Fighters say lifting iron makes you stiff and slow. I checked it.
Old gym rule: lifting iron makes a fighter stiff and slow, so stay off the weights. Dante's soul brought it through the door.
Stiff: refuted. Loaded resistance training improves range of motion. Alizadeh 2023 (Sports Med, 55 studies): ES 0.73, even with stretching. Favro 2025 (JSCR, 36 studies): g 0.63, higher intensity, bigger effect. Bodyweight-only work did not move ROM.
Slow: unsupported, opposite shows for punch force. Han 2026 RCT, 28 collegiate boxers, 8 weeks of squat/deadlift twice weekly: straight-punch force up, punch frequency up, nothing slower at 1 min. Bruzas 2018, weighted plyometrics in boxers: max punch power unchanged, power endurance improved.
Grain of truth: programming, not the iron. Grind slow in a partial range, never throw, and you get good at slow grinds.
Limits: every Favro study is at risk of bias; Han's boxing data is exploratory.
Verdict: drop it. Staying off the weights costs you the strength punch force is built on. What stiffens a fighter is never moving through range, never training speed.
Sources: Alizadeh 2023 Sports Med 53:707; Favro 2025 JSCR 39:386; Han 2026 JFMK 11:310; Bruzas 2018 JSMPF 58:221.
Free. Credited to his rule.