Paragliding Harness Impact Index:
an experimental study 

DRI_EN and DRI_BIOM

🔹 DRI_EN (Dynamic Response Index – Energy-based)

DRI_EN describes the dynamic response of the system in energy terms.
In the files, it is computed from the acceleration–time signal, taking into account:

• acceleration magnitude

• impulse duration

• cumulative energy contribution
  
  

👉 DRI_EN quantifies how much dynamic energy is transmitted during the impact, going beyond the simple peak acceleration value (G-peak).

Higher DRI_EN values indicate:

• more severe impacts

• higher transmitted energy

• reduced damping capability of the system
  
  

🔹 DRI_BIOM (Dynamic Response Index – Biomechanical)

DRI_BIOM is derived from the same dynamic data as DRI_EN but applies a biomechanical interpretation.

In the files:

• the dynamic signal is weighted according to human-body response models

• the resulting index better represents potential physiological stress
  
  

👉 In short:

• DRI_EN → energetic severity of the impact

• DRI_BIOM → biomechanical relevance of the impact

Spinal Load (FAR 27.562(c))

🔹 FAR

The FAR (Force Attenuation Ratio) quantifies the ability of the system to attenuate and reduce the transmitted force during an impact.

In the analyzed files, FAR is derived from the comparison between:

• the input force (or acceleration-derived force) generated by the impact

• the force effectively transmitted through the system
  
  

👉 FAR expresses how much of the original impact force is mitigated by the protection system.

Interpretation

• High FAR values indicate:

  • strong force attenuation

  • effective load distribution

  • reduced stress transmitted to the protected structure or body
    
    

• Low FAR values indicate:

  • limited force reduction

  • more direct transmission of impact loads
    
    

FAR complements DRI_EN and DRI_BIOM by focusing specifically on force reduction, rather than energy or biomechanical response alone.

Meaning of the reported metrics

✅ Effective up to xx% G-peak (≈ xx g)

This value indicates the operating effectiveness threshold of the protection system relative to the peak acceleration.

• xx% G-peak → percentage of the measured peak acceleration

• ≈ xx g → corresponding approximate acceleration value

👉 Up to this threshold:

• energy absorption remains efficient

• DRI_EN and DRI_BIOM increase in a controlled manner
  
  

Beyond this level, protective efficiency may progressively decrease.

✅ Low Energy Absorption Index (LEAI)

The LEAI measures the system’s ability to absorb energy at low impact levels.

👉 A high LEAI indicates:

• early activation of the protective syste

• effective absorption during moderate impacts

Final summary

• DRI_EN → energetic intensity of the impact

• DRI_BIOM → biomechanical relevance of the impact

• FAR → how effectively impact forces are attenuated 

• Effective up to xx% G-peak → protection effectiveness limit

• Overall Protection Effectiveness → overall quality of protection

• LEAI → low-energy absorption capability

=> LEAI isn’t the same as JERK,

 Jerk vs LEAI

• JERK measures how abruptly acceleration changes: sharp hits, sudden shocks, and discontinuities. It reflects impact harshness, not energy absorption.

• LEAI measures how much energy is absorbed over time under low-intensity conditions. Sudden spikes matter little; smooth, prolonged absorption counts most.
  
  

Key intuition:

• JERK → derivative of acceleration → highlights abruptness.

• LEAI → integral of absorbed energy → rewards gradual, sustained response.
  
  

Example:

• Slow, long acceleration → low jerk, high LEAI

• Sudden, short spike → high jerk, low LEAI
  
  

In short:
👉 Jerk tells you how “sharp” the hit is.
👉 LEAI tells you how well the system absorbs it gradually.

Low-Energy Absorption Index (LEAI):

Quantifying Harness Performance in Small and Moderate Vertical Impacts

Abstract

Current paragliding harness certification standards focus primarily on high-energy impacts associated with severe crashes. However, the vast majority of real-world pilot loads arise from low-energy vertical impacts, such as hard landings, micro-drops, flare misjudgments, and repeated “culates”.
To address this gap, the Low-Energy Absorption Index (LEAI) has been introduced as a complementary biomechanical metric designed to quantify how effectively a harness attenuates small and moderate impact energy before critical acceleration thresholds are reached.

Meaning of SIC_eq Ranges

(SIC_eq will be introduced with the calculation released after January 20, 2025)

Let us recall the key concept:

SIC_eq = 1 ≈ biomechanical reference threshold of the model
(i.e. the onset of significant injury risk)

🟢 Class A — SIC_eq < 0.5

Very effective energy absorption

• Impact well below the reference threshold

• Deceleration well distributed over time

• Low spinal loads and limited jerk

• Biomechanical comfort and safety zone

• Typical of highly progressive harness designs
  
  

👉 No biomechanical criticality expected

🟡 Class B — 0.5 ≤ SIC_eq < 1.0

Good energy absorption

• Impact close to, but still below, the reference threshold

• Body response remains within physiological limits

• Possible micro-stresses without injury
  
  

👉 Still a safe zone, but with reduced margin compared to Class A

🟠 Class C — 1.0 ≤ SIC_eq < 2.0

Critical zone (onset of biomechanical risk)

• SIC_eq ≈ 1 corresponds to the model threshold

• Possible exceedance of physiological tolerance under real conditions

• Injury risk depends on:

  • body posture

  • impact repetition

  • individual variability
    
    

👉 This is where real injury risk begins
👉 Class C = “caution” zone, not yet catastrophic

🔴 Class D — 2.0 ≤ SIC_eq < 3.0

Poor absorption / severe impact

• Impact well beyond the biomechanical threshold

• High probability of:

  • vertebral compression

  • disc and ligament damage

  • acute pain
    
    

👉 Probable injury zone
👉 The model remains informative, but the body is already outside the comfort range

⚫ Class E — SIC_eq ≥ 3.0

Extreme impact / out-of-scale condition

• Very violent impact

• Numerical value is no longer proportional to real injury severity
  
  

From a biomechanical perspective:

• human energy absorption capacity has already been exceeded

• differences between values such as 3, 4, or 6 do not significantly change the clinical outcome
  
  

👉 Severe or potentially catastrophic injury zone
👉 At this level, the value only indicates “far beyond the limit”

🚨 What Is the True Biometric Limit?

👉 The meaningful biomechanical limit is SIC_eq ≈ 1

• <1 → physiological regime

• ≈1 → injury risk threshold

• >1 → increasing real injury risk

• >2 → injury likely

• >3 → biomechanically out of scale
  
  

👉 Therefore, the true “human” threshold lies between Class B and Class C, not between Class D and Class E