FSHP Academy
Exercise Physiology — all lessons

Muscle Physiology

Muscle physiology: excitation–contraction and the sliding filament modelConcentric, eccentric and isometric muscle actionsMotor units, recruitment and rate codingNeuromuscular adaptations to training

Energy Systems

Energy systems overview: how the body makes ATPThe ATP-PC (phosphagen) systemAnaerobic glycolysis and lactateThe aerobic oxidative system

Cardiovascular Physiology

Heart anatomy and the cardiac cycleStroke volume, heart rate and cardiac outputBlood components and oxygen transport

Aerobic Fitness and Intensity

Aerobic fitness concepts and adaptationsVO₂ maxLactate thresholdHeart rate zones and RPE-based intensity control

Heart rate zones and RPE-based intensity control

How to prescribe and monitor exercise intensity with heart rate and ratings of perceived exertion — the formulas, the zone models, their errors, and when to trust which.

Beginner Evidence: Strong evidence 5 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Estimate maximal heart rate and understand the error in prediction equations
  • Calculate target heart rates using %HRmax and heart rate reserve (Karvonen)
  • Use the Borg 6–20 and CR-10 RPE scales, and session-RPE for training load
  • Choose between heart rate, RPE and other anchors for different clients and situations

Before this lesson

Why this matters

Intensity is the variable that most strongly shapes the response to cardiorespiratory training — and the one clients most often get wrong. Heart rate (HR) and ratings of perceived exertion (RPE) are the two most accessible ways to control it. This lesson shows how to calculate HR targets, how big their errors are, and how to use RPE as a robust alternative or complement.

International guidelines express aerobic activity in terms of moderate and vigorous intensity (e.g., 150–300 minutes per week of moderate or 75–150 minutes of vigorous activity for adults) [bull2020], so a trainer must be able to translate those words into numbers.

Fundamental concepts

  • HRmax — the highest heart rate achievable in all-out exercise.
  • Resting HR (HRrest) — measured on waking, at rest.
  • Heart rate reserve (HRR) — HRmax − HRrest.
  • RPE — a person’s rating of how hard the exercise feels, on a standardised scale.

Estimating maximal heart rate

HRmax ≈ 208 − 0.7 × ageTanaka et al. (2001), derived from a meta-analysis of 351 studies plus a laboratory cross-validation study.

The traditional 220 − age formula has no strong empirical basis and tends to underestimate HRmax in older adults. Tanaka and colleagues proposed 208 − 0.7 × age from a large meta-analysis and lab study [tanaka2001]. Both, however, describe population averages: individuals commonly differ from the prediction by around 10 bpm or more. A measured maximum (from a supervised maximal test or a hard, appropriately screened field effort) is always better than a formula.

Calculating target heart rate

1. Percentage of HRmax

Target HR = HRmax × intensity %Example: HRmax 180 bpm, 70% → 126 bpm.

2. Heart rate reserve (Karvonen) method

Target HR = (HRmax − HRrest) × intensity % + HRrestExample: HRmax 180, HRrest 60, 60% → (120 × 0.6) + 60 = 132 bpm.

The HRR method accounts for resting HR, and %HRR corresponds more closely to percentage of oxygen-uptake reserve than %HRmax does, which is why ACSM uses it for prescription [garber2011]. Try both in the heart rate zone calculator.

Intensity categories and zone models

Exercise intensity categories by heart rate and perceived exertion A horizontal scale of percentage of maximal heart rate from 45 to 100 percent. Bands show ACSM intensity categories: very light below 57 percent, light 57 to 63, moderate 64 to 76, vigorous 77 to 95, near maximal 96 and above, with matching Borg RPE ranges. Underneath, a three-zone physiological model is shown: zone 1 below the first lactate or ventilatory threshold, zone 2 between thresholds, and zone 3 above the second threshold. Threshold positions vary between individuals. ACSM category Borg RPE (6–20) Very light < 9 Light 9–11 Moderate 12–13 Vigorous 14–17 Near max ≥ 18 50%57%64%77%90%96%100% % HRmax 3-zone model Zone 1 · below LT1/VT1 Zone 2 Zone 3 · above LT2 LT1 / VT1 LT2 / VT2 Top: ACSM (Garber et al., 2011). Bottom: three-zone model (Seiler, 2010); threshold positions shown are typical of trained endurance athletes and vary widely between people — only a lab or field threshold test locates them for an individual.
Figure 1. ACSM intensity categories aligned with %HRmax and Borg RPE (top), and a physiologically anchored three-zone model (bottom). Formula-based bands are approximate; threshold-anchored zones require testing. — Original diagram based on Garber et al. (2011) and Seiler (2010).
ACSM category%HRmax%HRRRPE (6–20)
Very light< 57< 30< 9
Light57–6330–399–11
Moderate64–7640–5912–13
Vigorous77–9560–8914–17
Near-maximal to maximal≥ 96≥ 90≥ 18

Source: ACSM position stand [garber2011].

Three-zone (physiological) model. Endurance science commonly divides intensity using two thresholds: the first lactate or ventilatory threshold (LT1/VT1) and the second (LT2/VT2, near maximal lactate steady state or critical power). Zone 1 lies below LT1, zone 2 between thresholds, zone 3 above LT2. Observational studies of successful endurance athletes show most training time spent in zone 1, with a smaller amount in zone 3 — a “polarised” or pyramidal distribution [seiler2010]. Different laboratories define thresholds in different ways, and those definitions are not interchangeable [faude2009].

Five-zone models used by many coaches and devices (e.g., 50–60, 60–70, 70–80, 80–90, 90–100% HRmax) are conventions, not physiological boundaries. They are useful for communication but should be adjusted after testing.

Ratings of perceived exertion

Borg 6–20 scale. Designed so that ratings roughly track heart rate in young adults (rating × 10 ≈ HR), with verbal anchors from “very, very light” to “maximal exertion” [borg1982].

CR-10 scale. A 0–10 category-ratio scale with verbal anchors, often easier for clients, used in strength training and in session-RPE.

Session-RPE training load [foster2001]:

Session load (AU) = CR-10 rating of the whole session × duration (min)Example: 45-min session rated 6 → 270 arbitrary units (AU). Summing sessions gives weekly load.

Practical application

Teach RPE deliberately: explain the anchors, ask for ratings at different known workloads, and compare ratings with HR and performance over several sessions.

Common mistakes and misconceptions

  • Treating formula zones as precise. A ±10 bpm error in HRmax shifts every zone.
  • Trusting wrist HR during intervals. Optical wrist sensors are least reliable during rapid intensity changes and arm-intensive exercise; chest straps are more accurate.
  • Equating RPE with “it’s just subjective”. RPE integrates many physiological signals and is a validated tool [borg1982].

Case study

Client: Mr Rao, 63, hypertension managed with a beta-blocker, cleared by his physician for moderate exercise.

Problem: A formula gives HRmax 164 bpm (Tanaka) and a moderate zone of ~105–125 bpm. On his first session he cannot get above 98 bpm even when he reports “hard” effort, and becomes frustrated.

Solution: The trainer explains that his medication limits heart rate, switches to RPE 12–13 (“somewhat hard”) and the talk test, and records RPE, duration and walking speed each session. Over eight weeks his walking speed at RPE 12–13 rises from 5.0 to 5.8 km/h — a clear fitness improvement that heart rate alone would have hidden. Any change of medication is noted, as it alters HR response.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

Heart rate training zones explained

GCN / Global Triathlon Network (search)

You will understand: how zones are set and used in endurance training

Why: Practical sport-focused overview; verify the specific video.
Practical demo needs verification — opens a YouTube search

Borg RPE scale — how to use it

physiotherapy or exercise physiology channels (search)

You will understand: anchoring and teaching the RPE scale to clients

Why: Teaching RPE well is a practical coaching skill.
Technical needs verification — opens a YouTube search

Polarised training and intensity distribution — Stephen Seiler lecture

Stephen Seiler (conference / university lectures)

You will understand: the three-zone model and how elite endurance athletes distribute intensity

Why: Primary researcher explaining his own work.

Knowledge check

Knowledge check · 0/5

1. Using the Tanaka equation, the predicted HRmax of a 40-year-old is…

Answer A. 208 − 0.7 × 40 = 208 − 28 = 180 bpm. (220 − age gives 180 at this age too; the formulas diverge more at older ages.)

2. A client has HRmax 180 and resting HR 60. Using the Karvonen method, the target HR at 60% intensity is…

Answer B. HRR = 180 − 60 = 120; 60% × 120 = 72; 72 + 60 = 132 bpm.

3. According to ACSM (2011), an RPE of 12–13 on the 6–20 scale corresponds to…

Answer B. Moderate intensity corresponds roughly to RPE 12–13 and 64–76% HRmax.

4. Which client most clearly needs RPE rather than heart-rate zones?

Answer B. Beta-blockers blunt heart-rate response, so standard HR targets become unreliable; RPE (with medical guidance) is preferred.

5. Session-RPE training load is calculated as…

Answer A. Foster’s method multiplies the session’s CR-10 rating by its duration in minutes, giving arbitrary units (AU).

Short-answer & application questions

  1. Calculate %HRmax and Karvonen targets for moderate intensity for a 55-year-old client with resting HR 72 bpm. Which would you use, and why?
  2. Explain why heart-rate zones from a formula may be too easy for one client and too hard for another.
  3. Describe how you would teach a new client to use the RPE scale accurately.

Key takeaways

  • Age-predicted maximal heart rate formulas carry an individual error of roughly ±10 bpm or more; the Tanaka equation (208 − 0.7 × age) is more accurate across ages than 220 − age, but neither replaces a measured maximum.
  • ACSM classifies moderate intensity as ~64–76% HRmax (RPE 12–13) and vigorous as ~77–95% HRmax (RPE 14–17).
  • The Karvonen (heart rate reserve) method accounts for resting heart rate and aligns more closely with %VO₂ reserve.
  • RPE is valid, free and unaffected by heart-rate-lowering medication — essential for clients on beta-blockers.
  • Physiological zones anchored to thresholds are more individual than formula-based zones, but require testing.

Connected topics

physiology

VO₂ max

physiology

Lactate threshold

assessment

Cardiorespiratory assessments

personal training

Cardiorespiratory training: physiology, assessments and programming

strength conditioning

Overtraining: recognition and load monitoring

hybrid training · planned

Zone 2, threshold, VO₂ max and alactic work

References

  1. Garber CE, Blissmer B, Deschenes MR, et al.; American College of Sports Medicine (2011). Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Medicine & Science in Sports & Exercise, 43(7):1334–1359. doi:10.1249/MSS.0b013e318213fefb Position stand check pending
  2. Tanaka H, Monahan KD, Seals DR (2001). Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology, 37(1):153–156. doi:10.1016/S0735-1097(00)01054-8 Meta-analysis check pending
  3. Borg GA (1982). Psychophysical bases of perceived exertion. Medicine & Science in Sports & Exercise, 14(5):377–381. doi:10.1249/00005768-198205000-00012 Classic study check pending
  4. Foster C, Florhaug JA, Franklin J, et al. (2001). A new approach to monitoring exercise training. Journal of Strength and Conditioning Research, 15(1):109–115. Classic study check pending
  5. Seiler S (2010). What is best practice for training intensity and duration distribution in endurance athletes?. International Journal of Sports Physiology and Performance, 5(3):276–291. doi:10.1123/ijspp.5.3.276 · PubMed 20861519 Narrative review verified
  6. Faude O, Kindermann W, Meyer T (2009). Lactate threshold concepts: how valid are they?. Sports Medicine, 39(6):469–490. doi:10.2165/00007256-200939060-00003 · PubMed 19453206 Narrative review verified
  7. Bull FC, Al-Ansari SS, Biddle S, et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 54(24):1451–1462. doi:10.1136/bjsports-2020-102955 Guideline check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.