Jonah Rosner is a sport scientist, performance coach, and founder of Marathon Science, translating endurance research for runners and hybrid athletes.

Does everyone really need two to three hours of Zone 2 each week? Sport scientist Jonah Rosner joins Dr. Mike T Nelson to explore when higher-intensity work makes sense, how to separate cardiovascular stress from tissue stress, and what heat training and blood flow restriction may add to an endurance plan.

Expect to learn why time-crunched lifters may benefit from carefully selected intervals, how to separate cardiovascular load from tissue load, why sprinting needs a gradual runway, what heat acclimation may change beyond plasma volume, where oxygen strategies and blood flow restriction fit, and how to interpret heart rate alongside performance, and much more.

Connect with Jonah:

Marathon Science newsletter
Instagram: @rosnerperformance

Episodes you’ll enjoy next:

VO2 Max, Zone 2 Training & the Psychology of Human Performance — Ben Skutnik — #402

From Powerlifter to Trail Runner — Paul Oneid & Cody Miller — #393

Episode Timestamps:

03:00 Zone 2 Versus HIIT
05:00 Choosing Safer HIIT Modes
08:56 Building Toward Faster Sprints
13:30 Quality Density Running Repeats
15:48 Polarizing Your Running Training
19:36 Heat Training For Endurance
26:40 Exercising In The Heat
29:48 Cooling And Heat Perception
32:27 Cold Water Between Intervals
35:10 Altitude And Oxygen Strategies
40:35 Exercise With Oxygen Therapy
42:16 Blood Flow Restriction Training
45:10 Measuring Muscle Oxygen Extraction
52:04 Heart Rate Versus Output
57:26 Triphasic Training For Runners
61:25 Thinking Beyond Training Dogma

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

James de Lacey is a strength and conditioning coach with an MSc in Sport & Exercise Science and more than a decade of experience in professional sport spanning professional and international rugby/rugby league. He now focuses on combat sports to prepare fighters under Sweet Science of Fighting.

Do fighters really need zone 2 cardio? Strength and conditioning coach James de Lacey of Sweet Science of Fighting joins Dr. Mike T Nelson to challenge the "big aerobic base first" playbook for combat sports, from heart rate recovery and short-rest sprint intervals to muscle oxygen (NIRS) data. They also dig into VO2 max, wearables and why AI-written programs often miss the mark.

Expect to learn why James questions the “huge aerobic base” approach for fighters, how heart rate recovery and heart rate kinetics can reveal more than time in zones, how short-rest sprint intervals and a simple air bike baseline test can guide programming, what muscle oxygen (NIRS) data can and can’t tell you, why trends beat single data points from wearables, and why generic AI-written programs often miss the mark—and much more.

Connect with James:

• sweetscienceoffighting.com
• jamesdelacey.com
• Sweet Science of Fighting on Instagram
• Sweet Science of Fighting on YouTube

Episodes you'll enjoy next:

• Episode 326: Row Hard, Breathe Easy: Boosting Aerobic Capacity with Dr. Kenneth Jay: Dr. Kenneth Jay on rowing and boosting aerobic capacity (Mike credits Dr. Jay for the bioenergetic testing he mentions in this conversation).
• Episode 221: Training performance, nitric oxide, blood flow, and more via the NNOXX device with Evan Peikon: Evan Peikon on training performance, nitric oxide and blood flow via the NNOXX device (Mike mentions Evan in this conversation).

Episode Timestamps:

• 03:35 The biggest conditioning mistake in MMA
• 05:50 Why sprints are more aerobic than you think
• 07:46 Do fighters need a huge aerobic base?
• 09:44 VO2 max, muscle limits and oxygen testing
• 11:57 Conditioning trends and training volume
• 15:36 Zone 2, time costs and the 80/20 debate
• 22:10 Heart rate response and recovery between rounds
• 25:43 Mike’s rower test and heart rate recovery
• 28:25 Air bike sprints with short rests
• 31:44 Muscle oxygen and power between repeats
• 34:19 Testing and training each athlete’s limiter
• 41:47 Flexible Meathead Cardio and technical training
• 46:05 Elite athletes, VO2 max and training context
• 50:22 NIRS, oxygen drops and peak power
• 57:18 Why trends beat single test results
• 1:02:56 Wearables, coaching judgment and session design
• 1:06:57 AI programs and generic training blocks
• 1:13:02 Training around life and where to find James

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

Bryan Krahn has been a personal trainer since 1997, a CSCS since 2005, and a full-time online coach since 2014. He is a fitness writer and the author of two books with Men's Health.

Will AI replace online coaches, or only the ones who stop being human? Veteran online coach and Men's Health author Bryan Krahn joins Dr. Mike T Nelson for a candid, unfiltered conversation about paying for expertise, whether coaches should disclose AI use, personal experiences with peptides and TRT (opinion, not advice), and Mike's simple rower-based cardio plan.

Expect to learn why paying for expertise makes you a better coach, how Bryan and Mike use (and distrust) AI in coaching and writing, whether coaches should disclose their AI use, why stacking compounds makes personal experiments hard to interpret, how Bryan thinks about TRT and lab markers like HDL, LDL and PSA, and Mike’s simple rower-based cardio plan—and much more.

Bryan and Mike discuss peptides, TRT and other compounds from personal experience and opinion. Nothing here is medical advice; talk to a qualified healthcare professional before changing any medication or supplement routine.

Connect with Bryan:

• over50muscle.com
• Bryan on Instagram (@bryankrahn)

Episodes you'll enjoy next:

• Episode 137: Training Straight Talk with fitness writer, and online physique coach Bryan Krahn: Bryan's previous visit to the show: training straight talk from a fitness writer and online physique coach.
• AI Disclosure, Deepfakes & the Death of Expertise — Dean Guedo & Jeb Stuart Johnston — #404: Dean Guedo and Jeb Stuart Johnston on AI disclosure, deepfakes and the death of expertise (Mike mentions Dean in this conversation).

Episode Timestamps:

• 02:25 Online coaching's catch-22: taking clients you may not be set up to help
• 04:16 Bryan's niche: from over-40 clients to the over-50 guy, and why parents and older dads fit
• 06:10 Edge-case clients, referral networks and paying peers for expertise
• 08:06 Why paying for consults still matters, including Bryan's 1999 consult with Charles Poliquin
• 11:35 Why AI still struggles with niche training questions: PEDs, zone two and the Thomas Inch dumbbell
• 17:03 AI inside coaching software, and why chatbots are so agreeable
• 18:53 Would clients be accountable to a bot, and will live coaches last?
• 23:48 Should coaches disclose AI use to clients? Everyday AI wins like soundbars and grill repair
• 27:29 Contest-prep coaches, AI photo checks, and why coaches get second opinions
• 34:32 Peptide offers and appetite-suppressing drugs: personal experiences, not advice
• 39:38 DNP stories and risks as the speakers recount them
• 42:34 Mitochondrial peptides, NAD+ and IV infusions: why stacked self-experiments are hard to interpret
• 49:39 TRT: dialing in the basics first and working with a physician
• 52:41 Lab markers: HDL, LDL and PSA, and changing the marker versus the outcome
• 58:37 Traveling with a TRT prescription: Bryan's border-security story
• 1:01:25 Mike's rower cardio plan: baseline 2K test, progressive six-minute sessions and a smarter four-by-four
• 1:10:58 Should writers disclose AI use? Beating the blank page without losing your voice
• 1:19:06 Wrap-up: coaching availability, training from 50 to 53, and where to find Bryan

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