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SCIENCE·Methodology

Built on the latest scientific studies

Every FitForge plan is built by an algorithm following rules derived from current meta-analyses and official sports medicine and nutrition guidelines. No hunches, no fads: only methods that have held up in dozens of controlled studies with thousands of participants.

16
scientific sources
2017–2025
meta-analyses and guidelines
11/2026
last methodology review

Training

Volume: how many sets per muscle

We set the number of working sets for each muscle group in the range that research links to substantial gains. The largest analysis to date, covering 67 studies with 2,058 participants, confirmed that more weekly sets lead to more muscle growth, although with diminishing returns. So no pointless marathons, just precisely dosed volume.

Sources: [1]

Intensity and reps in reserve (RIR)

You finish every set with a precisely set number of reps in reserve. A meta-analysis of 55 studies showed that muscles grow more the closer you take a set to failure, while for strength the weight matters most. Because people typically underestimate their reserve by about one rep, we start with a reserve of 3 and lower it step by step.

Sources: [2], [3]

Weight and number of reps

The rep range matches your goal: heavy sets of 4 to 6 reps where strength is the aim, and 8 to 15 reps for muscle growth and toning. Meta-analyses confirm that muscles grow across a wide range of loads, but maximal strength requires heavy weights.

Sources: [4]

Frequency

We choose the training split (full body, upper/lower, push/pull/legs) based on how many days you train. With equal volume, frequency has only a small effect on muscle growth but it does matter for strength, so we repeat the main lifts several times a week.

Sources: [1]

Rest between sets

2 to 3 minutes for the main lifts, at least 60 seconds for accessory exercises. A 2024 Bayesian meta-analysis showed that rest periods shorter than a minute slightly hold back muscle growth, while resting longer than 90 seconds brings no further benefit.

Sources: [5]

Progression and deload

The plan has 4 weeks of structured progression: technique, adding load, the hardest week and finally a deload. We place the deload week at the end of the cycle so your body can recover after the most demanding week, because research shows that a deload in the middle of a programme does not improve results.

Sources: [6]

Cardio alongside strength training

We add cardio mainly for fat loss, gradually and mostly at a moderate pace. A meta-analysis of 43 randomised studies confirmed that combining cardio with strength training does not reduce muscle growth or maximal strength. Your total activity is in line with World Health Organization recommendations.

Sources: [7], [8]

Nutrition

Calories

We calculate your resting metabolism with the Mifflin-St Jeor equation, one of the most widely used and best validated formulas for healthy adults. We then add your daily activity and workouts to get your real daily energy expenditure.

Sources: [9], [10]

Rate of weight loss

The deficit corresponds to losing roughly 0.5 to 1% of body weight per week. Studies in people who train show that a slower pace preserves more muscle mass and leads to better body composition than fast, drastic diets.

Sources: [11]

Protein

1.8 to 2.2 g of protein per kilogram of body weight depending on your goal, at the upper end during a calorie deficit. A meta-analysis of 49 studies shows that the muscle-building benefit rises up to about 1.6 g/kg, with 2.2 g/kg as the upper end of the effective range. We spread protein across 3 to 5 meals a day, because an even intake supports muscle growth better than one large dose.

Sources: [12], [13], [14]

Young people aged 15 to 17

A safer version of the plan

Gentler rules apply to young people: a smaller calorie deficit, a higher calorie floor, no maximum weights and a focus on technique. According to the American Academy of Pediatrics and an international expert consensus, strength training is safe and beneficial for young people when it is properly guided.

Sources: [15], [16]

Sources

  1. [1]Pelland JC et al. The Resistance Training Dose Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gains. Sports Medicine, 2025. View study
  2. [2]Robinson ZP, Pelland JC et al. Exploring the Dose–Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions. Sports Medicine, 2024. View study
  3. [3]Halperin I et al. Accuracy in Predicting Repetitions to Task Failure in Resistance Exercise: A Scoping Review and Exploratory Meta-analysis. Sports Medicine, 2022. View study
  4. [4]Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis. Journal of Strength and Conditioning Research, 2017. View study
  5. [5]Singer A, Wolf M, Generoso L et al. Give it a rest: a systematic review with Bayesian meta-analysis on the effect of inter-set rest interval duration on muscle hypertrophy. Frontiers in Sports and Active Living, 2024. View study
  6. [6]Coleman M et al. Gaining more from doing less? The effects of a one-week deload period during supervised resistance training on muscular adaptations. PeerJ, 2024. View study
  7. [7]Schumann M et al. Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis. Sports Medicine, 2022. View study
  8. [8]Bull FC et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 2020. View study
  9. [9]Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990. View study
  10. [10]O'Neill JER, Corish CA, Horner K. Accuracy of Resting Metabolic Rate Prediction Equations in Athletes: A Systematic Review with Meta-analysis. Sports Medicine, 2023. View study
  11. [11]Ruiz-Castellano C et al. Achieving an Optimal Fat Loss Phase in Resistance-Trained Athletes: A Narrative Review. Nutrients, 2021. View study
  12. [12]Morton RW et al. 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, 2018. View study
  13. [13]Jäger R et al. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 2017. View study
  14. [14]Schoenfeld BJ, Aragon AA. How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 2018. View study
  15. [15]Stricker PR et al. Resistance Training for Children and Adolescents. Pediatrics (American Academy of Pediatrics), 2020. View study
  16. [16]Lloyd RS, Faigenbaum AD, Stone MH et al. Position statement on youth resistance training: the 2014 International Consensus. British Journal of Sports Medicine, 2014. View study

The plan is general guidance for healthy people and does not replace medical or nutritional care.

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