LONGEVITY SUMMARIES
Stay Strong. Stay Curious. Stay Informed.
Issue No. 1 · Power & Fast-Twitch Aging · longevitysummaries.com
60-SECOND SUMMARY
The Core Insight: Longevity isn’t just about how much you can lift (Strength); it’s about how fast you can move that weight (Power). While strength fades gradually, muscle power can plummet by 70% by age 80.
Why It Matters: Muscle power is your “safety net.” It’s what allows you to catch yourself during a trip, climb stairs with ease, and maintain independence. This relies on Fast-Twitch (Type II) fibers — the first to disappear as we age, but the most trainable back.
The Strategy: Move Fast. Trade a few slow, heavy sets for explosive, rapid movements (jump squats, medicine ball slams). Stop the set as soon as your speed drops. You are training velocity, not fatigue.
The 60-Second Test: Stand up from your chair as fast as possible 5 times today.
A Note from Michael
Welcome to the very first issue of Longevity Summaries.
I started this newsletter for a simple reason. The research I was reading every week — the studies, the podcast conversations, the clinical findings — was genuinely changing how I trained, ate, and thought about the decades ahead. And yet friends, family, and peers often had no idea this information was even out there.
Not because they didn’t care. They just didn’t have the time to find it, filter it, or figure out what actually mattered. So, I started sharing. And the response was always the same: “I had no idea this was out there. Keep sending me this stuff.”
That’s what this newsletter is. Each month I’ll dig through the latest research on exercise science, nutrition, and healthy aging — and distill what’s worth your attention into a clear read, with links to the original sources for anyone who wants to go deeper. This first issue opens with the topic I care about most: fast-twitch muscle and why preserving explosive power may be the single most important thing you can do for your long-term physical capability. I’ve also included our first nutrition feature on Fisetin — a plant compound with compelling research behind it.
Thank you for being here. Let’s get into it.
— Michael Britt
In This Issue
• Summary 1 — The muscle you’re losing faster than any other (and why it matters most)
• Summary 2 — Plyometrics after 60: safer than you think, more powerful than traditional lifting
• Nutrition Feature — Fisetin: the plant compound that targets zombie cells
• The Power Progression — Curated exercise demos for every level
• What I’m Reading This Month
EXERCISE SCIENCE
The Muscle You’re Losing Faster Than Any Other — And Why It Matters Most
Fast-twitch vs. slow-twitch muscle fibers — and the exercises that target each
Most people know they lose muscle as they age. Fewer know that the loss is not equal across all muscle types — and that the type disappearing fastest is also the most critical for independence, fall prevention, and long-term physical capability.
Fast-twitch muscle fibers (Type II) are responsible for everything quick and explosive in human movement: catching yourself when you stumble, standing up from a chair with force, sprinting for a bus, reacting instantly to uneven ground. They are the fibers that fire in milliseconds when your body needs to respond fast.
Research published in PMC on skeletal muscle aging confirms that the majority of motor units and fibers lost with advanced adult age are Type II. As these fibers atrophy and decline, the proportion of slow-twitch (Type I) fibers increases — and the body gradually loses the capacity for rapid, powerful movement. This shift is now understood to be a leading contributor to falls, loss of independence, and functional decline in older adults.
The data on prevalence is sobering. Sarcopenia affects nearly 25% of adults aged 65 and older and between 30 and 50% of those over 80. But the fast-twitch component begins much earlier, often in the 40s and 50s, and accelerates steadily if not specifically trained.
GLOSSARY
Sarcopenia — Age-related loss of muscle mass, strength, and function. Characterized by weakness, fatigue, balance problems, and reduced walking ability. Increases fall risk and can compromise a person’s ability to care for themselves independently.
The keyword is “specifically.” Standard aerobic exercise and even moderate resistance training do relatively little to target fast-twitch fibers. The nervous system recruits them primarily when movements are performed with maximal speed and intent — which is why training methodology matters as much as training volume.
Key Takeaway
Fast-twitch muscle fiber loss begins in your 40s and accelerates with age. It is a primary driver of falls, loss of independence, and functional decline — and it requires specific training to slow it down. Standard exercise alone is not enough.
What You Can Do This Week
→ Add intent to your existing lifts: perform the concentric (lifting) phase of any resistance exercise as explosively as possible, even if the actual movement is slow due to the weight. The neural signal matters.
→ Incorporate one power-focused movement per workout: box step-ups, medicine ball throws, or explosive chair stands all recruit fast-twitch fibers without high impact.
→ Think speed, not just strength: the research distinguishes between muscle strength (how much force) and muscle power (force times speed). Both matter, but power declines faster with age.
TRAINING METHODS
Plyometrics After 60: Safer Than You Think, More Powerful Than Traditional Lifting
The word “plyometrics” (plyometrics, or "jump training," are explosive exercises designed to increase power, speed, and agility by training muscles to exert maximum force in short intervals) tends to make older adults nervous. It conjures images of athletes leaping over boxes — activities that feel risky, high-impact, and designed for people half their age.
The research tells a very different story.
A systematic review published in PMC evaluated plyometric training in adults aged 60 and older across 18 trials involving nearly 300 subjects aged up to 79. Conclusion: not a single study reported increased injuries or adverse events. The researchers classified plyometric training as “a feasible and safe training option” with meaningful potential for improving power, functional performance, and bone health.
A separate randomized controlled trial compared 12 weeks of age-adapted plyometric exercise, traditional resistance training, and walking in men averaging 69 years old. The plyometric group improved significantly more on jump height, contraction speed, stair climbing performance, and functional capacity than both other groups.
The key to making plyometrics appropriate for older adults is adaptation. High-impact variations are not necessary as a starting point. The same fast-twitch recruitment can be achieved through low-impact alternatives: explosive chair stands, quick step-ups, mini-hops, or even rapid heel raises. The intent and speed of the movement is what matters neurologically — not the height or impact.
Key Takeaway
Age-adapted plyometric training is safe for adults in their 60s, 70s, and beyond — and outperforms traditional resistance training on key power and functional capacity measures. Movement speed and intent matter more than impact level.
What You Can Do This Week
• Start with explosive chair stands: sit in a sturdy chair, then stand as quickly as possible using only leg power (no arm push). Rest, repeat 8–10 times. Evidence-backed, zero-impact, highly effective.
• Add quick step-ups: step onto a low, stable surface as quickly as possible, emphasizing the drive through the planted foot. Slow the descent. 8–10 reps each side.
• Mini-hops in place: small, quick hops on both feet for 10–15 seconds, focusing on minimal ground contact time. Build over several weeks.
Source: The Efficacy and Safety of Lower-Limb Plyometric Training in Older Adults — PMC Systematic Review
Source: Age-Adapted Plyometric Exercise vs. Resistance Training in Older Men — PMC (2020)
NUTRITION FEATURE
CATEGORY: Cellular Cleanup – Age Proofing Your Cells
Plant-Based Benefit: The Power of Fisetin and Cellular Health
Before we dive into this specific plant compound, let’s look at the "why." As we age, some of our cells reach a state where they stop dividing but don't clear out as they should. These are known as senescent cells.
Think of them as "lingering cells" that have overstayed their welcome. Instead of being recycled, they remain in your tissues and release inflammatory signals that can "pollute" the environment for neighboring healthy cells. Scientists call this chronic, age-related inflammation "inflammaging," and it is a primary driver of biological aging.
Senotherapeutics is the exciting new field of health science dedicated to managing these cells—either by helping the body clear them away (senolytics) or by "quieting" their inflammatory signals (senomorphics). Fisetin is currently one of the most researched natural compounds leading this charge.
WHAT IS FISETIN?
Fisetin is a naturally occurring flavonoid found in common fruits and vegetables. While it has always been prized as a powerful antioxidant, longevity researchers are now focused on its role as a natural cleanup agent. It helps the body identify and prune away those senescent cells to make room for healthier cellular function.
THE LONGEVITY MECHANISM
• Senolytic Activity: Fisetin has shown a remarkable ability to selectively trigger the natural recycling of senescent cells without affecting healthy, active ones. In animal studies, this resulted in a lower inflammatory burden and a visible extension of healthspan.
• Cognitive Protection: Fisetin also boosts glutathione production — your body’s primary antioxidant — which helps protect brain cells from oxidative stress and supports long-term cognitive health.
BEST DIETARY SOURCES
To support your cellular renewal through whole foods, incorporate these high-concentration options into your meals:
Plant Source
Relative Concentration
Strawberries
Highest (approx. 160 μg/g)
Apples
Moderate (approx. 27 μg/g)
Persimmons
Moderate (approx. 10 μg/g)
Onions & Cucumbers
Low but consistent
THE SOURCER’S TIP
To get the most “bang for your bite,” opt for organic strawberries when possible. Plants often produce Fisetin in response to environmental stressors; organically grown berries often have to "work harder" than conventional ones, resulting in higher concentrations of these protective nutrients.
A Note on the Science
The research on Fisetin as a cellular cleanup tool is incredibly promising but still in its early chapters. While animal studies have shown dramatic results, human clinical trials are currently ongoing.
The good news? Strawberries, apples, and onions are foundational to a healthy diet regardless. They offer a massive range of benefits beyond Fisetin alone. If you are considering high-dose supplementation, that is a specific conversation to have with your healthcare provider to ensure it fits your personal health profile.
THE POWER PROGRESSION
Curated Exercise Demos for Every Level
I’ve searched through dozens of tutorials to find the clearest, most safety-conscious demonstrations for our community. These resources emphasize form and control — the same “form-first” principles I’ve spent decades studying. Use the level that matches where you are today, not where you’d like to be.
LEVEL 1 — Beginner / Inactive
Chair Sit to Stand — Watch demo · Drive up as fast as possible. The speed is the training.
Wall Push-Ups — Watch demo · Explosive intent on the push phase. Foundation for upper-body power.
LEVEL 2 — Active
5 Essential Exercises for Over 60 — Watch demo · Functional movements for real-world independence and power.
LEVEL 3 — Advanced
10 Advanced Functional Movements — Watch demo · Higher velocity to maximize fast-twitch fiber recruitment. Explosive concentric phase throughout.
THE SOURCER’S SAFETY RULE
Power training is not about exhaustion — it is about movement speed and quality.
Stop the set when your speed slows down. You are training velocity, not fatigue. Short, explosive sets are often more effective than long sets performed slowly. Quality of movement always takes precedence over quantity of repetitions.
RESEARCH SPOTLIGHT
The 8-Week Power Turnaround
One study published in the Journal of Aging and Physical Activity examined explosive training for older adults with an average age of 67.
WHAT THEY STUDIED
Researchers examined the effects of an 8-week high-velocity resistance training program in older adults (average age 67), measuring changes in neuromuscular function, jump performance, and markers of muscle damage.
WHAT THEY FOUND
14.2% increase in jump height. 22.9% improvement in neuromuscular efficiency. No significant increases in muscle damage or inflammation. The results held across the full age range of participants.
WHY IT MATTERS
This study directly addresses the concern that explosive training is too risky or ineffective for older adults. The data says otherwise — significant power gains are achievable in as little as 8 weeks, with no meaningful increase in injury risk.
WHAT YOU CAN DO TODAY
You don’t need 8 weeks to start. Begin with one explosive set per session — chair stands performed as quickly as possible, or explosive heel raises. Track your speed subjectively: are you moving faster than last week? That’s the measure that matters.
WHAT I’M READING THIS MONTH
Three pieces worth your time this month:
HIIT and Peak Power Development
High-intensity interval training recruits fast-twitch fibers more effectively than sustained moderate exercise — and the benefits apply at any age.
Empower Older Adults — VU Research →
Preserving Fast-Twitch Fibers Through Strength Training
Strength and power training preserve fast-twitch fibers at near-youthful levels in adults who train consistently across decades.
Journal of Applied Physiology →
Power Training and Fall Prevention
Meta-analysis showing meaningful improvements in Timed Up-and-Go test scores — one of the strongest fall risk predictors — from power-based training programs.
ResearchGate →
Until Next Month
One pattern appears repeatedly across the research covered this issue: the body remains remarkably adaptable, even later in life. The difference between ordinary aging and powerful aging often comes down to one simple variable: movement speed.
Next month, we’ll go deeper into Nutrition & Metabolic Health — protein timing for muscle preservation, the gut microbiome’s role in aging, and what the current evidence says about fasting protocols. Grip strength — one of the strongest single predictors of longevity — is also on the horizon.
Stay strong. Stay curious.
— Michael Britt
P.S. If you found this issue useful, consider sharing it with someone who would benefit. The goal of Longevity Summaries is to help people stay informed without spending hours doing the research themselves.