The Relationship Graph

Every exercise in the catalog is connected to others by curated relationships. This graph is what turns a flat list of 157 exercises into something you can reason about — "what can I do instead", "what comes next", "am I training this evenly". The V2 endpoints (substitutes, coverage, progression paths) all read this graph. This page explains what the edges mean before you use them.

Three kinds of edge

Each exercise carries three relationship lists, returned together by GET /exercises/{id}/related and individually by the /variations, /progressions, and /regressions endpoints.

Relationship	Meaning	Direction
Variation	A peer — the same movement done a different way (equipment, grip, angle) at broadly the same difficulty.	Symmetric
Progression	A harder movement that builds on this one — the next step up.	Directed (easier → harder)
Regression	An easier movement that leads up to this one — the step down.	Directed (harder → easier)

A variation is a sideways move; a progression is a step up a ladder. Both matter, and they are not interchangeable. dumbbell-bench-press is a variation of barbell-bench-press (peer, swap the implement). push-up is a regression of dumbbell-bench-press (genuinely easier, a rung down). Mixing the two is the most common modelling mistake, and this catalog is curated specifically to avoid it.

The edges are curated and reciprocal

These relationships are not computed from tags or muscle overlap. Each one is reviewed by a human, because "shares a muscle and is harder" produces nonsense — a barbell curl shares the biceps with a chin-up and is technically easier, but a curl is not a step toward a pull-up. The graph only contains edges that are the same movement, one honest step apart.

Two guarantees follow from that curation:

• Relationships are reciprocal. If A lists B as a variation, B lists A back. If A progresses to B, then B regresses to A. You never have to reconcile a one-sided edge.
• Empty is honest, not missing. Many exercises — most isolation and accessory movements — have no progression or regression, and that is correct. A cable lateral raise is a peer of other raises, not a rung on a ladder. An empty list means "there is genuinely no such relationship", not "we haven't filled it in".

Summaries, not details

Relationship endpoints return summaries (id, slug, name, difficulty, movementPattern, tags, …), not full detail records. Fetch the full record with GET /exercises/{id} when you need instructions or programming data. See the overview for the summary-vs-detail split.

The progression ladder

Progressions and regressions form directed ladders — chains of increasing difficulty within a single movement family. The push-up ladder, for example:

knee-push-up → incline-push-up → push-up → decline-push-up → dip

Each arrow is one reviewed step. Ladders branch (an exercise can progress to more than one harder movement) and different families are separate ladders — the barbell-squat line and the pistol-squat line don't connect, because progressing from one to the other isn't a real training step.

This ladder structure is what progression pathfinding walks: given a start and a goal in the same family, it returns the ordered chain between them.

Not every pair is connected

Because ladders are per-family and directed, plenty of exercise pairs have no path between them — they're on different ladders, or you asked to go down one (progressions only point up). That's a real answer, not an error. The pathfinding guide covers how the API reports it.

Where to go next

• Finding substitutes — variations filtered by the equipment a user actually has.
• Building a progression — walk the ladder from where a user is to where they want to be.
• Analyzing coverage — what a set of exercises trains, and where it's unbalanced.