Regarding Rick’s idea of leaving the Garmin and HRM at home – that’s probably a good way to learn how to run by ‘feel’. I find the HRM is most useful for easy/low aerobic runs – thus preventing them from becoming ‘grey’ runs. I can usually run the upper aerobic and threshold runs by feel.

Thanks for the response and apologies for the long delay, I’m snowed under at the moment.
I’ve since had a re-think on this issue (again) and realise my comment can not work in the way I thought it might – more on that at the end of the post.

Firstly though I would like to look at the torque mechanisms. In running there is a forward torque induced by gravity whilst on support from mid stance to some point between mid and terminal stance and I think we both agree the rotation caused by this torque has to be dealt with to avoid an eventual face plant.
There are various mechanisms that could deal with this issue; forward landing, toe-off and leg swing whilst on support.
I think you suggest that a landing ahead is the main mechanism and I think it probably plays a part tough the inherent problems with a forward landing make it far from desirable.
Some runners use a toe off – a push at terminal stance cause the hips to move forward and the upper body to move backwards; a counter rotation of that experienced previously on stance due to gravitational torque. This is particularly noticeable in runners driving off from the blocks when the lean angle is very large.
Finally, there is leg swing. Whilst on stance with one leg, the other leg swings forwards. The forward swing of the leg pushes back at the hips and as the hips are supported by the grounded foot, the whole body is rotated backwards around the foot pivot point.
So it is conceivable that the forward gravitational torque is balanced by this rearward torque from leg swing in that one acts and then the other acts so that the net effect is balance. I think this is probably the main stabilising mechanism in efficient running and allowing a ‘fall’ can automatically force a subconscious swing (and could force a subconscious overstride or toe off too depending on the runners habits and degree of ‘fall’).

My original point I now realise cannot work – not really for the reasons you gave, more because the torque of pulling and swinging the leg when not on support causes a counter torque that sends the upper body forwards – not a backwards balancing torque as I suggested i.e. pulling and swinging whilst unsupported has the opposite effect to a toe-off.

Hope that makes some sense.

Also, does the VT (low intensity) training include running at paces much slower than VT? For example, I’d presume VT pace would be about marathon race-pace and HR (99% aerobic), which doesn’t seem THAT easy to me. For example, 3:00 per km for a 2:07 marathoner.

Personally, I’m inclined to favour this type of training (big low, but some high), as there’s not the risk of ‘mechanical injury’ from the high intensity part, or the ‘pressure’ of running a large proportion of runs at mid-intensity (grey).

What I’d like to know, is how much high intensity is needed (for improvement), and how often? For example, would one session every 4 or 5 days (much less than 8%) be sufficient? Would higher weekly volume permit a smaller % of high intensity training? Similarly, would, say, 10% high intensity compensate for lower weekly volume. I’m guessing the answers to these questions are that a program needs to be individualised for athletes with different strengths and preferences.