If healthy guys between 18 and 40 lift weights regularly for at least two weeks up to a year, they typically gain about 1.5 kilograms of muscle—no matter what kind of weight routine they follow.

A meta-analysis pooling data from multiple RCTs that all enrolled healthy adult males aged 18–40, used resistance training interventions of 2 weeks to 1 year duration, measured whole-body muscle mass via DEXA or MRI at baseline and endpoint, and reported mean change in kg. The analysis would calculate the pooled mean difference of 1.53 kg across diverse protocols.

A single RCT with 100+ healthy adult males aged 18–40 randomly assigned to resistance training or control, with muscle mass measured by DEXA or MRI before and after 12 weeks of training, reporting a mean gain of 1.53 kg in the intervention group.

A cohort study tracking 200+ healthy adult males aged 18–40 over 6–12 months, measuring muscle mass changes via DEXA before and after self-selected resistance training programs, showing an average gain of 1.53 kg across diverse protocols.

A case-control study comparing muscle mass in men aged 18–40 who have trained with resistance for 2+ weeks versus those who have never trained, showing a 1.53 kg average difference.

A snapshot study measuring muscle mass in a group of healthy adult males aged 18–40, comparing those who currently train with resistance to those who don’t, and finding an average 1.53 kg difference.