The researchers called their paper ‘Hype.’ A McMaster University review examined whether post-workout hormone spikes actually drive muscle growth. Three lines of evidence. One answer.
Two hundred times less of the hormone everyone calls ‘the muscle-building hormone.’ The same relative growth.
The researchers called their paper "Hype."
Not an editorial. Not a blog post. A peer-reviewed narrative review in Exercise and Sport Sciences Reviews by Van Every, D'Souza, and Phillips at McMaster University — one of the most respected exercise science labs in the world. The full title: Hormones, Hypertrophy, and Hype.
The question: does the testosterone surge after a heavy training session, the growth hormone spike, the IGF-1 response — does any of it actually drive muscle growth?
Their conclusion, after synthesizing three independent lines of evidence: those hormonal spikes are "neither sufficient nor necessary" for building muscle.
For anyone who's been reading articles about declining testosterone, staring at bloodwork, or weighing whether a supplement or a clinic might be the missing piece — the evidence behind that conclusion is worth the next ten minutes.
Van Every's McMaster review tested the hormone-drives-growth belief across three independent evidence domains — and found the same answer from all three: the training itself, not the hormones around it, is what builds muscle.
- Six independent studies each measured the testosterone, growth hormone, and IGF-1 surge after heavy training — then tracked whether any of those hormonal spikes predicted how much muscle participants actually built.
- The sex-based testosterone comparison tests the hormone-growth premise using the largest hormonal gap in human biology — a difference so extreme it should produce an unmissable growth gap, if the premise were correct.
- The strongest published challenge to this review's conclusion comes from a study that pharmacologically crashed testosterone below normal levels. The result clarifies rather than contradicts the finding.
- Van Every assesses the evidence behind cycle-synced training — a trend with 285 million TikTok views — and calls the periodization advice 'premature and even misguided.'
- The review identifies what actually drives muscle growth when hormones within the normal range don't. For anyone already training, the answer changes the mindset, not the routine.
Six Studies Measured the Hormone Spike. All Six Found Nothing.
The post-workout testosterone boost is one of the most entrenched ideas in training. Heavy squats. Compound movements. Short rest periods. The logic: spike your hormones, grow more muscle.
Van Every's review tested that logic against six independent studies that each measured the relationship between acute post-exercise hormonal elevations and muscle growth.
West and colleagues in 2010. West and colleagues again in 2012. Mitchell and colleagues in 2013. Morton and colleagues in 2016. Morton again in 2018. Mobley and colleagues in 2018.
Each study measured the post-exercise spikes in testosterone, growth hormone, and IGF-1. Each tracked whether those spikes predicted how much muscle the participants actually built.
Across all six: zero significant correlations between the hormone spike and muscle growth.
Not one weak positive trend. Not one borderline finding. Six independent labs, six different study designs, six measurements of the same question. Six zeroes.
One of those studies made the test as direct as possible. West and colleagues had twelve young men train each arm under different hormonal conditions for 15 weeks. One arm trained alone. The other trained alongside heavy leg exercises designed to flood the body with testosterone, growth hormone, and IGF-1.
After 15 weeks, the arm bathed in elevated hormones grew 10%. The arm without the hormone spike grew 12%. The difference was not statistically significant.
The hormonal environment was deliberately manipulated to be as different as possible. The muscle didn't respond differently.
Six zeroes is a pattern. But those studies measured what happens in the hours after a workout. The deeper question — the one that keeps someone awake checking bloodwork at 40 — is about baseline hormones. The review's second line of evidence answers it with a number that's difficult to forget.
Two Hundred Times
After puberty, women have roughly 15 times less total testosterone and as much as 200 times less free testosterone than men.
If testosterone drove muscle growth the way it's marketed, women would barely build any.
Roberts and colleagues pooled data from ten studies that tracked how much muscle men and women built, as a percentage of their starting size, from the same types of training programs. The difference between sexes was effectively zero — statistically indistinguishable, with no variation between studies.
Two hundred times less of the hormone everyone calls "the muscle-building hormone." The same relative growth.
West and colleagues found the same pattern at the cellular level. Despite 45 times more testosterone flowing in men's blood during the first hour after training, the rate at which muscle fibers built new protein was nearly identical between sexes.
The largest hormonal gap in human biology. Zero difference in the outcome the hormone is supposed to predict.
The natural objection arrives immediately: what about someone whose testosterone drops below normal? Not a 40-year-old sitting in the normal range. Someone whose levels crash to a fraction of that. Does testosterone matter then?
The Light Switch
Gharahdaghi and colleagues ran a study that reads like the perfect challenge to everything above. They used a pharmaceutical agent to suppress testosterone in young men to approximately 45 ng/dL — far below any normal range — and had them train for six weeks. [1]
Muscle growth was blunted. Strength gains were attenuated. The rate of muscle protein building was significantly lower than in the control group. When testosterone crashed below the physiological floor, it mattered.
But here's the distinction the evidence draws: 45 ng/dL is not 480 ng/dL. The pharmaceutical suppression took testosterone below the threshold where the body can maintain normal function. That's a clinical state, not the natural variation that shows up on bloodwork after 40.
The pattern across all the evidence points to a single frame. Testosterone works like a light switch, not a volume dial. Below a certain threshold, the switch is off and muscle growth is impaired. Above that threshold — and every healthy adult is above it — turning the dial higher does nothing detectable for growth.
The switch is binary. The dial is a myth sold in bottles.
If the post-workout spike is noise and baseline variation within the normal range doesn't predict growth, that raises an uncomfortable question about the products and services built on the opposite assumption.
Testosterone works like a light switch, not a volume dial. Below a certain threshold, the switch is off. Above it, turning the dial higher does nothing detectable for growth.
$3.7 Billion Built on a Variable That Doesn't Predict the Outcome
The global testosterone booster supplement market was estimated at approximately $3.7 billion in 2023 and is projected to nearly double to $6.75 billion by 2030. [2] The market frames declining testosterone after 30 as a problem requiring supplementation.
Van Every's evidence suggests the problem — for anyone with testosterone in the normal range — doesn't exist in the way it's sold. The supplement bottle. The optimization clinic. The bloodwork interpretation that labels the normal range as "suboptimal." Each is a commercial response to a variable the review found doesn't predict muscle growth.
The review makes no claim about whether testosterone matters for energy, mood, libido, or general health. It makes a specific claim about whether optimizing within-normal testosterone levels produces more muscle from training. Six studies, the sex-based comparison, and the Gharahdaghi data converge on the same answer: it doesn't.
The hormone-drives-growth belief isn't limited to testosterone. The same logic — optimize the hormone, optimize the results — gets applied to every hormonal fluctuation in the body. The pattern that built a $3.7 billion testosterone booster industry runs wherever there's a hormone and a product to sell.
285 Million Views, 4% Citing Any Research
The fastest-growing version of the hormone-optimization claim has nothing to do with testosterone — which makes it the clearest test of whether the framework itself holds up.
Cycle syncing — adjusting exercise and diet according to menstrual cycle phases — has become one of the largest fitness trends on social media. Pfender and colleagues analyzed 100 TikTok videos under the #cyclesyncing hashtag, which had accumulated 285 million views. [3]
Of the creators, only 30% showed any credentials. Of those, the vast majority were health coaches — only four out of a hundred were clinicians. And the number who cited any scientific research at all: 4%. The remaining 96% recommended training and diet changes without referencing a single study.
Van Every's review assessed the evidence beneath the trend: menstrual cycle-based training periodization is "premature and even misguided." The hormonal fluctuations across the cycle don't appear to meaningfully impact muscle growth from resistance training.
The review draws an important distinction. Menstrual cycle symptoms — cramps, pain, bloating — are real and may affect how a workout feels. But those symptoms are not evidence that training by cycle phase produces different growth. The experience of training changes. The adaptation from training doesn't.
Six zeroes from the hormone spike. A 200× gap with zero difference. Cycle-based periodization without a scientific foundation. Three independent lines of evidence, the same conclusion from all three. If hormones aren't driving growth, what is?
The Thing You Already Do
Van Every's review proposes that mechanical stimulus — the physical force applied to muscle fibers during resistance training — is the primary driver of muscle growth. Not the hormones circulating around the muscle. The mechanical loading of the muscle itself.
The evidence points to local signals within the muscle: proteins activated by mechanical stretch, receptor changes within the fiber, pathways triggered by contraction against resistance. These local mechanisms do the work that hormones were assumed to do.
For the person who's been training at 6 AM three mornings a week, wondering if the effort still matters with lower testosterone than at 25 — the evidence says the effort was always the point. The training was never the response to the hormone. The hormone was always a passenger in the training.
That answer is strong enough to change a training mindset. It's also honest enough to require boundaries.
Six independent labs, six different study designs, six measurements of the same question. Six zeroes.
What This Review Does and Doesn't Prove
Van Every's team picked the studies they considered strongest and built their case from those. They didn't use a formal search protocol designed to catch every study ever published on the topic. That means the conclusions reflect their expert judgment — strong judgment, given the lab, but judgment rather than an exhaustive mechanical process.
Most of the hormone-spike studies tested young men in their twenties. The evidence for how women build muscle is thinner — built mainly on what happens inside the muscle during training and on pooling results from multiple smaller studies.
The review also draws heavily from the Phillips lab at McMaster. Stuart Phillips has spent decades building the research program that produced several of the key studies cited. That's a concentration of perspective worth naming — not a flaw, but a lens.
The conclusions apply to endogenous hormones within the normal physiological range. Supraphysiological doses — the kind used in steroid cycles — are, in the authors' words, "markedly anabolic." That line is the defining boundary of the paper.
And the mechanisms through which men and women achieve similar muscle growth may differ. The outcome is settled. The biology beneath it is still being mapped.
Weight of Evidence
Two of the six studies went deeper than measuring the spike — and what they found points directly at the mechanism.
Morton's 2016 study tested every post-exercise hormone individually — testosterone, free testosterone, growth hormone, IGF-1 — against every measure of muscle growth in 49 men over 12 weeks. Zero correlations across the board.
Mitchell asked the follow-up: if hormones don't predict who builds muscle, what does? The answer was signals inside the muscle itself — including a receptor that responds to testosterone and a growth-triggering protein — which together explained 46% of the variation in how much muscle each person built.
What Comes Next
The switch is on. It has been on. The 6 AM alarm, the gym, the work — that was always the driver. Not the number on the bloodwork. Not the bottle in the cabinet.
Van Every's team synthesized three independent lines of evidence and reached the same conclusion from all three directions. The post-exercise hormone spike is noise. Baseline variation within the normal range doesn't predict growth. The mechanical stimulus — the training — builds muscle.
If hormones aren't the barrier, the next question the evidence opens is practical: how much training does someone actually need after 50? The evidence behind that question rewrites a second set of assumptions. The hormone question is settled. The training prescription is next.
The evidence doesn't just answer a question about hormones. It closes a set of decisions the Hormone Worrier has been agonizing over for months.
The bloodwork result that came back at 480 ng/dL — or 450, or 520 — is above the threshold where testosterone predicts growth. It was never the reason training felt harder after 40. Reviewing it every six months for reassurance doesn't change what happens in the gym.
The supplement bottle — the $62 monthly spend on a testosterone booster — is optimizing a variable that six studies found doesn't predict the outcome it's sold on. The spend doesn't need to gradually taper. It can stop.
The TRT clinic appointment considered at $200 per month — if the motivation is muscle growth and testosterone is in the normal range — is solving a problem the evidence says isn't there. That doesn't mean TRT is never warranted. It means the hypertrophy argument for it, within normal ranges, is the argument Van Every's review dismantles across three evidence domains.
What changes Monday morning isn't the training. The training was already the answer. What changes is the anxiety around the training — the suspicion that biology turned against him, that the effort might be wasted, that something pharmaceutical might be the missing variable. The evidence says: the variable was never missing.
What other research found
What this means for you
That bloodwork result — the one that came back at 450 or 480 or even 380 ng/dL — is roughly ten times higher than the level where testosterone starts to impair muscle growth.
Gharahdaghi and colleagues had to use a pharmaceutical agent to suppress testosterone to approximately 45 ng/dL before muscle growth was measurably blunted. That's not a decline-after-40 number. That's a clinical suppression floor that virtually no healthy man reaches through aging alone.
The evidence Van Every's review synthesizes doesn't say testosterone is irrelevant. It says the range where it matters is far below where age-related decline lands. Normal age-related changes in testosterone — the kind that show up on bloodwork after 40 — sit comfortably above the threshold. Training, not the number on the lab report, is what predicts growth.
The physiological evidence from Roberts and colleagues, pooling data from ten studies, found no measurable difference in relative muscle growth between men and women from the same types of training programs.
Your testosterone level is not your growth ceiling. The sex-based hormone gap is the largest in human biology — and it produces zero difference in the outcome you're training for.
For training around your menstrual cycle: Van Every's review found no evidence that the hormonal fluctuations across cycle phases affect how muscle adapts to training. Symptoms — cramps, bloating, fatigue — are real and may affect how a session feels. Adjusting intensity or exercise selection on those days is responsive to your body. Restructuring your entire training week by cycle phase is not supported by the current evidence.
This is a decision-level question, and Van Every's review draws a line that most sources don't.
Within the normal physiological range, optimizing testosterone does not predict additional muscle growth. Six studies tested the post-exercise hormone hypothesis. The sex-based comparison tested the baseline hormone hypothesis. Both found the same answer.
The review explicitly does not cover exogenous hormones at supraphysiological doses — the authors acknowledge those are 'markedly anabolic.' That's a different biological territory.
The distinction the evidence draws: if testosterone is clinically below normal — in the range Gharahdaghi's study tested, around 45 ng/dL — the conversation is medical, involving a physician, not a supplement label. If testosterone is within the normal range and the goal is muscle growth, the evidence points toward training stimulus as the variable that matters, not hormonal optimization.
Van Every's review has direct programming implications for clients who train around their menstrual cycle or ask about hormone-optimized protocols.
The evidence does not support phase-based loading adjustments — structuring lighter weeks during the luteal phase or heavier weeks during the follicular phase has no demonstrated effect on muscle adaptation.
What the evidence does support: adjusting session intensity when a client reports cramps, pain, bloating, or fatigue. That's symptom management, not cycle periodization. The distinction matters — symptoms affect training experience, hormonal fluctuations do not appear to affect training adaptation.
Van Every's review also raises an autonomy point worth considering: prescribing cycle-based restrictions may limit a client's agency over her own training decisions by implying her hormonal cycle determines what she can handle. The evidence suggests she can handle what her body tells her she can handle on any given day — cycle phase notwithstanding.
Before you change anything
This evidence applies to males and premenopausal females with testosterone within the normal physiological range.
The review explicitly excludes anyone using exogenous hormones — including testosterone replacement therapy, anabolic steroids, or hormonal contraceptives that alter the natural hormonal profile. The authors note that supraphysiological doses are 'markedly anabolic,' which is the defining boundary of the paper's conclusions.
Pregnant females are excluded from the review's scope. Postmenopausal females are addressed separately — the HRT evidence for this population showed lean mass preservation of approximately 400 grams, within the measurement error of the scanning equipment used.
Most of the cited studies on acute hormonal responses used young males in their twenties. The evidence base for females is smaller, built primarily on protein synthesis measurements and meta-analytic comparisons of relative hypertrophy. Applying these findings to older adults requires the assumption that the hormone-growth relationship doesn't fundamentally change with age — an assumption supported by the evidence but not directly tested in older populations.
Does not apply to: clinical hypogonadism (testosterone below the normal range), children or adolescents, hormonal disorders affecting the endocrine system, or anyone using pharmaceutical hormone interventions.
Mechanisms of how males and females achieve RET-induced hypertrophy may be different, though the review acknowledges this without full elucidation.
Understanding of nongenomic and intracrinologic mechanisms of testosterone in RET adaptations requires further investigation.
The role of progesterone remains to be elucidated, including whether receptors for progesterone exist in skeletal muscle.
Research on whether females should periodize RET programming to account for hormonal fluctuations is
The direction of this finding is consistent across three independent evidence domains. Post-exercise hormone spikes don't predict growth. Baseline testosterone differences within normal range don't predict growth. Menstrual cycle-based periodization isn't supported. Three different questions, all pointing the same way.
This is a narrative review — the authors selected the evidence they considered most relevant based on their expertise. There is no formal search protocol, no predefined inclusion criteria, and no risk-of-bias assessment of the cited studies. That makes the synthesis a product of the authors' judgment, which is both its strength (the Phillips lab has spent decades building this evidence base) and its limitation (the perspective is concentrated).
The convergent confidence is high: six studies on the hormone spike, a meta-analysis on the sex-based comparison, and multiple cited reviews on menstrual cycle periodization all point in the same direction. When three independent evidence domains converge, the conclusion doesn't depend on any single study being correct.
What remains uncertain: whether the mechanisms through which men and women achieve similar growth are identical or different. The outcome is settled. The biology beneath it is still being mapped.
Van Every's review closed the hormone question: within the normal range, testosterone isn't the variable that determines muscle growth. The training is.
But if the training is the driver — and you're over 50 — a practical question opens immediately. How much training volume does someone actually need at that age? Is the answer what the fitness industry assumes, or does aging change the dose-response curve the way it apparently doesn't change the hormone-growth relationship?
Radaelli's 2025 meta-analysis tested that question across 151 randomized controlled trials. The answer surprised researchers who expected the volume prescription to scale the same way at every age.
What This Study Found
All findings from this paper, in plain language.
- According to Van Every's review, the post-exercise surges in testosterone, growth hormone, and IGF-1 are 'neither sufficient nor necessary' for muscle growth from resistance training. The hormonal spike after a heavy session is noise, not signal.
- Women have roughly 15 times less total testosterone and up to 200 times less free testosterone than men. Despite this, pooled data from ten studies (Roberts meta-analysis) found the difference in relative muscle growth between sexes was statistically indistinguishable from zero (effect size 0.07, P = 0.31).
- Despite 45 times more testosterone in men's blood during the first hour after training (West 2012), the rate at which muscle fibers built new protein was nearly identical between sexes — 2.3-fold increase in men versus 2.7-fold in women.
- Six independent studies (West 2010, West 2012, Mitchell 2013, Morton 2016, Morton 2018, Mobley 2018) each measured the relationship between acute post-exercise hormone spikes and muscle growth. Across all six, zero found a significant correlation.
- Van Every's review proposes that mechanical stimulus — the physical force applied to muscle fibers during resistance training — drives growth through local signals within the muscle (receptor changes, contraction-activated pathways), not through systemic hormone levels.
- Van Every's review found that menstrual cycle-based training periodization — adjusting exercise by cycle phase — is 'premature and even misguided.' The hormonal fluctuations across the menstrual cycle don't appear to meaningfully impact muscle growth from resistance training.
- In postmenopausal women, hormone replacement therapy preserved approximately 400 grams of lean mass — a difference that falls within the measurement error of the DXA scanning equipment used to detect it.
- Men and women achieve similar relative muscle growth from resistance training, but Van Every's review notes the biological mechanisms driving that growth may differ between sexes. The outcome is settled. The biology beneath it is still being mapped.
- The review draws a distinction between menstrual cycle symptoms (cramps, pain, bloating) and training adaptations. Symptoms are real and may affect how a workout feels. But symptoms affecting the experience of training is not the same as hormonal fluctuations affecting how muscle adapts to training.
- Van Every calls for future studies using gold-standard methodology — blinding, adequate sample sizes, standardized assessment tools, and consistent protocols — to strengthen the evidence base, particularly for female populations and older adults.
- The review draws a defining boundary: within the normal physiological range, testosterone variation doesn't predict muscle growth. Below normal (Gharahdaghi's approximately 45 ng/dL), growth is impaired. Above physiological limits (supraphysiological doses used in steroid cycles), the authors acknowledge hormones are 'markedly anabolic.' The review's conclusions apply to the normal range only.
- Van Every's review suggests that prescribing cycle-phase training restrictions may limit a person's autonomy and agency over their own training decisions, potentially contradicting individualized programming principles.