There's a couple different ways to do this, and if your resting HR is above 60 they can give extremely different results at the low end (60-70%, where you'd do LSS). Basically some take your resting heart rate into result and some don't. For me, a 35 year old man, it's the difference between my 60% being 109 and it being 131. That's a huge gap. It feels important to get this right since, going by the conditioning book of tactical barbell, LSS in that zone will promote the heart hypertrophy that we're looking for. It's also a pretty serious difference in effort between the two ranges. So which is the right way to calculate this for the purposes we want, LSS?