Building Muscle With Exercise And Reassessing Protein Intake | Stuart Phillips | AFP 50

The following is based on a conversation with Stuart Phillips, a professor of Kinesiology at McMaster University.

How does resistance training impact systemic health beyond muscle tissue?

Resistance training triggers molecular adaptations that extend well beyond localized muscular hypertrophy or increased oxidative capacity. When loaded, skeletal muscle acts as an endocrine organ, secreting hormone-like signaling molecules known as myokines or exerkines, as well as releasing extracellular vesicles. These factors circulate throughout the body, exerting beneficial biological effects on distant non-motor organs, including the brain, heart, and lungs. Consequently, resistance exercise alters systemic metabolic profiles and neural structures, such as increasing hippocampal volume, rather than simply improving localized mechanical strength or localized blood flow.

What is the relative contribution of dietary protein intake versus resistance training for muscle hypertrophy?

While adequate protein intake provides the necessary amino acid building blocks for muscle protein synthesis, resistance exercise serves as the primary metabolic driver for muscle hypertrophy. Mechanistically, loading muscle tissue generates the vast majority of the biological signal required for structural adaptation, a concept summarized by the metaphor that exercise “bakes the cake” while supplemental protein merely provides the “icing.” Comparative trial data demonstrates that incremental benefits from high-protein diets or supplementation represent a marginal slice of overall hyper-trophic gains compared to the stimulus provided by progressive resistance training itself.

How does end-of-range rep proximity drive adaptation during resistance training without high joint load?

Muscular hypertrophy and strength adaptations do not strictly require heavy external loading; rather, they depend on achieving mechanical tension near motor unit fatigue. By executing repetitions with lighter loads to the point of leaving only one or two repetitions in reserve (RIR), an individual recruits high-threshold motor units and induces a high degree of muscle fiber strain. This approach maximizes muscular plasticity while reducing peak joint stress and cumulative connective tissue damage, allowing long-term adaptation and mitigating the chronic wear associated with lifelong heavy lifting.

Cleaned Transcript

Jeroen Schreel: Welcome to Apple Finch Pudding, your gateway into the world of science. Today’s scientist is Stuart Phillips, a professor of kinesiology at McMaster University. His work focuses on skeletal muscle health. Welcome, Stuart.

Stuart Phillips: Thanks very much for having me, Jeroen. Pleasure to be here.

Jeroen Schreel: Before we start, do you have a fun science fact for our listeners?

Stuart Phillips: A fun science fact, yeah. Right off the bat, my fun science fact is that muscle, the tissue that I study, has been underappreciated—not just in terms of how it moves you, but in terms of the role that it plays in overall health.

Jeroen Schreel: We want to delve a little bit deeper into the relationship between muscles and health. You have dedicated years to this type of research. Was there a key moment in your life that triggered this?

Stuart Phillips: Yeah, I was an athlete my whole life—still very active—but I did my undergraduate degree in biochemistry. The entire time I was doing that degree, I played rugby. Just before my senior year, I was all set to come back. I was captain of the team, we had a great team, and we were going to win the championship. Then I broke my leg. I actually fractured the patella and had a cast from my hip to my ankle. I couldn’t play.

As a result, I took a lab course and realized how much I enjoyed research. When I got the cast off, I was amazed by the plasticity of human tissue—how quickly it disappeared, then reappeared, and how I had to regain control back of muscles I had forgotten how to use. In my last semester, I ran into a professor who taught human nutrition in the Department of Pediatrics here at McMaster. I asked if she was taking grad students; she said yes, and that was the start over 40 years ago.

We still study that plasticity today. In a controlled manner, we put a brace on someone’s leg—we don’t break their leg first because the ethics committee won’t let us do that—and observe muscle behavior.

Jeroen Schreel: That plasticity differs a lot between people, depending on age and individual factors. Is that something you look into as well?

Stuart Phillips: Yes, in both directions. We load muscles through weightlifting so muscle grows—it hypertrophies, getting bigger and stronger. On balance, that is more efficient in younger people than in older people. But we also look at muscle atrophy. The variability in individual response—how much you hypertrophy and how much you atrophy—is surprisingly large. Exercise or a lack of exercise follows some of the same principles as pharmacological drug responses: people’s responses vary tremendously.

Jeroen Schreel: It has been stated that if we could bottle the benefits of muscles and exercise into a pill, everyone would take it. Could you give us some insights on that?

Stuart Phillips: For a long time, we understood how muscle adapts to aerobic exercise; researchers in Scandinavia pushed that science early on. Now we are beginning to understand what resistance loading exercise does. Clearly, you need aspects of both forms of exercise for overall health.

We are beginning to appreciate the molecular complexity of making a muscle hypertrophic or oxidatively fit. Historically, people assumed exercise only affected the muscle, heart, and lungs. Now we see systemic effects on the brain and distant tissues. While people assume this is driven strictly by altered blood flow, that doesn’t fully explain it. Exercise stimulates muscle to release signaling molecules known as exerkines or myokines, as well as extracellular vesicles. This field has expanded rapidly alongside omics technologies that allow us to discover multiple biological pathways simultaneously.

Jeroen Schreel: There is a distinct difference between cardiovascular and resistance training, including their effects on mental state. For example, running immediately improves my mood, whereas resistance training doesn’t yield the exact same feeling.

Stuart Phillips: People gravitate toward what they are naturally good at, but the mental health benefits of exercise, walking, and being outdoors are significant. Ten years ago, if you told me exercise changes the size of brain structures like the hippocampus, I would have doubted it. But the data shows it does.

Jeroen Schreel: Generally speaking, is it just important to exercise regardless of whether it is cardio or resistance training, or is there a specific benefit to one over the other?

Stuart Phillips: Epidemiological data shows that humans are built to move. Sitting in front of screens all day is detrimental. Breaking up screen time, going for a walk, and maintaining fitness pays long-term dividends.

When I ran an exercise facility for 500 community members with an average age of 73, I saw that as people age, strength limits one set of daily activities while aerobic capacity limits another. Maintaining a higher functional ceiling protects your ability to perform activities of daily living. If you lose that capability, the risk for morbidity and early mortality increases. The most applicable advice is to do what you prefer, but aim to incorporate both modal forms of exercise.

Jeroen Schreel: What is the minimum amount of exercise people should be doing?

Stuart Phillips: Epidemiological data models mortality and morbidity curves relative to exercise volume. The single greatest reduction in risk occurs when you move an inactive individual into consistent, basic activity. After that initial transition, the curve flattens out. Running 10 miles a week yields substantial benefits; running 20 or 25 yields a bit more, but running 50 miles a week provides diminishing returns for general health. At extreme athletic levels, training demands cease to be about baseline health and become about performance requirements.

For average health, aim for roughly 150 minutes of moderate activity per week, plus two days of strength work. That strengthening work does not require heavy weights; bodyweight exercises like push-ups, sit-ups, and squats yield significant benefits.

Jeroen Schreel: When you state that exercise reduces mortality, why is that?

Stuart Phillips: The absolute rate of human mortality remains 1.0; everyone eventually dies. While people focus on longevity, what they generally care about is healthspan—the proportion of life spent in good health. Physical inactivity increases the incidence of early chronic diseases, such as cardiovascular disease, type 2 diabetes, and dementia.

Exercise is not a vaccine; it does not eliminate risk, but it manages and reduces risk. Managing healthspan requires physical activity, proper nutrition, regular sleep, stress management, and strong social connections within a community.

Jeroen Schreel: I appreciate the distinction between lifespan and healthspan. Regarding nutrition, you have updated your perspective over time on protein requirements for exercise. Could you explain that evolution?

Stuart Phillips: The quantitative intake targets I recommended previously remain sound, but my view on protein’s overall relative importance has shifted down. Decades ago, I viewed protein as paramount for muscle building. I previously argued that the standard Recommended Dietary Allowance (RDA) of 0.8 grams of protein per kilogram of body weight per day was a minimum threshold rather than an optimal target. I advocated for higher targets from 1.2 up to 1.6 grams per kilogram per day. Recent revisions to US dietary guidelines adopted those higher numbers.

However, subsequent controlled analyses forced me to reconsider protein’s relative impact compared to training itself. When comparing weightlifters taking protein supplements to those who do not, the overall variance in gains directly attributable to the supplement is minimal. Exercise bakes the cake; protein puts the icing on top. For most people, the act of resistance training performs the vast majority of the functional work. Protein is important, but relative to the stimulus of exercise, it is secondary.

Jeroen Schreel: Protein seems omnipresent in consumer food products now—there is protein yogurt, protein cheese, and protein water.

Stuart Phillips: Marketers use a “health halo” around protein to justify adding it to items where it doesn’t belong, like coffee, water, chips, and pretzels. The correct message that the 0.8 g/kg RDA was a minimum floor has been misconstrued to imply that populations are universally deficient. In reality, roughly 65 to 70 percent of Canadians—particularly men—already meet or exceed 1.2 to 1.6 g/kg daily protein levels through regular food intake.

If forced to choose between adding more dietary protein or adding an extra day of exercise, taking the extra exercise day is the correct health intervention almost every time. Protein deficiency is rare in developed economies; physical inactivity is widespread.

Jeroen Schreel: Can consuming too much protein cause adverse health effects, such as kidney damage or bone density loss?

Stuart Phillips: The hypothesis that high protein intake causes kidney failure in healthy individuals lacks supportive evidence. While restricting protein helps manage pre-existing renal disease, protein consumption does not originate kidney damage.

Similarly, the claim that protein weakens bones is false; bone mass is approximately 40% protein, making it a supportive nutrient when paired with adequate calcium and vitamin D.

Concerns about protein overstimulating growth factors to shorten lifespan stem primarily from model organism studies (like flies and rodents) and human observational data, where results are mixed depending on the source. Plant-based and fermented dairy proteins show neutral or positive outcomes, whereas processed red meat exhibits negative correlations. Double the effective intake threshold (e.g., exceeding ~3.2 g/kg/day) offers zero added benefit and wastes metabolic energy, but protein itself is rarely toxic at realistic dietary levels.

Jeroen Schreel: Beyond skeletal muscle, where does consumed protein go in the body?

Stuart Phillips: This comes down to protein turnover. Proteins consist of amino acids linked together like a brick wall. Nine of these amino acids are essential and must come from the diet.

While muscle contains a large reservoir of protein, its turnover rate is relatively slow. In contrast, internal organs—the liver, intestines, and splanchnic bed—are smaller in overall mass but turn over extremely rapidly. Consumed amino acids are preferentially directed toward remodeling intestinal tissues, internal organs, skin, blood proteins, and brain structures to maintain baseline systemic function.

Jeroen Schreel: A common performance supplement is creatine. How does creatine function in the body?

Stuart Phillips: Creatine is synthesized internally from amino acids, with over 90 percent stored in skeletal muscle as phosphocreatine. Phosphocreatine provides a rapid high-energy phosphate buffer during high-intensity metabolic bursts, like sprinting or lifting.

When supplemented (typically at 3 to 5 grams daily), muscle phosphocreatine saturation increases slightly. This extra capacity allows an individual to perform one or two additional work repetitions per set. Over time, that incremental training volume drives greater structural hypertrophy.

Supplemental response varies by individual based on baseline endogenous stores. “Responders” show clear weight and performance increases, whereas “non-responders” show little change. Women typically exhibit less dramatic fluid shifts and weight increases from creatine than men. If you do not see minor weight changes within the first two weeks of use, you are likely a non-responder. Creatine does not build muscle directly; it allows you to perform slightly more mechanical work, which then stimulates adaptation.

Jeroen Schreel: There is growing discussion about creatine supplementation for cognitive health and brain function. What is your perspective on that research?

Stuart Phillips: The brain relies on steady energy turnover, and conditions like dementia involve cellular energy failure. The hypothesis is that neural phosphocreatine stores might buffer against this decline.

I take creatine daily alongside winter vitamin D, partly as a low-risk bet on potential neuroprotective benefits. However, scientific validation remains in its early stages. We need large-scale, multi-center, double-blind clinical trials using brain imaging and validated cognitive metrics to confirm efficacy. While the evidence is not yet definitive, creatine is inexpensive, highly studied for safety over four decades, and presents minimal downside risk.

Jeroen Schreel: What daily dose of creatine do you use?

Stuart Phillips: I take 5 grams once per day year-round. High-dose “loading phases” are unnecessary because continuous daily dosing achieves muscle and tissue saturation over time. Excess creatine is simply excreted as creatinine in urine.

Jeroen Schreel: Aside from creatine and winter vitamin D, are there other supplements you personally take or recommend?

Stuart Phillips: I take a high-quality, third-party-tested fish oil supplement for long-chain omega-3 fatty acids, primarily for brain health, alongside eating whole fish. Algal-derived omega-3 sources are also effective alternatives.

Jeroen Schreel: Given reports that many commercial supplements lack claimed ingredients or contain contaminants, how can consumers identify high-quality products?

Stuart Phillips: Regulatory standards vary globally; the EU maintains strict baseline claims enforcement, whereas North American markets operate under looser dietary supplement legislation.

Consumers should look for third-party certifications intended for competitive athletes, such as NSF Certified for Sport or Informed Choice. These independent audits verify that products are free of banned substances and heavy metals, and confirm that label claims match actual contents. Our laboratory testing has uncovered commercial products containing minimal active ingredients or fillers like talcum powder. Independent testing stamps ensure manufacturing hygiene and product integrity.

Jeroen Schreel: Returning to the “cake” of physical training, what is your personal exercise routine?

Stuart Phillips: I achieve my 150 weekly minutes of cardio primarily via indoor cycling and daily walking, aiming for 6,000 to 7,000 steps. I strength train roughly three days a week using a home gym setup with moderate loads.

Instead of lifting heavy loads to absolute failure, I terminate sets with one or two repetitions left in reserve (RIR). Training close to failure without complete structural breakdown yields strong adaptive signals while protecting joints, tendons, and connective tissue. Continuous heavy loading over decades often results in cumulative joint damage that ends up restricting long-term mobility. Leaving repetitions in the tank allows you to train consistently over a lifetime.

Jeroen Schreel: What are the most accessible, high-impact exercise interventions for the general public?

Stuart Phillips: Purposeful walking is the lowest barrier to entry and consistently correlates with improved health outcomes. While 10,000 steps is an arbitrary number, mortality and morbidity benefits accrue rapidly between 6,000 and 8,000 steps per day, eventually plateauing near 12,000 steps.

However, walking should be paired with basic resistance activity. Preserving basic muscular strength—such as the ability to perform a bodyweight chair stand, push-up, or pull-up—is critical for preserving physical independence. Moving out of the lowest quartile of population strength yields the absolute largest reduction in health risks.

Jeroen Schreel: What major misconceptions lead people into that lowest health quartile as they age?

Stuart Phillips: People assume physical decline happens suddenly in their 50s or 60s, but age-related muscle and aerobic losses begin slowly in your 30s. As career and family responsibilities increase, physical activity often declines. Decades of small, compounding declines lead to significant physical limitations by middle age.

Making small, consistent investments in physical activity during your 30s and 40s prevents that steep trajectory. It is never too late to start—even studies in nonagenarians demonstrate that light strength training yields functional improvements—but starting earlier provides far greater compound benefits for long-term healthspan.

Jeroen Schreel: I think that is very essential, and it explains so well why we should exercise. We are made to move. Evolutionary, humans moved around a lot, and now evolutionary, we sit around a lot, sitting in chairs all day long.

Stuart Phillips: Yeah.

Jeroen Schreel: I feel we could keep talking, but we’re running out of time. So maybe before we close, do you have a take-home message for our listeners?

Stuart Phillips: Yeah. I come back to what I said before: first, it’s never too late to start. Even if you think you’re old, there’s always room to push back. Physical activity taken up at literally any age—even for people in their tenth decade of life, nonagenarians in their 90s—we can make them stronger and more physically able through gentle exercise. They can make gains. So it’s never too late to start, but the earlier you start to make that investment, the bigger the dividends will be.

Jeroen Schreel: Perfect. This was Apple Finch Pudding. I want to thank Stuart Phillips for all the information. Let’s meet again for the next episode of Apple Finch Pudding.

Relevant Papers

• Bauer et al., 2013. Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: A Position Paper From the PROT-AGE Study Group. Journal of the American Medical DIrectors Association, 14: pp. 542-559; https://doi.org/10.1016/j.jamda.2013.05.021
• Burgomaster et al., 2008. Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. The Journal of Physiology, 586: pp. 151-160; https://doi.org/10.1113/jphysiol.2007.142109
• Morton et al., 2018. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52: pp. 376-384; https://doi.org/10.1136/bjsports-2017-097608
• Tang et al., 2009. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. Journal of Applie Physiology, 107: pp. 987-992; https://doi.org/10.1152/japplphysiol.00076.2009
• Moore et al., 2009. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. The American Journal of Clinical Nutrition, 89: pp. 161-168; https://doi.org/10.3945/ajcn.2008.26401
• Moore et al., 2015. Protein Ingestion to Stimulate Myofibrillar Protein Synthesis Requires Greater Relative Protein Intakes in Healthy Older Versus Younger Men. The Journals of Gerontology: Series A, 70: pp. 57-62; https://doi.org/10.1093/gerona/glu103
• Greyvenstein et al., 2026. Tension to Translation: External to Internal Processes in Muscle Hypertrophy. Physiology, 41: pp. 325-343; https://doi.org/10.1152/physiol.00034.2025
• Badri Al-Mhanna et al., 2026. Comparative Effectiveness of Aerobic Exercise versus Resistance Training on Cardiometabolic Health in Patients with Diabesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Sports Science and Medicine, 25: pp. 637-655; https://doi.org/10.52082/jssm.2026.637