Center of Pressure (COP)

Original Editor - User:Anne Dixie Lim

Top Contributors - Anne Dixie Lim and Kapil Narale  

Introduction

The center of pressure (COP) is a fundamental concept in the study of human movement and balance. When a person is standing or walking, their body exerts a force on the ground, to which the ground responds by exerting an equal and opposite force, called the ground reaction force (GRF). The COP is the point at which the total force (the GRF) acting on a person's foot or feet is concentrated, and it is a crucial factor in maintaining stability and preventing falls.

The trajectory of the COP, commonly known as a stabilogram, during static balance is frequently used to measure postural control. When standing still, the COP is thought to be an indicator of the motor mechanisms involved in maintaining balance by keeping the center of mass (COM) within the base of support. Falls are correlated with the displacement of the COP at the limits of stability, highlighting the value of investigating dynamic balance to assess the risk of falling.

Biomechanics researchers use force platforms and other instruments to measure the COP during various activities such as standing, walking, jumping, and other dynamic movements. The COP measurements can provide insights into the mechanics of human movement and can be used to develop models and simulations to improve understanding of biomechanics and optimise performance in various applications such as sports and physical therapy.

COP Domain and their Variables

The parameters of COP refer to the various measurements and calculations that can be made based on the displacement and movement of COP data. Some of the most common parameters of COP include:

1. Displacement: the distance and direction that COP moves from a reference point or position
2. Velocity: the speed and direction of COP displacement over time
3. Acceleration: the rate of change of COP velocity over time
4. Range: the maximum distance between the COP and its reference point or position
5. Mean: the average position of the COP over a period of time
6. Standard deviation: the amount of variation in the COP position over a period of time
7. Frequency: the number of times that the COP moves beyond a predefined threshold in a given time frame
8. Area: the total area enclosed by the COP trajectory over a period of time
9. Power spectral density: the distribution of COP power over different frequencies
10. Entropy: the degree of irregularity or randomness in the COP trajectory.

These parameters are used to analyse COP data in various fields such as biomechanics, sports science, rehabilitation, and neuroscience.

The variables are classified into four domains based on their dependency on various features of the COP trajectories:

• Positional variables
  • Variables that describe aspects of the foot position dispersion without considering its local displacements
• Dynamic variables
  • Variables relying on the COP trajectory’s local displacements
• Frequency variables
  • Elements that describe the COP trajectory's power spectral density
• Stochastic variables
  • Variables obtained from stochastic process models in which the COP is depicted

*Learn more about the variables and their domains by visiting the original references

Center of Pressure (COP) vs. Center of Mass (COM)

	COP	COM
Definition	The point of application of the ground reaction force (GRF) on the foot or the contact area between a person and a support surface	The point in the body where it represents the average location of all the body's mass
Changes with	Variations in the shape, orientation, and angle of attack of the object, and depends on the distribution of weight and pressure on the support surface	Variations in the body's posture and movement, and depends on the distribution of mass in the body
Tools needed	Force plates or pressure sensors	Motion capture systems
Aspect	Reflects the neuromuscular response to maintain stability by monitoring movements of the CoM	Reflects movements (position, velocity, acceleration) of the body's center of mass

Importance

Determining the COP is crucial in various fields, such as clinical and sports biomechanics, ergonomics, and rehabilitation. It allows for the evaluation of balance control and postural stability, which can help with the identification and management of balance disorders. Measuring the COP can also provide insights into the mechanisms underlying postural control and help identify individuals at risk of falling, allowing for preventative measures to be taken. Understanding the COP can also help with the creation of assistive technology and with improving sporting performance.

COP can be used to assess various disorders related to balance and gait. These disorders include, for instance:

1. Parkinson's disease
2. Multiple sclerosis
3. Stroke
4. Peripheral neuropathy
5. Aging-related balance impairments

By analyzing the COP, healthcare professionals can obtain valuable information about postural control and balance, which can aid in the assessment, diagnosis, and treatment of these disorders.

Conclusion

Today, researchers use a variety of techniques to measure COP, including force platforms, pressure-sensitive insoles, and wearable sensors. The use of these technologies has led to a better understanding of the biomechanics of standing, walking, and other activities, and has helped to improve the diagnosis and treatment of balance disorders and other movement disorders.