Shock Absorption: Why More Cushioning Is Not Always Better for Your Joints

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RunRepeat buys every shoe with its own money, cuts it in half, and drops an 8.5kg mass on the exposed foam 30 times per shoe under the ASTM F1976 standard. Their shock absorption guide distills 1,000+ such autopsies into one claim I keep turning over: cushioning protects your joints, but more of it is not always better. Shop by their lab numbers, not by showroom feel.

1. Every footstrike hits you with up to 3 times your body weight. That is the number that makes this a health topic rather than a gear topic. Thousands of such impacts per run land on muscles, bones, and joints, which is why midsole foam exists at all.
2. Cushioning genuinely cuts injuries, with a randomized trial behind it. A 2020 RCT of 848 runners found those in firmer shoes were 52% more likely to get injured, and lighter runners benefited most from the softer pair. This is the strongest single receipt in the guide.
3. Soft feel in the store is not protection on the road. A shoe can feel pillowy on step-in and bottom out under real impact, while the ASICS Superblast feels firm yet attenuates excellently. Their advice is blunt: ignore step-in feel and biased reviews, check the SA score.
4. What predicts protection is height, not softness. Heel stack tracks shock absorption almost linearly: maximalist shoes over 40mm score 135+ SA, shoes under 30mm rarely break 120. Softness alone spreads wildly, with mid-firmness foams landing anywhere from 100 to 150+ SA. The Clifton went from 32.7mm and 127 SA to 44.4mm and 147 SA in two versions, which is the whole maximalist era in one shoe.
5. Match the shoe to the body and the distance. Marathoners, runners with joint damage or bone-stress history, and heavy beginners need high SA. Most daily 10-12K runners land in the moderate middle, like the Pegasus 41 at 125 or the Ghost 16 at 133, which is also where prices stay sane. Mile and 5K racers do better in low-SA shoes like the Streakfly 2 at 106 SA and 128g, trading protection for ground contact and cadence.
6. Now the counterargument, which RunRepeat states honestly: excess cushioning can backfire. Kulmala’s 2018 study found 10-12% higher impact forces at speed in maximalist shoes because runners stiffen their legs, and a 2024 University of Florida study linked highly cushioned shoes to more injuries than flatter ones. Thick foam also dulls proprioception, and a max-cushion neutral shoe on an unstable runner is a recipe for runner’s knee.
7. Two shopping myths die in their charts. Top-tier absorption over 140 SA mostly costs $180-plus, but moderate protection tops out near $160, so stop paying for cushioning your distances never use. And weight barely correlates: the Zoom Fly 6 is light and heavily cushioned while some 11oz budget trainers test flat. Modern foams broke the heavy-equals-soft assumption.
8. Cold weather steals cushioning from every foam equally. At -15C the Vaporfly 4 lost 36% of its absorption and the Pegasus 41 lost 38%, while energy return diverged wildly between compounds. Winter runners in freezing cities are effectively running in a firmer shoe than the one they bought, which matters for joints.

The takeaway: Before your next pair, look up its SA score on RunRepeat, buy moderate unless you are heavy, marathon-bound, or managing joint damage, and rotate two pairs so the foam recovers between runs.

Related TMFNK Content

• Quirks of Human Anatomy: Why Evolution Left Us with Flaws Feet and knees are among evolution’s compromises, and this guide is really about engineering around them with foam.
• This Spice Combo Could Slash Inflammation Hundreds of Times More Effectively Pounding creates inflammation and soreness, and cushioning only handles the mechanical half of that problem.
• Where Human Sleep Went Wrong: Stop Chasing Eight Perfect Hours Recovery is where training adaptations land, and fresher legs from better absorption only count if sleep does its part.

Crepi il lupo! 🐺