2nd/10_Wiki/Topics/Game_Design/Biomechanics-of-Injury.md

---
id: wiki-2026-0508-biomechanics-of-injury
title: Biomechanics of Injury
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Damage Modeling, Injury Simulation, Hit Reaction]
duplicate_of: none
source_trust_level: A
confidence_score: 0.85
verification_status: applied
tags: [game-design, simulation, damage-model, biomechanics]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: cpp
  framework: physics-sim / game-engine
---

# Biomechanics of Injury

## 매 한 줄
> **"매 force × tissue tolerance = injury"**. Biomechanics of injury 는 매 real-world impact physics (kinetic energy, pressure, strain rate) 를 매 game-grade damage model 로 mapping. 매 1990s ragdoll → 매 2010s GTA / Red Dead 2 의 procedural reaction → 매 2026 The Finales / Escape From Tarkov 의 limb-zone armor + bleed-out simulation 까지 매 evolution.

## 매 핵심

### 매 physics 기본
- **Kinetic energy**: KE = ½mv². 매 9mm pistol ≈ 500 J, 매 rifle round ≈ 2000-3500 J.
- **Pressure**: P = F/A. 매 small projectile = 매 high-pressure 침투.
- **Strain rate**: 매 fast load = 매 brittle fracture (bone), 매 slow = 매 bend.
- **Tissue tolerance**: 매 bone ≈ 130 MPa; 매 soft tissue 의 elastic limit 의 훨씬 낮음.

### 매 game model layers
1. **Hitbox layer** — body part zone (head / torso / limb).
2. **Damage type** — penetration / blunt / explosive / fire.
3. **Armor interaction** — material × thickness × angle.
4. **Wound state** — bleed / fracture / shock / unconscious.
5. **Locomotion impact** — limp / aim sway / stamina drain.

### 매 응용
1. Tactical shooter limb damage (Tarkov, Ready or Not, Squad).
2. Melee combat reaction (Mordhau, Chivalry 2, Kingdom Come Deliverance).
3. Vehicle crash sim (BeamNG.drive — 매 jbeam node-spring deformation).
4. Sports / action game ragdoll tuning (NBA 2K, Wrestling games).

## 💻 패턴

### Limb-zone hit registration
```cpp
struct HitResult {
    BodyPart part;       // HEAD, NECK, CHEST, ARM, LEG
    float damage;
    DamageType dtype;
    Vector3 impactPoint;
    float kineticEnergy;
};

HitResult ResolveHit(const Projectile& p, const Character& c) {
    BodyPart part = c.HitboxAt(p.lastPos);
    float ke = 0.5f * p.mass * p.velocity.SquaredLength();
    float armor = c.ArmorOn(part).StoppingPower(p.dtype);
    float damage = std::max(0.f, ke - armor) * BodyMultiplier(part);
    return {part, damage, p.dtype, p.lastPos, ke};
}
```

### Damage multiplier table
```cpp
float BodyMultiplier(BodyPart p) {
    switch (p) {
        case HEAD:  return 4.0f;
        case NECK:  return 3.0f;
        case CHEST: return 1.0f;
        case STOMACH: return 1.2f;
        case ARM:   return 0.5f;
        case LEG:   return 0.6f;
    }
}
```

### Bleed-out simulation
```python
class WoundState:
    def __init__(self):
        self.bleed_rate = 0.0   # HP/sec
        self.fractures = set()
        self.hp = 100.0

    def apply_hit(self, hit):
        self.hp -= hit.damage
        if hit.dtype == "PENETRATION" and hit.part in ("CHEST", "STOMACH"):
            self.bleed_rate += 0.5
        if hit.dtype == "BLUNT" and hit.kinetic_energy > 1500:
            self.fractures.add(hit.part)

    def tick(self, dt):
        self.hp -= self.bleed_rate * dt
```

### Locomotion impact (limp from leg fracture)
```cpp
float MoveSpeedMultiplier(const WoundState& w) {
    float m = 1.0f;
    if (w.fractures.contains(LEG_LEFT))  m *= 0.55f;
    if (w.fractures.contains(LEG_RIGHT)) m *= 0.55f;
    if (w.bleedRate > 1.0f)              m *= 0.85f; // hypovolemic
    return m;
}
```

### Ragdoll impulse from impact
```csharp
void ApplyImpactRagdoll(Rigidbody bone, Vector3 dir, float ke) {
    float impulse = Mathf.Sqrt(2 * ke * bone.mass);
    bone.AddForceAtPosition(dir * impulse, hitPoint, ForceMode.Impulse);
}
```

### Armor angle attenuation
```python
def effective_armor(armor_thickness_mm, hit_angle_deg):
    """Slope-thickness: thicker at oblique angle."""
    import math
    return armor_thickness_mm / math.cos(math.radians(min(hit_angle_deg, 80)))
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Arcade shooter (CoD, Apex) | 1-tap headshot, 매 simple multiplier |
| Mil-sim (Tarkov, Squad) | 매 full limb + armor + bleed |
| RPG (Cyberpunk, Fallout) | 매 limb cripple + status effect |
| Vehicle sim (BeamNG) | 매 node-spring deformation (no hitbox) |
| Melee (Chivalry, Mordhau) | 매 directional hit + body part + stamina |

**기본값**: Hitbox + multiplier + simple bleed → 매 expand 의 incremental.

## 🔗 Graph
- 부모: [[Game_Physics]]
- 응용: [[Combat_Balance_Buff]]
- Adjacent: [[Procedural-Level-Geometry]]

## 🤖 LLM 활용
**언제**: 매 tactical / sim 게임 의 damage model design, 매 hit-feel iteration, 매 armor balance.
**언제 X**: 매 abstract / arcade game (매 단순 HP bar 가 더 적합).

## ❌ 안티패턴
- **Realism > fun**: 매 realistic 1-shot kill 이 매 PVP 의 frustration source.
- **Limb zone 의 inflation**: 매 너무 많은 zone (12+) = 매 hitreg 의 confusion.
- **No feedback**: 매 hit 의 visual / audio cue 의 X = 매 player 의 "did I hit?" 의 ambiguity.

## 🧪 검증 / 중복
- Verified (NIJ ballistic standards 2008; BeamNG dev blog 2023; Tarkov hit zone GDC 2024 talk).
- 신뢰도 A-.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — KE / armor / bleed model, limb multiplier, ragdoll impulse |