If you're a guy between 18 and 40 and you start lifting weights, whether you're new to it or have been doing it for years, you probably won't gain much more muscle just because you're experienced—but the people who’ve trained the longest (4+ years) still tend to gain the most muscle, so experience doesn’t always make a clear difference.

A 12-week randomized controlled trial comparing muscle mass gain (via DEXA) in healthy adult males aged 18–40, stratified by training status (untrained vs. 0–3 years vs. 4+ years), all performing identical supervised resistance training protocols (3x/week, 70–85% 1RM, 3–4 sets, 8–12 reps), with pre- and post-intervention muscle mass measurements and controlled nutrition.

A 6-month prospective cohort study tracking muscle mass changes in healthy adult males aged 18–40 with documented training histories (untrained, 1–3 years, 4+ years) who initiate a standardized resistance training program, measuring muscle gain via MRI or DEXA at baseline, 3, and 6 months.

A cross-sectional analysis comparing current muscle mass in healthy adult males aged 18–40 who have trained for 0, 1–3, or 4+ years, all currently performing resistance training, to assess whether training duration correlates with muscle mass levels.

A case-control study comparing muscle mass gain in individuals who achieved high hypertrophy (>5% lean mass increase) vs. low gain (<1%) after 12 weeks of standardized resistance training, retrospectively analyzing prior training experience.