Issue #26: Durability and Fatigue Resistance

🥤 Does my fueling change for a HYROX doubles race?

👨‍💻 Introduction

Topic: Durability / Fatigue Resistance

There are generally three big performance markers for running performance: VO₂max, lactate threshold, and running economy. There's a sneaky fourth variable that is getting a little more attention in recent research -->  durability: the ability to maintain those physiological parameters as fatigue accumulates. I often refer to this as fatigue resistance. How long can you keep your engine running efficiently even as fatigue accumulates.

The paper we will specifically focus on today is one recently published in the European Journal of Sport Science – “Durability of Parameters Associated With Endurance Running in Marathoners” (Hunter et al.). Researchers tested marathoners before and after a 90‑minute run at their own lactate‑threshold speed (sLT) to see how key markers changed. I think this area of research is specifically useful for HYROX athletes as well, not just runners.

Source: Durability of Parameters Associated With Endurance Running in Marathoners

🔍️ Deep Dive

Study Overview

The authors aimed to investigate how key physiological parameters tied to endurance running deteriorate (their “durability”) during prolonged running, and whether the magnitude of that deterioration is associated with marathon performance.Specifically, they looked at:

• Maximal oxygen uptake (V̇O₂peak)

• Fractional utilization at lactate threshold (FULT)

• Running economy (RE)

• Speed at lactate threshold (sLT)

These are standard markers of endurance performance, but the idea here is: it’s not just what those values are fresh, but how well they hold up (durability) after a long-duration run that matters.

Methods

• Participants: 18 marathon-runners (11 males, mean age ~41 ± 12 y) who ran the 2024 London Marathon (their finish time ~3:17 ± 0:32 h:mm).

• Testing: Each runner attended two lab visits:

• PRE: tested in the “fresh” state (baseline) for V̇O₂peak, FULT, RE, and sLT.

• POST: after a 90-minute run at their sLT pace (i.e., prolonged running stress), they repeated the same measures.

• They then computed the change (decline) in those markers from PRE → POST and looked for associations with marathon finish time.

Key Findings

• V̇O₂peak and sLT declined after 90 minutes at sLT.

• V̇O₂peak decreased (PRE → POST).

• sLT decreased (PRE → POST).

• FULT and running economy were unchanged. Despite the prolonged load, these two markers did not show significant group‑level change.

• Importantly: The percentage change in sLT (the drop in speed at lactate threshold after the 90-min run) was significantly associated with marathon performance (r = 0.680, p < 0.01). In other words: runners whose sLT dropped less after prolonged running tended to run faster marathons.

Limitations / Considerations

• Sample size is modest (n = 18) and participants were recreational to semi-competitive marathoners (mean ~3:17 finish).

• The stress protocol: 90 minutes at sLT pace is meaningful, but marathon race fatigue is much longer, and HYROX has additional strength/endurance demands beyond pure running.

• As the authors note, durability is a useful concept but more work is needed to define it, standardize testing, and apply it across populations.

• Having some additional data on athlete training volume would be interesting to see.

Why it matters for HYROX?

In my opinion, durability / fatigue resistance is likely a characteristic that separates the elites in the sport of HYROX. The best of the best can maintain their lactate threshold pace and produce high power output on stations late in the race – likely due to (1) years and years of training volume and/or (2) very specific fatigue resistance training.

🧪 Lab Notes

• Build more training volume over time

  • This is almost a sure bet to better durability, but you must do it in a smart way

  • Eat more carbs, train more hours, recovery, adapt --> build better durability

• Practice producing high power output at the end of long runs or workouts.

  • This is a great way to work on fatigue resistance and it doesn't add a ton of workout time to your schedule

  • A lot of my 1:1 clients are used to doing long sets of lunges, step-ups, or wallballs at the end of a longer run

  • This is yet another plug for doing strides at the end of aerobic runs, as I talked about in issue #2, base training.

• Finish-fast workouts

  • Progressive runs are another tool to use – a continuous run where you get faster as it goes on

  • Something as simple as starting out at 9min/mile and taking off 5-10s/mile split for 60min is a protocol I will use.

• Practice good running form under fatigue

  • In HYROX workouts, don't let form fade under fatigue

  • If you practice perfect running form all the time, you will run that stride under stressful race conditions.

Thats it for this week – thanks for reading and if you find this helpful, please share it with a friend!