Kinematics and kinetics are the two main branches of mechanics used to study human movement. Kinematics describes motion itself: where body segments are, how joint angles change, and how fast and in what direction the body moves. Kinetics describes the forces and moments behind that motion, such as ground reaction force, muscle forces, and the moments acting around joints. Kinematics answers what the movement looks like; kinetics helps explain why it happens that way.
When to use each
- Kinematics suits technique review, comparing positions at key moments, measuring range of motion, and checking timing and sequencing.
- Kinetics suits questions about loading, force production, and how forces are absorbed, for example during landing or sprint acceleration.
- Many research settings combine both. Inverse dynamics uses kinematic data, measured external forces, and body segment estimates to calculate joint moments.
How to see it on video
Video captures kinematics. Frame-by-frame review, joint-angle measurement, and skeleton tracking all describe movement, and tools such as the 2D skeleton tracking and angle measurements in KineVision work in this domain. Kinetics cannot be read directly from ordinary video. Forces are normally measured with instruments such as force plates, or estimated with models that make assumptions about body mass and segment properties. Video can still provide useful context for kinetic data, for example by showing body position at the moment of peak force.
Common mix-ups
- A movement that looks similar on video can involve different forces. Two athletes with matching knee angles at landing may absorb load very differently.
- The coaching phrase kinetic chain describes how linked segments contribute to a movement. Using it does not mean forces were measured.
- Acceleration is a kinematic variable even though it relates directly to net force through mass.
Most coaching feedback is kinematic, because it is observable and easy to repeat. Kinetic measurement adds depth when loading or force output is the real question.