The evidence behind the numbers

The unit: sets per muscle

Training volume is counted in working sets per muscle. A set of bench press counts as a full set of chest and a fraction of a set of triceps, because the triceps assist rather than drive the movement.

One workout takes every muscle to 2-3 sets depending on your training goal - that is what 100% means, and it does not change with how often you train. Training more often multiplies it: at 2-3 workouts a week that is 4-9 sets per muscle. 11 fractional sets is the most one session can usefully deliver to a single muscle.

How a percentage becomes a dose

Every movement in the catalog carries a per-muscle activation percentage, and you can see all of them. Those percentages do NOT translate one-for-one into dose. For counting volume they are banded into three tiers:

The banding is deliberate, and the reason is the paper below: the precision needed to dose off a five-point difference in an activation estimate does not exist. The 1.0 and 0.5 tiers come from the published method. The 0.25 tier is ours - our vectors distinguish a real minor contributor from noise, and rounding those to zero would under-count real work.

How much each goal asks for

The per-workout dose is the one place a goal changes how MUCH you train rather than how you train, and it is not a separate constant: it is the goal’s own prescription, so “100% of a muscle” and “one exercise done as prescribed” are the same sentence. What IS ours rather than the papers’ is which band each goal aims at - the research gives a dose-response curve with diminishing returns, and that choice places each goal on it. Both numbers are shown here so they can be argued with.

Why every muscle group gets a bucket of its own

A muscle group earns its own line in the coverage map only if a realistic programme can leave it short while every other group sits at 100%. Finer than that is noise; coarser hides gaps. That rule is why there are 18 groups rather than the ten or fifteen a workout log usually keeps, why the shoulder is split three ways, and why the two groups people dismiss most often - the inner thigh and the outer hip - are on the list at all. It rules things out too: separating the upper traps from the rhomboids fails it, because almost every row and carry trains both.

The inner thigh is the one people argue with, so here is the arithmetic. The adductor group is the largest muscle mass in the lower body after the glutes Takizawa 2014, and the portions making up over 80% of the adductor magnus pull harder on hip extension than on adduction Takahashi 2025 - it is named after its smaller job. Squatting does train it, and how much depends on how you squat: ten weeks of full squats grew it more than twice as much as ten weeks of half squats Kubo 2019. A tracker that files a squat under “quads” cannot tell you that. Direct adduction work is also the only version of this with a randomised trial behind it Harøy 2019.

The outer hip is the opposite case: nothing hides it and almost nothing trains it. Gluteus medius and minimus hold the pelvis level every time you stand on one leg, and a barbell programme moves almost entirely front-to-back, so the plane they work in is simply absent. Adding hip work to knee work does beat knee work alone for patellofemoral pain Nascimento 2018, but we stop short of the claim usually made here: the evidence that weak abductors CAUSE knee pain is cross-sectional rather than prospective Barton 2013. They earn their place on coverage and on function, and that is enough. The question was never whether you train a group at all - the published floor is about four hard sets a week Iversen 2021, so the thing worth knowing is which of yours are under it.

What the model rests on

• The source of the fractional method. Compared three ways of counting an assisting set across 67 studies and 2,058 participants, and found counting it as half a set predicted real-world gains best - concluding that telling direct and indirect work apart is essential.

  Pelland JC, Remmert JF, Robinson ZP, Hinson SR, Zourdos MC (2025). The Resistance Training Dose Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gains. Sports Medicine. 10.1007/s40279-025-02344-w

• Why the app ORDERS a session but does not claim it grows more muscle. Pooled 11 studies and found no effect of exercise order on hypertrophy at all; what order moves is strength in whatever you do first, and single-joint work benefits about twice as much from going first as multi-joint does.

  Nunes JP, Grgic J, Cunha PM, Ribeiro AS, Schoenfeld BJ, de Salles BF, Cyrino ES (2021). What influence does resistance exercise order have on muscular strength gains and muscle hypertrophy? A systematic review and meta-analysis. European Journal of Sport Science. 10.1080/17461391.2020.1733672

• Why the unit is WEEKLY sets. Established the dose-response relationship between weekly set volume per muscle and muscle growth, and reported that even very low volumes produce substantial gains - which is why the app has a floor rather than an all-or-nothing target.

  Schoenfeld BJ, Ogborn D, Krieger JW (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis. Journal of Sports Sciences. 10.1080/02640414.2016.1210197

• Why one workout a week is called maintaining rather than wasted. A review of the minimum dose needed to preserve what training has already built: strength and muscle size were maintained for up to 32 weeks on as little as one session a week and one set per exercise in younger adults, provided the load stayed heavy. Older adults needed about twice that. It is the source for the lowest of our weekly bands.

  Spiering BA, Mujika I, Sharp MA, Foulis SA (2021). Maintaining Physical Performance: The Minimal Dose of Exercise Needed to Preserve Endurance and Strength Over Time. Journal of Strength and Conditioning Research. 10.1519/JSC.0000000000003964

• Why we argue for full body on schedule resilience rather than on frequency. A meta-analysis of training frequency found no meaningful difference in muscle growth between training a muscle once, twice or three times a week once total weekly sets were matched. Distribution is not the lever; weekly volume is. So the honest case for full-body training is that it protects your weekly volume when a day goes missing - not that hitting a muscle more often is inherently better.

  Schoenfeld BJ, Grgic J, Krieger J (2019). How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency. Journal of Sports Sciences. 10.1080/02640414.2018.1555906

• Why cutting is not prescribed less work. A review of resistance training during caloric restriction. It is explicit that higher volume is NOT proven better for sparing lean mass while dieting - and equally explicit that programmes which REDUCED volume preserved less of it than those that held or raised it. So the fat-loss goal is given the same frequency as muscle mass, rather than fewer sessions.

  Roth C, Schoenfeld BJ, Behringer M (2022). Lean mass sparing in resistance-trained athletes during caloric restriction: the role of resistance training volume. European Journal of Applied Physiology. 10.1007/s00421-022-04896-5

• Why general health is two sessions, and why beginners get the full dose. The ACSM position stand, drawn from 137 systematic reviews and over 30,000 participants, sets the baseline at all major muscle groups on two or more days a week, at 2-3 sets per exercise. That is the floor our general-health goal targets, and it is already what we prescribe - which is why a new account is not started on less.

  Currier BS, D’Souza AC, Fiatarone Singh MA, Lowisz CV, Rawson ES, Schoenfeld BJ, Smith-Ryan AE, Steen JP, Thomas GA, Triplett NT, Washington TA, Werner TJ, Phillips SM (2026). American College of Sports Medicine Position Stand. Resistance Training Prescription for Muscle Function, Hypertrophy, and Physical Performance in Healthy Adults: An Overview of Reviews. Medicine & Science in Sports & Exercise. 10.1249/MSS.0000000000003745

• Where the per-session ceiling comes from. Found returns stop being detectable at roughly 11 fractional sets for a single muscle in one session, which is the cap the app uses instead of a number we invented.

  Remmert JF, Pelland JC, Robinson ZP, Hinson SR, Zourdos MC (2025). Is There Too Much of a Good Thing? Meta-Regressions of the Effect of Per-Session Volume on Hypertrophy and Strength. SportRxiv (preprint). source

• Why effort matters, and why we flag it as a gap. Across 55 hypertrophy studies, growth increased as sets were taken closer to failure, while strength was largely indifferent. We do not record effort, so this is a known limitation rather than something the app models.

  Robinson ZP, Pelland JC, Remmert JF, et al. (2024). Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions. Sports Medicine. 10.1007/s40279-024-02069-2

• Why the inner thigh is not a detail muscle. A cadaver study of the adductor magnus's architecture - volume, fibre length and physiological cross-sectional area - establishing it as the largest of the adductors and, after the gluteus maximus, the largest muscle of the lower limb. Cited wherever we say that skipping the adductors is not skipping something small.

  Takizawa M, Suzuki D, Ito H, Fujimiya M, Uchiyama E (2014). Why adductor magnus muscle is large: the function based on muscle morphology in cadavers. Scandinavian Journal of Medicine & Science in Sports. 10.1111/j.1600-0838.2012.01466.x

• Why “who needs adduction” is the wrong question. Diffusion-tensor imaging of fifteen living adults found that the portions making up over 80% of the adductor magnus's volume and cross-section have a longer moment arm for hip EXTENSION than for adduction. It is a hip extensor that was named after its smaller job.

  Takahashi K, Tozawa H, Kawama R, Wakahara T (2025). Redefining muscular action: human "adductor" magnus is designed to act primarily for hip "extension" rather than adduction in living young individuals. Journal of Applied Physiology. 10.1152/japplphysiol.00600.2024

• Why the squat carries an adductor number rather than an adductor tick. Ten weeks of squat training grew the adductors 6.2% at full depth against 2.7% at half depth, while quadriceps and hamstring growth was similar either way. We cite it knowing it cuts both ways - the squat IS adductor work - because that is the point: whether a lift trains a muscle is a question with a number attached, and the number moves with how you do the lift.

  Kubo K, Ikebukuro T, Yata H (2019). Effects of squat training with different depths on lower limb muscle volumes. European Journal of Applied Physiology. 10.1007/s00421-019-04181-y

• The one randomised trial behind direct adductor work. Across 35 semi-professional Norwegian football teams, an adductor strengthening programme cut self-reported groin problems by about 41% over a season. Cited for what it shows - that direct adductor work does something compound lifting does not - and never as an injury-prevention claim about this app, which prescribes neither that protocol nor any rehab.

  Harøy J, Clarsen B, Wiger EG, Øyen MG, Serner A, Thorborg K, et al. (2019). The Adductor Strengthening Programme prevents groin problems among male football players: a cluster-randomised controlled trial. British Journal of Sports Medicine. 10.1136/bjsports-2017-098937

• Why the outer hip gets a slot of its own. Across 14 trials and 673 participants, adding hip strengthening to knee strengthening beat knee work alone for both pain and activity in patellofemoral pain. Read it with the caveat its own authors state: the benefit appeared WITHOUT a measured change in strength, so the mechanism is not settled.

  Nascimento LR, Teixeira-Salmela LF, Souza RB, Resende RA (2018). Hip and Knee Strengthening Is More Effective Than Knee Strengthening Alone for Reducing Pain and Improving Activity in Individuals With Patellofemoral Pain: A Systematic Review With Meta-analysis. Journal of Orthopaedic & Sports Physical Therapy. 10.2519/jospt.2018.7365

• The floor under the second pillar. A review of time-efficient training puts the minimum at roughly four hard sets per muscle per week. That is the lowest of our weekly bands, and it reframes the coverage question entirely: what is worth knowing is never whether you train a muscle, it is which of your muscles are under four sets.

  Iversen VM, Norum M, Schoenfeld BJ, Fimland MS (2021). No Time to Lift? Designing Time-Efficient Training Programs for Strength and Hypertrophy: A Narrative Review. Sports Medicine. 10.1007/s40279-021-01490-1

What the evidence does not support

This is the part most fitness apps leave out. Our activation percentages are in-house estimates informed by movement mechanics and published EMG work. They are not laboratory measurements of your body, and one paper in particular sets the ceiling on how precisely they can be read:

• THE LIMIT ON OUR OWN METHOD. Concludes that acutely measured surface EMG amplitude is not a validated predictor of muscle growth, and that the mechanical chain assumed between the two breaks down at several points. This is exactly why our activation percentages are banded into three coarse tiers for dosing instead of being used at face value - and why we show them to you rather than hiding them behind a score.

  Vigotsky AD, Halperin I, Trybulski R, Vigotsky ED (2022). Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy. Sports Medicine. 10.1007/s40279-021-01619-2

• A LIMIT ON WHAT WE SAY ABOUT THE ABDUCTORS. Ten case-control studies and no prospective ones: gluteal activity differs in people who already have patellofemoral pain, which does not establish that weak abductors caused it. “Weak glute medius causes knee pain” would sell a hip abduction slot very comfortably and the evidence for it is not there, so the abductors earn their place on coverage and on function instead.

  Barton CJ, Lack S, Malliaras P, Morrissey D (2013). Gluteal muscle activity and patellofemoral pain syndrome: a systematic review. British Journal of Sports Medicine. 10.1136/bjsports-2012-090953

• A set only counts if it is taken close enough to failure. We record weight and reps but not effort, so every logged set is counted as a hard set. If you stop well short, the app will over-credit you.
• The per-workout dose for each goal, the beginner ramp and the third (0.25) tier are clinical judgements placed on the published dose-response curve. The papers give the curve; they do not give those numbers.
• Activation percentages are reviewed in-house. No external trainer or laboratory has signed them off, and we say so rather than implying otherwise.

Why we publish this at all

The product exists because black-box workout generators ask you to trust a number you cannot inspect. Publishing only the research that flatters the model would be the same trick with extra footnotes. Every percentage is visible in the app, the method is on this page, and so is its ceiling.

Citations last checked 2026-09-30.