Optimize your aerobic endurance and fat metabolism by finding your target heart rate range.
Karvonen Formula (Most Accurate)
Standard (60-70% of MHR)
Male
Female
Your Personalized Zone 2 Range
— to —
Beats Per Minute (BPM)
Understanding Zone 2 Heart Rate Training
Zone 2 training is often referred to as "base training" or "aerobic capacity training." It is the intensity level where your body primarily uses fat as its main fuel source while maximizing mitochondrial efficiency. This training intensity is sustainable for long periods and is essential for building a solid endurance foundation.
How Zone 2 is Calculated
There are two primary ways to calculate your Zone 2 heart rate range:
The Standard Method: This uses a percentage of your Maximum Heart Rate (MHR). Traditionally, Zone 2 is defined as 60% to 70% of your MHR. While simple, it doesn't account for individual fitness levels.
The Karvonen Formula: This is a more advanced method that incorporates your Heart Rate Reserve (HRR). By using your Resting Heart Rate (RHR), the Karvonen formula adjusts the intensity zones to match your current cardiovascular fitness.
Example Calculation (Karvonen Method)
If you are a 40-year-old with a resting heart rate of 60 BPM:
Max HR: 220 – 40 = 180 BPM
Heart Rate Reserve (HRR): 180 – 60 = 120 BPM
60% Intensity: (120 x 0.60) + 60 = 132 BPM
70% Intensity: (120 x 0.70) + 60 = 144 BPM
In this example, your Zone 2 target range would be 132 to 144 BPM.
The Benefits of Zone 2 Training
Benefit
Why it matters
Mitochondrial Density
Increases the number and efficiency of mitochondria in muscle cells.
Fat Oxidation
Teaches the body to utilize fat stores more effectively at higher intensities.
Recovery
Builds a base that allows you to recover faster from high-intensity interval sessions.
Lower Injury Risk
Lower intensity means less stress on joints and connective tissues.
The "Talk Test"
A practical way to check if you are in Zone 2 without a monitor is the "Talk Test." You should be able to hold a full conversation without gasping for air, but your breathing should be deep and rhythmic. If you can only speak in short sentences, you have likely crossed into Zone 3.
function calculateZone2() {
var age = parseFloat(document.getElementById("z2Age").value);
var rhr = parseFloat(document.getElementById("z2RHR").value);
var method = document.getElementById("z2Method").value;
var resultArea = document.getElementById("z2-result-area");
var rangeDisplay = document.getElementById("z2-range-display");
var explanation = document.getElementById("z2-explanation");
if (!age || age 120) {
alert("Please enter a valid age.");
return;
}
// Determine Max HR (using Tanaka formula for better accuracy: 208 – 0.7 * age)
var mhr = 208 – (0.7 * age);
var lowerBound, upperBound;
if (method === "karvonen") {
if (!rhr || rhr 120) {
alert("Please enter a valid Resting Heart Rate (30-120 BPM) for the Karvonen method.");
return;
}
var hrr = mhr – rhr;
lowerBound = Math.round((hrr * 0.60) + rhr);
upperBound = Math.round((hrr * 0.70) + rhr);
explanation.innerText = "Calculated using the Karvonen method (incorporating your Resting Heart Rate).";
} else {
lowerBound = Math.round(mhr * 0.60);
upperBound = Math.round(mhr * 0.70);
explanation.innerText = "Calculated using the Standard method (60-70% of Maximum Heart Rate).";
}
rangeDisplay.innerText = lowerBound + " – " + upperBound;
resultArea.style.display = "block";
// Smooth scroll to result
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}