Essentials: How to Exercise for Strength Gains & Hormone Optimization | Dr. Duncan French

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now my conversation with Dr. Duncan French. Duncan French, great to see you again.

**Duncan French** (0:22)
Likewise, likewise, thank you. I don't often have many Stanford professors in the Performance Institute, so I'm really excited.

**Andrew Huberman** (0:29)
Oh, well, this place is amazing, and you have a huge role in making it what it is. I found dozens of papers on how weight training impacts hormones and your names on all of them. What is it about engaging motor neurons under heavy loads, sends a signal to the endocrine system, hey, release testosterone. I've never actually been able to find that in a textbook.

**Duncan French** (0:54)
Yeah, I mean, I think it's the stress response, right? It's mechanical stress and it's metabolic stress. And these are, you know, the downstream regulation of testosterone release at the gonads comes from many different areas. You know, my work primarily looked at, you know, catecholamines and sympathetic arousal.

**Andrew Huberman** (1:13)
So things like epinephrine, adrenaline.

**Duncan French** (1:15)
Yeah, epinephrine, adrenaline, you know, noradrenaline. How they were signaling, they're signaling cascade using, you know, the HPA axis, releasing cortisol, and then, you know, looking at how that also influenced the adrenal medulla to release, you know, androgens, and then signaling that at the gonads.

**Andrew Huberman** (1:35)
That raises an interesting question. So in presumably weight training in women, people who don't have testes, also it increases testosterone. And is that purely through the adrenals? When women lift weights, their adrenal glands release testosterone.

**Duncan French** (1:49)
Absolutely. I mean, that is the only area of testosterone release for females. And yes, it's the same downstream cascade. Obviously, the extent to which it happens is significantly less in females. But that's how you, there's good data out there that shows, you know, females can increase their anabolic environment, their internal anabolic milieu, using resistance training as a stressor. And then they get the consequent muscle tissue growth, you know, whether it's tendon, ligament adaptations, you know, the beneficial consequences of resistance training, which is driven by anabolic stimuli.

**Andrew Huberman** (2:21)
Yeah, I have two questions about that. The first one is something that you mentioned, which is that the androgens, the testosterone comes from the adrenals under resistance loads. In women, is the same true in men? I mean, we hear that the testes produce testosterone when we weight train, but do we know whether or not it's the adrenals or the testes in men that are increasing testosterone?

**Duncan French** (2:40)
Yeah, I think-

**Andrew Huberman** (2:41)
More or both? A little bit from each?

**Duncan French** (2:42)
The field is divided presently. I mean, as much as understanding the acute adrenergic response in terms of anabolic response to exercise in an acute phase and the exposure to a stimulus that is stress-driven, which might be partly from the adrenal glands, partly from the gonads, versus a longitudinal exposure to anabolic environments, which is primarily driven by obviously the gonads and the release of the endocrine environment from testosterone release at the gonads. So the field is split in terms of how exercise is promoting hypertrophy, muscle tissue growth, and whether that is very much an adrenal stimuli or if that's significant enough in these acute responses versus the longitudinal exposure to elevated basal levels of anabolic testosterone at habitual levels.

**Andrew Huberman** (3:37)
And then you mentioned that testosterone can have enhancing effects or growth effects on tendon and ligament also. You don't often hear about that. People always think, you know, testosterone muscle. But testosterone has a lot of effects on other tissues that are important for performance, it sounds like. What's the story there?

**Duncan French** (3:55)
Yeah, absolutely. I mean, the testosterone hormone is, I mean, listen, there's androgen receptors on neural tissue, on neural axons.

**Andrew Huberman** (4:02)
Pretty much everywhere.

**Duncan French** (4:03)
Exactly. So, you know, the binding capacity of testosterone and influencing different tissues within the body, I touched on, you know, muscle tissue, but you know, the ligaments, the tendons, even bone to some extent, you know, testosterone is potential to influence that in terms of removing osteopenic kind of characteristics, et cetera. So yeah, it's a magic hormone, let's say, with many end impacts in terms of adaptation.

**Andrew Huberman** (4:32)
Could you say that there's some general principles of training that favor testosterone production in terms of that somebody who's not an elite athlete could use, who's trying to use weight training to build or maintain muscle, lose body fat, so body recomposition and or stay strong and healthy for sport of a different kind.