So we’re still stuck in the zone 4 rut, huh? It’s like riding a fixie uphill—good luck getting anywhere fast. Heart rate’s a fickle beast, sure, but why do we still treat it like the gospel? With the tech we’ve got now, how are we still playing the guessing game with those 5 zones? What if we chucked the old playbook and went all in on heart rate variability and cardiac output instead? Seems like clinging to zone 4 could be the equivalent of trying to win a race on a rusty old bike. What are we really scared of?
