The evidence

The evidence behind Aretia.

Aretia is a calculator, not an opinion. Every number the plan engine uses, and every flag the split analyser raises, traces to a published, peer-reviewed study that I have read and checked against its source. This page lists them.

Each entry gives the full citation, an identifier you can look up yourself, a plain statement of what the study found, and the part of the app it drives. The findings are written to match what the paper actually showed. If a claim cannot be backed this way, it stays out of the app. I would rather leave a number out than dress up a guess.

Training volume

The master dial
Schoenfeld, Ogborn & Krieger (2017)

Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis

Journal of Sports Sciences, 35(11), 1073-1082  ·  PMID 27433992
Found

Muscle growth rises with the number of hard sets per muscle per week, with roughly ten sets a week a productive anchor and more adding benefit up to a point.

Drives

The weekly set targets per muscle, and the "in the productive range" band the analyser scores against.

Pelland, Remmert, Robinson, Hinson & Zourdos (2026)

The resistance training dose response: meta-regressions exploring the effects of weekly volume and frequency on muscle hypertrophy and strength gains

Sports Medicine, 56(2), 481-505  ·  PMID 41343037
Found

Size and strength both keep increasing as weekly sets increase, with diminishing returns that are sharper for strength. Counting an indirect set as half of a direct set predicted the results best.

Drives

The diminishing-returns shape of the volume targets, and the rule that a secondary muscle earns half a set while the primary earns a full set.

Frequency

Carrying the volume
Schoenfeld, Ogborn & Krieger (2016)

Effects of resistance training frequency on measures of muscle hypertrophy: a systematic review and meta-analysis

Sports Medicine, 46, 1689-1697  ·  PMID 27102172
Found

At matched weekly volume, training a muscle at least twice a week grew it more than training it once a week.

Drives

The rule that every muscle is trained at least twice a week, and the analyser flag for muscles trained only once.

The Pelland 2026 meta-regression above adds that, once volume is accounted for, frequency has little independent effect on size. So frequency is used as a way to spread the week's volume across sessions, rather than chased for its own sake.

Load and rep range

Schoenfeld, Grgic, Ogborn & Krieger (2017)

Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis

Journal of Strength and Conditioning Research, 31(12), 3508-3523  ·  PMID 28834797
Found

Muscle growth was similar across light and heavy loads taken to failure, while one-rep-max strength favoured the heavier loads.

Drives

Heavier loads and lower reps on the main compound for its strength carry-over, with higher reps on the isolation work.

Proximity to failure

Refalo, Helms, Trexler, Hamilton & Fyfe (2023)

Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis

Sports Medicine, 53(3), 649-665  ·  PMID 36334240
Found

Training to momentary failure was not better for growth than stopping a few reps short, as long as the sets were taken close enough to failure.

Drives

The target of roughly zero to three reps in reserve on each set, rather than grinding every set to failure.

Range of motion

The lengthened position
Pallarés et al. (2021)

Effects of range of motion on resistance training adaptations: a systematic review and meta-analysis

Scandinavian Journal of Medicine & Science in Sports, 31(10), 1866-1881  ·  PMID 34170576
Found

Full range of motion produced larger gains in strength and lower-limb size than partial range training.

Drives

The preference for exercises trained through a full range.

Sato et al. (2021)

Elbow joint angles in elbow flexor unilateral resistance exercise training determine its effects on muscle strength and thickness

Frontiers in Physiology, 12, 734509  ·  PMID 34616309
Found

Curls trained through the lengthened, extended elbow angles grew the elbow flexors more than the same range worked at the shortened angles.

Drives

Favouring exercises that load the muscle in a stretched position.

Maeo et al. (2023)

Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position

European Journal of Sport Science, 23(7), 1240-1250  ·  PMID 35819335
Found

Overhead triceps extensions, which hold the long head at a long length, grew it more than pushdowns done with the arm by the side.

Drives

The same lengthened-position preference, applied to exercise choice.

Protein

Morton et al. (2018)

A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults

British Journal of Sports Medicine, 52(6), 376-384  ·  PMID 28698222
Found

Gains in lean mass kept rising with protein up to about 1.6 g per kg of bodyweight a day, then levelled off.

Drives

The daily protein floor and target.

Energy balance

Gaining and losing
Helms, Aragon & Fitschen (2014)

Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation

Journal of the International Society of Sports Nutrition, 11, 20  ·  PMID 24864135
Found

Dieting at about 0.5 to 1% of bodyweight a week, with high protein per unit of lean mass, protected muscle while losing fat.

Drives

The rate of weight loss on a cut and the higher cut-phase protein.

Garthe et al. (2011)

Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes

International Journal of Sport Nutrition and Exercise Metabolism, 21(2), 97-104  ·  PMID 21558571
Found

Losing weight slowly, around 0.7% a week, kept lean mass and built strength, while losing faster cost muscle.

Drives

The default cut rate.

Iraki, Fitschen, Espinar & Helms (2019)

Nutrition recommendations for bodybuilders in the off-season: a narrative review

Sports, 7(7), 154  ·  PMID 31247944
Found

A modest surplus aiming for a quarter to a half percent of bodyweight a week limited fat gain while supporting muscle growth.

Drives

The default bulk rate and surplus.

Cardio alongside lifting

Wilson et al. (2012)

Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises

Journal of Strength and Conditioning Research, 26(8), 2293-2307  ·  PMID 22002517
Found

Lifting alongside running cost some muscle and strength, while cycling did not, and the interference grew with more frequent and longer endurance work.

Drives

The low-impact, moderate cardio prescribed on a cut.

Exercise selection

Muscle activation
Campos et al. (2020)

Different shoulder exercises affect the activation of deltoid portions in resistance-trained individuals

Journal of Human Kinetics, 75, 5-14  ·  PMID 33312291
Found

Overhead pressing drove the highest front-delt activation of the lifts measured, while the lateral raise led for the side and rear delt.

Drives

Matching shoulder exercises to the head they train best.

Rodríguez-Ridao et al. (2020)

Effect of five bench inclinations on the electromyographic activity of the pectoralis major, anterior deltoid, and triceps brachii during the bench press

International Journal of Environmental Research and Public Health, 17(19), 7339  ·  PMID 33049982
Found

Upper-chest activation peaked at a 30-degree incline. Past 45 degrees the front delt took over and chest activation fell.

Drives

The incline guidance on incline pressing.

Williams et al. (2021)

Activation of the gluteus maximus during the back squat, split squat, and barbell hip thrust

Journal of Strength and Conditioning Research, 35(1), 16-24  ·  PMID 33332802
Found

At a heavy load, the barbell hip thrust drew higher peak glute activation than the back squat or the split squat.

Drives

The role of the hip thrust as a direct glute movement.

Resting metabolism

The BMR equation
Mifflin et al. (1990)

A new predictive equation for resting energy expenditure in healthy individuals

American Journal of Clinical Nutrition, 51, 241-247
Found

A regression equation that estimates resting energy expenditure, named by the Academy of Nutrition and Dietetics as the standard for adults.

Drives

The starting point of the calorie and macro calculator.

Studies are added only after the source has been read and checked, so the findings match what the paper showed. If you spot an error in how a study is represented here, that is a bug, and I want to fix it. Write to [email protected].

Want to know when it is ready?