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

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

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

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