This file format describes the dimensions of the human skeleton and a set of motion data using anatomical terminology. The content in this format is converted from a BVH file.
Standard Anatomical Pose
The standard anatomical pose of the human body is defined as: standing upright, eyes looking straight ahead, arms hanging naturally at the sides, palms facing forward, feet together, and toes pointing forward.
While this is the standard anatomical reference pose, in practical applications, a slight variation is used—the A-pose, where the palms face inward toward the thighs. All subsequent data is based on the A-pose as the standard reference position.
Common Directional Terms
Based on the standard anatomical pose, the following directional anatomical terms are defined:
- Superior: toward the head
- Inferior: toward the feet
- Anterior: toward the front (abdomen)
- Posterior: toward the back
- Superficial: toward the surface
- Deep: away from the surface
- Medial: toward the midline
- Lateral: away from the midline
- Proximal: closer to the trunk (for limbs)
- Distal: farther from the trunk (for limbs)
- Radial side: outer side of the forearm
- Ulnar side: inner side of the forearm
- Fibular side: outer side of the lower leg
- Tibial side: inner side of the lower leg
Basic Planes of the Human Body
According to anatomical principles, the human body can be divided into three mutually perpendicular planes:
- Sagittal plane: A vertical plane that runs along the front-to-back axis of the body. The plane that passes directly through the midline is called the median plane or midsagittal plane.
- Frontal plane (also called the coronal plane): A vertical plane that runs along the left-to-right axis of the body, dividing it into front and back sections.
- Transverse plane (also called the horizontal plane): A horizontal plane that cuts across the body, dividing it into upper and lower sections, and is parallel to the ground.
Basic Axes of the Human Body
According to anatomical orientation, the human body has three primary axes that are perpendicular to each other. Most joint and segment movements occur around these axes:
- Frontal (coronal) axis: Runs horizontally across the body and is perpendicular to the sagittal plane; also known as the coronal axis.
- Sagittal axis: Aligned horizontally and perpendicular to the frontal (coronal) plane.
- Vertical axis: Runs vertically through the body and is perpendicular to the transverse (horizontal) plane.
Joint Motions
The table below describes standard motions, referencing the anatomical pose:
| Joint | Motion Type | Description | Axis & Plane |
|---|---|---|---|
| Head | Flexion/Extension | Looking down is flex (+), up is extend (-) | Coronal axis in sagittal plane |
| Rotation | Left rotation is (+), right is (-) | Vertical axis in transverse plane | |
| Lateral Flexion | Bending left is (+), right is (-) | Sagittal axis in coronal plane | |
| Trunk | Flexion/Extension | Bending forward is (+), backward is (-) | Coronal axis in sagittal plane |
| Rotation | Left is (+), right is (-) | Vertical axis in transverse plane | |
| Lateral Flexion | Left is (+), right is (-) | Sagittal axis in coronal plane | |
| Shoulder | Flexion/Extension | Raising arm forward is (+), backward is (-) | Coronal axis in sagittal plane |
| Internal/External Rotation | Right arm: internal is (+), external is (-); opposite for left | Vertical axis in transverse plane | |
| Adduction/Abduction | Moving inward is (+), outward is (-) | Sagittal axis in coronal plane | |
| Elbow | Flexion/Extension | Bending is (+), straightening is (-) | Coronal axis in sagittal plane |
| Adduction/Abduction | Inward is (+), outward is – | Sagittal axis in coronal plane | |
| Forearm | Pronation/Supination | Right arm: pronation is (+), supination is (-); same for left | Vertical axis in transverse plane |
| Wrist | Flexion/Extension | Palm toward forearm is (+), back of hand is (-) | Coronal axis in sagittal plane |
| Internal/External Rotation | Right hand: internal is (+), external is (-); opposite for left | Vertical axis in transverse plane | |
| Ulnar/Radial Deviation | Ulnar (+), radial (–) | Sagittal axis in coronal plane | |
| Hip | Flexion/Extension | Leg forward is (+), backward is (-) | Coronal axis in sagittal plane |
| Internal/External Rotation | Right leg: internal is (+), external is (-); opposite for left | Vertical axis in transverse plane | |
| Adduction/Abduction | Inward is (+), outward is – | Sagittal axis in coronal plane | |
| Knee | Flexion/Extension | Bending backward is (+), straightening is (-) | Coronal axis in sagittal plane |
| Internal/External Rotation | Right lower leg: internal is (+), external is (-); opposite for left | Vertical axis in transverse plane | |
| Adduction/Abduction | Inward is (+), outward is (-) | Sagittal axis in coronal plane | |
| Ankle | Flexion/Extension | Toe down is (+), up is (-) | Coronal axis in sagittal plane |
| Internal/External Rotation | Right foot: internal is (+), external is (-); opposite for left | Vertical axis in transverse plane | |
| Inversion/Eversion | Inward turn is (+), outward is (-) | Sagittal axis in coronal plane |
- “Left” and “Right” refer to the subject’s own body orientation in the anatomical pose.
- Terms like flexion, rotation, lateral flexion follow standard anatomical definitions (see “Exercise Anatomy,” p. 47).
- Sign conventions: flex (+), extend (–); internal (+), external (–); pronation (+), supination (–); adduction (+), abduction (–); ulnar dev. (+), radial dev. (–); inversion (+), eversion (–).
- Although elbow and knee normally only flex/extend, definitions for internal/external rotation and adduction/abduction are included.
- For forearm pronation/supination, sensors should be placed close to the wrist to ensure accurate capture.
Data Example
SIZE Head,Trunk,Hip,LeftCollar,LeftUpArm,LeftLowArm,LeftHand,RightCollar,RightUpArm,RightLowArm,RightHand,LeftUpLeg,LeftLowLeg,LeftFoot,RightUpLeg,RightLowLeg,RightFoot 9.83,61.21,13.23,14.07,30.38,25.22,17.78,14.07,30.38,25.22,17.78,46.58,44.12,8.79,46.58,44.12,8.79 MOTION Frames: 2 Frame Time: 0.033333 head‑fle‑ext,head‑rot,head‑lat,trunkus‑fle‑ext,…,rankle‑inv‑eve 0,0,0,0,…,0 10,0,0,0,…,0
- SIZE: lists key skeletal segments and their lengths (in cm).
- MOTION: defines the number of frames, frame time, and per-frame joint angles.
SIZE Details
Defines relationships between skeletal segments and joints. E.g.:
- LeftCollar → LeftUpArm = Left Shoulder joint
- LeftUpArm → LeftLowArm = Left Elbow
- … etc., for both arms and legs
MOTION Details
Defines frame count, rate, and each joint’s rotation angles per frame.
Field Abbreviations & Meaning:
head-fle-ext: head flexion-extensionhead-rot: head rotationhead-lat: head lateral flexion- … etc., following the same format for trunk, shoulders, elbows, forearms, wrists, hips, knees, ankles.
Units & Conventions:
- Angles are in degrees, ranging from –360 to +360.
- Positive/negative values represent motion directions per the table above.
The example shows all zeros, meaning the subject is in the standard anatomical (A‑Pose).
Field names and order are not strict—as long as they match in count and comma-separated order.
Input: standard BVH data
Output: anatomy-based motion data as defined above