Gommaar D’Hulst is an exercise physiologist at ETH Zurich and the mind behind the WOD Science YouTube channel, with a background rooted in CrossFit and a growing focus on HYROX and hybrid endurance sports. Through his research and applied lab work, Gommaar bridges elite performance, physiology, and real-world training decisions for functional fitness athletes.

In this episode, Gommaar breaks down the key physiological differences between CrossFit and HYROX, why HYROX is best understood as an endurance-dominant sport, and how muscle fiber types, VO2 max, lactate threshold, and anaerobic power shape performance. He shares insights from lab testing with elite athletes—including novel functional ramp tests using burpees and thrusters—explains why fatigue dramatically alters running economy in HYROX, and explores how tools from endurance science (like threshold training, Zone 2 work, and power metrics) can be adapted to functional movements. We also dive into interference effects, fueling strategies, and where sports science is headed as HYROX continues to professionalize.

Episode breakdown:

00:00 — Intro: Gommaar (ETH Zurich) + WOD Science + CrossFit → HYROX

00:24 — CrossFit vs HYROX demands: longer duration, lower intensity, aerobic bias

01:40 — Can you excel at both? Specialization, rising level, and the Tia example

03:13 — Is HYROX endurance or strength? Why it’s primarily endurance (and sled/turf impact)

04:48 — Muscle fibers 101: slow vs fast twitch and what they’re built for

07:50 — Why strong powerlifters can struggle: strength vs strength-endurance

11:01 — HYROX strength training: when (and if) low-rep work fits in the season

12:17 — VO2 max + lactate threshold: what they are and why they matter

15:56 — Elite CrossFit VO2 findings: lower-than-expected on the bike + specificity issue

18:27 — Functional ramp test: burpees + thrusters protocol + what lactate curves show

21:55 — Run → lunges/deadlifts → run: fatigue increases VO2 cost (running economy drop)

26:02 — What predicts HYROX performance beyond VO2: fatigue-resistance across stations

28:22 — Heart rate: good for running, limited for stations + why VO2 can drop in strength work

34:15 — Interference effect: separating strength and endurance (same-day vs split) outcomes

46:53 — Nutrition rapid-fire: carbs (timing + high intakes) and bicarb/creatine practicality

This is a public episode. If you would like to discuss this with other subscribers or get access to bonus episodes, visit johngetstrong.substack.com

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