113. Why Isn’t Everyone Getting Fit in 5 Minutes? with Ulrich Dempfle

2026-03-10

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What if the reason you're not exercising isn't laziness — it's that no one told you it could take five minutes? In this episode of Why Isn't Everyone Doing This?, Emily sits down with Ulrich Dempfle, mechanical engineer and co-founder of Carol Bike, to explore a form of exercise most people have never heard of — and that science says is the most efficient workout on the planet. Ulrich introduces ReHIT — Reduced Exertion High Intensity Interval Training — a five-minute workout with just two 20-second all-out sprints that ha...

What if the reason you're not exercising isn't laziness — it's that no one told you it could take five minutes?

In this episode of Why Isn't Everyone Doing This?, Emily sits down with Ulrich Dempfle, mechanical engineer and co-founder of Carol Bike, to explore a form of exercise most people have never heard of — and that science says is the most efficient workout on the planet.

Ulrich introduces ReHIT — Reduced Exertion High Intensity Interval Training — a five-minute workout with just two 20-second all-out sprints that has been clinically shown to produce a 12% improvement in VO2 max in just eight weeks with only two to three sessions per week. He breaks down why VO2 max is the single most important health marker for longevity, why low cardiorespiratory fitness causes more preventable deaths than smoking, diabetes, and obesity combined, and why the "no pain, no gain" belief is keeping most people from getting healthy at all.

Emily connects the science to her own experience — linking the fight-or-flight spike of a sprint to hormesis, mitochondrial biogenesis, and heart rate variability — and why intentional, acute stress is the perfect complement to the chronic stress release she's spent 17 years teaching through meditation.

In this episode, they explore:

What ReHIT is and why it outperforms traditional cardio for VO2 max improvement
The biological pathway that makes two 20-second sprints more powerful than an hour of zone 2
Why 40% of people see zero VO2 improvement from zone 2 training alone
How sprint training supports hormonal health in perimenopause and beyond
How to combine ReHIT with strength training for a complete weekly routine
Why breathing in the recovery period may be the most important part of the workout
What changes on the planet when everyone gets fit in five minutes

Key Moments:

00:00 — The statistic that changes everything: fitness vs. smoking, diabetes & obesity combined
07:00 — What is ReHIT? The paradox of reduced exertion and high intensity, explained
14:43 — VO2 max: the strongest predictor of life expectancy you're probably not tracking
19:07 — The fight-or-flight connection and why this is "good stress"
22:54 — Clinical results: 12% VO2 improvement in 8 weeks, 20% in 20 weeks
26:01 — The biological pathway: glycogen → AMPK → PGC-1 alpha → mitochondria
33:40 — Hormones, perimenopause & why long endurance cardio can work against you
44:52 — Why breathing in recovery might be the most powerful part of the ride
53:00 — What changes on the planet when everyone gets fit in five minutes

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