Super shoes helped less on steeper climbs

Super shoes have changed road racing, but hills complicate the story. This study matters because it tested whether the energy-saving benefit of a carbon-plated road shoe holds up when runners start climbing.

Reference: Askew et al. Running Economy Benefits of Shoes Incorporating Advanced Footwear Technology Decrease With Increasing Incline and Are Negligible Above Moderate Gradients. Scandinavian Journal of Medicine & Science in Sports (2026) DOI: 10.1111/sms.70298. PMID: 42121353. PubMed link: https://pubmed.ncbi.nlm.nih.gov/42121353/.

Study snapshot

A quick, practical summary for runners and coaches.

Quick answer

This randomizedRandomization means assigning people to different parts of a study (e.g., groups in a randomised controlled trial) by chance, not by choice. This helps make the groups similar at the start and reduces bias, so any differences you see are more likely due to the treatment, not background differences. In a crossover study, randomization usually decides the order in which each person gets the treatments (for example, Treatment A first then B, or B first then A). This way, order effects—like learning, fatigue, or simple time passing—are less likely to skew the results. repeated-measures treadmill study tested 12 competitive male runners. The Nike Vaporfly reduced oxygen cost on flat running and gentle uphill running, but the benefit faded as the incline got steeper. The main caution: the study was small, short, male-only, and lab-based.

Key takeaways

  • The Vaporfly helped most on flat running and shallow uphill running.
  • The benefit was small or unclear on steeper inclines.
  • For hilly races, shoe choice should match the course, not just the carbon-plate hype.

How confident should we be?

Evidence confidence: Moderate

The study used a useful within-runner design and direct oxygen-cost measurements. But the sample was small, included only young male runners, and tested short treadmill trials rather than real races.

Bottom line

Super shoes probably still help most when the course is flat or gently rolling. On sustained steep climbs, the benefit may shrink enough that grip, stability, comfort, and confidence become just as important, especially for trail and ultra runners.

Read the deep dive below for a practical interpretation, actionable decisions, my thoughts, my Rating of Perceived scientific Enjoyment, the study details, full results, strengths, and limitations.

Running science research reviews for endurance runners

The deep dive

The details behind the headline result, including the practical meaning, full findings, limitations, and my interpretation.

Practical meaning

What does this research mean for runners and coaches?

For runners

For road runners, the study supports a simple idea: super shoes may be most useful on flat ground and gentle climbs. That fits many road marathons and rolling races, where the course still includes plenty of faster, smoother running.

For trail runners and ultra runners, the practical message is more cautious. The study did not test technical trails, long descents, fatigue, mud, rocks, or shoe grip. So, the trail and ultra take-home is interpretation, not a direct study finding: on steep or technical terrain, the best shoe may be the one that keeps you stable, comfortable, and moving well, not the one with the flashiest lab number.

For coaches

Coaches can use this study to frame shoe choice as a course-specific decision. A carbon-plated road shoe may make sense for flatter road races or rolling courses. For steep climbs, mountain races, and technical trails, athletes should test shoes in race-like conditions before trusting the shoe box poetry.

Practical decision

Should runners change anything?

Maybe. Use super shoes where their strengths match the course, but avoid treating one treadmill study as a universal shoe-choice rule.

Consider this if

  • Your target race is mostly flat or gently rolling.
  • You already run comfortably in super shoes.
  • The course uses smooth road or predictable surfaces.
  • You are choosing shoes for a road marathon or fast road race.

Do not overreact if

  • Your race includes long steep climbs.
  • The course is technical, rocky, muddy, or unstable.
  • You need grip and confidence more than a small oxygen-cost benefit.
  • The shoe feels unstable, awkward, or too aggressive for your stride.

A sensible next step

Use super shoes where their strengths match the course. For steep trail races and mountain ultras, test shoes on race-like climbs and descents before deciding. The stopwatch matters, but your ankles also get a vote.

TIP: Never make any major changes to your training or lifestyle habits based on the findings of one study, especially if the study is small or provides low-quality evidenceA low quality of evidence means that, in general, studies in this field have several limitations. This could be due to inconsistency in effects between studies, a large range of effect sizes between studies, and/or a high risk of bias (caused by inappropriate controls, a small number of studies, small numbers of participants, poor/absent randomisation processes, missing data, inappropriate methods/statistics). When the quality of evidence is low, there is more doubt and less confidence in the overall effect of an intervention, and future studies could easily change overall conclusions. The best way to improve the quality of evidence is for scientists to conduct large, well-controlled, high-quality randomised controlled trials.. Check whether other trials confirm the findings. If there is a meta-analysisA meta-analysis quantifies the overall effect size of a treatment by compiling effect sizes from all known studies of that treatment. on the topic, look at the effect sizeA standardised measure of the magnitude of an effect of an intervention. Unlike p-values, effect sizes show the size of the effect and how meaningful it might be. Common effect size measures include standardised mean difference (SMD), Cohen’s d, Hedges’ g, eta-squared, and correlation coefficients., the variability between studies, and the quality of evidenceCertainty of evidence tells us how confident we are that the published results accurately reflect the true effect. It’s based on factors like study design, risk of bias, consistency, directness, precision, and publication bias. High certainty means that the current evidence is so strong and consistent that future studies are unlikely to change conclusions. Whereas, low certainty means more doubt and less confidence, and that future studies could easily change current conclusions..

Expert interpretation

My thoughts

Running science from Thomas Solomon at Veohtu

This is a tidy little study. Not massive. Not definitive. But it asked a question runners actually care about: do super shoes still help uphill?

The answer seems to be yes, but less. When compared to the Streakfly (a not quite Supershoe that lacks a carbon plate despite having a curved plastic plate, lots of foam, and a massive stack height), the Vaporfly looked useful for lowering the energy cost of running (increasing running economyThe rate of energy expenditure (measured in kiloJoules [KJ], kilocalories [kcal] or oxygen consumption [VO2]) per kilogram body mass (kg) per unit of distance, i.e. per 1 kilometre travelled. A runner with a lower energy cost per kilometre has a higher economy than a runner with a higher energy cost.) on flat running and gentle climbs. On steeper inclines, the benefit became small enough to make me put my celebratory hulks hands back in the cupboard.

That matters because runners often talk about super shoes as if the benefit is a fixed number. It probably isn’t. Course profile, surface, gradient, runner mechanics, and shoe comfort all matter. Annoying, yes. But also kinda reassuring, because it means sensible shoe choice still needs a human brain attached to it.

For road marathoners, this study does not weaken the case for super shoes. For trail and ultra runners, it nudges the conversation toward the whole shoe: grip, stability, protection, comfort, and how the shoe behaves when you’re tired and mildly questioning your hobbies. So, should you wear super shoes for a hilly race? Maybe. But first ask where, exactly, they are gonna help.

Also, this study talaks a lot about performance benefits, but only running economyThe rate of energy expenditure (measured in kiloJoules [KJ], kilocalories [kcal] or oxygen consumption [VO2]) per kilogram body mass (kg) per unit of distance, i.e. per 1 kilometre travelled. A runner with a lower energy cost per kilometre has a higher economy than a runner with a higher energy cost. was assessed not performance. So, we can't make too many bold predictions about performance outcomes based on a short-duration low-speed treadmill run that only measured the energy cost of running.

My Rating of Perceived scientific Enjoyment

owlRPsE: 6/10

I experienced moderate scientific enjoyment because the study used a neat within-runner design, clear oxygen-cost measures, and a practical runner question, but the small male-only sample and short treadmill setting keep us far from making bold conclusions.

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Read on for further details about the paper.

Research question

What did the researchers ask?

The authors aimed to test whether the running economyThe rate of energy expenditure (measured in kiloJoules [KJ], kilocalories [kcal] or oxygen consumption [VO2]) per kilogram body mass (kg) per unit of distance, i.e. per 1 kilometre travelled. A runner with a lower energy cost per kilometre has a higher economy than a runner with a higher energy cost. benefit of the Nike Vaporfly Next% decreases as uphill gradient increases.

In plain English, they asked whether the shoe still saves energy when running shifts from flat ground to steeper climbing.

Study design

What type of study was this?

This study was a randomized repeated-measures treadmill study. It was effectively a crossoverCrossover means that all subjects completed all interventions (control and treatment) usually with a wash-out period in between. design because each runner tested every shoe and every gradient condition.

This design can test whether the shoes caused short-term differences in oxygen cost under the study conditions. It cannot tell us exactly how much time runners would save in a real road race, trail race, or ultra, because real races include corners, changing pace, downhill sections, weather, fatigue, surfaces, and at least 1 person who starts too fast and makes everyone twitchy.

Participants

Who took part?

The study included 12 competitive male runners. The participants were aged 21.4 years on average, weighed 70.5 kg (155 pounds), and were 181.3 cm tall (71 inches). They could run 5 km in less than 18 minutes, with an average 5 km time of 16 minutes 22 seconds. The study did not include female runners, older runners, recreational runners, or runners identified as trail-specific athletes.

Methods

What did the researchers do?

Who? 12 competitive male runners
What? Nike Vaporfly Next% versus Nike Streakfly
How long? 4 to 5-minute treadmill trials

The researchers compared 2 Nike shoes: the Nike ZoomX Vaporfly Next% and the Nike ZoomX Streakfly.

The Vaporfly had ZoomX PEBA foam and a curved carbon fibre plate. The Streakfly had ZoomX PEBA foam and a flexible plastic plate, but no carbon fibre plate. The Streakfly was slightly lighter than the Vaporfly.

The runners ran on a treadmill at 12 km per hour (7.5 miles per hour). They completed trials at 4 gradients: level running, 3 percent incline, 6 percent incline, and 9 percent incline. Each trial lasted 4 to 5 minutes, until the runners reached steady oxygen uptake and carbon dioxide production.

The researchers measured oxygen use during each trial. They used this as the marker of running economy, which means how much oxygen the runner needs at a given speed. Lower oxygen use at the same speed usually means the runner is using less energy.

The researchers also tested the shoes in the lab. They measured how much energy the shoes stored and returned under compression and bending. This helped them explore why the shoe benefit might change with incline.

Main findings

What did the study find?

Level running 4.22 percent predicted benefit
3 percent incline 2.42 percent predicted benefit
9 percent incline 0.52 percent predicted benefit

The Vaporfly reduced oxygen cost during level running and at a 3 percent incline. In practical terms, the runners used less oxygen at the same speed in the Vaporfly than in the Streakfly. Those differences were statistically significantEvidence that a result is unlikely to be due to chance under a “no effect” model (or null hypothesis). Statistical significance is often judged by a p-value below 0.05 to flag that “something” is going on, but not how big or important that “something” is. One statistically significant result doesn’t mean proof; replication is needed. And, a statistically significant result doesn’t necessarily indicate clinical significance..

The size of the Vaporfly benefit dropped as the incline increased. The predicted running economy benefit was 4.22 percent on level running, 2.42 percent at a 3 percent incline, 1.05 percent at a 6 percent incline, and 0.52 percent at a 9 percent incline. That is a tidy slide from “interesting” to “probably not buying you much cake at the finish line.”

At 6 percent and 9 percent inclines, the difference between the shoes was not statistically significant. That does not prove the Vaporfly had no benefit at all. It means any benefit was small, uncertain, and hard to detect in this sample.

The shoe tests showed that the Vaporfly stored more energy under compression than the Streakfly, but returned a smaller proportion of that stored energy. In bending, the Vaporfly was about 4.26 times stiffer than the Streakfly, while the 2 shoes had similar bending resilience.

The authors interpreted the results to mean that the Vaporfly’s benefit likely comes from the combined elastic behaviour of the foam and plate. But as uphill running gets steeper, elastic energy storage and return seems to matter less, because runners need to do more active work to lift the body uphill.

The authors concluded that the Vaporfly provides the greatest benefit on flat courses, with smaller gains on shallow inclines, and negligible benefit above moderate gradients.

What helps my confidence in the findings?

The strengths

  • The within-runner design was useful because each runner tested both shoes and all gradients.
  • The shoe order and gradient order were randomized.
  • The researchers used direct oxygen-cost measurements rather than only timing performance.
  • The study compared shoes with some shared foam technology, although the shoes still differed in several ways.
  • The authors included mechanical shoe testing, which helped connect the physiology results to shoe behaviour.

What limits my confidence in the findings?

The limitations

  • The study included only 12 runners, so the estimates are not rock solid.
  • The sample included only young competitive male runners, so the findings may not apply equally to female runners, older runners, recreational runners, or slower runners.
  • The study used short treadmill trials, not real races or long efforts with fatigue.
  • The researchers tested uphill running only; they did not test downhill running.
  • The study compared 1 Vaporfly model with 1 Streakfly model, so the results should not be treated as a universal rule for all super shoes.
  • The researchers did not record prior familiarity with advanced footwear technology.
  • Foot strike pattern was not controlled, and uphill running can change how the foot lands.
  • 1 runner’s 9 percent incline data were excluded because their respiratory exchange ratioRER is the ratio of carbon dioxide you breathe out to oxygen you use. It hints at the type of fuel your body is predominantly burning: around 0.7 = mostly fat, around 1.0 = mostly carbs, >1.0 = all-out effort. exceeded 1.0, whch means they were not running at a submaximal pace and that introduces error into the running economy estimate.

Funding and conflicts

Who funded the study?

The study was funded by the University of Leeds. The authors declared no conflicts of interestA conflict of interest happens when a person or group has a personal, financial, or professional interest that could influence their judgment. It does not always mean they did something wrong. But it can create bias or make others question whether the decision or result is fully fair and trustworthy..

That reduces concern about direct shoe-company influence. Still, clean funding does not make the evidence bulletproof. The small sample, treadmill setting, and the comparison between only 2 shoes still matter.

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