2 workouts per week.
There is a suggestion that staying just below LT2 is better as you can accumulate more time, recovery is quicker, and it’s more specific to triathlon than HIIT workouts way above LT2. However, it’s nowhere near as good at improving vo2 max or anaerobic power as training at much higher intensities. This is perhaps where coggins 7 zone model is much more clear in terms of showing what physical adaptations differing training intensities target.