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Impact in Running: The Hidden Force Behind Injury

 


Powered by Beflex’s BiomechEngine™

Most runners track pace.

Very few track impact.

But impact loading — not speed — is one of the strongest biomechanical predictors of overuse injury.

StrideCoach measures impact using BiomechEngine™, developed by Beflex’s biomechanics research team, transforming raw motion data from AirPods into meaningful loading metrics.

What Is Running Impact?

Impact refers to the acceleration spike that occurs at foot strike.

When your foot hits the ground:

  • A rapid deceleration occurs

  • Ground reaction forces travel upward

  • Bones, cartilage, and soft tissues absorb the load

This loading happens hundreds — sometimes thousands — of times per run.

The problem is not one impact.

It is repetition.

Why Impact Matters

Research has consistently linked higher vertical loading rates to injury risk.

Evidence

  • Milner et al., 2006 – Runners with tibial stress fractures showed significantly higher vertical loading rates.

  • Zadpoor & Nikooyan, 2011 (Systematic Review) – Strong association between impact loading and stress-related injuries.

  • Davis et al., 2016 – Gait retraining to reduce impact loading decreased injury symptoms.

Impact loading is especially associated with:

  • Tibial stress fractures

  • Patellofemoral pain

  • Shin splints

Importantly, runners often feel “fine” while impact loading is gradually increasing.

Symptoms appear later.

How BiomechEngine™ Measures Impact Using AirPods

AirPods contain:

  • 3-axis accelerometer

  • Gyroscope

  • High-frequency motion sampling

BiomechEngine processes this data in several stages:

  1. Stride segmentation

  2. Foot-strike detection

  3. Acceleration peak extraction

  4. Signal filtering (noise reduction)

  5. Normalized impact scoring

Unlike wrist-based devices, head-centered sensing reduces arm swing noise and better reflects vertical loading transmission through the kinetic chain.

Head acceleration patterns correlate with whole-body impact propagation because impact forces travel upward through the skeletal system.

This allows BiomechEngine to estimate relative impact loading trends across runs.

What Causes High Impact?

Common contributors:

  • Overstriding

  • Low cadence

  • Heel-dominant landing pattern

  • Downhill running

  • Fatigue-induced form collapse

Studies show that increasing cadence by 5–10% reduces vertical loading rates
(Heiderscheit et al., 2011).

Small mechanical adjustments can significantly reduce cumulative stress.

Why Small Reductions Matter

Consider this:

If you reduce impact by 10%,
and you take 8,000 steps in a long run,

that’s 800 “units” of stress removed per session.

Over weeks and months,
that reduction becomes substantial.

Impact is cumulative.

BiomechEngine tracks trend changes, not just single-run spikes.

Impact vs. Speed

Running faster does not automatically mean higher injury risk.

What matters more:

  • How abruptly you load

  • How consistently you load

  • Whether loading increases over time

StrideCoach focuses on loading quality, not just performance output.

When Should You Pay Attention?

Watch for:

  • Sudden upward trend in impact score

  • Asymmetry combined with high impact

  • Increasing impact during fatigue phases

These patterns may precede injury.

Early awareness allows earlier intervention.

The Bigger Picture

Most runners analyze pain after it starts.

BiomechEngine™ monitors loading patterns before pain develops.

Impact is not visible.
It is not obvious.
But it is measurable.

With nothing but your AirPods.

References

  • Milner CE et al. (2006). Biomechanical factors associated with tibial stress fracture.

  • Zadpoor AA & Nikooyan AA. (2011). Relationship between lower-extremity stress fractures and impact loading.

  • Davis IS et al. (2016). Gait retraining to reduce impact loading.

  • Heiderscheit BC et al. (2011). Step rate manipulation reduces joint loading.

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