Heart Rate Zone Calculator Based on Lactate Threshold

Lactate Threshold Heart Rate (LTHR) Zone Calculator

Your LTHR is typically the average heart rate from the last 20 minutes of a 30-minute all-out time trial.

Your Custom Training Zones

Zone	Description	Range (BPM)

function calculateLTHRZones() { var lthr = parseFloat(document.getElementById('lthrInput').value); var resultsArea = document.getElementById('resultsArea'); var body = document.getElementById('zoneResultsBody'); if (isNaN(lthr) || lthr 220) { alert('Please enter a valid heart rate (typically between 40 and 220 BPM).'); return; } var zones = [ { name: "Zone 1", desc: "Recovery", min: 0, max: 0.85 }, { name: "Zone 2", desc: "Aerobic / Endurance", min: 0.85, max: 0.89 }, { name: "Zone 3", desc: "Tempo", min: 0.90, max: 0.94 }, { name: "Zone 4", desc: "Sub-Threshold", min: 0.95, max: 0.99 }, { name: "Zone 5a", desc: "Super-Threshold", min: 1.00, max: 1.02 }, { name: "Zone 5b", desc: "Aerobic Capacity", min: 1.03, max: 1.06 }, { name: "Zone 5c", desc: "Anaerobic Power", min: 1.06, max: 1.15 } ]; var html = ""; for (var i = 0; i < zones.length; i++) { var z = zones[i]; var lowBpm = Math.round(lthr * z.min); var highBpm = Math.round(lthr * z.max); var displayRange = ""; if (z.name === "Zone 1") { displayRange = "Less than " + highBpm; } else if (z.name === "Zone 5c") { displayRange = "Greater than " + lowBpm; } else { displayRange = lowBpm + " – " + highBpm; } html += ""; html += "" + z.name + ""; html += "" + z.desc + ""; html += "" + displayRange + " BPM"; html += ""; } body.innerHTML = html; resultsArea.style.display = "block"; }

Understanding Lactate Threshold Heart Rate (LTHR) Training

Training by heart rate is one of the most effective ways to ensure you are working at the correct intensity for your specific fitness goals. While many beginners use the "220 minus age" formula, serious athletes prefer Lactate Threshold Heart Rate (LTHR) because it accounts for individual fitness levels and physiological differences.

What is Lactate Threshold?

Your lactate threshold is the point during exercise where lactate begins to accumulate in your bloodstream faster than your body can remove it. This usually corresponds to the maximum intensity you can sustain for about 40 to 60 minutes. By basing your training zones on this specific "tipping point," your zones become much more accurate than those based on a predicted maximum heart rate.

How to Find Your LTHR

The most common field test to find your LTHR is the Joe Friel 30-minute Time Trial:

1. Perform a thorough warm-up.
2. Start a 30-minute time trial (running or cycling) at the hardest pace you can sustain for the full duration. This should be a solo effort.
3. 10 minutes into the test, hit the "Lap" button on your heart rate monitor.
4. Finish the remaining 20 minutes at your maximum sustainable effort.
5. Your average heart rate for the final 20 minutes of the test is your estimated LTHR.

The 7 Training Zones Explained

• Zone 1 (Recovery): Used for active recovery days. Very light effort.
• Zone 2 (Endurance): The "all day" pace. Vital for building mitochondrial density and fat metabolism.
• Zone 3 (Tempo): A moderate effort that requires concentration to maintain but is not yet "hard."
• Zone 4 (Sub-Threshold): Just below your threshold. This is where you build the "engine."
• Zone 5a (Super-Threshold): Just above threshold; helps increase the threshold itself.
• Zone 5b (Aerobic Capacity/VO2 Max): High-intensity intervals used to improve oxygen uptake.
• Zone 5c (Anaerobic Power): All-out sprints and short, explosive bursts.

Example Calculation

If an athlete performs a time trial and finds their average heart rate for the final 20 minutes is 170 BPM, their zones would be calculated as follows:

• Zone 2 (85-89%): 145 – 151 BPM
• Zone 4 (95-99%): 162 – 168 BPM
• Zone 5a (100-102%): 170 – 173 BPM

Using these precise numbers ensures that on "easy" days, the athlete stays truly easy, and on "hard" days, they hit the physiological stimulus required for improvement.