Standard (60-70% of Max HR)
Karvonen Formula (Based on HR Reserve)
MAF 180 Formula (180 – Age)
Your Zone 2 Range
— – — BPM
function calculateZone2() {
var ageInput = document.getElementById('z2-age');
var rhrInput = document.getElementById('z2-rhr');
var methodSelect = document.getElementById('z2-method');
var resultBox = document.getElementById('z2-result');
var rangeDisplay = document.getElementById('z2-range-display');
var explanationDisplay = document.getElementById('z2-explanation');
var age = parseFloat(ageInput.value);
var rhr = parseFloat(rhrInput.value);
var method = methodSelect.value;
// Validation
if (isNaN(age) || age 120) {
alert("Please enter a valid age.");
return;
}
// Estimate Max Heart Rate (Standard Formula 220-Age)
// While Tanaka (208 – 0.7*age) is newer, 220-age is standard for general calculators
var maxHR = 220 – age;
var lowerZone, upperZone;
var methodText = "";
if (method === 'maffetone') {
// MAF 180 Formula
// Target is usually a single number (max aerobic function), usually range is -10 to +0
var mafNum = 180 – age;
lowerZone = mafNum – 10;
upperZone = mafNum;
methodText = "Based on the MAF (Maximum Aerobic Function) Method (180 – Age).";
} else if (method === 'karvonen') {
// Karvonen: Target = ((MaxHR – RestingHR) * %Intensity) + RestingHR
if (isNaN(rhr) || rhr 120) {
alert("Please enter a valid Resting Heart Rate to use the Karvonen formula.");
return;
}
var hrr = maxHR – rhr; // Heart Rate Reserve
// Zone 2 is typically 60% to 70% of HRR
lowerZone = (hrr * 0.60) + rhr;
upperZone = (hrr * 0.70) + rhr;
methodText = "Based on the Karvonen Formula using a Resting HR of " + rhr + " BPM.";
} else {
// Standard Percentage: 60% to 70% of Max HR
lowerZone = maxHR * 0.60;
upperZone = maxHR * 0.70;
methodText = "Based on 60-70% of your estimated Maximum Heart Rate (" + maxHR + " BPM).";
}
// Display Results
resultBox.style.display = "block";
rangeDisplay.innerHTML = Math.round(lowerZone) + " – " + Math.round(upperZone) + " BPM";
explanationDisplay.innerHTML = methodText + "Training in this zone improves mitochondrial efficiency and fat oxidation.";
}
What is Zone 2 Training?
Zone 2 training refers to exercise performed at a low-to-moderate intensity where your body relies primarily on aerobic metabolism. In this zone, your body is efficient at oxidizing fat for fuel and clearing lactate as quickly as it is produced. It is often described as a pace where you can maintain a conversation comfortably, but you would prefer not to.
Why Calculate Your Zone 2 Heart Rate?
Knowing "what's my zone 2 heart rate" is crucial for building a massive aerobic base. Professional cyclists, runners, and triathletes spend nearly 80% of their training time in this specific zone. Training too hard (Zone 3 or 4) creates too much fatigue for daily volume, while training too easy (Zone 1) provides insufficient stimulus for mitochondrial growth.
The Talk Test: If you don't have a heart rate monitor, you can estimate Zone 2 by trying to speak in full sentences. If you can speak comfortably, but retain a slight strain in your breathing, you are likely in Zone 2. If you are gasping, you are in Zone 3 or higher.
Calculation Methods Explained
1. Standard Percentage Method
This is the simplest method used by most fitness trackers. It estimates your Maximum Heart Rate (Max HR) using the formula 220 – Age. Zone 2 is then defined as 60% to 70% of that maximum.
Example: For a 40-year-old, Max HR is 180. Zone 2 is 108 to 126 BPM.
2. The Karvonen Formula (Heart Rate Reserve)
This method is more accurate because it accounts for your fitness level via your Resting Heart Rate (RHR). It calculates your Heart Rate Reserve (HRR = Max HR – Resting HR). Zone 2 is calculated as (HRR × 0.60 to 0.70) + RHR.
Example: A 40-year-old with a resting heart rate of 50:
Max HR: 180
HR Reserve: 130 (180 – 50)
Lower Limit: (130 × 0.60) + 50 = 128 BPM
Upper Limit: (130 × 0.70) + 50 = 141 BPM
Notice how the Karvonen method yields a higher, often more accurate range for fit individuals.
3. MAF 180 Formula
Developed by Dr. Phil Maffetone, this method determines the maximum aerobic heart rate simply by subtracting your age from 180. The training zone is typically the range between (180 – Age – 10) and (180 – Age).
Benefits of Zone 2 Training
Mitochondrial Density: Increases the number and efficiency of mitochondria in your cells.
Fat Utilization: Teaches the body to burn fat as the primary fuel source.
Lactate Clearance: Improves the body's ability to recycle lactate, preventing fatigue during higher intensity efforts.
Recovery: Allows for high training volume with lower systemic fatigue compared to threshold training.