Last updated: 2026-10-05. This is general information from published research, not medical advice. If you have an injury, a heart condition, or are new to exercise after a long break, talk to a doctor first.
Most gym arguments are about the weight on the bar. The research points somewhere else. For building muscle, how hard the set is matters more than how heavy it is.
Number 1: the last few reps are the ones that count
A 2017 analysis that pooled the published studies compared light loads (60% of your one-rep maximum or less) with heavy loads (above 60%). When the sets were taken to the point where another rep was not possible, muscle growth was about the same in both groups. Strength on a one-rep test went up more with the heavy loads.
In practice:
- You can build muscle with 6 reps or with 25 reps. Pick a weight where the last two or three reps are a real struggle and your form still holds.
- If you can chat during the last reps, the set is too easy to count.
- If your goal is to lift the heaviest single weight, you do need to train heavy. That is a skill as well as a muscle.
Number 2: about 10 hard sets per muscle each week
A second analysis looked at how many sets people did per muscle group per week. More sets meant more growth, and the authors put the mark for getting most of the benefit at 10 or more sets per muscle per week.
In practice:
- Count sets per muscle, across the whole week. Three sets of chest on Monday, four on Wednesday and three on Friday is 10.
- Splitting them over two or three days is easier to recover from than doing all 10 in one session.
- Beginners grow on fewer. Start with 5 or 6 a week and add as it stops being hard.
Number 3: about 1.6 grams of protein per kilo of body weight
An analysis of 49 studies and 1,863 people found that eating more protein helped muscle gain from training, up to about 1.6 g per kg of body weight per day. Above that, extra protein did not add more.
In practice:
- For a 70 kg person that is about 112 g a day. For 90 kg, about 144 g.
- It is a daily total. Food counts the same as powder.
- The same analysis found the effect was smaller in older adults and larger in people who already train.
A week that uses all three
| Day | What | Why |
|---|---|---|
| Mon | Push: chest, shoulders, triceps, 3 to 4 hard sets each | Part of the weekly 10 |
| Wed | Pull: back, biceps, 3 to 4 hard sets each | Part of the weekly 10 |
| Fri | Legs, then one more round for the muscle you care most about | Finishes the count |
Any rep range from about 6 to 25 works, as long as the last reps are hard.
Where these numbers stop
- They describe averages. People respond differently. Use the numbers as a starting point and adjust by what your own body does over two or three months.
- "To failure" is a research condition, not an order. Stopping one or two reps short is safer on heavy lifts like squats and deadlifts and still works. Go all the way only on movements where failing is safe.
- The studies are mostly in healthy adults over 8 to 12 weeks. They do not tell you what happens over years, and they are not written for injuries or medical conditions.
- Muscle is not the only goal. For health, the weekly habit matters more than any of the three numbers.
Sources
- Schoenfeld, Grgic, Ogborn, Krieger (2017). Strength and hypertrophy adaptations between low- vs. high-load resistance training. Journal of Strength and Conditioning Research.
- Schoenfeld, Ogborn, Krieger (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass. Journal of Sports Sciences.
- 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. Explained here.
- Schoenfeld et al. (2021). Loading recommendations for muscle strength, hypertrophy, and local endurance: a re-examination of the repetition continuum. Sports.