Five sports, one common foundation

Five different sports, one shared root: the measurable threshold as your compass, percentages as the structure.

Running, cycling, swimming, triathlon, and HYROX share a common foundation: pacing by percentage of a measurable threshold. The same logic — anchor your effort to a number you can actually test, not to how you feel — works across all five, with roots in Daniels (running), Coggan and Allen (cycling), and Friel (multi-sport). This article explains why that framework holds, where each sport applies it differently, and where the model breaks down.

The problem with feel-based pacing

Any experienced runner has lived the same scene: you start a race feeling strong from the gun, you feel extraordinary in the first few kilometers, you push the pace — and at kilometer 15 of a marathon, everything starts to fall apart. It's not a lack of training. It's poorly managed pacing.

The fundamental problem with feel-based pacing is that perceived effort is not a precise instrument. The Borg scale — the standard system for quantifying perceived effort — shows deviations of up to 15–20% between perceived and actual effort under competition conditions. Heat raises perceived exertion. Pre-race nerves distort it downward in the opening minutes. Caffeine suppresses it artificially. Accumulated fatigue from the days before drives it up.

Under those conditions, trusting how you feel is like calibrating a scale while staring at the sky. The instrument may be well built, but what affects it isn't the load — it's the external environment.

The solution isn't to ignore how you feel — it's still valuable information — but to anchor it to a measurable reference point that doesn't get distorted by how you feel on a given day. That's the role of the threshold.

What threshold effort means

The threshold is the maximum effort an athlete can sustain steadily over an extended period without irreversibly accumulating lactate. Above that threshold, the effort is — by definition — unsustainable; below it, it's manageable.

In each sport, the threshold has a concrete expression:

• Running: threshold pace, approximated to the race pace an athlete can hold for one hour at maximum effort. For intermediate runners, this corresponds to competitive half marathon pace.
• Cycling: FTP (Functional Threshold Power), defined as the average power a cyclist can hold for 60 minutes. In practice it's estimated with a 20-minute test multiplied by 0.95.
• Swimming: CSS (Critical Swim Speed), calculated as the difference between your 400 m and 200 m times divided by two. It represents critical aerobic velocity in the pool.
• Triathlon: each discipline maintains its own threshold. Load is distributed across all three: swimming accounts for 8–12% of total time; cycling, 50–55%; and running, 35–40%.
• HYROX: the model is different because the event combines aerobic running with functional strength stations. There's no single threshold — there's a target time per station and a target run pace, each planned independently.

Percentage-based pacing in practice

Once the threshold is defined, all training sessions and races are expressed as percentages of that reference value. The zone structure that emerges is consistent across all five sports:

The exact percentages vary slightly by sport. In cycling, the sweet spot zone — popularized by TrainerRoad — sits between 88 and 93% of FTP, slightly more conservative than running tempo. In swimming, pure CSS sets are worked at 100% of critical velocity in efforts of 50 to 200 m. But the structural logic holds: you define a threshold and you train at fractions of it.

This structure has one key property that makes planning easier: it scales. If you measured your FTP three months ago and measured it again today, the percentage increase is exactly the increase in your aerobic capacity. If your threshold pace dropped two seconds per kilometer, all your training zones adjust proportionally. The model scales with the athlete.

How training is structured in each sport

Running — where it all started (Jack Daniels and VDOT)

Percentage-of-threshold pacing in running has its formal roots in Jack Daniels' work — VDOT — and Matt Fitzgerald's 80/20 methodology. Daniels demonstrates that there's a consistent mathematical relationship between VO₂max, running economy, and times across different distances. That relationship allows you to take a known time at one distance and project precise equivalent times at every other distance.

The Splits run pace calculator uses that known time as an anchor point and generates target splits for training in each zone. The Daniels model is the source for the equivalence tables.

Full running methodology →

Cycling — power as the master metric

In cycling, power replaced pace as the primary metric twenty years ago. The reason is physical: pace varies with wind, gradient, and weight; power doesn't. Coggan and Allen formalized the FTP-based zone system that virtually every training platform uses today.

Coggan's zones range from 55% of FTP in Zone 1 to 150%+ in Zone 7 (anaerobic sprint). For most endurance cyclists, the relevant work sits between Zone 2 (endurance) and Zone 4 (threshold). The sweet spot, between 88 and 93%, maximizes aerobic adaptation per unit of accumulated fatigue.

Full cycling methodology →

Swimming — critical velocity as the reference

Swimming shares with cycling the advantage of being able to isolate the technical component from the metabolic one. A swimmer can be in metabolic Zone 2 but with poor technique, which degrades movement economy without the heart rate reflecting it.

CSS partially solves that problem because it's measured as velocity, not perception: if you swim 400 m in 6:00 and 200 m in 2:45, your CSS is 1:37.5/100m. All your threshold sets are planned around that number. When CSS improves, the training scales.

Full swimming methodology →

Triathlon — three thresholds, one race

Triathlon doesn't have a single threshold because it combines three sports with distinct mechanics. What it does have is a characteristic load distribution that periodization studies — Friel, Fitzgerald — document consistently: swimming concentrates the lowest time volume but demands the highest technical cost; cycling represents the largest accumulated energy load; and running is where pacing decides the final result.

Smart pacing in triathlon means managing each threshold independently, but with awareness of the cumulative effect. Coming out of the water at 105% of your CSS has a cost on the bike that you pay for on the final run leg.

Full triathlon methodology →

HYROX — stations + running, dual model

HYROX is the most recent of the five sports and the one that departs furthest from the pure aerobic threshold model. The format is fixed: eight kilometers of running alternating with eight functional strength stations. No variable distance. No open terrain.

The HYROX pacing model runs on two tracks: your run pace — planned as a percentage of your 1K threshold pace — and your station time, planned against the performance benchmarks for your division (Open, Pro, or Doubles) and your level. Both parameters are optimized independently but validated together against your target total time.

Full HYROX methodology →

Where the model breaks down

Percentage-of-threshold pacing has clear limits that are worth documenting.

Ultra-distance. Above 50 km in running or 150 km on the bike, aerobic power degrades along non-linear curves that the zone model doesn't predict well. In ultras, pacing is done by feel adjusted for conditions — altitude, heat, accumulated elevation gain — rather than by percentage of threshold.

Trail with significant gradient. Pace on a trail with 2,000 m of accumulated elevation gain can't be compared directly to track pace. Normalized graded pace — NGP — partially corrects this by adjusting your observed pace to its flat-ground equivalent, but the correction breaks down on gradients above 15%.

Very short events. Below five minutes of maximum duration (800 m in running, a one-kilometer time trial on the bike), the anaerobic component dominates the aerobic one. The VO₂max-based zone model loses resolution because the effort is out of range.

Extreme conditions. Heat shifts the perceived threshold downward by 5–15% depending on temperature. Altitude has similar effects. In those conditions, percentage-based pacing requires manual adjustment, or switching to power as the reference instead of pace.

Calculators by sport

Each sport has its own threshold metric and its own calculator. Start with the discipline you're training for right now.

Sources and references

• Jack Daniels — Daniels' Running Formula (Human Kinetics, 4th ed. 2014). https://en.wikipedia.org/wiki/VDOT
• Matt Fitzgerald — 80/20 Running (NAL Trade · 8020endurance.com). https://www.8020endurance.com
• Andrew Coggan & Hunter Allen — Functional Threshold Power (Wikipedia / Training and Racing with a Power Meter). https://en.wikipedia.org/wiki/Functional_threshold_power
• Phlex Swim Coaching Team — The Importance of Training Zones and How to Individualize Training (phlexswim.com). https://www.phlexswim.com/blog/the-importance-of-training-zones-and-how-to-individualize-training
• Joe Friel — Periodization of Intensity (Triathlete's Training Bible) (joefrieltraining.com). https://joefrieltraining.com/periodization-of-intensity/