The End of Cardio? Burn Fat & Boost VO₂ Max in Just 8 Minutes a Week – with REHIT | Ulrich Dempfle

Dave Asprey

Apr 25, 2025

Episode description

You’ve probably heard of HIIT—but have you heard of “REHIT?” This isn’t just another workout trend...it’s a new science-backed way to train with maximum efficiency and zero wasted time. If you’re still jogging, you’re wasting hours for minimal results.

In this episode of The Human Upgrade, Dave Asprey sits down with Ulrich Dempfle, German-trained engineer and co-founder of CAROL Bike, to dismantle outdated cardio advice and introduce the 5-minute protocol that’s obliterating fitness myths.

Forget the treadmill grind. REHIT (Reduced Exertion High-Intensity Training) exercising delivers:

• 12% VO₂ max increase

• 6x the fitness gains of daily jogging

• 62% drop in diabetes risk

• 5x more BDNF for brain power

—all with just 8 minutes of effort per week.

But was it? Ulrich unpacks the hard data, crushes the Zone 2 obsession, and shows how a brand-new way of exercising is giving explosive results—no matter your age or fitness level.

What You’ll Learn in This Episode:

• Why Zone 2 cardio is outdated advice for most people

• The science of REHIT and how 2 sprints beat 2-hour workouts

• The shocking data on VO₂ max, insulin sensitivity, and lifespan

• How CAROL uses AI to personalize exercise for any age or ability

• Why most people fail at fitness—and how to fix it

• The real role of lactate, BDNF, and HRV in recovery and resilience

• How perimenopausal women benefit more from REHIT than HIIT or jogging

• Why adherence—not intensity—is the #1 predictor of results

• What to do when you’re traveling or don’t have access to the tech

Resources:

• Dave Asprey’s New Book - Heavily Meditated: https://daveasprey.com/heavily-meditated/

• CAROL Bike Website and use code ‘DAVE’ for a discount – https://carolbike.com/

• CAROL Bike Instagram - https://www.instagram.com/thecarolbike/?hl=en

• 2025 Biohacking Conference: https://biohackingconference.com/2025

• Danger Coffee: https://dangercoffee.com

• Dave Asprey’s Website: https://daveasprey.com

• Dave Asprey’s Linktree:

Mindsip insights from this episode:

Utilize Cardarine to enhance mitochondrial density like Zone 2 training

The substance Cardarine (GW501516), banned by the International Olympic Committee, is mentioned as a biohack to increase mitochondrial density, mimicking a key benefit of extensive Zone 2 training.

#biohacking

#mitochondria

Utilize AI to discover your optimal workout intensity

A new feature for the CAROL bike will use real-time heart rate variability complexity to precisely find the optimal intensity for Zone 2, identifying the exact point you switch from fat to carb metabolism.

#AI

#exercise

Flip molecular switch with two 20-second all-out sprints

Two 20-second all-out sprints are enough to flip a molecular switch, releasing powerful signaling molecules that saturate the adaptation pathway, making longer or more sprints unnecessary for the main benefit.

#adaptation

#exercise

Debunk the zone 2 training myth for general fitness

The popular 80/20 training split for Zone 2 comes from elite athletes who train 25-35 hours a week and lacks scientific evidence for the general population.

#exercise

#zone-2

Achieve 62% reduction in metabolic risk with 15 minutes of REHIT weekly

In an eight-week study, a REHIT protocol of just 15 minutes per week led to a 62% reduction in the risk of developing metabolic syndrome.

#exercise

#metabolism

Maximize BDNF release with high-intensity exercise

High-intensity exercise like REHIT can stimulate four to five times more BDNF release, a key protein for brain neuroplasticity, compared to regular exercise.

#BDNF

#exercise

Utilize REHIT to enhance fitness in perimenopausal women

For perimenopausal women, the very short but intense stress of REHIT provides a strong training stimulus without overwhelming their compromised stress-handling systems like longer cardio sessions would.

#exercise

#perimenopause

Utilize hill sprints as effective REHIT alternative

If you don't have access to a specialized bike, hill sprints are the most effective and safest alternative for replicating a REHIT workout, whereas treadmills and rowers are not recommended.