Dr. Duncan French — Sports scientist and Vice President of Performance at the UFC Performance Institute. His research focuses on how resistance training drives hormonal responses like testosterone and growth hormone.
The gist
Andrew Huberman talks with UFC Performance Institute scientist Dr. Duncan French about the mechanisms that link heavy weight training to testosterone and growth hormone release. They cover the specific rep/intensity/rest protocols that maximize muscle growth, why short rest periods drive a stronger metabolic stimulus, and how acute stress can transiently raise testosterone. The conversation then turns to recovery, arguing that cold exposure should be periodized because it can blunt the inflammation and mTOR signaling needed for hypertrophy. They close on metabolic flexibility, tactical carbohydrate timing, ketones, and heat acclimation via sauna, all framed around French's philosophy of adaptation-led, individualized programming.
Big reveals
- In women, testosterone from weight training comes entirely from the adrenal glands, not the gonads.
- A big acute stressor like a parachute jump can transiently increase testosterone, not just suppress it.
- Cold exposure after training can blunt strength, power, and muscle hypertrophy by dampening the mTOR pathway.
- Cold should be periodized: avoid it during muscle-building phases, use it during competition phases to maximize recovery.
- At the elite UFC level, the best athletes aren't training harder, they're recovering well enough to reproduce quality daily.
- UFC fighters work up to 30-45 minute continuous sauna sessions, with adaptations kicking in around 14 exposures.
- Roughly 99% of physiological adaptations show clear progression or regression within three months.
Things worth remembering
- Testosterone release is driven by both intensity and volume, while growth hormone is driven mainly by intensity.
- The protocol used to study testosterone release was 6 sets of 10 reps at ~80% of one-rep max with 2-minute rests.
- Shorter rest periods increase muscle growth by amplifying the metabolic stimulus (lactate, glycogenolysis).
- Of two lifters doing the same sets, the one with shorter rest (2 vs 3 min) likely sees greater muscle gains.
- Athletes' epinephrine and adrenaline begin rising up to 15 minutes before a workout they know will be hard.
- Athletes with the highest adrenergic (stress) response sustained force output longer through the workout.
- Skill acquisition is quality over quantity; a 90-minute focused session beats a 3-hour one for motor learning.
- UFC fighters eat a largely ketogenic diet but time carbohydrates immediately pre-, during, and post-training.
- Heat acclimation for fighters must begin 8-10 weeks before a fight; it improves sweat rate for weight cuts.
- French recommends athletes keep journals of training, mood, and sleep, since 15 people respond 15 different ways to the same workout.