- Aug 14, 2018
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"What is testosterone?" is one of the most searched questions in the entire testosterone keyword set, and that is worth pausing on. A hormone that dominates so much gym conversation is still, for a lot of people, a word they have heard far more often than they have actually understood. The forum gets the question constantly in different forms, so it is worth answering it plainly, from the ground up.
Testosterone is a steroid hormone, part of a family of hormones called androgens. It is produced mainly in the testes in men and in smaller amounts in the ovaries and adrenal glands in women, and it circulates in the blood bound mostly to a protein called sex hormone-binding globulin, with a small fraction travelling free. That free fraction is the biologically active part — the portion that can actually enter cells and bind to androgen receptors. Total testosterone, the number most blood tests report, is not the whole story on its own.
Its jobs are broad. In puberty it drives the development of male secondary sex characteristics — deeper voice, facial and body hair, increased muscle mass. In adulthood it continues to influence muscle protein synthesis, bone density, red blood cell production, fat distribution, mood, energy, and libido. In women, smaller amounts contribute to muscle and bone maintenance, energy, and sexual function. It is not a "muscle hormone" in any narrow sense; it is a whole-body signalling molecule that happens to matter a great deal to lifters because muscle tissue is one of the places its signal lands most visibly.
Levels vary enormously between healthy people and across the day — highest in the morning, lower in the evening — and they decline gradually with age. Sleep, body composition, illness, and stress all move the number. That variability is exactly why a single reading, taken out of context, tells you so little, and why the conversation around testosterone so often goes wrong: people compare numbers as if they were comparing bench presses.
This is general information, not medical advice. Anyone with questions about their own hormone levels should talk to a doctor.
What surprised you most when you first learned what testosterone actually does — and what do you wish someone had explained sooner?
Testosterone is a steroid hormone, part of a family of hormones called androgens. It is produced mainly in the testes in men and in smaller amounts in the ovaries and adrenal glands in women, and it circulates in the blood bound mostly to a protein called sex hormone-binding globulin, with a small fraction travelling free. That free fraction is the biologically active part — the portion that can actually enter cells and bind to androgen receptors. Total testosterone, the number most blood tests report, is not the whole story on its own.
Its jobs are broad. In puberty it drives the development of male secondary sex characteristics — deeper voice, facial and body hair, increased muscle mass. In adulthood it continues to influence muscle protein synthesis, bone density, red blood cell production, fat distribution, mood, energy, and libido. In women, smaller amounts contribute to muscle and bone maintenance, energy, and sexual function. It is not a "muscle hormone" in any narrow sense; it is a whole-body signalling molecule that happens to matter a great deal to lifters because muscle tissue is one of the places its signal lands most visibly.
Levels vary enormously between healthy people and across the day — highest in the morning, lower in the evening — and they decline gradually with age. Sleep, body composition, illness, and stress all move the number. That variability is exactly why a single reading, taken out of context, tells you so little, and why the conversation around testosterone so often goes wrong: people compare numbers as if they were comparing bench presses.
This is general information, not medical advice. Anyone with questions about their own hormone levels should talk to a doctor.
What surprised you most when you first learned what testosterone actually does — and what do you wish someone had explained sooner?