Heavy lower-body exercises like squats and deadlifts do cause a short-lived spike in circulating testosterone, but the increase is modest, temporary, and almost certainly too brief to drive meaningful muscle growth on its own. The idea that “leg day boosts testosterone” is one of the most persistent claims in gym culture, and it is built on a kernel of real physiology wrapped in a lot of wishful extrapolation. What the research actually shows is more nuanced and, in some ways, more interesting than the simple story.
The Acute Spike Is Real
When you perform a demanding bout of resistance exercise, your blood levels of testosterone rise. This has been documented repeatedly across different protocols and populations. In a study comparing lower-body exercise protocols, both total testosterone and bioavailable testosterone increased during a standardized exercise session, along with growth hormone.1PubMed Central. Effects of Different Types of Lower Body Resistance Exercise on Upper-body Strength in Men and Women, with Special Reference to Anabolic Hormones The rise tends to happen during and immediately after the workout, with levels returning to baseline within about 30 to 60 minutes in most studies.
Legs are home to some of the largest muscles in the body, and working them hard creates a massive metabolic demand. That demand appears to be the key driver. Research on the acute hormonal response has consistently found that higher-volume sessions with shorter rest periods produce the strongest testosterone bump.2PubMed. Testosterone physiology in resistance exercise and training: the up-stream regulatory elements This is why squats, leg presses, and deadlifts get singled out: they recruit a lot of muscle mass and allow you to move heavy loads, which checks both the volume and intensity boxes.
What Drives the Spike
The acute testosterone response is sensitive to a few workout variables. One of the most studied is the rest interval between sets. In trained men, a hypertrophy-style protocol with 60-second rest periods produced significant increases in total testosterone from pre- to post-exercise, with values climbing from roughly 7.3 to 8.9 ng/mL immediately after training and remaining elevated at 15 and 30 minutes post-exercise.3PubMed Central. Influence of rest interval length on acute testosterone and cortisol responses to volume-load-equated total body hypertrophic and strength protocols Strength protocols showed a smaller and less consistent bump at the same rest intervals.
But the picture with rest periods is not as straightforward as “shorter is better.” When researchers measured the testosterone-to-cortisol ratio, a marker some use to gauge anabolic balance, protocols with very short rest (60 seconds) actually produced a worse ratio than longer rest (120 seconds) because cortisol surged alongside testosterone.4Apunts Sports Medicine. Effects of very short rest periods on testosterone to cortisol ratio during heavy resistance exercise in men So hammering yourself with minimal rest might boost raw testosterone numbers while simultaneously raising a stress hormone that counteracts some of those anabolic signals.
Volume of work matters too. Salivary testosterone and cortisol both increased after a hypertrophy-style scheme but showed little change after power or maximal-strength protocols performed over the same workout duration.5The Journal of Strength & Conditioning Research. The Salivary Testosterone and Cortisol Response to Three Loading Schemes The greater total volume of weight moved during hypertrophy training likely explains the difference, which fits the broader pattern: metabolic stress and accumulated fatigue seem to signal the endocrine system more powerfully than simply lifting heavy for a few reps.
The Spike Fades Fast and Does Not Stick Around
Here is where the leg-day-testosterone narrative starts to crumble. That post-workout spike returns to baseline quickly, usually within an hour. More importantly, training over weeks and months does not raise your resting testosterone. A systematic review and meta-analysis pooling data from multiple trials of insufficiently active men found that exercise training had essentially zero effect on resting total testosterone concentrations. The effect was negligible regardless of whether participants did resistance or aerobic training, and regardless of whether they were younger or older.6The Journal of Strength & Conditioning Research. Effects of Exercise Training on Resting Testosterone Concentrations in Insufficiently Active Men: A Systematic Review and Meta-Analysis
This finding is crucial because resting testosterone is what determines your hormonal environment for the other 23 hours of the day when you are not training. If leg day produced a meaningful, lasting testosterone increase, you would expect resting levels to climb over a training program. They do not. The acute spike, while real, is a transient physiological event, not a shift in your baseline hormonal status.
Does the Acute Spike Even Help Build Muscle?
This is the question that matters most to people repeating the “never skip leg day for your hormones” mantra, and the evidence here is surprisingly clear. One well-designed training study tracked hormonal responses and strength gains in men over 10 weeks. In the first week, short rest intervals between sets produced greater post-exercise testosterone than longer rest intervals. But by week five, the difference had shrunk, and by week ten it had disappeared entirely. Crucially, the hormonal response was “highly variable and may not necessarily be predictive of strength and lean tissue gains.”7The Journal of Strength & Conditioning Research. The Effect of Resistive Exercise Rest Interval on Hormonal Response, Strength, and Hypertrophy With Training
In other words, the guys who got the biggest testosterone spikes did not necessarily gain the most muscle or strength. That is a pattern that has held up across multiple studies and has shifted how exercise scientists think about the role of hormones in training adaptation.
Androgen Receptors May Matter More Than Circulating Hormones
If the brief post-workout testosterone bump is not the main driver of muscle growth, what is? A growing body of research points to what happens inside the muscle cell rather than what floats through the bloodstream. One study found that high-load resistance exercise increased androgen receptor-DNA binding and activated growth-related signaling pathways in muscle tissue, all without any significant increases in muscle testosterone, dihydrotestosterone, or serum total testosterone.8PubMed Central. High-Load Resistance Exercise Augments Androgen Receptor-DNA Binding and Wnt/β-Catenin Signaling without Increases in Serum/Muscle Androgens or Androgen Receptor Content
Separately, researchers found that androgen receptor content in muscle tissue was higher in men who responded well to resistance training than in those who responded poorly, even though systemic hormone levels were similar between the groups.9Frontiers in Physiology. Muscle Androgen Receptor Content but Not Systemic Hormones Is Associated With Resistance Training-Induced Skeletal Muscle Hypertrophy in Healthy, Young Men This suggests that how sensitive your muscles are to the testosterone already circulating in your body may be far more important than whether your workout briefly spiked that circulating level by a few percent. Think of it like a radio signal: turning up the volume a little for 30 minutes matters less than having a better antenna all the time.
The Hemoconcentration Problem
Some of the post-exercise testosterone rise may not even represent an actual increase in hormone production. A study of older men found that testosterone rose about 39% during exercise, but total serum protein also rose about 13% at the same time, and the sex hormone-binding globulin increase correlated strongly with the testosterone increase. The researchers concluded that hemoconcentration, meaning the loss of plasma volume through sweating and fluid shifts during exercise, partly contributed to the apparent rise in circulating testosterone levels.10PubMed. Exercise increases serum testosterone and sex hormone-binding globulin levels in older men Both testosterone and protein concentrations returned rapidly to baseline after exercise, consistent with fluid rebalancing rather than sustained hormone production.
This does not mean the entire spike is an artifact. Genuine increases in testosterone secretion do occur during exercise. But it means some of the numbers you see cited in gym forums are inflated by a concentration effect, the way a cup of soup gets “saltier” as water evaporates even though no salt was added.
What About Age?
Older men have lower baseline testosterone than younger men, which raises a practical question: does exercise-induced testosterone matter more for them? Middle-aged and older men do experience an acute testosterone increase after high-intensity resistance exercise, and the relative magnitude of that increase is similar to what younger men experience.11PubMed. Effects of age on testosterone responses to resistance exercise and musculoskeletal variables in men The absolute values are lower because they are starting from a lower baseline, but the proportional spike is comparable.
That said, the meta-analysis on resting testosterone found no chronic elevation in either younger or older subgroups after exercise training programs. So while older men get the same acute response as younger men, they do not get any lasting hormonal benefit from consistent training either. The benefits of resistance training for older adults are enormous, including preservation of muscle mass, bone density, and functional capacity, but those benefits are driven by mechanical loading and neuromuscular adaptations rather than by hormonal shifts.
Does Nutrition Around Your Workout Change the Hormone Response?
Protein shakes and carbohydrate drinks are a staple of gym culture, and some people time them around leg day specifically in the hope of amplifying the testosterone spike. The research does not support this strategy. When researchers tested the effects of ingesting protein with various forms of carbohydrate after resistance exercise, they found no significant differences between groups in testosterone, cortisol, or the testosterone-to-cortisol ratio.12PubMed Central. Effects of ingesting protein with various forms of carbohydrate following resistance-exercise on substrate availability and markers of anabolism, catabolism, and immunity Another study using a liquid carbohydrate and essential amino acid drink during a single bout of resistance exercise similarly found no between-group differences in exercise-induced growth hormone or testosterone levels compared with a placebo.13PubMed. Effects of liquid carbohydrate/essential amino acid ingestion on acute hormonal response during a single bout of resistance exercise in untrained men
Post-workout nutrition is still valuable for recovery, muscle protein synthesis, and glycogen replenishment. But the idea that a specific shake or meal can amplify the hormonal response to training lacks support. Your endocrine system responds to the mechanical and metabolic stress of the exercise itself, not to what you eat in the window around it, at least when it comes to testosterone.
Morning Versus Evening Training
Testosterone follows a circadian rhythm, peaking in the early morning and declining throughout the day. You might assume that training in the morning, when baseline testosterone is highest, would produce a larger post-exercise spike, or that evening training would be less hormonally productive. Research on this question found that the testosterone response to resistance exercise was similar regardless of whether the workout took place in the morning or afternoon.14The Journal of Strength & Conditioning Research. Intensive Resistance Exercise and Circadian Salivary Testosterone Concentrations Among Young Male Recreational Lifters If you prefer morning sessions, great. If evenings work better for your schedule, the hormonal difference is not something worth rearranging your life over.
The Leg Day Priming Effect on Upper Body
One version of the leg-day-testosterone claim goes further: that training legs before or alongside your upper body will boost testosterone enough to enhance upper-body gains. There is some intriguing evidence on exercise sequencing, though the mechanism may not be testosterone-dependent. In one study, a group that performed high-volume hypertrophy training for the lower body alongside maximal-strength training for the upper body saw greater bench press strength gains, bench press power, and arm muscle size compared with a group that did high-intensity strength work for both upper and lower body.15PubMed Central. Effect of Lower-Body Resistance Training on Upper-Body Strength Adaptation in Trained Men
That looks like it supports the hormone-priming theory at first glance. But consider that the high-volume lower-body group was doing fundamentally different training than the comparison group. They performed more total work, accumulated more metabolic stress, and stimulated more systemic recovery demand. Any number of mechanisms could explain the upper-body benefit, including greater systemic growth factor release, upregulation of protein synthesis pathways, or simply the training effect of higher total work volume. Pinning it on testosterone specifically goes beyond what the data show.
Why the Variability in Study Results
If you dig into the research, you will find studies showing dramatic post-exercise testosterone spikes and others showing almost nothing. A review of the existing literature concluded that this variability can be explained by numerous factors, including the type of exercise performed, training intensity and rest period duration, study population characteristics such as age and fitness level, and the time point at which testosterone was measured.16PubMed Central. Various Factors May Modulate the Effect of Exercise on Testosterone Levels in Men Measuring testosterone five minutes after a workout produces very different numbers than measuring it an hour later. Studying lean, trained 25-year-olds yields different results than studying sedentary 65-year-olds. These methodological differences explain why you can find a study to support almost any claim if you cherry-pick.
Long-Term Strength Training and Bone Density
A related claim you sometimes hear is that the hormonal changes from resistance training contribute to improvements in bone mineral density. While strength training does benefit bone health over time, a study specifically investigating the hormonal relationships underlying those bone density changes found no significant changes in growth hormone, insulin-like growth factor I, testosterone, osteocalcin, or skeletal alkaline phosphatase after training.17PubMed Central. Effects of strength training on bone mineral density: hormonal and bone turnover relationships The mechanical loading on the bones themselves, not the hormones released during exercise, appears to be what drives adaptation. This echoes the broader pattern: resistance training works, but it works through local mechanical signals more than through systemic hormonal changes.
Practical Takeaways for Your Training
None of this means you should skip leg day. Lower-body training builds the largest and most functional muscles in your body, improves athletic performance, protects your joints and bones, and contributes to metabolic health in ways that have nothing to do with testosterone. The problem is not with leg training itself but with the idea that its hormonal effects are a meaningful contributor to your results.
If you have been structuring your workouts around the belief that squats will flood your system with testosterone and make your biceps grow, the evidence suggests you are overcomplicating things. Train your legs because legs matter. Train your upper body because upper body matters. The best program for muscle growth is one that provides sufficient mechanical tension and volume to each muscle group you want to develop, with progressive overload over time. Whether a brief hormonal blip happens during the session is, based on the evidence available, a footnote rather than a chapter in the story of how your body adapts to training.