Back Muscles

What muscles make up your back?

Eight, as far as BackMaxx is concerned. That is not the anatomical count — the back layers up dozens of muscles, most of them buried or too small to read in a photograph. The eight below are the ones a single back photo can distinguish and a training plan can actually change.

Read the right-hand column as a map of what the corpus can reach, not as a ranking of importance. The Lats are tagged to 38 of 77 movements because almost every pull touches them. The Infraspinatus is tagged to 8 because very few movements ask the shoulder to rotate under light load.

The eight, one at a time

Lats — Latissimus dorsi. The largest single muscle here, running from the armpit down to the lower back and across to the spine. It is the width itself: everything people mean by a V-taper is lat mass seen from behind. It needs a full stretch at the top of every rep and a long range, which is why vertical pulling comes first and rows come second. Thirty-eight movements are tagged to it, 20 of them hangs, pull-ups or pulldowns.

Teres Major — Teres major. A short muscle above the lat, running from the outer edge of the shoulder blade to the upper arm. Visually it is the small bulge just under the armpit, and it is the reason two backs with the same lat length can taper differently. Every one of its 17 tagged movements drives the elbow down and back: pull-ups, chin-ups, pulldowns, straight-arm pulldowns. There is not a single row on the list.

Rhomboids — Rhomboid major & minor. They sit between the shoulder blades and pull them toward the spine, which is exactly what you see as mid-back thickness and the ridge down the centre. They grow from rowing where the blades actually meet and pause at the top, so retraction comes first and load second. Fifteen of the 22 movements tagged to them are rows.

Lower Traps — Trapezius (mid & lower). The wide, flat sheet under the upper traps, pulling the shoulder blades down and in. It is the muscle that makes an upper back read broad from behind rather than bunched up around the neck. Light prone work beats heavy pulling here — Prone Y raises, reverse snow angels, scapular pull-ups. Eighteen movements carry the tag, and about half of them need nothing but a floor, which is why the Lower Traps page is the one most people should read first.

Upper Traps — Trapezius (upper). The slope from the base of the skull out to the shoulder. It responds to heavy, simple loading and to time under tension more than to rep count. Its list is short and blunt: of the 12 movements tagged to it, four are deadlift variants, three are shrugs and one is a farmer carry.

Rear Delts — Posterior deltoid. The back third of the shoulder, and the detail that finishes an outline when you are photographed from behind. Small muscle, high frequency: light weight, strict form, and more sets than you would guess. Sixteen movements are tagged to it, though only eight of them lead the Rear Delts zone — the rest pick it up while doing something else.

Infraspinatus — Infraspinatus & teres minor. A flat plate covering the lower two-thirds of the shoulder blade, visible as separation once a back is lean. It trains as a rotator rather than a puller, so it lives on face pulls and external rotation at loads that never feel heavy. Its eight tagged movements are the shortest list in the corpus: six fly or face-pull variants, plus arm circles and a cross-body shoulder stretch.

Erectors — Erector spinae. The two columns running either side of the spine from the pelvis up. Developed, they read as the Christmas tree, and they are the base every heavy pull is built on. Hinge patterns and holds train them, and they recover slowly, so two hard sessions a week is plenty. Eleven of their 23 tagged movements are loaded hinges — five deadlift variants and six Romanian deadlift variants.

How do eight muscles become six zones?

The zones are what your Back Score reports. Each is a bundle of muscles that move together and read as one shape in a photo.

Upper Back is the crowded one. Three muscles feed it because thickness arrives from three directions — the rhomboids pulling the blades together, the lower traps setting them down, and the infraspinatus filling the plate between them. A low Upper Back score tells you the region is behind but not which of the three is; that is what the per-muscle scores are for.

Traps, Rear Delts and Lower Back map one muscle to one zone, which makes them the easiest scores to act on. If Traps comes back low, there is nothing to interpret. Upper Traps is behind, and the eight movements that lead the Traps zone are the whole answer.

Lat Width bundles two muscles that are trained by the same movements, so it behaves like a single-muscle zone in practice. What separates the two is grip width and arm path, not exercise selection.

Why Symmetry has no muscle behind it

Symmetry is a comparison, not a tissue. It scores how closely the left side of your back matches the right across the other five zones, which means no muscle can be assigned to it and no movement can lead it.

Eight movements carry Symmetry as a secondary tag, and the pattern is exact: every one of them is loaded on one side or resists rotation. The one-arm dumbbell row, single-arm cable row, kettlebell single-arm row, Meadows row, commando pull-up, landmine Romanian deadlift, single-leg Romanian deadlift and bird dog. Nothing bilateral qualifies, because a bar held in both hands lets the stronger side take over.

Which exercises train which muscle?

The overlap is the useful part. Because the lats sit on 38 of 77 movements, width is the one thing you will train by accident — almost any back session moves it. The other seven have to be chosen on purpose. That is why a plan built from your weakest zone rather than your favourite movements changes the shape faster, and why the four-week Thickness Block puts horizontal pulling in the lead slot instead of leaving it to chance.

The short lists deserve attention for the opposite reason. Eight movements for the infraspinatus and 12 for the upper traps means there is no hiding: if you skip face pulls and shrugs, those two go untrained for months. The back zones guide walks through how the six scores relate to each other once you have a scan to read.

What the per-muscle scores are, and what they are not

BackMaxx estimates all eight from one photograph of your back. An AI vision model reads shape, width, separation and left-right balance, then returns a 0–100 Back Score, a rank from Newbie to GOAT, six zone scores and eight muscle scores.

They are visual estimates for training motivation. They describe how developed each region looks in the photo you took, at that angle, in that light. They are not anatomical measurements of anything, and the model does not claim to see under your skin.

That is also why the weekly re-scan matters more than any single number. One photo tells you which of the eight is furthest behind. Twelve photos over twelve weeks tell you whether the work moved it.

Get your Back Score first

Everything here works better when you know which zone is actually behind. One photo tells you.

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