Muscle Power vs Strength for Longevity

In the 1970s, a group of scientists sealed themselves inside a glass terrarium in California called Biosphere 2, meaning to grow every calorie they ate. The crops failed. The team ended up on an accidental diet of calorie restriction and low protein. When they emerged, some biomarkers of aging had improved. They had also lost their sex drive, their mood, and a good deal of muscle. Psychophysiologist Paul Taylor brings up this episode on Dr. Stephanie Estima's podcast, BETTER!, as the biggest accidental human experiment ever run on a low protein diet (79:39). His verdict: you might live longer that way, but, as he puts it, life will be crap (80:31).

That small, dry joke sits at the center of a much larger argument. Taylor, who holds a PhD in psychology plus a master's in exercise science and nutrition, spends nearly two hours making the case that the culture has the wrong scorecard for aging well. The scorecard most people use rewards thinness. The one Taylor wants people using rewards muscle, and specifically a quality of muscle that almost nobody measures: power.

The Pharmacy You Already Own

Start with the chemistry. Every time a muscle contracts, whether from lifting weights, doing housework, or walking the dog, it releases proteins and peptides called myokines. Scientists have identified more than 600 candidate myokines and understand what roughly 60 of them do (06:18). These molecules travel through the bloodstream and signal to organs well beyond the muscle itself.

"Exercise is medicine, and we now know the ingredients of that medicine, and the ingredients are myokines." — Paul Taylor [06:18]

Two of these molecules, irisin and lactate, cross the blood-brain barrier and trigger the release of brain-derived neurotrophic factor, or BDNF, a protein that helps grow new brain cells even in old age and protects existing ones from damage (08:21). Taylor's example is blunt: if two people suffer an identical stroke, the one who had exercised that morning, and so had more BDNF circulating, will come away with less brain damage.

This is also why Taylor treats inactivity as more than a missed opportunity. He quotes a line from exercise physiologist Frank Booth's 2012 paper in the Journal of Applied Physiology: the human genome has not changed in 45,000 years, and it still expects high physical activity for normal function, not optimal function (11:17).

"The human genome requires and expects us to be highly physically active for normal functioning." — Paul Taylor, quoting Frank Booth [11:17]

To see what normal once looked like, Taylor points to a 2016 Harvard study of the Hadza, a hunter-gatherer community in Tanzania. Hadza women average around 10,500 steps a day, and the group as a whole logs about 945 minutes of moderate to vigorous activity every week (13:14). Public health guidelines recommend 150 to 300 minutes. Taylor's point isn't that everyone should hit Hadza numbers starting Monday. It's that current guidelines are a floor, not a finish line, and that the modern, sedentary default is itself doing active harm to mood, calling it, in Taylor's phrase, an active depressant (11:17) that works against the six separate feel-good brain chemical systems exercise switches on at once, including dopamine, serotonin, and norepinephrine (10:52).

Power, Not Just Strength

If myokines explain why movement matters, the second half of the conversation explains which movement matters most as people age. Muscle size matters for longevity. Muscle strength matters more than size. But the newest research Taylor cites puts muscular power ahead of both (22:38). Power is simply how fast force gets produced, force times distance divided by time. It's the quality that lets someone catch themselves after a trip instead of falling.

People lose power at roughly three times the rate they lose strength, and the loss hits women harder, since women tend to carry more slow-twitch fiber on average while men carry more fast-twitch fiber, the type that disappears fastest with age (25:19). Taylor's prescription is specific: train with 30 to 50 percent of a one-rep max, and move the weight as fast as possible on the lifting phase, whether that's a jump squat, a box jump, or simply exploding up out of a squat after a slow, controlled descent (23:48).

The numbers behind this recommendation are what make the conversation land. Drawing on hazard-ratio studies covering more than a million people, Taylor runs through comparative risks of death over 15 years: hypertension carries a hazard ratio of 1.21, coronary artery disease 1.29, diabetes 1.4, and being a current smoker 1.41 (90:10). Low cardiorespiratory fitness compared with elite fitness carries a hazard ratio of 5.04 (91:00). Low muscular power compared with high muscular power carries a hazard ratio of roughly 5 for men and 6 for women, meaning the gap between weak and powerful muscle predicts death more strongly than smoking does (100:41). Nobody's doctor measures grip strength or muscular power at a checkup. Taylor thinks that's a bigger miss than it sounds.

Stress gets the same treatment. Taylor distinguishes a threat response from a challenge response, drawing on research by University at Buffalo psychologist Mark Seery. Facing a stressor as a threat routes the body through the HPA axis and cortisol, which clamps down blood vessels and reduces blood and oxygen to the brain, producing shutdown, procrastination, and avoidance (51:58). Facing the same stressor as a challenge activates the sympathetic nervous system instead, dilating blood vessels and priming the body and brain to act (51:25). The chemical difference matters because of how long it lasts: adrenaline and noradrenaline have a half-life of one to two minutes, so their effects clear within about ten minutes, while cortisol's half-life runs over an hour, meaning a stressful event can leave someone chemically affected three or four hours later (52:22). Chronic occupational stress compounds this: Taylor cites workplace research showing it causes the amygdala, the brain's threat-processing region, to enlarge, while the frontal lobes, responsible for judgment and self-control, shrink (47:10). That combination makes a stressed brain more reactive to threats and less able to regulate the eating, drinking, and avoidance behaviors that follow.

Diet gets a simpler filter than most listeners will expect. Taylor's rule: if a food recently grew out of the ground, off a tree, or ran, flew, or swam, and humans haven't interfered with it much, eat it (66:17). He cites an umbrella review, a review of reviews, showing ultra-processed food intake carries class one evidence, rare in nutrition research, of raising cardiovascular disease and death risk by 50 percent, anxiety disorder risk by 48 percent, and common mental health disorder risk by 53 percent, across 32 total negative outcomes (67:38). On protein, Taylor recommends 1.6 to 2.0 grams per kilogram of body weight for people past 40, to counter anabolic resistance, the age-related decline in how efficiently muscle turns protein into new tissue, though he stresses protein alone does nothing without resistance training behind it (70:08). He also flags the omega-3 index, a blood test measuring omega-3 levels in red blood cells over roughly the prior three months: people with an index of 8 or higher live about five years longer on average than those at 5 or below (72:44).

Which brings the conversation back to Biosphere 2 and the Blue Zones, the regions researcher Dan Buettner popularized as longevity hotspots eating low protein diets. Taylor calls the framing "blue zone bullshit" and argues the underlying research has been misrepresented, comparing it to the fraudulent reputation now attached to Ancel Keys's six-country study on saturated fat (77:50). Whatever the regions' true dietary patterns, Taylor's objection isn't really about data forensics. It's about what a culture chooses to optimize for. Estima closes the episode returning to the same idea in her own words, describing thinness as a dead end for the qualities that make a life worth living.

"That is where you go to die, you know? Like, your power goes to die there, your strength goes to die there, your muscle size goes to die there." — Dr. Stephanie Estima [101:06]

Taken together, the episode makes a quiet but pointed substitution. Instead of asking how little a body can weigh, it asks how much force that body can produce, how fast it can produce it, and how well its chemistry recovers from stress. None of that shows up on a bathroom scale. All of it, according to the hazard ratios Taylor cites, shows up in how long someone actually lives.