How the adjustment works

Grade-Adjusted Pace (GAP) answers one question: if you'd spent the same energy running on flat ground, how fast would that pace have been? It uses the metabolic cost-of-running curve measured by Minetti et al. (2002), where the energy per metre at gradient i is C(i) = 155.4·i⁵ − 30.4·i⁴ − 43.3·i³ + 46.3·i² + 19.5·i + 3.6 J/kg/m. Each course is expanded into a high-resolution profile of ~480 points and the model integrates that cost over every one of those small segments — so the constant micro-undulation you see on a Garmin trace is actually priced in, not averaged away. Dividing raw pace by the resulting effort factor gives your GAP.

The Boston paradox

Here's the counter-intuitive part most calculators get wrong: on road gradients the metabolic penalty is small, and Boston is net downhill — so purely by oxygen cost it's about 1% easier than flat, not harder. Yet almost everyone runs Boston slower than a flat course. The reason isn't in your lungs, it's in your legs: the steep early descents cause eccentric muscle damage that wrecks your quads, and the Newton Hills arrive at 26–34 km, exactly when you're already cooked. Metabolic GAP can't see that, so the difficulty score above is a separate measure that folds in total climb, net-downhill damage, and where the hills fall.

Bottom line: GAP tells you what your effort was worth in oxygen terms; difficulty tells you why the clock still punished you.

How the profiles are built

Each profile combines a macro shape (where the real climbs and descents fall) with realistic high-frequency micro-undulation, tuned so the profile's total ascent equals the surveyed figure for that race. This deliberately avoids raw-GPS inflation: a watch might read 400–600 m on Boston because of sensor noise, but the calibrated profile sums to the true ≈248 m while still showing constant small ups and downs. The visible min/max reflect real course elevations; exact micro-placement is representative, not a survey.

Elevation data

Ascent figures compiled from findmymarathon, RunDida, worldmarathoner and official race material. Boston ≈248 m gain (net −140 m); NYC ≈294; Berlin ≈73; Chicago ≈57; London ≈127; Tokyo ≈60; Valencia ≈60; Sydney ≈317; Paris ≈180; Cape Town ≈260 (sources range 205–380 m; high point ~53 m near km 33; no official figure published); Warsaw 93 m (official 47th-edition profile, net-zero loop); Poznań ≈130 m (estimated — official sheet gives min 55 / max 95 m but no ascent sum). Descent is derived from gain and net elevation change.

Ascent figures compiled from official race material and findmymarathon / RunDida / worldmarathoner. Marathon majors use sourced gain figures; the two Warsaw shorter races use official/Garmin data (ING Biegnij Warszawo from the 2026 route profile; Bieg Powstania Warszawskiego 10 km shaped from a recorded run). Most other 1-mile to half-marathon courses are schematic — shaped to reflect each course's character (flat, rolling, bridge climbs, net-downhill) with an approximate gain, not a survey. GAP is a physiological estimate, not a race predictor; heat, wind, altitude, fitness and pacing move the clock more than terrain does.

What you're actually doing

Your team of five lines up at the track. One runner runs a single 400 m lap, hands over, and the next runs their lap — around and around for a full hour. The team that completes the most laps in 60 minutes wins. In practice each of you runs roughly 10–14 laps across the hour, and between your turns you get about four minutes of rest while the other four take theirs. That work-to-rest ratio — one lap hard, four laps' worth of standing — is the whole key to how you prepare.

Why it trains like intervals, not distance

A single hard 400 m sits right at the top of your aerobic ceiling and into the sprint range — it's a VO₂max-and-above effort, not a cruise. The long rest changes everything: in those ~4 minutes your muscles rebuild their stored energy (phosphocreatine — the "refill the tank" system) and clear fatigue, so the next lap can come back nearly as fast. The upshot is that you run each lap close to 3000 m effort — well quicker than 5K pace — and you close the final laps near mile pace. So the training currency isn't long easy miles; it's 400 m repeats with generous recovery (classic Daniels R/I-pace work), sitting on top of an easy aerobic base whose only job is to make that recovery faster. Train the laps for speed; train the easy runs to refill the tank between them.

The phases of the plan

1. Weeks 1–2 · foundationLearn the lap. If you're starting from scratch, run/walk until one continuous 400 m feels comfortable, and get used to running a few times a week. The goal here is consistency, not speed.
2. Early–mid · interval volumeBuild repeatable 400s. Run 400 m repeats at a controlled, comfortably-hard effort with long rests, and grow the number of laps you can repeat without falling apart.
3. Mid · specificityMatch the real spacing. Move toward the true ~1:4 rhythm — fewer, faster laps with full recovery — and add "broken" 400s to rehearse closing hard when tired.
4. Late · specific peakHit and hold target lap pace. Lock onto your goal lap time and hold it across a full rotation; start running relay simulations.
5. ~1 week out · dress rehearsalFull team run-through. Practise in race order: changeovers, the hand touch, and staying warm in the gap — so nothing on the day is new.
6. Final days · taper → raceArrive fresh. Cut the volume right down, keep a couple of short strides for sharpness, and turn up rested.

Why each session is there

• 400 m repeats — the race is literally repeated 400s, so this is pure specificity: it trains the exact pace judgement and leg turnover the event demands.
• Broken 400s & last-lap work — rehearse the anaerobic burn of pushing the final turns, when the laps are won or lost.
• Easy aerobic runs — the unglamorous engine. A bigger aerobic base clears fatigue and rebuilds energy faster in the four-minute gaps, so your laps still hold up in the last 15 minutes.
• Relay simulation — the only session that rehearses the real format: run a lap, rest ~4 min, go again. Do it with your team and the changeover becomes automatic.
• Strides — short, fast, easy accelerations that keep the legs quick and economical at almost no metabolic cost.

On the day

• Team order — spread your quickest runners through the rotation rather than bunching them, and give your steadiest, toughest runner the final slot for the last 10 minutes. Don't stack two of your slowest back-to-back.
• The changeover — agree one spot on the home straight for every exchange. The next runner stands ready 20–30 s early, already warm, and starts on a hand touch — no standing around at the line.
• The gap is not a cool-down — jog or walk for the first minute, put a layer on, then do a couple of strides and strip the layer before your turn. Never sit down; cold legs start the next lap flat.
• Pace each turn — run the first lap of each turn 2–3 s slower than target on purpose, keep the middle even, and push the last two turns. Going out too hard on lap one is the classic mistake.
• Warm-up & fuel — 10–15 min easy jog, drills and 4–6 strides before the start (skip static stretching). A small carb snack 30–60 min before, sips of water or isotonic between turns, and caffeine ~3 mg/kg about 45 min before if you use it. Nothing new on race day.