- Like any medicine, exercise has a dose — and two simple tools help you find it: RPE (how hard it feels) and METs (a standardized measure of intensity).
- RPE (rating of perceived exertion) lets you self-regulate effort without any equipment — Zone 2 is a conversational ~3–4 out of 10.
- METs quantify activities on a standard scale; general guidelines target about 500–1,000 MET-minutes per week.
- Matching dose to your goal and starting point — easy base work plus some harder efforts — beats grinding at one random intensity.
"Exercise is medicine" is true — but medicine without a dose is just a suggestion. Take too little and nothing happens; take too much, too soon, and you get hurt or burn out. The good news is that you do not need a lab to dose your training. Two simple tools — one based on how effort feels, one based on standardized numbers — let you hit the right intensity every time.
RPE: let your body be the gauge
RPE stands for rating of perceived exertion — a self-reported measure of how hard an effort feels, usually on a scale of 0 to 10 (or the original Borg 6–20 scale). It sounds low-tech, and that is exactly its strength: it requires no device, adjusts automatically to your fitness and the day's fatigue, and works for anyone.
Here is a practical translation:
- 2–3 / 10 — very easy, could do it all day. Warm-up or recovery.
- 3–4 / 10 — "Zone 2." You can hold a conversation but would rather not sing. This is where most of your training should live.
- 5–6 / 10 — moderately hard. Talking gets choppy.
- 7–8 / 10 — hard. A few words at a time. This is interval territory.
- 9–10 / 10 — maximal. Not sustainable, and not where most training belongs.
The single most common mistake is spending too much time in the vague 5–6 middle — too hard to build a big aerobic base, too easy to drive top-end fitness. Aim for mostly easy, occasionally hard.
METs: the standardized dose
If RPE is the subjective gauge, METs are the objective one. A MET (metabolic equivalent) is roughly the energy you burn sitting at rest; an activity rated at 4 METs uses about four times that. Researchers have catalogued the MET value of hundreds of activities — brisk walking is about 3–4 METs, cycling 6–8, running 8–10 or more.
METs let you quantify a total dose. General physical-activity guidelines translate to roughly 500 to 1,000 MET-minutes per week — for example, 150 minutes of brisk (≈4-MET) walking lands around 600 MET-minutes. And the mortality data reward that dose richly: pooled research shows a steep drop in death risk as activity rises, with the biggest gains coming when people move from doing almost nothing to doing some.
Putting it together: a simple weekly recipe
You do not need to track every number forever. Use RPE day to day and METs to sanity-check your weekly total:
- Build an easy base. Several hours a week at RPE 3–4 (Zone 2) — walking, easy cycling, hiking. This is the foundation most people skip.
- Add a little intensity. One or two sessions with harder intervals at RPE 7–9, once you have a base.
- Strength train twice a week. Effort here is about challenging the muscle in the last few reps, not cardiovascular burn.
- Check your total. Are you in the ballpark of 500–1,000 MET-minutes? If not, add easy volume first.
Dose it to your starting point
The most important principle in exercise dosing is the same as in prescribing any medicine: meet the person where they are. A deconditioned beginner and a trained athlete need very different doses, and someone recovering from illness — say, Long COVID with post-exertional malaise — may need to cap intensity carefully and expand slowly. RPE shines here, because it scales to you automatically. Start where you are, progress gradually, and let the dose grow with your capacity. That is how exercise stops being a punishing chore and becomes what it should be — a well-dosed, sustainable treatment you actually keep taking.
In practice: why this matters
Most people are told to 'exercise more' without any guidance on how hard, leading to workouts that are either too easy to help or too punishing to sustain. Simple, teachable intensity tools like RPE turn a vague instruction into a usable prescription — helping far more people find the effective, sustainable middle. Better dosing literacy could meaningfully raise the share of the population getting a truly beneficial amount of activity.
Frequently asked questions
How hard should I actually be working out?
It depends on the goal. The bulk of your training should be easy 'Zone 2' effort — about a 3–4 out of 10 on perceived exertion, where you can still hold a conversation. A smaller portion can be harder (a 7–9 out of 10) intervals. Most people invert this — too much moderate-hard, not enough easy base.
What's a MET, in plain terms?
One MET is roughly your energy use sitting quietly at rest. An activity rated at 4 METs uses about four times that energy. Brisk walking is around 3–4 METs, running about 8–10. Guidelines suggest accumulating roughly 500–1,000 MET-minutes per week — for example, 150 minutes of brisk (about 4-MET) walking.
References
- Ainsworth BE, Haskell WL, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine & Science in Sports & Exercise. 2011;43(8):1575–1581. doi:10.1249/MSS.0b013e31821ece12
- Ekelund U, Tarp J, et al. Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality. BMJ. 2019;366:l4570. doi:10.1136/bmj.l4570
Peer-reviewed sources located via PubMed and cited for education. Citations reflect published research at time of writing.
Dr. Andrew Simon, ND, BCB
Licensed naturopathic physician and board-certified biofeedback practitioner in Seattle. Clinic Director of Rebel Med NW, adjunct clinical faculty at Bastyr University, six-time Seattle Met Top Doctor, and the naturopathic advisor to Washington State on Long COVID. Read full bio →
This article is for educational purposes and is not a substitute for individualized medical care. Talk with a qualified clinician about your specific situation.