I did my 2nd Spinervals workout today with the new trainer, this time the focus was "building the aerobic base". They say to keep your heartrate about 10 b.p.m. below your lactate threshold. Well, I have no idea what my lactate threshold is, and it seems to be a rather complicated measurement. Does anyone here know of an easy-ish way to approximate where one's lactate threshold is? Thanks!

(Incidentally I kept my HR average at about 145-150 for this workout....I hope that was at least ballpark....)