REF-1497 · Fernández-Navarrete et al., 2026 · German Journal of Exercise and Sport Research · Paper

Which HYROX sections are hardest on the body?

In a simulated race of 29 athletes a strain index of HR, ventilation and RER peaked at wall balls, sled push and burpees; typical HR above 90% HRmax from run 3. No training test.

Main caveat: Abstract, figures and one table only. The publisher sells the article and OpenAlex lists no open copy.
limited, mixed evidenceMeasured on recreational to highly trained athletes

Fernández-Navarrete and colleagues had 29 athletes do an incremental treadmill test and then a simulated HYROX race, recording heart rate, respiratory exchange ratio (RER), minute ventilation (VE) and breathing frequency throughout, and built a cardiorespiratory strain index (CRI) from them.

The figures show all eight runs and eight stations, so the simulation was a full one, on an oval course marked 325 m. The abstract says heart rate exceeded 90% of HRmax from run 3 on, rising further at wall balls and burpees; Fig. 3 shows individuals below that in every section (our reading of the figure).

RER often passed 1.00 after stations and sat around 0.92-1.00 on runs; VE after stations ran above 100 L/min in men and above 60 L/min in women. The CRI was highest at wall balls, sled push and burpees. Running speed fell from km 1 to km 5. The authors suggest that runners used the runs as relative recovery; that is their reading, not a measurement.

Our reading: the base's first HYROX numbers with gas exchange by section and with both sexes shown, agreeing with REF-510 that wall balls peak. The word "recovery" is relative only, since heart rate on those runs was above 90% of HRmax. Without the methods we cannot say how the index weights its parts or whether the ranking would survive a different one.

Protocol

Who: n = 29; 17 men (age 28 ± 6 y, 176.77 ± 5.95 cm, 76.91 ± 7.22 kg, body fat 12.23 ± 3.43%) and 12 women (28 ± 5 y, 162.42 ± 3.48 cm, 61.18 ± 4.97 kg, body fat 19.78 ± 4.51%) (Supplementary Table 1; "body fat" is our reading of its label PGC). Level, HYROX experience and division are not in what was read.
Tests: an incremental treadmill test, then a simulated race. Order, rest between them and whether on one day are not in what was read.
Simulation: full by the figures: runs 1 to 8 and SkiErg, sled push, sled pull, burpee broad jumps, row, farmers carry, lunges, wall balls in the race order (Figs. 2 to 4); Fig. 1 sketches an oval marked 325 m, a sled lane of 12.5 m (50 m), a burpee lane of 40 m (80 m), a lunge lane of 50 m (100 m), a farmers lane of 100 m (200 m), 100 wall balls, 1000 m SkiErg and row. Loads are not in what was read.
Measures: heart rate, RER, VE, breathing frequency, with the CRI calculated from them. Device: not in what was read (the reference list includes a validity paper on a portable breath-by-breath system; that it was used is our inference). Lactate and RPE are not mentioned in the abstract.
Not read: the formula of the index, statistics, how HRmax was set. On the page's public declarations: no funding was received and the authors declare no competing interests; data on reasonable request.

Key Results

MeasureMenWomen
Running speed, km 1 to km 5 (abstract)~13.2 to ~11.3 km/h~11.9 to ~10.3 km/h
RER on runs (abstract, no split by sex)~0.92-1.00~0.92-1.00
RER after high-intensity stations (abstract)frequently above 1.00frequently above 1.00
VE after stations (abstract)above 100 L/minabove 60 L/min
Heart rate (abstract)above 90% HRmax from run 3 on; further up at wall balls and burpeessame
Highest strain index (abstract)wall balls, sled push, burpeessame

Read off the figures by us, approximate, no printed values and no captions visible:

Km12345678
Men, mean km/h (Fig. 2)13.212.311.2511.711.2511.511.7511.7
Women, mean km/h (Fig. 2)11.911.210.610.710.2510.5510.710.7
After km 5 (Fig. 2): speed did not keep falling; means held or rose a little to km 8. The abstract's fall covers km 1 to 5 only. This differs from race results, where the last run is the slowest (REF-1496, REF-902, REF-1502); a simulation, and these figure readings are rough.
Strain index (Fig. 4): run 1 lowest (about −1.2), wall balls highest (about 0.8 to 1.05), burpees about 0.5 to 0.6, sled push about 0.55, lunges about 0.4 to 0.55, most runs about −0.4 to 0.0, run 8 about 0.2. In the figure burpees and sled push are level, though the abstract's conclusion names wall balls and sled push.
Individual heart-rate points (Fig. 3): a few sit at about 42 to 52% of HRmax (run 1, run 2, sled push, run 5) and some at or above 100%. Whether these are sensor drop-outs or real is not stated in what was read.
Prediction: the abstract reports no predictor of finish time and no correlation. Nothing was read on what predicted what.

Mechanisms

Measured: heart rate, RER, VE and breathing frequency across the 16 sections.
Authors' interpretation: stations, particularly wall balls and sled push, are the more demanding parts, and the lower strain on the runs suggests athletes may have used the runs as a relative recovery zone against cumulative fatigue. Not measured, and nothing separates this from the runs simply being less demanding.
Inference: a composite index that includes heart rate and ventilation lags the work, so run 1, starting from rest, reads lowest and a run after a hard station carries over some of that station's load. The ranking mixes how hard a section is with what came before it, in a fixed order. Wall balls are always last.

Practical Application

Which HYROX sections are hardest on the body? In a simulated race of 29 athletes a strain index of HR, ventilation and RER peaked at wall balls, sled push and burpees; typical HR above 90% HRmax from run 3. No training test.
Runs are not rest: the "relative recovery" reading holds only against the stations. RER of about 0.92-1.00 and heart rate above 90% of HRmax on the runs (abstract) leave little room; this fits REF-510 (79.5% of the time at very hard heart-rate intensity, n = 11).
Do not read a ranking as a training priority: the highest-strain section is not thereby the one to train most, and the study tests no training. Not from this paper; the base's own practice for station work is in SYNTH-71.
For women: the pattern looks alike in the 12 women and 17 men in the figures, descriptively (the abstract splits only speed and VE by sex); VE is lower in absolute terms, as expected with smaller bodies (our inference).

Limitations

Abstract, figures and one table only. The publisher sells the article and OpenAlex lists no open copy. All of protocol detail, loads, division, device, the index formula and statistics are unknown here; funding and interests are known only from the page's public declarations. Numbers marked as figure readings are ours and approximate.
A simulation. No race field, no crowd, and an oval course; speed and strain may differ from a race. The sample's km 6 to km 8 speeds behave differently from race data.
Composite index. Built from four correlated measures that lag the work; not shown here to be validated. Rankings by it are not rankings of metabolic cost.
Gas exchange during burpees, sled and wall balls is hard to measure well (our inference), and its method here was not read.
Small and mixed. 17 men and 12 women; level unknown; descriptive. No control.
Fixed order. Wall balls always come last and the runs always follow a station, so section and race position cannot be separated.
How this entry was checked and changed
Why this level

a cross-sectional study of 29 is B by design; held at B- because the paper is a subscription article and its methods were not read (abstract-only small study in the rubric's terms): the analyser, how stations were measured, the loads and division, the strain-index formula and how HRmax was set are all unknown here. If the full text is obtained, regrade