Methodology
The math behind your numbers
Every chart, target and suggestion in Shojin is computed by formulas you can read on this page. Nothing is a black box, and where the evidence is soft we say so instead of pretending it isn’t.
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What counts as a set
A working set is one hard set taken reasonably close to failure — the kind that asks the muscle to adapt. Warm-ups don’t count, and neither do sets you started but didn’t finish. When Shojin says you did “12 sets of back this week,” it means 12 real working sets. Mixed kg/lb history is normalized before anything is added up.
Each set counts fully toward the muscle an exercise primarily trains, and a fraction toward the muscles that assist. A flat ½ for every helper is too blunt — on a deadlift, the hamstrings and glutes are the lift — so Shojin grades contributions from EMG research:
1.00 prime mover bench press → chest
0.75 co-prime deadlift → hamstrings, glutes
0.50 clear secondary bench press → shoulders, triceps
0.25 stabiliser bench press → core
A bench press is a full set of chest, half a set each of shoulders and triceps, and a quarter-set of core.
The progression engine
Under every exercise in the logger, Shojin suggests your next load. The baseline is the heaviest working sets of your last session — warm-ups and drop sets never drive progression — and the verdict follows three rules, keyed on RPE, where an unlogged RPE counts as “had more in the tank”.
The rules
Three rules, no black box
- top-set RPE ≤ 8 → add one equipment increment
- RPE 9–10 → hold the weight, consolidate
- reps down at the same weight, two hard sessions → deload ~5%
Increments follow the equipment: barbell, machine and cable 2.5 kg · dumbbell 2 kg · 5 lb in pound mode. Timed movements progress by +10 s; unweighted bodyweight movements by +1 rep.
Stall detection uses the same verdicts with a deliberately high bar: a lift is flagged only after two consecutive non-increase sessions, and only for lifts trained in the last 45 days. One rough day never flags anything.
Try it — last session’s top set
80 kg × 5barbell bench
How hard was it?
2 reps left in the tank
Next session
Go up · 82.5 kg
top-set RPE ≤ 8 → add one barbell increment (+2.5 kg)
This demo runs the same suggestNextLoad() function the app ships — it can’t drift from the product.
Estimated one-rep max
Strength charts need a common currency across rep ranges — 100 kg × 5 and 110 kg × 2 are both progress, but you can’t plot them on one line raw. The standard answer is an estimated one-rep max. Shojin computes three published formulas and plots their average, because each skews differently across rep ranges and the blend is steadier than any single one.
Try it — the formulas the charts use
A single at r = 1 is just the weight. Past ~12 reps all three formulas drift from reality — Shojin still plots the blend, but treat high-rep estimates as a rough guide, not a max attempt plan.
Weekly volume targets
Progress → Weekly sets shows each muscle against a target like 12/16. The model is a floor and a ceiling, borrowed from the volume-landmark framework: below the floor a muscle gets too little stimulus to grow; far above the ceiling, extra sets mostly buy fatigue. Anywhere inside the band is productive training.
The design rule that governs everything: the floor is sacred. Personalization only ever moves the ceiling. Shojin will never tell you to do less than the minimum that works — at worst it narrows the band to “just hit your minimum,” which is exactly the right message on a busy week.
Baseline bands — working sets per week (MEV → MAV)
Rendered from the app’s source constants. Legs and arms also split into per-muscle bands (quads, hamstrings, glutes, calves, biceps, triceps) at their own landmarks — a healthy “legs” total can’t hide starved hamstrings.
Four things you tell Shojin, or that it learns, scale your ceiling:
Goal
Building muscle keeps the full band; strength, fat loss and consistency taper the ceiling in that order — maintaining muscle takes less volume than building it.
Training days
More days means more room to do and recover from work, so the ceiling rises with frequency.
Age
The ceiling tapers gently from 40 and more clearly from 60. The 60+ direction is well-evidenced; the 40–59 numbers are a conservative estimate, and we label them as such.
Experience
Inferred from your logged history, never a quiz. Newer lifters grow on less; experienced lifters already working near the top of the band earn a higher ceiling.
Frequency and experience are blended with a geometric mean rather than multiplied — a newer lifter training twice a week would otherwise be double-cut into a band below the minimum effective dose. The ceiling is also reality-checked against what you’ve demonstrated: if your best week of hamstrings is 10 hard sets, the app suggests a realistic step up, not 20.
Anything Shojin doesn’t know about you simply doesn’t apply — missing information never counts against you. Sex barely moves set targets, and height and bodyweight don’t affect them at all.
Honest limits
The two anchors — the volume dose-response and the ~12–20 set sweet spot — are well-supported meta-analytic findings. The finer details around them (the exact multiplier for “fat loss,” the precise age taper, the 0.25–1.0 contribution grades) are practitioner heuristics drawn from established coaching frameworks: sensible, widely-used defaults, not values proven to the decimal by a clinical trial.
We’d rather be honestly approximate than falsely precise — targets are soft guidance by design, and your own logged training is what makes them yours over time.The whole philosophy, in one line
References
Where a claim rests on a coaching framework rather than a trial, the entry says so.
- 01
Schoenfeld, Ogborn & Krieger (2017)Journal of Sports Sciences 35(11)
Dose-response between weekly set volume and muscle growth — why the floor exists.
- 02
Baz-Valle et al. (2022)Journal of Human Kinetics 81
The ~12–20 sets/muscle/week sweet spot — backbone of the default bands.
- 03
Schoenfeld, Grgic & Krieger (2019)Journal of Sports Sciences 37(11)
Training frequency meta-analysis — why more days raises the ceiling.
- 04
Refalo et al. (2023)Sports Medicine 53(3)
Proximity-to-failure and hypertrophy — what makes a set a working set.
- 05
Roberts, Nuckols & Krieger (2020)Journal of Strength and Conditioning Research 34(5)
Sex differences meta-analysis — why sex barely moves set targets.
- 06
Borde, Hortobágyi & Granacher (2015)Sports Medicine 45(12)
Dose-response in older adults — the evidence behind the 60+ ceiling taper.
- 07
Contreras et al. (2015)Journal of Applied Biomechanics 31(6)
Squat vs hip-thrust EMG — behind the graded muscle contribution weights.
- 08
Youdas et al. (2010)Journal of Strength and Conditioning Research 24(12)
Pull-up vs chin-up EMG — why a chin-up credits biceps more than a pull-up.
- 09
Israetel, Hoffmann & Smith (2021)Scientific Principles of Hypertrophy Training, Renaissance Periodization
The MEV/MAV volume-landmark framework and fractional-set convention (coaching resource, not a peer-reviewed trial).