Intensity Distribution Calculator

Training intensity distribution describes how an athlete divides total weekly volume across three primary effort zones: easy, moderate, and hard. Rather than training at a single steady pace every session, structured endurance athletes deliberately mix intensity levels to maximize physiological adaptation while managing fatigue and injury risk.

The concept emerged from sports science research showing that elite endurance athletes rarely train at medium or "grey zone" intensities. Instead, they spend a large majority of their mileage at low aerobic effort and a smaller but targeted portion at high intensity. This intensity distribution calculator helps you apply that same principle to your own training by computing exact kilometer targets and estimated time in each zone based on your weekly mileage and chosen philosophy.

Understanding intensity distribution is especially valuable when you are preparing for a goal race, rebuilding after injury, or transitioning between training cycles. By knowing precisely how many kilometers to run easy versus hard, you avoid the common mistake of doing too much moderate-intensity work, which accumulates fatigue without delivering the full benefit of either low-intensity base building or high-intensity neuromuscular stimulus.

This calculator supports four widely studied distribution models: polarized, pyramidal, threshold-focused, and traditional. Each model assigns a fixed percentage to easy, moderate, and hard efforts. The calculator then multiplies those percentages by your weekly mileage to give you concrete targets, and estimates weekly training hours using average paces of 6.5 min/km for easy running, 5.5 min/km for moderate running, and 4.5 min/km for hard running.

Using the intensity distribution calculator takes only a few seconds. Set your weekly mileage using the slider (range: 20–150 km), select your training philosophy from the dropdown, and enter your maximum heart rate using the second slider (range: 150–220 bpm). The calculator instantly displays your easy, moderate, and hard kilometer allocations, the corresponding estimated training hours for the week, and your five heart rate zones derived from your max HR.

The Weekly Mileage input is your total planned distance for the week in kilometres. Use a typical week's mileage, not your peak week or a recovery week, unless you are specifically planning for one of those.

The Training Philosophy dropdown lets you choose from polarized (80/5/15), pyramidal (75/15/10), threshold-focused (65/25/10), or traditional (70/20/10) models. Each number represents the percentage of total mileage devoted to easy, moderate, and hard running respectively. Select the model that matches your coaching approach or experiment with different philosophies to see how your weekly structure changes.

The Max Heart Rate slider sets your personal maximum heart rate in beats per minute. The calculator uses this value to compute your five heart rate training zones, which range from Recovery (50–60% of max HR) up through VO2max (90–100% of max HR). These zones tell you the exact BPM ranges to target during each type of session.

Once you have your distribution, plan your weekly schedule so that your long run, easy runs, and recovery jogs together account for the easy kilometer target, your tempo or cruise intervals account for the moderate target, and your intervals or race-pace sessions account for the hard target.

Each of the four models in this calculator reflects a distinct training philosophy backed by exercise science literature.

Polarized (80/5/15): The polarized model keeps 80% of mileage at easy aerobic effort (Zones 1–2), just 5% at moderate intensity (Zone 3), and 15% at hard effort (Zones 4–5). Research by Norwegian sports scientist Stephen Seiler found that elite cross-country skiers, cyclists, rowers, and runners naturally gravitate toward this distribution. The logic is physiological: Zone 3 moderate running is hard enough to produce significant fatigue but not intense enough to drive the same VO2max adaptation as Zone 4–5 work. By minimizing Zone 3 and investing those "training dollars" in either easy aerobic base or high-intensity sessions, athletes get a cleaner stimulus-recovery cycle.

Pyramidal (75/15/10): The pyramidal model allocates 75% easy, 15% moderate, and 10% hard. It is the most common distribution seen in national-level distance runners who include a meaningful amount of threshold and tempo work but still prioritise easy mileage. The shape mirrors a pyramid: high volume at the base, decreasing as intensity rises.

Threshold-Focused (65/25/10): This model reduces easy mileage to 65% and increases moderate (lactate threshold) work to 25%, keeping hard effort at 10%. It is popular in programs that emphasise tempo runs, marathon-pace long runs, and lactate threshold intervals. Athletes who respond well to sustained aerobic efforts often thrive here, but it demands greater recovery capacity.

Traditional (70/20/10): The traditional model sits between pyramidal and threshold-focused at 70% easy, 20% moderate, and 10% hard. This is a practical default for recreational runners following coach-written plans that include one tempo run, one interval session, and the remainder as easy or long runs each week.

The calculator maps intensity zones onto five heart rate bands derived from your maximum heart rate. Each zone corresponds to a physiological state and a training purpose.

Zone 1 — Recovery (50–60% of max HR): Used for active recovery runs, warm-ups, and cool-downs. Effort is conversational and fully aerobic. At a max HR of 185 bpm this zone spans 93–111 bpm.

Zone 2 — Easy Aerobic (60–70% of max HR): The engine room of endurance training. Zone 2 runs develop mitochondrial density, fat oxidation, and aerobic base without meaningful fatigue accumulation. Together with Zone 1 these efforts make up the easy allocation in the intensity distribution calculator.

Zone 3 — Moderate (70–80% of max HR): Often called the "grey zone," this is the intensity that many recreational runners spend too much time in. It is harder than easy but not hard enough to drive the same performance gains as Zone 4–5 intervals. The moderate allocation in this calculator captures all Zone 3 running.

Zone 4 — Threshold (80–90% of max HR): Running near lactate threshold. Breathing is controlled but laboured. Classic threshold workouts — tempo runs, cruise intervals — live here. This is part of the hard allocation.

Zone 5 — VO2max (90–100% of max HR): Short intervals at maximum aerobic capacity. These sessions are highly demanding and require ample recovery. Together with Zone 4, Zone 5 forms the hard percentage in every distribution model.

Heart rate zone boundaries are calculated as follows: minHR = round(maxHR × minPct / 100) and maxHR_zone = round(maxHR × maxPct / 100). For example, with maxHR = 185: Zone 3 lower bound = round(185 × 0.70) = 130 bpm, upper bound = round(185 × 0.80) = 148 bpm.

Beyond kilometer targets, this calculator estimates how long each intensity block will take in hours. The time estimates use fixed average paces for each effort level: 6.5 min/km for easy running, 5.5 min/km for moderate running, and 4.5 min/km for hard running.

The formulas are: easyTime (hours) = easyKm × 6.5 / 60, moderateTime (hours) = moderateKm × 5.5 / 60, hardTime (hours) = hardKm × 4.5 / 60. Total weekly training time is the sum of these three values.

These paces are approximations designed to give a realistic time budget. A slower runner will spend more hours on the same kilometer total; a faster runner will spend fewer. If your actual easy pace differs significantly from 6.5 min/km, scale the displayed hours proportionally to get a more accurate time estimate for your individual fitness level.

Time estimates are useful for planning your weekly schedule. If total time exceeds your available training hours, reduce weekly mileage until the numbers are realistic. Conversely, if you know you can train for a certain number of hours per week, you can work backwards to find the right mileage target for your chosen distribution model.

Understanding your time commitment also helps with race-specific preparation. Marathon training plans often specify sessions by time rather than distance, particularly for long runs. Knowing that your polarized 80 km week requires roughly 8–9 hours of running helps you block out calendar time and arrange recovery days appropriately.

Selecting the right intensity distribution model depends on your experience level, current fitness, race goal, and training history. There is no universally superior model; research supports gains across all four approaches when applied consistently and matched to athlete needs.

Beginners and runners returning from injury generally benefit from the traditional (70/20/10) or pyramidal (75/15/10) model. These provide enough moderate-intensity stimulus to build fitness without the sharp intensity spikes that can cause injury in undertrained muscles and tendons.

Intermediate runners targeting half marathon or marathon PRs often do well with the threshold-focused (65/25/10) model during the race-specific phase of training. The elevated moderate percentage supports sustained marathon-pace adaptation and lactate threshold improvement.

Well-trained runners and athletes with high weekly volume (70+ km/week) tend to respond best to the polarized (80/5/15) model. At high volume, the recovery demands of moderate training accumulate rapidly. Polarized training sidesteps this by concentrating hard work into a small number of high-quality sessions while keeping the bulk of mileage truly easy.

You can also periodise your distribution model, using a more polarized approach during base-building phases and shifting toward a pyramidal or threshold distribution as your race approaches. Many elite coaching systems follow exactly this pattern.