Aerobic Base Training Method Explained

Your weekly hours9h

Fits your week. Coherent from 0 to any number of hours a week.

Where the time goes

Compare with

By time; this method publishes no session count. The 3% above LT1 is the mandated race-pace rehearsal — the only work above the cap.

A representative week

Show the week for

Across all three sports.

Mon

Rest

Tue

Run 60 min, HR 135–14512 min ramp up, ~36 min in the band, 12 min ramp down. Flat or rolling. Walk the hills. Once a month this becomes the MAF Test: same warm-up, then 3 flat miles at exactly 145, splits recorded.

Swim 45 min techniqueDrills and steady 100s at the converted swim pace ceiling. Stroke rate and RPE are the controls; do not chase heart rate mid-set.

Wed

Bike 90 min at power ceilingHeld at or below the wattage from the 45-minute conversion ride. Flat route or trainer, cadence free. If the ceiling forces sub-100 W on a climb, spin it or reroute.

Thu

Run 50 min, HR 135–145Same construction as Tuesday, shorter: 12 min ramp up, ~26 min in the band, 12 min ramp down. No strides at the end — this method has no place to put them.

Swim 45 minContinuous or long-rest sets at the converted pace ceiling. Swim goes first when it shares a day with another sport.

Fri

Bike 60 min at power ceilingShort and genuinely easy. This is where drift, sleep debt or a hot afternoon shows up first, as a cap breach at lower power than usual — note it, do not push through it.

Sat

Bike 3 h at power ceilingThe volume session. Fuel it properly: the cap lowers carbohydrate cost per hour, but three hours still needs feeding. Flat to rolling — the ceiling is unexecutable on a mountainous route.

Sun

Run 80 min, HR 135–145Longest run of the week, still entirely inside the band. Expect a slower pace than Tuesday at the same heart rate; that is drift over duration, not a fitness problem.

What Tuesday looks like

Run 60 minutes with every beat between 135 and 145 bpm. For a 35-year-old in the 0 category the cap is 145 and the band is cap−10 to cap, so 135–145 is the whole session. Twelve minutes ramping up from around 115, roughly 36 minutes held inside the band, twelve minutes ramping back down. Flat or gently rolling route. Walk the hills. If heart rate touches 146 you slow until it comes back, and in the first fortnight that will sometimes mean walking on the flat. No strides, no pickups, no finishing surge. Nothing else that day beyond an optional 45-minute technique swim at the converted swim pace ceiling. Once a month this Tuesday becomes the MAF Test instead: same warm-up, then three miles on a flat track at exactly 145, splits recorded individually.

Signature sessions

There are no named workouts. That is the defining feature — this method produces duration-and-cap prescriptions, not interval structures. A "long run" here is simply a longer session inside the same band. Four things do have real structure.

THE MAF TEST (the method's only signature session, and its entire feedback loop). Twelve to fifteen minutes progressive warm-up. Then three miles on a flat 400 m track at exactly the cap — this is the one time the athlete sits on the ceiling rather than under it. Record each mile split separately. Successive splits should get slightly slower; that is normal. The first split must be the fastest, and if it is not, the warm-up was too short. Control shoes, course, time of day and weather: heat and dehydration produce cardiac drift that reads as a false loss of fitness. Maffetone's own instruction is to test monthly. Faster pace at the same heart rate is aerobic improvement. A plateau or regression means back off, re-check the formula category, or look at sleep, diet and life stress — within this method it is never a signal to add intensity. Three consecutive months without measurable improvement is his own instruction to extend the aerobic period rather than exit it, so Form extends toward the 16-week ceiling instead of ending on the named date. If the test still has not moved at 16 weeks, the block ends and the finding gets discussed, because a cap that has produced nothing in four months is not what is limiting this athlete.

THE BIKE CONVERSION (week one, and not optional). Ride 45 minutes at the bike heart-rate ceiling and record average power. That wattage is the ceiling from then on. Power survives cardiac drift, heat and fatigue in a way heart rate does not, and it is the only thing that makes the cap executable in a Queensland summer. Use %FTP as a sanity check only, never as the prescription: a derived ceiling landing far outside roughly 55–75% of FTP means re-measure rather than accept. For the reference athlete at 250 W FTP that is a 140–185 W region. Maffetone's own bike test is a fixed flat or stationary course taking about 30 minutes, scored by elapsed time or speed — the average-power version is a sensible modern adaptation, not his.

THE SWIM CONVERSION. One swim at the swim heart-rate ceiling over a fixed distance, heart rate taken on the wall, converted into a pace band per 100 m. Prescribe that pace thereafter, with stroke rate and RPE as the in-session control; heart rate is unusable mid-set. The commonly quoted CSS + 8–12 s/100 m has no source behind it — for the reference athlete with CSS 1:40 that would be 1:48–1:52, and it is illustrative only. Measure it.

RACE-PACE REHEARSAL (mandatory inside 10 weeks of a 70.3 or Ironman, and it breaks the cap on purpose). Bike 3 × 20 min at goal race power off 5 min easy, then 20 minutes running at goal race pace off the bike. Once every 10–14 days. It is the only hard session in the block and counts as one of the whole-athlete two to three for that week, which leaves room to spare. This exists because a competitive age-grouper's 70.3 bike power sits above the cap, and many athletes' Ironman race heart rate is at or slightly above it. Without it, the athlete arrives at an intensity they have never trained.

Who it suits

Athletes who run their easy days too hard. This is the most common error in endurance training and the one thing this method is genuinely excellent at fixing — it removes the judgement call entirely and replaces it with a number.

Also: injury-prone runners, and athletes coming back from injury, illness or a long layoff; athletes showing signs of overreaching — stalled performance, poor sleep, recurrent infections, elevated resting heart rate; beginners and returners with no aerobic base and no tissue tolerance for intensity; time-poor athletes with high life stress, where training intensity and life stress draw on the same recovery budget; masters athletes; long-course and ultra athletes whose race intensity genuinely sits near the cap; anyone with a clinically imposed heart-rate ceiling; and any athlete deep in an off-season block with a long way to go before a race.

The honest version of who this suits: someone whose problem is that they cannot go easy, not someone whose problem is that they are not fast enough.

Not for you if

Do not run this block inside 8–12 weeks of a race that depends on top-end speed — draft-legal sprint or Olympic triathlon, 5 km to 10 km running, criterium racing. There is no mechanism in the method for developing those qualities.

Do not use the formula at all with beta-blockers, atrial fibrillation, a pacemaker, POTS, thyroid dysfunction, or any condition that decouples heart rate from metabolic intensity. The number is meaningless there.

Two failure modes turn on the athlete's own physiology, and both need checking against a known HRmax or a field threshold test before the cap is trusted. If true LT1 sits well above 180 minus age, the cap prescribes a permanently sub-stimulus intensity and produces real loss of durability and speed while the athlete believes they are building base. The mirror case — a low HRmax for age, or a high resting heart rate — puts the cap at or above LT2, so the athlete does daily threshold work believing it is easy.

Also unsuitable: wrist optical heart rate alone (cadence lock and lag produce both false breaches and false compliance — this needs a chest strap); sustained training in significant heat, humidity or at altitude, where cardiac drift collapses the prescribed pace to walking; and hilly-only terrain with no option to walk.

Below about 4 h/week, intensity is usually the only realistic stimulus and the MAF Test has too little to work with. That is a caution rather than a gate — this method has no volume floor, and Form will write the block at any volume, while saying what the low-volume version costs.

Combination limits: this option blocks the Reverse overlay outright — Reverse front-loads intensity, which is exactly what the block forbids — and blocks Blocks, because there is no intensity to concentrate. It fits Base → Build → Peak as the base phase only, and fits a Repeating Week for the duration of the block.

In a triathlon week

Per-discipline caps are mandatory. This does not transfer as a single number, and one cap across three sports is the standard botch.

Heart rate at a given metabolic intensity is lower in the water and slightly lower on the bike. The direction is solid, and Allen states it himself — running has to go a little higher than cycling for the same effect, and cycling a little higher than swimming. The magnitudes are smaller and far more variable than the numbers usually quoted. The best modern measurement, in 12 elite swimmers, found swim HRmax 193.6 ± 7.5 against run 199.8 ± 7.7 — 6.7 ± 5.3 bpm lower, p = 0.015 — and swim against cycling only 5.7 ± 6.5 bpm lower, not statistically significant. The often-repeated 15 bpm figure comes from 1970s research in children. Those authors explicitly advise against a fixed correction factor and recommend testing each swimmer individually, because the standard deviation is nearly as large as the mean. A runner-versus-cyclist comparison found about 2 bpm, not 5.

So: run applies the heart rate directly — it is the discipline the formula was built around, and where the cap is most often violated. Bike is cap minus 0 to 5 bpm, and the conversion to a power ceiling is mandatory rather than an improvement: one 45-minute ride at bike cap heart rate, record average power, prescribe watts thereafter. Power survives drift, heat and fatigue; heart rate does not. Swim is cap minus 5 to 10 bpm, converted once to a pace band per 100 m, because heart rate is unusable mid-set. Treat all three offsets as provisional starting estimates that the conversion tests then replace.

Where it fits in a season: as an off-season or general preparation block of 8–16 weeks, and thereafter as a permanent rule governing the easy portion of the week. For a triathlete carrying three sports' worth of load, capping all the easy work is often the only way to raise total volume without breaking.

Where it does not fit: inside a 70.3 or Ironman race-specific block. A competitive age-grouper's 70.3 bike power is above the cap, and even Ironman race heart rate is at or slightly above it for many athletes. Inside 10 weeks of either race, Form schedules race-pace rehearsal regardless of the selection — otherwise race day is an untested intensity.

A useful middle path Form will offer: keep the cap on every run all season, which protects the discipline that breaks, and periodise the bike and swim normally. That is a hybrid rather than this option, and it does not unlock anything — with Aerobic Base selected, Reverse and Blocks stay blocked, because the block itself cannot start with intensity or concentrate intensity it does not have.

What the evidence says

Supported, though none of it is unique to this method. The general case for a large majority of low-intensity training is strong and comes from the polarised and pyramidal literature rather than from Maffetone — elite distance runners cover 160–220 km/week (marathon) or 130–190 km/week (track), across 11–14 sessions a week, with at least 80% of total running volume at low intensity. Speed or power at a fixed submaximal heart rate is a legitimate, well-validated performance surrogate, so the MAF Test is a reasonable field test on its own terms. And reducing the intensity of easy sessions genuinely lowers carbohydrate cost and recovery demand.

Weak or unvalidated, and this is the part athletes are not told. The 180 formula has no validation study. The only peer-reviewed articulation by the originators — Maffetone and Laursen, Frontiers in Physiology 2020 — is explicitly a "Hypothesis and Theory" article. It states that neither the 220- nor the 180-formula replaces laboratory testing for VT1, aerobic threshold, FATmax or maximal fat oxidation, and that the claimed relationships must be verified scientifically. The strongest supporting data offered is an uncontrolled clinical series: 223 experienced runners trained at or below the cap for three to six months, of whom 170 improved their 5 km.

The formula also carries a systematic age bias. Against the best meta-analytic estimate of maximum heart rate — 208 minus 0.7 × age, from 351 studies and 18,712 subjects, cross-validated in 514 — a 25-year-old's cap of 155 is about 82% of predicted HRmax, while a 55-year-old's cap of 125 is about 74%. Whether the cap lands below LT1, on it, or above it is therefore partly an artefact of the athlete's date of birth. This is a cross-sectional problem, not a claim that the cap should drop a beat a year; Maffetone rejects annual decrements explicitly.

Fixed anchors are imprecise in general. In 165 recreational runners, heart-rate-based fixed anchors estimated LT1 with a mean absolute error of 4.9–7.4 bpm, against 0.6–0.8 km/h for speed-based anchors — speed outperformed heart rate. The same study found women had higher relative heart rate, VO2 and speed at LT1 than men, and concluded that sex-specific intensity anchors are needed. That is a second axis on which one age-only number is systematically biased.

Contested and lore. The fat-burning framing is the weakest part of the case: FATmax ranges from 22.6% to 88.8% of VO2max across 1,121 athletes, which undermines the idea that a single age-based number locates it, and high-carbohydrate fuelling outperforms fat-emphasis fuelling at race intensity anyway. The plateau critique is real and widely reported — athletes training only below LT1 lose neuromuscular and biomechanical stimulus and can fade or cramp when they try to race hard, which is consistent with Allen's own trajectory of fast gains for about three years and then a plateau. Also lore: the four-month transformation story, and the idea that a traditional aerobic base phase meant capped easy running only.

The bottom line Form works from: the principle is defensible — make easy genuinely easy, and track pace at a fixed heart rate. The formula is a rough heuristic with a known bias, and belongs in a plan as a starting estimate to be corrected against a measured threshold or against the athlete's own test trend. It is not a physiological fact and Form will not present it as one.

How it goes wrong

The Mark Allen story. The repeated claim is that Allen went from 8:15/mile to 5:20/mile at 155 bpm in four months. His own account is roughly 8:45/mile at the start, reaching about 5:20/mile at that heart rate over about three years, after which he plateaued. Form must never quote the four-month version: it sets an expectation nobody meets, and it is why athletes abandon this at week ten. Allen also describes the base period as age-dependent — a 20-to-24-year-old might plateau aerobically in one or two months, while an older athlete might keep getting faster for three, four or five months.

Quoting the 90-day "100 percent aerobic" block as the general prescription. Maffetone scopes it verbatim to anyone who is chronically ill, injured or overtrained — it is the compromised-athlete protocol. For everyone else he names no calendar length at all, only the test-based exit. The 8–16 week box is Form's, and the coach should say so rather than attribute it to him.

Treating it as permanent. Maffetone's own post-base position is roughly 80% aerobic / 20% anaerobic year-round. The zero-intensity-forever reading is a community invention.

One cap across three sports. This is the adaptation most often botched, and it is specific to triathlon.

Running at the cap instead of under it. The cap is the top of a ten-beat band.

Blaming the formula when the diet is the problem. His own line is that for those who try the formula without success, it is usually the diet at fault rather than the formula — which is why poor eating subtracts 20 beats before anyone argues about the number.

Guessing the +5 category upward. It requires all four of: more than two years without physical, biochemical or mental-emotional injury; measurable progress in competition; not overfat by waist-to-height; and an improving MAF Test. Maffetone's own line is that most people do not qualify, and his tie-break is to subtract 10 when in doubt.

Recomputing the cap every birthday. Maffetone explicitly rejects an annual one-beat decrement: because the athlete has progressed, the cap does not need reducing by 1 and can stay the same, and over five years a 2–3 beat reduction is typical — and only for those still improving. He runs it the other way too: if pace plateaus or injuries appear, drop the cap back to the rate that allowed progress. Store the number and revise it against the test.

Cross-checking against a Mark Allen calculator and getting a different answer. Allen's published formula is not Maffetone's: his +5 needs only four sessions a week for one year, and he adds 5 for anyone under 25 or over 55 — a rule with no counterpart in Maffetone, whose under-16 case is a fixed 165 and whose over-65 allowance of up to 10 beats applies only to the top category and is explicitly not automatic. The two can differ by 5–10 bpm on the same athlete. Form implements Maffetone's.

Comparing MAF Tests across different courses, surfaces or temperatures, and reading heat-driven cardiac drift as lost fitness.

Reading a test plateau as "time to add speedwork". Inside this method it means the opposite.

Racing at the cap. It is a training ceiling, not a race intensity. For a mid-pack Ironman athlete the two can coincidentally land close together, which causes more confusion rather than less.

Skipping the warm-up and cool-down ramps. Maffetone treats them as part of the method, not padding.

Assuming "aerobic base" historically meant this. It did not. Lydiard's conditioning phase — the block this option borrows its name from — ran about 69% of weekly distance at quarter effort, 22% at half effort and 10% at three-quarter effort, with a weekly steady-state run at roughly marathon effort, and he described it as 70–100% of maximum aerobic effort and explicitly not Long Slow Distance. A heart-rate-capped block is considerably stricter than the tradition it is named after. Note also that his effort scale runs the opposite way to how it is usually quoted: three-quarter effort is the hard steady run, quarter effort is the easy one. His base was also a phase inside a structure — in the Lydiard-branded 28-week plan, 12 weeks base, 8 weeks hills and speed development, 6 weeks sharpening, then 10 days taper — which is the strongest argument for time-boxing this option rather than letting it run.

Sources: philmaffetone.com philmaffetone.com philmaffetone.com philmaffetone.com frontiersin.org jacc.org pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov extramilest.com 3-fitness.com bobhodge.us championseverywhere.com runnersworld.com lydiardfoundation.org pmc.ncbi.nlm.nih.gov