";
}
// 7. Update DOM
document.getElementById('zoneTableBody').innerHTML = tableHtml;
var detailsText = "Calculated using Max HR: " + mhr + " bpm";
if (rhr > 0) {
detailsText += " and Resting HR: " + rhr + " bpm (Karvonen Method).";
} else {
detailsText += ". Resting HR not provided (Simple Max HR % used).";
}
document.getElementById('calcDetails').innerHTML = detailsText;
document.getElementById('resultsDisplay').style.display = "block";
}
Mastering Your Cycling Heart Rate Zones
Training with a heart rate monitor is one of the most effective ways for cyclists to improve endurance, speed, and overall fitness. Unlike training by "feel" (Rate of Perceived Exertion), heart rate data provides an objective metric of how hard your body is working. This calculator helps you define specific intensity zones based on your physiology.
The Importance of the Karvonen Formula
While many simple calculators only look at your age to determine heart rate zones, this tool utilizes the Karvonen Formula (when a Resting Heart Rate is provided). This method is superior for cyclists because it accounts for your Heart Rate Reserve (HRR).
Your HRR is the difference between your Maximum Heart Rate and your Resting Heart Rate. By factoring in your resting rate, the zones are tailored to your current fitness level. A fitter cyclist typically has a lower resting heart rate, meaning their training zones will be calculated differently than a beginner's, even if they are the same age.
Breaking Down the 5 Zones
Successful cycling training plans require a mix of time spent in different zones. Here is what each zone represents:
Zone 1 (Active Recovery): Very light intensity. Used for warming up, cooling down, or recovery rides the day after a hard race. It promotes blood flow to flush out metabolic waste without stressing the muscles.
Zone 2 (Endurance): Often called the "all-day" pace. This is where you build your aerobic base. You should be able to hold a conversation comfortably. Pro cyclists spend a vast majority of their training time here to build mitochondrial efficiency.
Zone 3 (Tempo): This is the "grey zone"—harder than endurance but not quite race pace. It requires concentration to maintain. It improves aerobic efficiency and muscular endurance but can be fatiguing if overused.
Zone 4 (Lactate Threshold): This is roughly your time trial pace. You are riding right on the edge of where your body can clear lactate. Training here raises your functional threshold power (FTP). Breathing is labored; conversation is limited to single words.
Zone 5 (VO2 Max): Maximum effort. These are short bursts, sprints, or steep climbs lasting a few minutes. This zone trains your heart's ability to pump blood and your muscles' ability to use oxygen at the highest rates.
How to Determine Max Heart Rate
The standard formula (220 minus Age) is a good estimation for the general population, but it can vary significantly for individuals. For the most accurate results, perform a field test (such as a 20-minute time trial effort) or use the highest heart rate observed during a maximal sprint effort at the end of a hard ride. You can enter this custom value in the "Known Max Heart Rate" field above for better precision.