';
}
// Update DOM
maxHrDisplay.innerText = maxHr;
zonesBody.innerHTML = html;
methodDisplay.innerText = useKarvonen
? "Calculated using the Karvonen Formula (considers Resting HR)."
: "Calculated using the Standard Formula (Percentage of Max HR).";
resultsArea.style.display = 'block';
}
Why Calculate Your Heart Rate Zones?
Calculating your heart rate range is essential for optimizing your cardiovascular training. By identifying specific heart rate zones, you can tailor your workout intensity to meet specific fitness goals, whether that is burning fat, building endurance, or increasing maximum speed.
Heart rate training prevents "junk miles"—training that is too hard for recovery but too easy to trigger significant adaptation. Instead, it provides a data-driven roadmap for your fitness journey.
Understanding the Heart Rate Zones
Most training models divide heart rate intensities into five distinct zones, based on a percentage of your Maximum Heart Rate (MHR) or Heart Rate Reserve (HRR).
Zone 1 (50-60%): Very Light. Used for warm-ups, cool-downs, and active recovery. It promotes blood flow and helps muscles recover.
Zone 2 (60-70%): Light. Often called the "Fat Burning Zone." Here, the body becomes efficient at oxidizing fat for fuel. It is crucial for building a solid aerobic base.
Zone 3 (70-80%): Moderate. The aerobic zone. Training here improves blood circulation and the efficiency of the heart. It is harder than Zone 2 and builds rhythmic endurance.
Zone 4 (80-90%): Hard. Also known as the anaerobic threshold. At this intensity, your body produces lactate faster than it can clear it. Training here improves your ability to sustain high speeds.
Zone 5 (90-100%): Maximum. All-out effort used for short intervals. This zone develops fast-twitch muscle fibers and top-end speed.
The Formulas: Standard vs. Karvonen
This calculator uses two primary methods depending on the data you provide:
1. Standard Formula (Fox Method)
This is the simplest method. It estimates your Maximum Heart Rate (MHR) as 220 – Age. The zones are then calculated as straight percentages of this maximum. While easy to use, it does not account for individual fitness levels.
2. Karvonen Formula
Used when you enter a Resting Heart Rate (RHR). This method is generally considered more accurate for athletes because it takes your fitness level into account. It calculates the Heart Rate Reserve (HRR = MHR – RHR) and applies percentages to the reserve, adding the RHR back at the end.
To get the most accurate results from the Karvonen formula, you need an accurate Resting Heart Rate measurement. The best time to measure this is in the morning, right after you wake up naturally, before getting out of bed or drinking caffeine.
Locate your pulse on your wrist (radial artery) or neck (carotid artery).
Count the beats for 60 seconds (or for 15 seconds and multiply by 4).
Repeat this for 3-4 days and take the average for the most reliable number.