*Estimate based on weight and heart rate zone intensity.
function calculateHeartRate() {
var ageInput = document.getElementById("currentAge").value;
var weightInput = document.getElementById("currentWeight").value;
var gender = document.getElementById("gender").value;
// Basic validation
if (!ageInput || !weightInput) {
alert("Please enter both your age and weight.");
return;
}
var age = parseFloat(ageInput);
var weightLbs = parseFloat(weightInput);
// Calculate Max Heart Rate (Fox Formula: 220 – age)
// Note: The Tanaka formula (208 – 0.7 * age) is also popular, but 220 is standard for general use.
var maxHeartRate = 220 – age;
// Calculate Zones
var fatBurnMin = Math.round(maxHeartRate * 0.60);
var fatBurnMax = Math.round(maxHeartRate * 0.70);
var cardioMin = Math.round(maxHeartRate * 0.70);
var cardioMax = Math.round(maxHeartRate * 0.80);
// Calculate Calories Estimate
// Formula Approximation: METs * 3.5 * Weight(kg) / 200 * duration(min)
// Fat burning zone (brisk walking/light jog) is approx 5.0 METs
var weightKg = weightLbs * 0.453592;
var mets = 5.0; // Average for moderate intensity
// Adjust METs slightly for gender logic if needed, but METs is activity based.
// We can use a different formula for more specificity:
// Cals/min = (0.4472 x H) – (0.05741 x W) + (0.074 x A) – 20.4022 for Men
// Cals/min = (0.4472 x H) – (0.1263 x W) + (0.074 x A) – 20.4022 for Women
// Let's use the Gross Metabolic Estimate which is simpler and relies heavily on weight:
// Calories = 0.0175 * MET * Weight(kg) * Minutes
var caloriesBurned = Math.round(0.0175 * mets * weightKg * 60);
// Display Results
document.getElementById("resMHR").innerHTML = maxHeartRate + " bpm";
document.getElementById("resFatBurn").innerHTML = fatBurnMin + " – " + fatBurnMax + " bpm";
document.getElementById("resCardio").innerHTML = cardioMin + " – " + cardioMax + " bpm";
document.getElementById("resCalories").innerHTML = "~" + caloriesBurned + " kcal";
document.getElementById("mhrResult").style.display = "block";
}
Understanding Max Heart Rate and Weight Management
Calculating your maximum heart rate (MHR) is a fundamental step in designing an effective exercise program, especially if your goal involves weight management. While your age is the primary determinant of your maximum heart rate, your body weight plays a significant role in how much energy you expend during exercise.
Why Weight Matters in Heart Rate Calculations
While the standard formula for Maximum Heart Rate (220 minus age) does not explicitly include weight variables, your weight is crucial for two reasons:
Caloric Expenditure: Heavier individuals require more energy to move their bodies. Therefore, a person weighing 200 lbs will burn significantly more calories at the same heart rate zone than a person weighing 140 lbs.
Perceived Exertion: If you are carrying extra weight, your heart may need to work harder to achieve the same physical output, meaning you might reach your target heart rate zones more quickly than a lighter individual.
Heart Rate Zones Explained
To maximize your workouts, you should aim to train in specific "zones" based on a percentage of your MHR:
1. Fat Burning Zone (60-70% of MHR)
This represents moderate intensity activity, such as brisk walking or gentle cycling. In this zone, your body relies more heavily on fat stores for fuel rather than carbohydrates. This is often the recommended zone for sustainable weight loss programs because it can be maintained for longer durations.
2. Cardio/Aerobic Zone (70-80% of MHR)
Training in this zone improves your cardiovascular system and respiratory health. While the percentage of fat calories burned is lower than in the fat-burning zone, the total number of calories burned is often higher due to the increased intensity.
How to Use This Data for Weight Loss
Using the calculator above, identify your Fat Burning Zone. To optimize weight loss, aim for 150 to 300 minutes of moderate-intensity activity within this heart rate range per week. Remember that consistency is more important than intensity when starting a weight management journey.
Disclaimer: This calculator provides estimates based on standard metabolic formulas. Always consult with a healthcare professional before starting a new exercise regimen, especially if you have pre-existing health conditions.