The center of mass (COM), also called center of gravity, is the point at which the entire mass of a body or system can be considered to be concentrated. For the human body, it's the balance point where all mass is equally distributed in all directions.
In an average standing adult, the center of mass is typically located:
- Approximately at the level of the second sacral vertebra
- Slightly anterior to the spine
- About 55-57% of total height from the ground
However, the COM location constantly changes based on:
- Body Position: Different postures shift the COM location
- Segment Positions: Raising arms overhead moves the COM upward
- External Loads: Carrying objects shifts the COM toward the load
The center of mass is crucial for understanding:
- Balance and Stability: The COM must remain within the base of support to maintain balance
- Movement Efficiency: Controlling COM motion is key to efficient locomotion
- Athletic Performance: Many sports skills involve manipulating the COM trajectory (jumping, diving, gymnastics)
- Gait Analysis: COM displacement patterns reveal walking and running efficiency
In video analysis, the whole-body center of mass can be estimated by calculating the weighted average position of all body segments. Tracking COM movement provides insight into overall movement strategy and control.
The velocity and acceleration of the center of mass are particularly important in kinetic analyses, as they relate directly to the forces acting on the body through Newton's laws of motion.