Where our recommendations come from

How much you do

TrainArk sets a weekly number of sets per muscle group, and that number rises with training experience rather than being the same for everyone.

• 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, 35(11), 1073–1082 · doi:10.1080/02640414.2016.1210197

  The more weekly sets people did for a muscle, the more it grew.

• Baz-Valle E, Balsalobre-Fernández C, Alix-Fages C, Santos-Concejero J (2022). A systematic review of the effects of different resistance training volumes on muscle hypertrophy. Journal of Human Kinetics, 81, 199–210 · doi:10.2478/hukin-2022-0017

  In trained men, 12 to 20 sets per muscle per week was enough for growth, and going above 20 only helped the triceps.

• Schoenfeld BJ, Contreras B, Krieger J, et al. (2019). Resistance training volume enhances muscle hypertrophy but not strength in trained men. Medicine & Science in Sports & Exercise · doi:10.1249/MSS.0000000000001764

  Trained men gained the same strength from 1, 3 or 5 sets per exercise, but those doing more sets gained more muscle size.

• Currier BS, McLeod JC, Banfield L, et al. (2023). Resistance training prescription for muscle strength and hypertrophy in healthy adults: a systematic review and Bayesian network meta-analysis. British Journal of Sports Medicine · doi:10.1136/bjsports-2023-106807

  Every style of lifting beat doing nothing; heavier loads with several sets ranked best overall.

Where it is not settled: The upper limit is not settled. One meta-analysis finds more sets keep helping; another finds little beyond about 20 sets per muscle per week, and it differs by muscle. TrainArk does not claim more is always better. Volume for size and volume for strength also come apart — extra sets can add muscle without adding strength — so the app does not treat them as one number.

How long you rest

Rest between sets is prescribed as a band rather than a single number, and compound lifts get longer rests than isolation work.

• Grgic J, Lazinica B, Mikulic P, Krieger JW, Schoenfeld BJ (2017). The effects of short versus long inter-set rest intervals in resistance training on measures of muscle hypertrophy: A systematic review. European Journal of Sport Science, 17(8), 983–993 · doi:10.1080/17461391.2017.1340524

  Both short and long rests built muscle, with early signs that trained lifters do better with longer ones.

• Grgic J, Schoenfeld BJ, Skrepnik M, Davies TB, Mikulic P (2018). Effects of rest interval duration in resistance training on measures of muscular strength: A systematic review. Sports Medicine, 48(1), 137–151 · doi:10.1007/s40279-017-0788-x

  Beginners got stronger on rests of 60 to 120 seconds, while trained lifters needed more than two minutes.

• Singer A, Wolf M, Generoso L, et al. (2024). 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, 6, 1429789 · doi:10.3389/fspor.2024.1429789

  Resting longer than about a minute gave a small extra boost to muscle growth, and resting beyond 90 seconds added nothing more.

Where it is not settled: The direction is agreed, the size of the effect is not. One review finds no clear winner between short and long rests; a more recent one finds a small advantage past 60 seconds and nothing gained past 90.

How often you train

The plan spreads each muscle group across at least two sessions a week rather than one.

• Schoenfeld BJ, Ogborn D, Krieger JW (2016). Effects of resistance training frequency on measures of muscle hypertrophy: A systematic review and meta-analysis. Sports Medicine, 46(11), 1689–1697 · doi:10.1007/s40279-016-0543-8

  Training a muscle twice a week built more of it than training it once a week.

• Grgic J, Schoenfeld BJ, Davies TB, Lazinica B, Krieger JW, Pedisic Z (2018). Effect of resistance training frequency on gains in muscular strength: A systematic review and meta-analysis. Sports Medicine, 48(5), 1207–1220 · doi:10.1007/s40279-018-0872-x

  Training more often produced more strength mainly because it added up to more total work.

Where it is not settled: Twice a week beating once is well supported. Whether three or more beats two, once the weekly number of sets is held equal, is not — the reviews say so explicitly.

Which exercises you get

Swapping an exercise keeps the same primary muscle and movement pattern, and the plan varies exercises deliberately rather than shuffling them.

• Kassiano W, Nunes JP, Costa B, Ribeiro AS, Schoenfeld BJ, Cyrino ES (2022). Does varying resistance exercises promote superior muscle hypertrophy and strength gains? A systematic review. Journal of Strength and Conditioning Research, 36(6), 1753–1762 · doi:10.1519/JSC.0000000000004258

  A few different exercises chosen on purpose helped muscles grow more evenly, but swapping exercises constantly held gains back.

• Zabaleta-Korta A, Fernández-Peña E, Torres-Unda J, Francés M, Zubillaga A, Santos-Concejero J (2023). Regional hypertrophy: the effect of exercises at long and short muscle lengths in recreationally trained women. Journal of Human Kinetics, 88, 259–270 · doi:10.5114/jhk/163561

  An exercise that loads the muscle while it is stretched grew a different part of it than one that does not.

Where it is not settled: This is the thinnest section here. Two studies, both narrow. The app's rule is conservative for that reason.

How hard each set is

TrainArk does not ask you to train to failure, and progression can come from adding reps rather than always adding weight.

• Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ (2023). Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: A systematic review with meta-analysis. Sports Medicine, 53(3), 649–665 · doi:10.1007/s40279-022-01784-y

  Taking sets all the way to failure did not build more muscle than stopping short of it.

• Grgic J, Schoenfeld BJ, Orazem J, Sabol F (2022). Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: A systematic review and meta-analysis. Journal of Sport and Health Science, 11(2), 202–211 · doi:10.1016/j.jshs.2021.01.007

  Going to failure was not needed for strength or size, and did not appear to do harm either.

• Plotkin DL, Delcastillo K, Van Every DW, Tipton KD, Arroyo E, Schoenfeld BJ (2022). Progressive overload without progressing load? The effects of load or repetition progression on muscular adaptations. PeerJ, 10, e14142 · doi:10.7717/peerj.14142

  Over eight weeks, adding reps at the same weight worked about as well as adding weight.

Where it is not settled: Whether training to failure adds a small amount for already-trained lifters is an active dispute, not a settled question.

Actually keeping it up

Check-ins, training with friends and easing back in after a break are features, not decoration. The best plan is the one somebody is still following in six months.

• Garber CE, Blissmer B, Deschenes MR, et al. (2011). American College of Sports Medicine position stand: Quantity and quality of exercise for developing and maintaining fitness in apparently healthy adults. Medicine & Science in Sports & Exercise, 43(7), 1334–1359 · doi:10.1249/MSS.0b013e318213fefb

  Alongside its exercise targets, the panel states that behaviour-change methods and exercise people actually enjoy improve whether they keep going.

• Michie S, Abraham C, Whittington C, McAteer J, Gupta S (2009). Effective techniques in healthy eating and physical activity interventions: a meta-regression. Health Psychology, 28(6), 690–701 (PMID 19916637)

  Programmes that had people track their own behaviour worked noticeably better than those that did not.

• Samdal GB, Eide GE, Barth T, Williams G, Meland E (2017). Effective behaviour change techniques for physical activity and healthy eating in overweight and obese adults: systematic review and meta-regression analyses. International Journal of Behavioral Nutrition and Physical Activity, 14, 42 · doi:10.1186/s12966-017-0494-y

  Goal setting and self-tracking helped in the short run; lasting past a year also took feedback, gradually harder steps and a supportive coaching style.

• Howlett N, Trivedi D, Troop NA, Chater AM (2019). Are physical activity interventions for healthy inactive adults effective in promoting behavior change and maintenance, and which behavior change techniques are effective?. Translational Behavioral Medicine, 9(1), 147–157 · doi:10.1093/tbm/iby010

  Activity programmes shifted behaviour and the shift was still there six months later, helped most by planning, reminders and gradually harder steps.