Cardio: Making sense of the targets

Your fitness tracker says you need 75 minutes of vigorous activity. The research says 10,000 steps. Your training plan says 150 minutes of Zone 2. These aren't the same thing — but they're not as different as they look.

Why there are so many targets

Three distinct frameworks have shaped how we measure physical activity — each developed independently, for different purposes, by different communities. The public health world cares about getting sedentary populations moving. Exercise scientists care about specific physiological adaptations. Consumer wearable companies care about simple, motivating metrics that keep users engaged. Each produced a different number.

The result is genuine confusion. Someone training seriously for longevity might hit 150 minutes of Zone 2 in a week, walk four miles a day, and still have their Garmin telling them they're falling short on "vigorous activity." All three of those things can be simultaneously true — and none of them means the training isn't working.

Why it matters

Understanding how these frameworks relate to each other matters because conflating them leads to real training errors. Targeting the wrong zone because you're chasing the wrong metric is not a hypothetical problem — it's what happens when people train at medium intensity all week, feeling like they're doing the right thing, when they're actually in the grey zone that produces inferior adaptations at both ends.¹

The steps framework emerged from epidemiological research tracking large populations over time. The evidence is robust: more daily steps are associated with meaningfully lower mortality risk, independent of structured exercise.² A 2024 meta-analysis found approximately a 9% reduction in all-cause mortality per additional 1,000 steps per day, with the protective effect plateauing around 8,000–10,000 steps for most adults.³ The 10,000-step target is not arbitrary — though it originated from a Japanese marketing campaign in the 1960s, the research has since validated it as a reasonable population target. Steps measure one thing well: overall movement volume throughout the day.

The vigorous activity framework comes from the World Health Organisation's physical activity guidelines and the supporting epidemiological evidence. The headline recommendation — 75 minutes of vigorous activity per week, or 150 minutes of moderate activity, or an equivalent combination — is based on large studies showing those thresholds meaningfully reduce cardiovascular and all-cause mortality risk.⁴ Crucially, research published in Circulation tracking over 100,000 adults for 30 years found that people doing two to four times the minimum — 150–300 minutes of vigorous activity per week — reduced their mortality risk by a further 10 percentage points beyond those who just met the guidelines.⁵ The minimum is a floor, not a target.

The Zone 2 / VO₂ max framework is the most mechanistically precise of the three. It doesn't just count movement or minutes — it specifies which physiological adaptations you're driving. Zone 2 targets mitochondrial development; VO₂ max intervals target cardiac output and aerobic ceiling. Neither steps nor vigorous minutes capture this distinction. A 30-minute Zone 2 session and a 30-minute grey-zone jog might look identical in a step count or vigorous-minute calculation while producing fundamentally different physiological outcomes.

How they fit together

The three frameworks are not competing — they occupy different layers of the same picture.

Steps are your movement baseline. They capture the accumulated low-intensity activity throughout your day — walking to meetings, taking the stairs, an evening stroll. This is sometimes called NEAT (non-exercise activity thermogenesis), and it carries genuine longevity benefit independent of your structured training. A 7-hour hike that keeps your heart rate at 110 bpm the whole way contributes almost nothing to your vigorous minute count or your Zone 2 total — but it's still 25,000 steps, and the research is clear that this matters.

Vigorous minutes are a useful sanity check on your training intensity distribution. The key thing to understand is the conversion: one minute of vigorous activity counts as two minutes of moderate activity in the WHO equivalence formula. So 150 minutes of Zone 2 (moderate) plus 33 minutes of VO₂ max intervals (vigorous) equals approximately 108 vigorous-equivalent minutes — just above the basic guideline threshold, and well below the optimal 150–300 minute range. The vigorous minutes metric makes visible whether your week has enough genuine high-intensity work.

Zone 2 and VO₂ max are your training precision layer. They tell you not just how much, but what kind — which is the part that most directly determines your healthspan trajectory. Meeting the vigorous activity guidelines by spending all your time in the moderate-intensity grey zone produces worse adaptations than the same minutes split between genuine Zone 2 and genuine high-intensity intervals.¹

A week that works for longevity looks something like this: 8,000–10,000 daily steps as background movement, 150+ minutes of true Zone 2 training, one VO₂ max session, and enough strength work to maintain muscle. The vigorous minutes total will follow naturally — and it will fall in the right range — without needing to be tracked separately.

The wearable zone problem

If you use a wearable and it shows heart rate zones, there's one more layer to navigate. Not all wearables define zones identically, and even those using the same methodology (most use Heart Rate Reserve, or %HRR) apply different percentage boundaries to each zone. The practical consequence: your device's "Zone 2" label may sit slightly lower than the physiological Zone 2 described in this article and tracked by the 100 Great Years Cardio widget.

The most reliable way to check whether your zones are correctly calibrated is to ensure your device has your actual resting heart rate and measured maximum heart rate entered — not the defaults. If your device is using the generic 220-minus-age formula for maximum heart rate without your resting heart rate, the resulting zone boundaries will be less accurate. Once correctly configured, your device's Zone 2 should correspond to an effort level where you can hold a full conversation in complete sentences — the talk test remains the universal fallback.⁶

One specific pattern to watch for: if Zone 2 sessions feel almost effortless — easier than a brisk walk — your target heart rate may be set too low. True Zone 2 should feel sustained and aerobically engaged, not leisurely. If in doubt, trust the talk test over the zone label.

The 100 Great Years perspective

The reason these frameworks feel confusing is that they were built for different audiences. Public health guidelines are designed to get the least active people in the population moving. Wearable metrics are designed to be simple and motivating. Longevity science is designed to understand what actually drives healthspan. 100 Great Years operates at the longevity layer — which means steps, vigorous minutes, and zone-based training are all useful inputs, but none of them is the whole story on its own. Use steps to stay moving throughout the day. Use Zone 2 minutes as your primary training target. Use vigorous minutes as a periodic sanity check. And use VO₂ max as your long-term KPI — the number that, more than any other single metric, tells you where your healthspan trajectory is heading.

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This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making decisions about your health.