Heart Rate Zone Calculator Lactate Threshold

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Lactate Threshold Heart Rate (LTHR) Zone Calculator

Enter the average heart rate from the last 20 minutes of a 30-minute all-out time trial.

Your Training Zones

Zone Intensity BPM Range
function calculateLTHR() { var lthr = document.getElementById('lthrInput').value; var resultsDiv = document.getElementById('lthrResults'); var tbody = document.getElementById('resultBody'); if (!lthr || lthr 220) { alert("Please enter a valid Lactate Threshold Heart Rate (typically between 120 and 200 BPM)."); return; } var lthrNum = parseFloat(lthr); var zones = [ { name: "Zone 1", desc: "Recovery (Active)", min: 0, max: Math.round(lthrNum * 0.85) – 1 }, { name: "Zone 2", desc: "Aerobic (Base)", min: Math.round(lthrNum * 0.85), max: Math.round(lthrNum * 0.89) }, { name: "Zone 3", desc: "Tempo", min: Math.round(lthrNum * 0.90), max: Math.round(lthrNum * 0.94) }, { name: "Zone 4", desc: "Sub-Threshold", min: Math.round(lthrNum * 0.95), max: Math.round(lthrNum * 0.99) }, { name: "Zone 5a", desc: "Super-Threshold", min: Math.round(lthrNum * 1.00), max: Math.round(lthrNum * 1.02) }, { name: "Zone 5b", desc: "Aerobic Capacity (VO2)", min: Math.round(lthrNum * 1.03), max: Math.round(lthrNum * 1.06) }, { name: "Zone 5c", desc: "Anaerobic Capacity", min: Math.round(lthrNum * 1.06) + 1, max: "+" } ]; var html = ""; for (var i = 0; i < zones.length; i++) { var range = zones[i].max === "+" ? (zones[i].min + "+ BPM") : (zones[i].min + " – " + zones[i].max + " BPM"); html += ""; html += "" + zones[i].name + ""; html += "" + zones[i].desc + ""; html += "" + range + ""; html += ""; } tbody.innerHTML = html; resultsDiv.style.display = "block"; }

Understanding Lactate Threshold Heart Rate (LTHR)

Lactate Threshold Heart Rate (LTHR) is arguably the most important metric for endurance athletes like cyclists, runners, and triathletes. Unlike the "220 minus age" formula, which is a generic estimate of maximum heart rate, LTHR is a personalized data point that represents the highest intensity you can maintain for a prolonged period (usually 60 minutes) before lactic acid begins to accumulate in your blood faster than your body can clear it.

Why Training by LTHR is Superior to Max HR

Maximum Heart Rate (MHR) is largely determined by genetics and age. It doesn't tell you much about your fitness level. LTHR, however, changes as you get fitter. As your aerobic capacity improves, you can sustain a higher heart rate for longer durations. Using Joe Friel's 7-zone system (which this calculator uses), you can target specific physiological adaptations more accurately than with generic Max HR zones.

How to Find Your LTHR: The 30-Minute Time Trial

To use this calculator, you first need to determine your LTHR through a field test. The most common method is the 30-minute solo time trial:

  1. Warm-up: 15 minutes of easy effort with a few short bursts.
  2. The Test: Perform a 30-minute all-out effort (as if it were a race). Maintain the highest steady effort you can sustain for the full duration.
  3. The Data: 10 minutes into the test, hit the "Lap" button on your heart rate monitor.
  4. The Result: Your average heart rate for the final 20 minutes of that 30-minute test is your estimated Lactate Threshold Heart Rate.

The 7 Training Zones Explained

The zones calculated above serve different purposes in a training plan:

  • Zone 1 (Recovery): Very light effort. Used for active recovery after hard sessions.
  • Zone 2 (Aerobic): This is your "all day" pace. It builds metabolic efficiency and heart strength.
  • Zone 3 (Tempo): A "comfortably hard" pace. Useful for building muscular endurance.
  • Zone 4 (Sub-Threshold): Just below your threshold. This is critical for increasing your LTHR.
  • Zone 5a (Super-Threshold): Pushing just beyond your limit. Often used for long intervals.
  • Zone 5b (VO2 Max): Extremely hard effort. Builds maximal oxygen uptake.
  • Zone 5c (Anaerobic): All-out sprints. Focused on power and speed.

Example Calculation

If an athlete performs the 30-minute test and their average heart rate for the final 20 minutes is 170 BPM, their zones would be:

  • Zone 2: 145 – 151 BPM (Fat burning and aerobic base)
  • Zone 4: 162 – 168 BPM (Threshold intervals)
  • Zone 5b: 175 – 180 BPM (VO2 Max training)

Note: You should re-test your LTHR every 8-12 weeks, as it will likely increase as your fitness improves, requiring you to adjust your training zones accordingly.

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