What is Zone 2 cardio?

Zone 2 is light-to-moderate aerobic exercise where your body primarily burns fat for fuel and builds mitochondrial density. You should be able to maintain a conversation without gasping.

Heart & Cardio

Heart Rate Zone Calculator

Calculate 5-zone cardiovascular training boundaries using the Karvonen Heart Rate Reserve method

Input Parameters

Real-time calculation updates dynamically as you adjust inputs. Values remain strictly local on your device.

Zone 2 (Aerobic Base)Optimal Fat Oxidation

136 – 149bpm

Max Heart Rate: 187 bpm (Tanaka) | Reserve (HRR): 127 bpm

Zone	Name	Target Range	Primary Adaptation
Zone 1	Zone 1 — Active Recovery	124 – 136 bpm	Promotes blood flow, cellular recovery, and low-stress aerobic conditioning.
Zone 2	Zone 2 — Aerobic Base / Fat Burn	136 – 149 bpm	Mitochondrial biogenesis, capillary density, and high aerobic efficiency.
Zone 3	Zone 3 — Aerobic Tempo	149 – 162 bpm	Improves glycogen storage capacity and steady-state cardiovascular pace.
Zone 4	Zone 4 — Lactate Threshold	162 – 174 bpm	Increases lactate clearance rate and fatigue tolerance during hard sustained efforts.
Zone 5	Zone 5 — Neuromuscular / VO2 Max	174 – 187 bpm	Maximizes peak stroke volume, cardiac output, and top-end anaerobic capacity.

Clinical Responsibility Note: Target heart rate ranges are demographic statistical estimates. Individuals taking beta-blockers, antiarrhythmics, or with cardiovascular conditions should consult their physician.

Mathematical Formula & Scientific Methodology

Formula: Karvonen Heart Rate Reserve (HRR) Equation

Target HR = [(HRmax - HRrest) × % Intensity] + HRrest

Published in 1957 by Martti Karvonen, this method scales training intensity to the individual's functional cardiovascular reserve rather than gross percentage of max.

Model Assumptions

Resting heart rate measured upon waking prior to stimulants

Variables & Standard Units

Symbol	Physiological Meaning	Unit
HRmax	Maximal heart rate via Tanaka formula: 208 - 0.7 × Age	bpm
HRrest	True resting morning heart rate	bpm
HRR	Heart Rate Reserve (HRmax - HRrest)	bpm

Scientific Limitations

Cardiac drift in hot environments can cause heart rate to rise independent of metabolic workload

Peer-Reviewed Scientific Citations

The effects of training on heart rate; a longitudinal study (1957)

Karvonen MJ, Kentala E, Mustala O (1957) — Annales Medicinae Experimentalis et Biologiae Fenniae, 35(3), 307-315

Key Finding: Target HR = ((HRmax - HRrest) * %Intensity) + HRrest. Uses Heart Rate Reserve (HRR) to individualize training zones.

Age-predicted maximal heart rate revisited (2001)

Tanaka H, Monahan KD, Seals DR (2001) — Journal of the American College of Cardiology, 37(1), 153-156

Key Finding: HRmax = 208 - (0.7 * age). Validated across 18,712 subjects as significantly more accurate than the traditional 220 - age equation.

Frequently Asked Questions

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