Some articles suggest training at specific percentages of VO₂max. If I know my VO₂max, HRmax, lactate threshold and resting heart-rate, is there a straightforward way to determine heart-rate corresponding to a specified %VO₂max? I'm assuming it's not a simple percentage of HRmax, as sometimes I see >100% VO₂max specified.
When you perform aerobic exercise, your body utilises oxygen to perform work. As you increase the amount of work you do, the amount of oxygen used—oxygen uptake—increases until it has hit a maximum.
That is VO₂max (or V̇O₂max, to make it clear that the "O₂" refers to oxygen, and where the dot above the V is because it is often given per kilogram of body weight), which is an indicator of aerobic fitness. And for non-athletes, it is typically in the range 20-55 mL/(kg·min).
It typically corresponds to a work rate that can be sustained for around 8 minutes or so.
Sometimes I see >100% VO₂max specified
Yes, this is perfectly possible, since anaerobic systems can contribute energy to the work done.
Is there a straightforward way to determine [the] heart-rate corresponding to a specified %VO₂max?
Exact correspondence between heart rate and V̇O₂max will vary from one individual to another, but there are broad approximations. The page at brianmac.co.uk gives a formula
%HRmax = 0.64 × %VO₂max + 37
which itself is from a paper by David Swain et al. (1994) Target HR for the development of CV fitness. Medicine & Science in Sports & Exercise, 26 (1), pp. 112-116. There are no doubt others.
However, this formula doesn't work very well for either
%VO₂max close to 100%, but that is actually to be expected, given the physiology.
Heart rate lags behind work done, and since work at V̇O₂max is a very high rate of work—as I said, that can typically only be sustained for 8 minutes or so—using heart rate to gauge efforts around V̇O₂max, or above that, does not work very well. Thus, using perceived effort can be better. That is, 100% V̇O₂max could be the pace you think you can hold for 8 minutes; 95% V̇O₂max could be the pace you think you could hold for 15 minutes.