How to Measure Your Exercise Intensity

This is Part 3 of a three-part NiaHealth series on exercise intensity. Part 1 covered how intensity is defined; Part 2 covered why it matters for your health. This post is the practical payoff: how to measure intensity, how we approach it at NiaHealth, and what to actually do depending on where you're at. A companion deep-dive digs into wearables and heart-rate zones.

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By now we've established two things. Intensity matters for your health and fitness (Part 2), but the different fields define it in frustratingly different ways (Part 1). That leaves the practical question: how do you know whether you're actually exercising at the intensity you're aiming for?

We've already touched on the different ways intensity can be measured. Harder exercise shows up as higher external load — your speed, your power output, the METs of the activity. It also shows up as higher internal load — your heart rate, your oxygen use, how hard the effort feels, whether you can still talk, and where you sit relative to your own metabolic thresholds.

But which of these should you actually be measuring? Let's look closer at the options.

The gold standard: a cardiopulmonary exercise test (CPET)

If you want to know the intensity at which you hit your metabolic thresholds and VO₂ max, a lab-based graded exercise test is the way to go. The most common one is a cardiopulmonary exercise test (CPET). It measures your VO₂ max and pinpoints your two personal thresholds, MT1 and MT2. 

Once you know those anchors, the recommended way to set and track intensity is by work rate — for example, your running speed or your cycling power in watts. This recommendation comes from a 2025 joint statement on exercise intensity from the American College of Sports Medicine (ACSM) and Exercise and Sport Science Australia (ESSA).¹ It works very well for people training for a sport, like competitive runners or cyclists. It's less handy for people who do lots of different activities and want one way to measure intensity across all of them. In these cases, it can help to link intensity to how the effort felt during the test — for example, "this feels the same as when I hit my VO₂ max."

What about heart rate? Interestingly, exercise scientists generally advise against judging intensity by heart rate alone — even the heart rate that matched your thresholds during a test.¹ That's because heart rate drifts with heat, fatigue, and other daily factors, so it isn't always accurate. Still, heart rate is one of the easiest things to measure, so it remains popular in practice.

A CPET is genuinely useful for some people: those chasing a higher VO₂ max, those training for a sport, or those with heart or lung conditions who need supervised exercise (for example, recovering from a heart attack). But not everyone needs one. And they have their limitations: a CPET is uncomfortable, expensive, and needs special equipment and trained staff. Also, the result is a single snapshot: as you get fitter, your thresholds shift and the numbers go out of date. And first-timers often don't get a fully accurate result, because the breathing mask and the all-out effort take some getting used to.

For all these reasons, many people rely on the more practical, everyday measures below.

Rate of perceived exertion (the Borg scale)

Rate of perceived exertion (RPE) is simply your own rating of how hard you're working. The classic Borg scale runs from 6 ("no exertion at all") to 20 ("very, very hard"), and there's also a simpler version that runs from 0 to 10.²

RPE costs nothing and needs no equipment. The downside is that it's subjective: at the same true RPE, two people can give different ratings depending on how they are experiencing a workout. Wearables can't measure it, either. Even so, the 2025 ACSM/ESSA statement backs RPE as a good way to gauge intensity when a CPET isn't an option.¹

The talk test

This one is simple: pay attention to how easily you can speak.²

• If you can talk comfortably, you're likely in the light range, below MT1.
• When a conversation becomes difficult, you've probably reached moderate intensity, at or above MT1.
• If you can barely get out more than a few words, or become speechless, you're in the vigorous range, at or above MT2.

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The talk test is cheap and easy, and it's been checked against the first threshold in many groups — athletes, healthy adults, and people with heart disease.^2,3 Its main weakness: it doesn't work well for very short intervals (say, 30 to 60 seconds), and a fitness tracker can't measure it for you.

Heart rate

Heart rate is popular because it's easy to measure — especially with a wearable — and most people understand the idea behind it. The simplest method is to work out a percentage of your maximum heart rate. You can estimate your max with a formula. The best-known one is:

Max HR = 220 − age

The catch: this formula can be off from your true max by 10–15 beats per minute. NiaHealth uses the Tanaka formula instead, which tends to be more accurate, especially in older adults:⁴

Max HR = 208 − (0.7 × age)

An even more personal version is heart rate reserve (HRR), worked out with the Karvonen formula. It also factors in your resting heart rate, and tends to be more accurate in athletes:²

Target heart rate = (max HR − resting HR) × intensity % + resting HR

Whatever formula you use, heart rate has real limits as a measure of intensity. It's affected by heat, humidity, stress, caffeine, dehydration, fatigue, illness, and medications like beta-blockers.² It also lags behind your effort. That makes it unreliable for very short, very hard bursts, like interval and sprint training — by the time your heart rate catches up, the interval may be over.

One more wrinkle: the heart rate "zones" that different sources use don't agree with one another, and none of them line up perfectly with your metabolic thresholds. The zones built into your watch aren't the same as the ones a sport scientist or the ACSM would use. So if you rely on heart rate, treat it as a rough guide and check it against how hard the effort feels. (We dig into the heart-rate-zone mess — and how accurate wearables really are — in our companion post on wearables and heart-rate zones.)

Accelerometer data (your "active minutes" tracking)

Most wearables estimate your activity with an accelerometer — a motion sensor that tracks how often and how forcefully you move.² Large studies using research-grade accelerometers show this kind of data can predict how long people live, with higher-intensity movement giving the biggest benefit.^5–7

The catch: consumer wearables aren't research-grade. Their intensity estimates can be well off, and they struggle with activities like cycling and weightlifting that don't involve much arm or whole-body movement. So your watch's "active minutes" are a helpful nudge, not a precise measurement. (Again, the full accuracy picture is in the companion wearables post.)

METs

We covered these in Part 1. METs are a decent way to compare how hard one activity is versus another, and research shows that doing higher-MET activities is linked to a longer life and less chronic disease — no matter how they line up with your metabolic thresholds. But for any one person, METs don't tell you much about how hard you're working.

Our approach to measuring exercise intensity at NiaHealth

Just as we did for classifying intensity, we've combined the findings from our evidence review with the 2025 ACSM/ESSA recommendations to build our own approach to measuring it — practical, and without adding to the confusion. Here are the key points:

• Effort-based measures like RPE and the talk test work for everyone, at any fitness level.
• Heart rate is useful but imperfect. It won't reliably tell you where you are relative to your thresholds. By default we estimate your max heart rate, calculate HRR with the Karvonen formula, and use your thresholds if you know them. Because heart rate doesn't tell the whole story, pair it with RPE.
• There’s no clear “best” way to set heart rate ranges for different intensity zones; we default to the ranges that you’re most likely see on your wearables, but our ranges are customizable so you can adjust depending on what is most appropriate for your current fitness (and your metabolic thresholds, if you’ve had a CPET).
• METs can be a fine starting point if you're new to exercise, but they often get intensity wrong — especially for fitter people — so we don't recommend them when better measures are available.
• If you know your thresholds and VO₂ max, you can fine-tune the HR and RPE ranges for each category to match. You can also gauge intensity by the speed or power that lines up with your thresholds and VO₂ max — though that's sport-specific and usually best set with a coach.

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NiaHealth exercise intensity framework

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(The public health effort anchors — moderate ≈ 5–6, vigorous ≈ 7–8 — and the talk-test cues are well supported, but the alignment to specific training zones is approximate. RPE-to-zone cutoffs aren't standardized and shift from person to person, so treat this as a practical guide, not a precise conversion.)

Putting it all together: a practical approach

So where does this leave you? Here's a sensible way to translate our approach into action, depending on where you're at with your fitness.

Building

If you're new to exercise, or coming back after a break, any aerobic exercise at any intensity is a win. The goal is consistency — the fitness will follow.

For your harder efforts, aim for short vigorous bursts — climbing stairs, carrying groceries, walking briskly — of 1 to 4 minutes, at least 5 times a day. There’s no need to track your heart rate here. Just focus on how hard it feels: at least a 7 out of 10, and a little breathless.

Active

Once you're consistent, aim to meet the Canadian guideline of 150 minutes of moderate-to-vigorous activity (MVPA) a week — while giving priority to the vigorous work that has the best evidence for raising VO₂ max.

So aim for at least 150 minutes a week at moderate intensity or higher — an effort of at least 5 out of 10, where holding a conversation gets hard, with your heart rate in Zone 3 or above. Try to make 60 of those minutes vigorous — an effort of at least 7 out of 10, where you can't say more than a few words at a time. Remember that heart rate lags during interval work, so trust your effort there. And if you can't fit in the full 150 minutes, protect your vigorous minutes first.

This is also a good point to consider a VO₂ max test that includes your thresholds. The results can help you dial in your intensity and show where your fitness stands.

Athlete

If you're already exceeding the 150-minute MVPA guideline, getting at least 60 minutes of vigorous exercise a week, and/or training for a sport, the goal shifts. Keep hitting the guideline amounts of MVPA, but leave room for more specific goals — like training for a particular race or event.

Aim for 60 to 75 minutes of vigorous activity a week, and fill out the rest of your aerobic minutes at lower intensity (Zones 1, 2, and 3). Depending on your goals and total training load, you might even limit your time in moderate work (Zone 3) — keeping easy sessions easy and hard sessions hard, to protect your recovery.

This is where a VO₂ max test pays off most, with repeat tests every 6 to 12 months to keep your thresholds current and confirm your training is moving your VO₂ max in the right direction.

The takeaway

If there's one thing to take from this whole series, it's this: intensity matters, vigorous exercise most of all — and for most people, the best way to tell you're working hard enough is how it feels. 

The most accurate way to ensure that you’re exercising at your intended intensity is to get a CPET that pins down your thresholds and VO₂ max, and basing your training on pace or power. This approach is genuinely useful for athletes and for people with specific medical needs. For everyone else, the everyday tools work well — as long as you use them with their limits in mind. Perceived effort and the talk test are free, need no gear, and work at any fitness level. Heart rate is a handy second opinion, as long as you remember it's a rough guide that lags during hard intervals and whose "zones" are far less exact than they look. METs are fine as a rough starting point, but they blur the individual picture.

The most reliable approach isn't any single number — it's cross-checking. Ask yourself how hard this feels (RPE), whether you can still talk, and roughly where your heart rate is. When all three agree, it’s more likely that you can trust them.

A final reminder: what you do with this information depends on where you're starting. If you're building, just move — short vigorous bursts through your day are a great start. If you're active, aim for 150 minutes of moderate-to-vigorous activity a week, and protect your vigorous minutes. If you're an athlete, keep hitting those targets while tailoring the rest to your goals. Whatever stage you're in, the same rule holds: the best measure of intensity is the one you'll actually use.

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This article is for general education and isn't a substitute for personalized medical advice. Talk to a qualified health professional before starting a new exercise program, especially if you have an existing health condition.