My usual 5k requires little adherence to my lactate threshold heart rate (LTHR). That’s probably a level of effort you can maintain for an hour.
With my impending Hever Gauntelt HIM then I just want to check out where my LTHR is right now as for longer races, eg IM and HIM distances, then you can’t stay over your LTHR. Well I can’t anyway.
So am doing a few tests, mostly for my bike as I can pace the run by ‘feel’, to make sure that my ‘limits’ are updated in line with my current fitness (or lack of it) as well as any kind of loading I may well do…notably caffeine. Just had to buy some ProPlus today just for that purpose in fact. Take 300-400mg 1 hour before the race and replenish 100 – 150 towards the end of the bike in a HIM.