In this episode of the Flex Diet Podcast, I break down why I built the Physiologic Flexibility Certification (PhysFlex) as a “level two” continuation after you’ve already got the basics of nutrition, training, and recovery mostly dialed in. I explain how Phys Flex targets four overlapping homeostatic regulators—temperature (heat/cold exposure), pH (acidity/alkalinity shifts), expanded fuels (ketones and lactate), and oxygen/CO2 regulation (breathing)—and why taking a systems view matters more than treating everything in silos.

I share examples of how these pillars can become the real limiter in recovery and performance, including high-intensity work, long-duration events, and signs like elevated overnight respiration rate. Enrollment is open from Monday, October 12 through midnight PST Monday, October 19, 2026, and I’m offering direct email access for questions.

Enroll here: https://physiologic.miketnelson.com/sales

Episode Timestamps:

• 00:00 Welcome and Podcast Focus
• 00:19 Course Enrollment Window
• 01:44 Who This Certification Is For
• 02:48 Why Four Pillars Together
• 03:41 The Four Homeostatic Pillars
• 05:05 Systems Thinking Over Silos
• 08:07 Applying the Framework to Recovery
• 11:41 Course Structure and Interventions
• 13:09 Support, Email Access, Next Guest
• 13:58 Medical Disclaimer and Closing

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Dr. Jordan Shallow, D.C., known as “The Muscle Doc,” is a chiropractor, strength and conditioning coach, and former competitive powerlifter. He is the founder of Pre-Script®, an education company that teaches coaches applied biomechanics and resistance training.

Is getting stronger really about muscle, or about how well your nervous system learns the lift? Dr. Jordan Shallow, “The Muscle Doc,” explains why strength and size follow skill, how your senses shape movement, and how simple sensory inputs may change the way you train.

Expect to learn when internal versus external cues make sense for strength and hypertrophy, how an intermediate lifter can use practice volume and frequency, why great lifters treat the empty bar like the heavy one, how touch, vibration, skin stretch and pressure may influence movement, and how neuroplasticity, lucid dreaming and film study connect to learning skills — and much more.

Connect with Jordan:

• Website: themuscledoc.com
• Pre-Script: pre-script.com
• Instagram: @the_muscle_doc
• Pre-Script on Instagram: @pre_script

Episodes you'll enjoy next:

• #401 — Psychedelics, Neuroplasticity and the Military-to-Spiritual Journey with Rick Alexander: A former Special Operations combat medic explains how a psychedelic experience reshaped his worldview, and what it taught him about neuroplasticity.
• #311 — Maximizing Athletic Performance with Neurology: Insights from Dr. Dylan Seeley: Dr. Dylan Seeley on how applying neurology can improve athletic performance.

Episode Timestamps:

• 03:47 Internal vs. external cues for strength and hypertrophy
• 06:24 Longevity culture and why skill comes before loading
• 09:58 Intermediate bench press case study: practice volume and frequency
• 17:34 Ed Coan, intent and moving the empty bar like the heavy bar
• 23:30 Sensory-motor savants: Tiger Woods, Nick Kyrgios and Brian Shaw
• 27:29 How trainable is the sensory system?
• 29:35 Foam rollers, kinesio tape and cupping through a neurological lens
• 32:10 Perception, the electromagnetic spectrum and the limits of our senses
• 36:23 Mechanoreceptors and vibration
• 41:05 Light touch, vibration, skin stretch and deep pressure
• 47:14 Fast feedback: testing and iterating with the nervous system
• 51:38 Neuroplasticity, psychedelics and learning skills faster
• 1:02:45 Reality Switch Technology, tropanes and perception
• 1:05:08 Dreams, hypnagogic hallucinations and altered perception
• 1:12:26 Lucid dreaming and practicing the deadlift without the load
• 1:23:19 Film study, muscle memory and watching good reps
• 1:26:37 Where to find Dr. Jordan Shallow

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Dr. Martin Gibala is a Professor of Kinesiology at McMaster University and one of the world's leading researchers on high-intensity interval training.

Can short bursts of hard cardio outperform hours of Zone 2 for the average person? Exercise physiologist Dr. Martin Gibala explains how HIIT can improve VO2 max and metabolic flexibility, why elite athletes' 80/20 split may not fit a time-strapped schedule, and how to judge vigorous effort without chasing a perfect heart-rate zone.

Expect to learn how to scale HIIT for beginners, what RPE and the talk test reveal about vigorous effort, when short sprints differ from VO2 max intervals, why elite athletes’ 80/20 approach may not fit your schedule, how Zone 2 definitions can mislead, and what metabolic flexibility and mitochondrial capacity really mean—and much more.

Connect with Martin:

• Website: martingibala.com
• X: @gibalam
• Book: The One-Minute Workout (Avery, 2017; with Christopher Shulgan)

Episodes you'll enjoy next:

• #402 — VO2 Max, Zone 2 Training & the Psychology of Human Performance — Ben Skutnik: Dr. Ben Skutnik cuts through Zone 2 hype and discusses VO2 max and aerobic-training evidence.
• #387 — Nathan T. Jenkins on Metabolic Flexibility, Aerobic Base, and First Principles: a look at aerobic development, energy systems, and repeated high-intensity performance.

Episode Timestamps:

• 2:25 Can beginners benefit from HIIT?
• 4:20 Interval training basics and scaling effort
• 7:13 Defining vigorous effort with RPE, heart rate, and the talk test
• 11:32 Designing HIIT workouts around time and preference
• 13:48 VO2 max intervals versus shorter sprints
• 16:39 Moderate versus vigorous exercise: guidelines and time efficiency
• 18:36 Is Zone 2 and the 80/20 rule right for everyone?
• 22:50 Why Zone 2 definitions and wearables cause confusion
• 29:12 Do you need an aerobic base before starting intervals?
• 33:00 Why elite athlete training is not a blueprint for everyone
• 35:22 What low-intensity volume may do for endurance athletes
• 38:46 Double-threshold sessions, training stress, and recovery
• 41:17 Carbohydrate intake and gut training in endurance sports
• 44:31 Emerging recovery strategies and exogenous ketones
• 49:12 Lactate supplementation: promise versus current evidence
• 51:19 Fat max, metabolic flexibility, and mitochondrial capacity
• 55:31 Exercise Science podcast and evidence over hype

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Matthew Paul Clemons, MD, is a diagnostic radiologist specializing in nuclear medicine and body imaging. He is Head of Nuclear Medicine at Radiology Partners Houston and a rectal and prostate cancer specialist.

Whole-body MRI promises a detailed look under the hood—but what can a quick screening scan actually see, miss, and send you chasing? Dr. Paul Clemons explains why a whole-body MRI is a limited study, how incidental findings can lead to further tests, and why standard screening remains the better choice for most people.

Expect to learn how MRI creates images and why scan protocols take time, why open MRI systems can have important image-quality limits, how PET/MRI adds functional information, why CT and MRI can be complementary rather than redundant, how radiation and implanted devices factor into decisions, why spine findings do not always match symptoms, when conservative care deserves consideration, and where DEXA versus MRI can be useful for tracking body-composition trends.

Episodes you'll enjoy next:

• #237 — Demystifying Body Composition Testing with Dr Grant Tinsley and Dr Eric Helms: a practical companion discussion on body-composition measurement and its limits.
• #159 — Advice, Mentorships, Askholes, and Diagnostics: An Interview with Dr. Adam Sumarski: a related conversation on diagnostics and imaging in sports medicine.

Episode Timestamps:
1:50 Whole-body MRI and preventive screening
2:52 How MRI works: magnets, noise, and safety
7:05 Open MRI, magnet strength, and image quality
9:05 MRI sequences, scan time, and diagnostic protocols
11:47 Why whole-body MRI is a limited screen
12:46 Incidental findings and downstream testing
13:57 High-risk screening, rare genetic conditions, and lung limits
17:53 Sensitivity, specificity, and standard screening
24:15 PET/MRI and where whole-body imaging has a clinical role
27:05 Why MRI and PET/CT systems are expensive to install
31:59 MRI safety, implants, and pacemakers
36:36 CT versus MRI: why one scan can lead to another
38:52 Whole-body CT, radiation, and its limits
43:47 Back-pain scans: why an image may not explain symptoms
51:44 Physical therapy, surgery, and warning signs
58:46 Evaluating evidence for peptides, stem cells, and biologics
1:05:47 Choosing an orthopedic surgeon for athletic goals
1:15:24 DEXA versus MRI for body-composition trends

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Dean Guedo is an Edmonton, Alberta-based online nutrition coach and strength/nutrition professional with roughly a decade in fitness, athletics and strength sports, and Jeb Stuart Johnston is a National Board Certified Health & Wellness Coach and the Charleston, SC-based founder of Food on the Mind, specializing in emotional eating and food obsession.

Dean and Jeb join Dr. Mike T Nelson for their yearly AI check-in, getting into whether creators should disclose AI use and why deepfaked video is a very different beast than AI-assisted writing. The conversation ranges into dead internet theory, why so much hard-won fitness expertise never made it onto the internet at all, and why demanding physical skills may become more valuable, not less, as AI accelerates.

Expect to learn whether creators should disclose their AI use and why deepfaked video is a fundamentally different risk category than AI-assisted writing, why LLM writing may have already "peaked" and regresses toward the average, why fitness's hard-won oral tradition (Charlie Francis, Louie Simmons, old forums) never made it onto the internet at all, why oral defense of your own thinking may be the most AI-proof skill you can build, and why demanding physical skills could become more valuable — not less — as AI accelerates, and much more.

Connect with Dean:

• Instagram: @walk.more.king
• Website: getfluxed.ca

Connect with Jeb:

• Website: foodonthemind.com
• Instagram: @jebstuartjohnston
• Newsletter: Tangential, Inconsequential, Existential and Experiential (Substack)

Episodes you'll enjoy next:

• Episode 136 — Flex Diet, Phys Flex, Metabolism and Nutrition Research for Compound Performance (Jeb and Dean interview Dr. Mike T Nelson): Listen here
• S2 Ep 28 — High Flux Model and More for Fat Loss and Client Coaching, an interview with Dean Guedo and Jeb Johnston of StrongerU: Listen here

Episode Timestamps:

• 01:35 Welcome to the podcast & guest introductions
• 03:15 Should you disclose your AI use?
• 06:32 Deepfake video vs. AI-assisted writing: a different risk category
• 07:53 AI's exponential growth and the "singularity" question
• 11:11 What is "AI slop," and does it actually matter?
• 12:42 Why LLMs regress toward average (and the Reddit problem)
• 15:15 Falsely accused of "AI slop" for your own writing style
• 21:36 "Automate your business with AI" — the wrong things to automate
• 25:23 Dead internet theory: has AI writing already peaked?
• 26:34 Why AI can't reason about truly novel, hypothetical situations
• 28:37 Hemingway's unfinished-thought trick and "open-loop" thinking with AI
• 35:06 Why weird, opinionated writing might be AI-proof
• 44:49 Fitness's lost oral tradition: Charlie Francis, Louie Simmons, old forums
• 47:03 Stoner, the trivium, and teaching without teaching
• 48:06 Oral defense as the AI-proof assessment
• 56:08 Research vs. coaching: the application gap (Norwegian 4x4, tabata)
• 1:07:26 Will AI push us back toward hard physical skills?
• 1:15:00 Where to find Jeb & Dean

Get the Daily Fitness Insider newsletter (free): https://www.miketnelson.com/newsletter

Don Saladino is a New York-based coach and health entrepreneur who has trained A-list clients like Ryan Reynolds, Hugh Jackman, and Blake Lively since founding Drive495 in 2005.

Don Saladino has spent nearly three decades training A-list stars like Ryan Reynolds and Hugh Jackman — and in this episode, he shares the single business lesson he wishes he’d learned sooner. He and Dr. Mike also dig into why Don closed his $2M-overhead NYC gym, how tracking respiratory rate reshaped his approach to Zone 2 training, and the sobering personal loss that changed how he views performance enhancers.

Expect to learn why Don stopped over-certifying and started looking at what’s leaking in his business, how he built 17 years of trust with a client like Ryan Reynolds, the real financial toll of running a NYC gym (think $1M rent and $2M overhead), what tracking respiratory rate taught him about Zone 2 training volume, his honest take on performance enhancers at 49 (natural), and the personal loss that reshaped how he views unsupervised PED use, and much more.

Connect with Don:

• Website
• Instagram
• YouTube

Episodes you'll enjoy next:

• #402 — VO2 Max, Zone 2 Training & the Psychology of Human Performance — Ben Skutnik: Listen here
• #397 — How Elite Bodybuilders Think About Problem-Solving, Business and Nutrition with Coach Cliff Wilson: Listen here

Episode Timestamps:

• 2:26 — #1 Business Lesson: Stop Over-Certifying, Start Looking at What’s Leaking
• 5:43 — “Content Is King, Distribution Is the Kingdom”
• 8:35 — Take Risks Early: Betting on Yourself Before Responsibilities Pile Up
• 10:58 — Learning Business Over Breakfast: The NYC Advantage
• 12:01 — The Art of Adding Value Without an Agenda
• 13:32 — Working With Ryan Reynolds for 17 Years: Trust, Humility & Knowing You’re Replaceable
• 21:12 — What It Really Takes to Work With High-Profile Clients
• 26:26 — Actors vs. Athletes: Which Is Harder to Train?
• 28:39 — Performance Enhancers: Don’s Honest Take at 49, Natural
• 36:31 — Tracking Respiratory Rate & Rethinking Zone 2 Volume
• 38:37 — Closing the NYC Gym & Pivoting to Digital
• 43:35 — The Real Cost of Running a NYC Gym: $1M Rent, $2M Overhead
• 44:32 — Business Lessons You Can’t Learn at Harvard
• 46:09 — The “Integrated Wellness” Facility Trend: Is Anyone Actually Getting It Right?
• 1:05:26 — The Rise of Recovery Studios: New Happy Hour or Legit Wellness?
• 1:08:44 — A Personal Loss & a Stark Warning on Unsupervised PED Use
• 1:16:27 — Where to Find Don Saladino

Get the Daily Fitness Insider newsletter (free): https://www.miketnelson.com/newsletter

Dr. Ben Skutnik, PhD, CSCS*D, NSCA-CPT*D, is an Assistant Professor of Kinesiology and Human Performance Lab Director at Butler University and Head of Nutrition Coaching at Power Athlete.

Dr. Ben Skutnik joins the show to separate fact from fad in aerobic training, debunking zone 2 hype and explaining why VO2 max matters but isn't everything.

Expect to learn why reading scientific literature is its own skill, how uncontrolled variables quietly derail hypertrophy and menstrual-cycle training research, why treating people as fragile backfires, why anecdote in human performance often outruns the research, how "closing the loop" with clients beats chasing mechanisms, what the Norwegian 4x4 method gets right (and what most zone 2 research gets wrong about training zones), and how to actually build VO2 max with the critical power model, and much more.

Connect with Ben:

• Power Athlete Coach Bio
• LinkedIn
• Google Scholar

Episodes you'll enjoy next:

• #400 — Build Aerobic Fitness Before Mitochondrial Peptides: AMPK, VO2 Max & Recovery — Dr. Dwayne Jackson: Listen here
• #374 — Zone 2 Cardio: What the Science Really Says (Pros, Cons & Better Options) with Kristi Storoschuk: Listen here

Episode Timestamps:

• 1:46 — Why Ben was recommended for this conversation on cardiovascular and aerobic programming
• 7:31 — Reading scientific literature is a skill set of its own
• 14:05 — Hypertrophy training to failure and uncontrolled variables in research
• 16:27 — Debunking myths about training around the menstrual cycle
• 18:20 — Human resilience and the danger of treating people as fragile
• 22:09 — Why consistency beats trying to "hack" optimization
• 22:40 — Nutrition fear-mongering and overly restrictive diets
• 27:25 — Changing one variable at a time vs. the "kitchen sink" approach
• 29:55 — Why anecdotal evidence in human performance is often ahead of the research
• 34:48 — The ethics of placebo and "closing the loop" with clients
• 37:34 — The psychology of performance: the NFL kicker example
• 43:13 — The Norwegian 4x4 method and zone 2 training myths
• 46:40 — Why most zone 2 research relies on the wrong zone model
• 52:53 — HYROX, CrossFit, and Goodhart's Law in training
• 1:05:18 — Is VO2 max overrated? Performance vs. health tradeoffs
• 1:15:25 — Building VO2 max: interval protocols and the critical power model
• 1:26:02 — Life-changing results: taking deconditioned clients from VO2 max 18 to 35
• 1:30:09 — Where to find Ben Skutnik and his work at Butler University and Power Athlete

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Rick Alexander is a depth-psychological counselor, psychedelic practitioner, and interfaith spiritual care provider currently completing his Ph.D. in Mythology/Depth Psychology and a former Naval Special Operations combat medic.

Rick was a Special Operations combat medic until a single psychedelic experience shattered his worldview and sent him back to school to study psychedelic spiritual care. He and Dr. Mike dig into neuroplasticity windows, why “good trip/bad trip” is the wrong question, and what may really be happening in DMT space.

Expect to learn how a rough teenage salvia trip and a later psilocybin experience redirected Rick's entire career, what life is really like as a Special Operations Combat Medic supporting SEALs and Green Berets, why military training narrows emotional range and makes civilian re-entry so hard, how integration (not the trip itself) determines whether a psychedelic experience heals or destabilizes you, what the "third wave" of psychedelic science gets right that the DSM's "hallucinogen" label gets wrong, whether neuroplastic windows could help athletes learn skills faster, and what a brutal 5-MeO-DMT experience taught Rick about his own running form and breathing.

Connect with Rick:

• Website
• Instagram

Episodes you'll enjoy next:

• #47 — Tools to Down-Regulate in Response to Stress (an earlier conversation with Rick Alexander): Listen here
• #194 — The Pros and Cons of Psychedelic Compounds with Psychedelic Researcher Rebekah Senanayake: Listen here

Episode Timestamps:

• 2:49 – Rick's PhD progress and the psychedelic experience that redirected his career
• 3:38 – A rough first psychedelic experience with salvia at 18
• 4:46 – The psilocybin experience that "peeled back" his worldview
• 7:00 – Life as a Special Operations Combat Medic supporting SEALs and Green Berets
• 8:23 – How military training narrows emotional range and worldview
• 10:01 – Why veterans struggle to re-enter civilian life after specialized training
• 13:34 – The double-edged sword: psychedelics can destabilize as easily as they heal
• 14:32 – The "third wave" of psychedelic science and the flawed DSM "hallucinogen" label
• 23:49 – Integration: do you have time to process what comes up?
• 24:43 – "Psychedelic myth-making" and building a new personal mythology
• 31:05 – Could neuroplastic windows help athletes learn skills faster?
• 37:01 – Yogic energy channels (nadis) and psychedelics amplifying subtle perception
• 39:17 – How a brutal 5-MeO-DMT trip changed Rick's running form and breathing
• 56:16 – What's really happening in DMT space: Strassman, Gallimore, and "reality switch technologies"
• 59:43 – Henri Corbin's "psycho-cosmology": consciousness and reality as mirrored levels
• 1:06:45 – "Functional consequentialism": why you shouldn't dismiss someone else's experience
• 1:10:46 – Where to find Rick and his counseling and breathwork work

Get the Daily Fitness Insider newsletter (free): https://www.miketnelson.com/newsletter