3D motion analysis

Static kinematics

Many applications do not need kinematic measurements during the whole movement but concentrate on certain points in time, which are often called events.
Typical examples for events are

• gait analysis: 'initial contact' ('heel strike', 'start of stance phase')
• gait analysis: 'terminal contact' ('toe off', 'end of stance phase')
• gait analysis: 'start of double support phase'
• racket sports: 'ball contact'
• athletics: 'javelin release
• swimming: 'start of main movement phase'

This type of motion analysis can be done easily and quickly with almost no processing time for the operator since complex image processing tasks are not necessary.

Usually two or more synchronized video cameras are used to capture the movement from different perspectives (e.g. sagittal and frontal view). The user scrolls the synchronized video clips with a few mouse clicks to the desired point in time and uses the mouse to digitize the body landmarks in order to measure in 2D or 3D.

For certain applications it is very effective to combine dynamic measurements (e.g. ground reaction forces) and other analog devices (e.g. EMG) with static measurements. Analog data acquisition can provide detailed and more accurate timing information such as

• force plate: maximum vertical ground reaction force
• force plate: end of brake impulse / start of accelerating impulse
• foot switch: start and end of stance phase
• EMG: onset / offset of certain muscles

which can then be used to measure kinematic data by digitizing the synchronized images. Static measurements can be used to determine

• time intervals (e.g. between ground contacts)
• positions (e.g. max. height of toe tip during swing phase)
• distances (e.g. step length, height difference of left and right hip)
• angles (e.g. knee angle, pronation / supination)

as well as their variation over time:

• mean linear velocity
• mean angular velocity

The resulting values can automatically be transferred to a report which can include the selected images, the measured values and some additional text (diagnosis, comments etc.).