.tm-calculator-container {
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 30px;
background-color: #f8f9fa;
border-radius: 12px;
box-shadow: 0 4px 15px rgba(0,0,0,0.1);
border-left: 5px solid #28a745;
}
.tm-calculator-title {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 24px;
font-weight: 700;
}
.tm-input-group {
margin-bottom: 20px;
display: flex;
flex-direction: column;
}
.tm-input-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
}
.tm-col {
flex: 1;
min-width: 200px;
}
.tm-label {
font-weight: 600;
margin-bottom: 8px;
color: #495057;
display: block;
}
.tm-input {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 6px;
font-size: 16px;
transition: border-color 0.2s;
box-sizing: border-box;
}
.tm-input:focus {
border-color: #28a745;
outline: none;
box-shadow: 0 0 0 3px rgba(40, 167, 69, 0.2);
}
.tm-select {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 6px;
font-size: 16px;
background-color: white;
box-sizing: border-box;
}
.tm-btn {
width: 100%;
padding: 15px;
background-color: #28a745;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: 600;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.tm-btn:hover {
background-color: #218838;
}
.tm-result-box {
margin-top: 25px;
padding: 20px;
background-color: #ffffff;
border: 1px solid #e9ecef;
border-radius: 8px;
text-align: center;
display: none;
}
.tm-result-value {
font-size: 36px;
color: #28a745;
font-weight: 800;
margin: 10px 0;
}
.tm-result-label {
font-size: 14px;
color: #6c757d;
text-transform: uppercase;
letter-spacing: 1px;
}
.tm-content-section {
margin-top: 50px;
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
}
.tm-content-section h2 {
color: #2c3e50;
margin-top: 30px;
border-bottom: 2px solid #28a745;
padding-bottom: 10px;
display: inline-block;
}
.tm-content-section h3 {
color: #495057;
margin-top: 25px;
}
.tm-content-section p {
margin-bottom: 15px;
}
.tm-content-section ul {
margin-bottom: 15px;
padding-left: 20px;
}
.tm-content-section li {
margin-bottom: 8px;
}
.tm-info-box {
background-color: #e8f5e9;
padding: 15px;
border-radius: 5px;
border-left: 4px solid #28a745;
margin: 20px 0;
}
function calculateTreadmillStats() {
var gender = document.getElementById('tm_gender').value;
var age = parseFloat(document.getElementById('tm_age').value);
var weightLbs = parseFloat(document.getElementById('tm_weight').value);
var hr = parseFloat(document.getElementById('tm_heart_rate').value);
var duration = parseFloat(document.getElementById('tm_duration').value);
// Validation
if (isNaN(age) || isNaN(weightLbs) || isNaN(hr) || isNaN(duration) || age <= 0 || weightLbs <= 0 || hr <= 0 || duration <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// 1. Calculate Max Heart Rate (Standard Formula 220 – Age)
var maxHr = 220 – age;
var intensity = (hr / maxHr) * 100;
// 2. Convert Weight to KG
var weightKg = weightLbs * 0.453592;
// 3. Calculate Calories using Keytel Formula (Published in Journal of Sports Sciences)
// Formula calculates kJ per minute, we convert to kcal/min
var energyExp = 0; // kJ per minute
if (gender === 'male') {
// Male Formula: kJ/min = -55.0969 + (0.6309 x HR) + (0.1988 x Weight) + (0.2017 x Age)
energyExp = -55.0969 + (0.6309 * hr) + (0.1988 * weightKg) + (0.2017 * age);
} else {
// Female Formula: kJ/min = -20.4022 + (0.4472 x HR) – (0.1263 x Weight) + (0.074 x Age)
energyExp = -20.4022 + (0.4472 * hr) – (0.1263 * weightKg) + (0.074 * age);
}
// Convert kJ/min to kcal/min (1 kcal = 4.184 kJ)
var kcalPerMinute = energyExp / 4.184;
// Total Calories
var totalCalories = kcalPerMinute * duration;
// Display Results
var resultBox = document.getElementById('tm_result');
var caloriesDisplay = document.getElementById('tm_calories_val');
var intensityDisplay = document.getElementById('tm_intensity_val');
resultBox.style.display = "block";
caloriesDisplay.innerHTML = Math.round(totalCalories) + " kcal";
intensityDisplay.innerHTML = Math.round(intensity) + "% of Max HR";
}
How Does a Treadmill Calculate Heart Rate and Calories?
When you step onto a modern treadmill, the console often displays your heart rate (BPM) and an estimate of calories burned. While these numbers seem magical, they rely on specific biological algorithms and sensor technology. Understanding the math behind the machine can help you interpret your workout data more accurately.
1. Detecting the Pulse: Sensor Technology
Before any calculation can occur, the treadmill must acquire your heart rate data. There are two primary technologies used to detect the electrical or optical signals of your heart:
Hand Grip Sensors (EKG/ECG)
Most commercial treadmills feature silver metal plates on the handlebars. These are Pulse Grip sensors. They work similarly to an Electrocardiogram (EKG). When you hold the sensors with both hands, you complete a mild electrical circuit across your chest. The machine detects the tiny voltage spike generated by your heart muscle contracting (the R-wave) to calculate the beats per minute.
Accuracy Note: Hand grip sensors are notoriously prone to error if your hands are sweaty or if you are moving vigorously, which creates "noise" in the electrical signal.
Wireless Telemetry (Chest Straps)
Higher-end treadmills contain a radio receiver (often Polar-compatible 5kHz). When you wear a chest strap, electrodes pressed against your skin detect your heart's electrical activity and transmit a wireless radio pulse to the treadmill console. This method is significantly more accurate than hand grips because it maintains constant contact near the heart source.
2. The Algorithms: Calculating Calories from Heart Rate
Once the treadmill knows your Heart Rate (HR), it feeds this number into a mathematical formula to estimate energy expenditure. The calculator above uses the Keytel Formula, which is widely considered more accurate for machine-based estimation than simple distance-based formulas.
Without heart rate data, a treadmill can only guess your calorie burn based on speed and incline (physics). However, with heart rate data, it measures your biological response to the work. The formula generally factors in:
- Gender: Men generally have more muscle mass and burn calories faster than women at the same heart rate.
- Age: Metabolic rate and maximum heart rate decline with age.
- Weight: Heavier individuals require more energy to move, even on a treadmill.
- Heart Rate: The direct indicator of aerobic intensity.
3. Heart Rate Zones
Treadmills also calculate "Target Heart Rate" zones to help you train safely. The standard calculation used by most machines is the simple age-predicted maximum:
Max HR = 220 - Age
Using this number, the treadmill defines zones:
- Fat Burn Zone: Usually 60-70% of Max HR.
- Cardio Zone: Usually 70-80% of Max HR.
- Peak/Performance Zone: 80-90%+ of Max HR.
4. Why Treadmill Numbers Vary
You may notice different treadmills giving different calorie counts for the same workout. This happens because manufacturers use different proprietary algorithms. Some assume a higher baseline muscle mass, while others might not account for your specific weight if you didn't enter it before starting the belt.
For the most accurate data, always enter your correct weight and age into the console before starting, and use a chest strap rather than hand grips for continuous, accurate heart rate monitoring.