"Pay Attention to the Caravan"
We've been led to believe this low-intensity grey area is the cornerstone of aerobic development. Born from high-volume training blocks, Zone 2 was a tool for managing load and limiting stress. Since then it's been absorbed by the mainstream, promoted across Instagram feeds and podcasts as the definitive standard for endurance. The problem begins with the practicality of actually training in it. Whatever model you follow, most platforms can only approximate your zones, and between them, thresholds for the same zone vary considerably. The likelihood that you're genuinely training in Zone 2 is low; you're more probably sitting somewhere within an interpretation of one.
The 220-minus-age formula carries a standard deviation of ±10–12 bpm. Your lactate threshold, the true anchor of Zone 2, requires blood testing to measure accurately. A field test gives you one number, on one day, under one set of conditions. What we're dealing with is a stack of variables, many poorly understood, governed by a formula we've trusted to optimise our aerobic capacity. These zones are inherently dynamic. One calculated on a fresh Monday morning is moot by the time you've accumulated load through Sunday's long run. You're chasing a moving target.
When did Zone 2 become the catch-all term for easy running? What's wrong with just easy running? If the goal is to build an aerobic base, long slow distance will do it. I do believe we love to dress simple things up, to breathe new life into ideas we're attached to. The truth is it's straightforward, and constraining yourself to heart rate zones may not only be holding you back, it may be putting you at risk.
In states of relative energy deficiency, bradycardia is a recognised physiological response as the body downregulates to conserve fuel, suppressing both resting and exercise heart rate. The consequence is a growing gap between actual exertion and the data your device is reading. You may be working considerably harder than your zones indicate, yet the number on your wrist signals clearance to continue. I fear we have become so detached from our own bodies that we trust the algorithm over the sensation. This is the risk I keep returning to: the progressive outsourcing of effort perception to a device, at the cost of rate of perceived exertion, the most immediate and honest signal your physiology can produce.
And yet the inverse is equally true. The deeper your understanding of your body's inner workings, the truer your sense of progression becomes, and sometimes that means your heart rate isn't a floor to stay above but a ceiling holding you back. Desperate to remain within the sacred green zone, we forget that unlocking the next level sometimes means leaving it behind. Everything is so simple until you think about it. Nuanced, yet not.
Your easy-state heart rate is yours alone. It belongs to your physiology, and nobody else's. This is especially true if you're new to running or endurance sport. All I ever hear is "gosh my heart rate was so high", of course it was. You can't borrow the heart rate regulation of a lifetime endurance athlete. There's no Zone 2 if you're new.
Rate of perceived exertion isn't new. Gunnar Borg developed the scale in the 1960s, formalised in 1982, decades before anyone strapped a heart rate monitor to their wrist. The science of perceived exertion predates the technology we've since replaced it with. Research by Foster et al. showed RPE-based load monitoring to be as effective as heart rate in tracking internal training stress. The tools were already there. And here's what's worth knowing about Stephen Seiler, whose research on polarised training quietly underpins most of the Zone 2 conversation: his work was conducted on elite athletes logging upwards of twenty hours a week. The population now applying this method are training on average far less than the studies intended.
What RPE asks of you is simpler and harder in equal measure. It asks you to be present. To notice. Not the number, but the conversation your body is having with the effort. How does your breathing feel? Could you hold a sentence? Is this sustainable, or are you already negotiating with yourself? These are not soft questions. They are the most precise data points available to you, because they are happening in real time, inside the very system you're trying to train. The talk test has been shown to correlate reliably with lactate threshold.
I've been reading The Alchemist, Paulo Coelho's novel on fate, intuition and the quiet wisdom of paying attention. There's a moment in it that I keep returning to. Santiago tells the Englishman to pay more attention to the caravan. The Englishman, surrounded by his books, can't understand why the boy doesn't need them. Santiago has already learned what the Englishman is still searching for, not through study, but through presence. Through feel. The Englishman counters that books are like caravans, they take detours, but they get there eventually. He misses the point entirely.
We are the Englishman. Heads down, eyes on the watch, searching the numbers for something our body has been trying to tell us the whole time. RPE doesn't require a formula or a device. It requires you to pay attention to the caravan.