Marathon Science

Most runners are already eating more sodium than they need. Adding more during exercise often does nothing for performance.

McCubbin (2025) reviewed decades of research on sodium in athletes (Monash University, Performance Nutrition). The picture that emerges challenges how the endurance world talks about salt.

What athletes typically eat:

○ Australian male endurance athletes: about 3,869 mg/day
○ Female endurance athletes: about 3,176 mg/day
○ National guidelines: under 2,400 mg/day

The kidneys handle the surplus. McCubbin (2019) fed athletes double their normal intake for three days. Only about 21% was retained. By contrast, Goulet (2018) gave a single dose four hours before exercise and about 77% was retained. The mechanism: kidneys adjust how fast they clear sodium within about two hours. Days of loading get cleared. One dose, taken close to the start, sticks around.

So when does sodium during exercise matter? The modelling (a fluid-sodium model from the review) suggests three conditions need to line up:

○ The athlete can replace more than 70% of fluid losses
○ They tolerate that fluid volume
○ It’s practical within event rules

Typically this means ultra-endurance events and prolonged team-sport in heat. Below the 70% fluid-replacement threshold, blood sodium rises naturally as you lose more water than salt. Adding sodium at low fluid replacement can push blood sodium too high.

For everyone else, the evidence points to “season to taste.” Sodium during exercise doesn’t appear to influence performance unless it also drives greater fluid intake.

One caveat: most of these studies used non-elite, predominantly male, non-weight-bearing athletes. Generalising to elite runners and females is less certain.

Huge thanks to McCubbin for this work.

Paper: https://doi.org/10.1186/s44410-025-00011-9

Also Fueling Endurance Podcast one of the best ones out there.

Speed, hills, and cadence change which leg tissues take the most damage. Cadence was the only lever that helped all three. Same kilometers, different tissues take the hit.

Van Hooren et al. (2024) modeled tissue loads at the knee, shin, and Achilles in 19 recreational runners. Treadmill, 1-minute bouts, modeled not directly measured.

Faster running lowered total stress per km on every tissue because there were fewer steps. The model predicted damage on the knee rose at the same time. Shin and Achilles damage trended upward but did not reach statistical significance.

Damage uses load raised to a tissue exponent. A step twice as hard counts about 128x as much for bone, more than 600x for tendon. Fewer-but-harder steps can raise damage even when total stress falls.

I’m not a huge fan of changing running form when their is no pain or injury but sometimes manipulating cadence, surface and speed can be important when coming back from injury.

Cadence at about 6% above preferred (roughly +10 steps/min) was the only lever linked to lower modeled damage on all three tissues at the same running speed.
How to cue it: set a metronome at your current cadence × 1.06. Or filter your music library by BPM. Hold the new cadence on easy runs first.

Knee: the authors suggest raising cadence and avoiding large volumes of downhill running.

Achilles: cut fast-interval volume first. Then raise cadence and cut uphill volume.

Shin: raise cadence first. Cutting uphill volume also lowers modeled damage.

Observational modeling, not a training trial. n = 19 recreational runners, treadmill. Knee loading lacks in-body reference data. Framework, not prescription. “Run faster to reduce injury load” is the framing the authors warn against.

Huge thanks to Van Hooren, van Rengs, and Meijer for this work.
Van Hooren et al., Scand J Med Sci Sports, 2024.

doi:10.1111/sms.14570

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Eight days of taurine raised whole-body sweat loss by about 26 to 27% in the heat.

Naddafha, Stout, and Evans (Nutrients, 2026) reviewed the small human trial base on taurine and heat tolerance. The pooled studies put trained-to-active adults on cycling and walking protocols at 35 to 37.5 °C.

The pattern across trials is consistent. Acute dosing at ~50 mg/kg, 1.5 to 2 hours pre-exercise, may lift end-exercise sweat rate by about 12.7% and drop final core temperature from 38.5 to 38.1 °C. Cycling time to exhaustion went up by roughly 10%. Eight days at ~50 mg/kg/day appears to recruit 22 to 32% more active sweat glands. In one trial, the heat-balance ceiling shifted upward from ~21.7 to ~25.0 mmHg.

The authors suggest taurine may act in the hypothalamus, lowering the temperature at which the brain turns on sweating. Animal work supports this. Direct human confirmation is missing.

The catch is real. The evidence base is small: about 2 to 3 primary trials, n=11 to 15 per trial, mostly young trained men, cycling and walking, not running. More sweat means more fluid and sodium to replace. Taurine may also dampen perceived exertion in a way that masks physiological strain. It won’t help if sweat can’t evaporate, or if you’re already fully heat-acclimated.

Where this matters: racing in heat without full acclimation. Promising, but preliminary.

Huge thanks to Naddafha, Stout, and Evans for this careful review.

Source: Naddafha S, Stout JR, Evans C. Nutrients, 2026.
doi:10.3390/nu18040592

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New research: stiffer runners are typically more economical. But there’s no universal optimum.

Masson, Millet, and Kerhervé just published a narrative review in Sports Medicine synthesizing studies on stiffness and running through March 2025.

The headline finding is consistent. Higher whole-body stiffness is linked to better running economy. Kubo et al. (2010) reported plantar-flexor tendon stiffness correlated with 5000 m time at r = 0.76. Arampatzis et al. (2006) found the most economical runners had a stronger calf and a stiffer Achilles tendon.

Then the picture gets more nuanced.

“Stiffness” isn’t one thing. Whole-body, joint, muscle-tendon, and tissue-level stiffness have different units and measurement methods. They don’t always change together.

More important: most runners naturally settle on stiffness, contact time, and stride frequency that follow an inverted-U curve. Too low and too high are both detrimental. The authors note that an “individually defined optimal stiffness” hasn’t been systematically researched.

Two practical signals:

→ Long-term: 6 to 14 weeks of plyometric or combined strength training improved tendon stiffness and running economy.

→ Warm-ups: a plyometric warm-up improved economy, and the change tracked rising leg stiffness. In male well-trained runners, greater flexibility from static stretching was linked to worse economy and shorter distance in a 30-minute run. The same protocol didn’t change economy in female runners.

Most cross-sectional data is correlational. Stiffer runners may already be more economical for other reasons, like training history or anatomy.

The takeaway isn’t “be stiffer.” Each runner likely sits on their own inverted-U. The biggest movers are weeks of plyometric or strength work.

Huge thanks to Masson, Millet, and Kerhervé for this work.

Paper: https://doi.org/10.1007/s40279-026-02406-7

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training

New research: a ketone monoester did not improve exercise capacity at the modern 120 g/h fueling target. It also reduced how efficiently the body used those carbs by about 10%.

Martyn et al. (2026, Journal of Applied Physiology) ran a single-blind crossover RCT in 8 trained male cyclists (VO2max ~66 mL/kg/min). Each rode three trials: placebo, 120 g/h CHO, and 120 g/h CHO + 75 g ketone monoester (KME). The ride was 3 hours at 95% of lactate threshold, followed by an exhaustion test at 150% LT.

Three metabolic shifts moved together with KME, all in the same direction:

Mean blood glucose: 4.4 vs 4.9 mmol/L
Exogenous CHO oxidation: 1.35 vs 1.50 g/min
Oxidation efficiency: 67% vs 75%

Then the capacity test. Time to exhaustion was 349 s on CHO and 319 s on CHO + KME. Median gap of 17 seconds, P = 0.48. Effectively a tie. Both far outperformed placebo (75 s).

Why the disconnect? The authors suggest KME slowed the rate at which ingested carbs reached the bloodstream. By the start of the capacity test, blood glucose and whole-body CHO oxidation had equalized between the two CHO conditions. Carb availability wasn’t the limiter at that moment.

KME also reduced markers of fat breakdown (NEFA, glycerol). The marketed “more fat oxidation” effect didn’t show up here.

For the trained male cyclist already fueling near 120 g/h: this study doesn’t support adding KME for a capacity edge. It also fits a growing body of literature that ketone esters do not improve prolonged endurance performance. Whether the reduced CHO oxidation efficiency matters for longer events, harder finishes, or higher CHO intakes is an open question this study did not test. Translating to women, runners, or fasted exercise would need more evidence.

Huge thanks to Martyn et al. for this work. Paper: https://doi.org/10.1152/japplphysiol.01072.2025

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New research says endurance athletes need more protein on recovery days than on training days. The repair bill comes due after the work, not during it.

Witard, Hearris, and Morgan reviewed a decade of metabolic studies in Sports Medicine. In endurance-trained men, indicator amino acid oxidation (IAAO) data point to about 1.8 g/kg/day on a standard training day, about 1.95 g/kg/day on a low-carb training day, and over 2.0 g/kg/day on a recovery day. Endurance athletes habitually eat about 1.5 g/kg/day. The training-day target is roughly 2.3 times the RDA for sedentary adults.

After a hard endurance session, early evidence suggests a per-meal dose of about 0.5 g/kg supports myofibrillar repair. For a 70 kg runner, that’s roughly 35 g. Worth flagging: this estimate comes from a single dose-response study in trained cyclists and triathletes, with a wide confidence interval (0.26 to 0.72 g/kg). The post-endurance dose is about twice the post-strength dose.

Where the evidence is still thin: no IAAO study has been done specifically in female endurance athletes, the luteal-phase guideline is extrapolated from team-sport data, no IAAO study has covered masters athletes over 65, and most cited studies recruited cyclists or triathletes rather than runners.
Huge thanks to Witard, Hearris, and Morgan for this review.

Witard, Hearris, and Morgan (2025), Sports Medicine.

New research: strength training didn’t change fresh-state running economy. The benefit appeared at 90 minutes.

Zanini et al. (2025) ran a 10-week RCT in 28 well-trained male runners. The strength group added two supervised sessions per week. Both groups kept their habitual running.

Back squat and single-leg press progressed from 3x6-8 at 65-80% 1RM to 3x4-5 at 85-90%. Isometric calf raises stayed heavy. Plyometrics progressed from pogo jumps and hop-and-stick to drop jumps and bounds.

Every runner did a 90-minute treadmill run at marathon effort, pre and post. Then a time-to-exhaustion test at 95% VO2max.

When fresh, the strength group matched controls at 10 km/h, 12 km/h, and at the 15-minute mark. No difference in running economy.

The gap opened late. At 90 minutes, economy changed by -2.1% in the strength group versus +0.6% in controls. Negative means better economy.

Look at the deterioration, not just the endpoint. Pre-training, economy fell 4.7% from minute 15 to minute 90. After 10 weeks of strength work, that fall shrank to 2.1%. Controls didn’t move.

Then came the time-to-exhaustion test at about 16 km/h. The strength group improved by 35%, from 247 to 324 seconds. Controls didn’t change. Same VO2 at exhaustion. More time before failure.

The work also felt easier. Perceived effort dropped at 90 minutes. Blood lactate stayed lower at 75 and 90 minutes. Heart rate didn’t move.

The strength group made measurable gains: leg press 1RM up 22%, jump peak power up 7.5%, plantar flexor force up 14%. The authors suggest stronger, stiffer muscle-tendon units may return more elastic energy at lower metabolic cost as fatigue builds. Those mechanisms weren’t directly measured here.

Huge thanks to Zanini et al. for this work.

physiology and are two of my favorites to follow. Recommend you check out their work!

References:
Zanini, Folland, Wu, & Blagrove (2025). Medicine & Science in Sports & Exercise. https://doi.org/10.1249/MSS.0000000000003685

90 g/h was a research ceiling. Not a biological one.

For over a decade, the ACSM guideline capped fueling at 90 g/h from glucose-fructose blends. Events over 2.5 to 3 hours. That number reflected what had been studied, not what the body could handle.

Morton et al. (2026) revisit that guideline in a new narrative review. Trained male cyclists ingested 120 g/h during 3 hours of steady-state cycling. CHO stayed the dominant fuel the entire time. At 90 g/h, the crossover to fat dominance was only delayed.

In elite male marathoners (PB under 2:30), 120 g/h improved running economy by 3%. That was vs 60 g/h, on a treadmill, not in a race. GI discomfort was greatest at 120 g/h.

More is not automatically better. Smith et al. found that in 51 recreationally trained cyclists and triathletes, performance gains plateaued above 78 g/h. Whether that curve holds for elites is unknown.

A fructose-to-glucose ratio of 0.6 to 1.0 consistently maximizes exogenous CHO oxidation across three studies. Fluids, gels, and chews all achieve comparable oxidation rates. Solid bars do not.

Gut training works. Structured carb exposure during training (30 to 90 g/h) consistently reduces GI discomfort. And body size matters. Larger trained athletes oxidize meaningfully more exogenous CHO at the same intake.

The review flags real gaps. No definitive performance trial has tested CHO dose-response under standardized race conditions. Over 80% of feeding studies used recreationally trained participants. Fewer than 3% were female-only cohorts.

The evidence shifted. The next step is finding your ceiling in training.

Huge thanks to Morton et al. for this work.

References (selected):
Morton JP, Fell JM, Gonzalez JT, Hearris MA, Podlogar T, Pugh JN, Wallis GA. From Metabolism to Medals: Contemporary Perspectives and Revisiting Carbohydrate Guidelines for Fueling Endurance Athletes during Exercise. J Nutr. 2026;156:101442. doi:10.1016/j.tjnut.2026.101442.

Moving forward, I want more of my content to focus on research reviews from papers I’m reading, learning from, and excited about, while highlighting the researchers behind that work.

Carb loading isn’t for every race. Stored fuel covers around 75 to 90 minutes of hard running. Shorter than that, normal eating tends to handle it. 5Ks, 10Ks, and most sub-90 minute half tend not to need a large load.

Above that threshold, the tank can run low.

The protocol has changed. The old 7-day depletion approach has fallen out of favor. A meta-analysis flagged two factors as decisive. Fitness, and how many carbs you eat beforehand.

A 1-2 day high-carb load with a taper appears to fill the tank. A 1-day version in trained athletes.

Targets tend to be tiered. First-timers around 6 to 8 g/kg. Intermediate runners 7 to 10. Experienced loaders 8 to 12.

Gut comfort tends to beat perfect numbers. When in doubt, go lower.

A 75 kg runner targeting 10 g/kg lands at around 750g of carbs. Not a pasta dinner. A full day of focused eating.

What’s your go-to loading-day food? Drop it in below.

Sources: Areta and Hopkins (2018). Bussau et al. (2002).