I can't tell you how many times a new client has sat down with me and said some version of, "I want to tone up, but I don't want to get bulky." Every single time, I ask the same follow-up question: "What does 'toned' actually mean to you?" And almost every single time, nobody can quite answer it.
Here's the thing — I get it. That fear is everywhere, and nobody ever explained the actual biology behind it. So let's fix that. No bro science, no guessing, just what the research actually shows about how women's muscles respond to training.
There's No Such Thing as "Toning" Your Muscles
I'm going to say something that might sound blunt: "toning" isn't a real physiological process. A muscle doesn't have a special "toned" setting. Physiologically, a muscle only does one of three things — it grows (hypertrophy), it stays the same, or it shrinks (atrophy). That's it. There's no fourth option where it gets "long and lean" instead of "big."
This isn't just semantics. Brad Schoenfeld's widely cited 2010 review in the Journal of Strength and Conditioning Research lays out the actual mechanisms behind muscle growth — mechanical tension, metabolic stress, and muscle damage — and none of them produce a different kind of muscle tissue depending on who's lifting. Your muscle fibers respond to the same biological signals whether you're a 25-year-old guy or a 45-year-old mom. The word "toned" is really just shorthand people use for "some visible muscle, not a lot of fat covering it." We'll come back to that.
Why Testosterone Is the Real Reason Women Don't "Bulk" by Accident
So if muscle only grows or shrinks, why don't women who lift heavy turn into bodybuilders overnight? Testosterone. Specifically, how little of it women's bodies produce compared to men's.
This isn't a small gap — it's enormous. Clark and colleagues, writing in Clinical Endocrinology in 2019, documented that circulating testosterone in men runs roughly 15 to 20 times higher than in women, with essentially zero overlap between the two populations. Handelsman, Hirschberg, and Bermon's 2018 review in Endocrine Reviews goes even further, showing just how central testosterone is to building and maintaining skeletal muscle mass.
Here's why that matters for you: testosterone is one of the primary hormonal drivers of how much muscle protein synthesis you can stack up over time. With dramatically less of it circulating, your body simply doesn't have the hormonal environment to pack on size the way a man's does — even if you train exactly as hard, eat the same way, and lift the same weights. You'd have to train with serious intent, for years, eating in a structured surplus, to build a noticeably "bulky" physique. It doesn't happen by accident from a few months of squats and deadlifts.
Women and Men Build Muscle at Nearly the Same Rate (Percentage-Wise)
Now here's the part that surprises my clients the most. Less testosterone doesn't mean your training is "working less." A 2025 systematic review and Bayesian meta-analysis by Refalo and colleagues, published in PeerJ, compared how men and women respond to the same resistance training programs.
The finding: when you look at absolute muscle growth — the raw amount of tissue added — men gain slightly more, which tracks with their larger starting muscle mass and higher testosterone. But when you look at relative growth — the percentage increase from each person's own starting point — women and men build muscle at essentially the same rate. Your muscle is just as responsive to the stimulus as anyone else's. You're not training a "weaker" or "slower" system. You're training a smaller one, with different hormonal support, that adapts proportionally just as well.
I tell my female clients this constantly: your results aren't smaller because your effort matters less. They're smaller in raw numbers because your baseline and your hormones are different — not because your body is bad at building muscle.
So What Actually Creates That "Toned" Look?
Let's close the loop on the word that started this whole conversation. If "toning" isn't real, what are people actually seeing when they say someone looks toned?
Two things, working together. First, some degree of actual muscle hypertrophy — even a modest amount of added muscle changes the shape and firmness of the area underneath your skin. Second, and just as important, a lower body fat percentage that allows that muscle shape to show through instead of staying hidden under a layer of subcutaneous fat. "Toned" is really just visible muscle definition — and definition requires both ingredients. You can build plenty of muscle and still not look "toned" if body fat is high enough to obscure it. You can also be lean with very little muscle and look soft rather than defined. The look everyone's chasing comes from combining the two, not from doing some special lightweight, high-rep routine that trains muscle differently.
The Takeaway
Stop training around a fear of something that isn't physiologically possible by accident. Your muscles grow, stay the same, or shrink — full stop. Thanks to dramatically lower testosterone, you're not going to wake up bulky from a progressive lifting program. And the research shows your muscle is just as responsive to training as anyone else's, percentage-wise. Lift heavy, progressively overload, eat to support your goals, and let your body fat come down where it needs to. That combination — real muscle, visible under lower body fat — is what "toned" has always actually meant.
References
- Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research, 24(10), 2857–2872.
- Handelsman, D. J., Hirschberg, A. L., & Bermon, S. (2018). Circulating testosterone as the hormonal basis of sex differences in athletic performance. Endocrine Reviews, 39(5), 803–829.
- Clark, R. V., Wald, J. A., Swerdloff, R. S., Wang, C., Wu, F. C. W., Bowers, L. D., & Matsumoto, A. M. (2019). Large divergence in testosterone concentrations between men and women: Frame of reference for elite athletes in sex-specific competition in sports, a narrative review. Clinical Endocrinology, 90(1), 15–22.
- Refalo, M. C., Nuckols, G., Galpin, A. J., Gallagher, I. J., Hamilton, D. L., & Fyfe, J. J. (2025). Sex differences in absolute and relative changes in muscle size following resistance training in healthy adults: a systematic review with Bayesian meta-analysis. PeerJ, 13, e19042.
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