Exploring Factors to Explain Interindividual Responses to Running Economy in Advanced Footwear Technology Shoes: A Randomised Crossover Laboratory Trial with an Explanatory Predictor Analysis
Sports medicine - open · 2026
AFT shoes boost running economy by 4% on average, but calf stiffness and navicular drop only explain a quarter of who actually benefits.
Studien
Randomised crossover laboratory trial, n=64 recreational/trained runners (50% female), Waikato, New Zealand.
Vad de fann
Advanced footwear technology (AFT) improved running economy by 4.13 ± 1.6% on average versus a control shoe, but individual responses ranged from -2.62% (worse) to +11.01% (better). Above-threshold responders (n=53, >2.5% improvement) had greater normalised gastrocnemius medialis stiffness than below-threshold responders (n=11, Hedges' g=0.86, 95% CI 0.20 to 1.51, p=0.046), and a regression using GM stiffness (p=0.015) and navicular drop (p=0.028) explained only 27.3% of variance in RE response (r=0.35 and r=0.31 respectively).
Studiedesign
Randomised crossover laboratory trial (n=64 runners) with a secondary explanatory predictor analysis, comparing running economy in advanced footwear technology versus a control shoe; this sits as primary experimental evidence, but the predictor analysis itself is an exploratory, hypothesis-generating observational sub-study nested within the trial rather than a confirmatory test.
Metodik
The crossover design controls for between-runner confounding on the headline RE comparison since each participant serves as their own control, but the interindividual response analysis is a post-hoc split into above- and below-threshold groups (53 vs 11), and an unequal, small below-threshold cell makes that comparison highly sensitive to a handful of individual data points. The regression drew on a large panel of candidate predictors, anthropometric, biomechanical, neuromuscular and perceptual, with no stated correction for multiple comparisons, so the two significant hits (GM stiffness, navicular drop) carry a real risk of being chance findings rather than true signals. A clinician trying to ascertain GM stiffness or navicular drop would need shear-wave elastography or ultrasound and a navicular drop test, equipment and measurement expertise not available in routine practice, so even if the association holds up, it is not currently something a clinic floor can screen for.
Granskningen
The headline AFT effect on RE is real and consistent with prior literature, but the interindividual variability finding is the more clinically relevant part, and the predictors identified (GM stiffness, navicular drop) only explain about a quarter of that variability, meaning three-quarters of why someone responds or not remains unexplained. This is hypothesis-generating association, not a validated screening tool: the small below-threshold group (n=11) means the stiffness comparison could easily not replicate, and because many candidate characteristics (age, sex, anthropometrics, speed, VO2 peak, neuromuscular performance, biomechanics, perceptual measures) were tested and only GM stiffness reached significance with no stated correction for multiple comparisons, there's a real chance this is a false positive rather than a true signal.
Begränsningen
With only 11 below-threshold responders, the subgroup comparison is fragile, replication in a larger sample with correction for multiple comparisons is needed before GM stiffness or navicular drop could be used to predict who benefits from AFT shoes.
Referensstudie
This builds on the now well-established literature (following the 2018 Hoogkamer et al. work on the original Nike Vaporfly) showing AFT improves RE by around 4% on average, and extends it by probing the mechanistic and individual-characteristic drivers of the variability that has been repeatedly observed but rarely explained.
Vad du gör på måndag
Don't change anything on Monday: this doesn't give clinicians or coaches a validated way to predict which runners will or won't benefit from AFT shoes, so shoe recommendations should still rely on individual trial-and-response (test the shoe, measure or ask about perceived benefit) rather than calf stiffness or foot posture screening.
In practice
This applies to distance runners already using or considering carbon-plated AFT shoes, in return-to-run rehab and in endurance performance programming, not to sprinters or field-sport athletes. Keep doing what already works: matched-pace shoe trials judged by RPE, heart rate at fixed pace, or lab RE if you have access, rather than screening calf stiffness or navicular drop, since those explain only a quarter of the response and carry a real chance of being a statistical fluke given how many variables were tested. On the S&C floor, treat AFT shoes as 'trial it, don't assume it' for race-day selection, about one in six runners here got no meaningful benefit or actually ran less efficiently, so they're not a blanket upgrade. In the clinic, remember a stiffer, more rockered AFT shoe changes calf-Achilles loading, if you're introducing one during return-to-run for a calf or Achilles issue, monitor symptoms on introduction since this study measured economy, not tissue tolerance.
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