function calculateOrangeZone() {
var ageInput = document.getElementById("ozAge").value;
var rhrInput = document.getElementById("ozRHR").value;
var resultBox = document.getElementById("ozResult");
// Validate Age
var age = parseFloat(ageInput);
if (isNaN(age) || age 110) {
alert("Please enter a valid age between 10 and 110.");
return;
}
var rhr = parseFloat(rhrInput);
var mhr = 220 – age; // Standard Fox Formula for Max HR
var zoneLow, zoneHigh;
var methodText = "";
// Check if RHR is provided to use Karvonen Formula
if (!isNaN(rhr) && rhr > 0 && rhr < 150) {
// Karvonen Formula: TargetHR = ((maxHR − restingHR) × %Intensity) + restingHR
var hrr = mhr – rhr; // Heart Rate Reserve
zoneLow = Math.round((hrr * 0.80) + rhr);
zoneHigh = Math.round((hrr * 0.90) + rhr);
methodText = "Calculation based on the Karvonen formula (using Resting HR) for higher accuracy.";
} else {
// Standard Percentage of Max HR
zoneLow = Math.round(mhr * 0.80);
zoneHigh = Math.round(mhr * 0.90);
methodText = "Calculation based on standard percentage of Maximum Heart Rate.";
}
// Display Results
document.getElementById("resMHR").innerText = mhr + " bpm";
document.getElementById("resLow").innerText = zoneLow + " bpm";
document.getElementById("resHigh").innerText = zoneHigh + " bpm";
document.getElementById("resRange").innerText = zoneLow + " – " + zoneHigh + " bpm";
document.getElementById("calcMethod").innerText = methodText;
resultBox.style.display = "block";
}
How to Calculate Your Orange Zone Heart Rate
The "Orange Zone" is a popular term in fitness communities, particularly in HIIT (High-Intensity Interval Training) programs. It refers to a specific heart rate intensity level—typically Zone 4—where your body works at 80% to 90% of its maximum capacity. Training in this zone is often associated with the "afterburn effect" (EPOC), which helps burn calories even after the workout is finished.
Understanding the Formulas
Our calculator uses two primary methods to determine your specific Orange Zone, depending on the data you provide:
1. The Standard Age-Based Formula (Fox Formula)
This is the most common method used when you do not know your resting heart rate. It provides a general baseline.
Pushing your heart rate into the Orange Zone (80-90% MHR) yields significant physiological benefits:
Anaerobic Threshold: It improves your body's ability to tolerate and clear lactic acid, allowing you to run faster or lift harder for longer periods.
Caloric Efficiency: While you burn a mix of fat and carbohydrates, the total caloric expenditure per minute is very high.
EPOC (Afterburn): High-intensity effort creates an oxygen debt that the body must repay post-workout, keeping your metabolism elevated for hours.
Safety and Monitoring
While the Orange Zone is effective for performance, it is physically demanding. It is not recommended to stay in this zone for an entire workout. Instead, it is best utilized during intervals (e.g., 1 to 5 minutes of effort followed by recovery).
Always consult with a physician before starting a high-intensity training program, especially if you have pre-existing cardiovascular conditions.