Force plates are mechanical sensing systems designed to measure the ground reaction forces and moments involved in human movements. They generally look like a simple square or rectangle pedestal that sits flat on top of gym floors but can also be embedded into the ground to sit flush. With the help of force plates, we can interpret how forces are generated and transferred during a variety of different movements. A force plate allows us to demonstrate the kinematics of the body through Pressure Mapping.
Pressure measurement solutions offer the ability to segment views by foot and even isolate ground reaction force and center of pressure by foot region, thereby furthering analysis into foot function, balance, and sway. Due to the force plate’s versatility and capacity to isolate force measurements, force plates, and pressure mapping should be considered an important element in biomechanical analysis.
Balance control has always been a problem in the elderly and because of lack of balance control, they may experience falls which might be fatal. According to WHO, 35% of people aged above 64 years experience falls every year. To improve balance, first, we need to quantify it, and then provide treatment strategies based on clinical findings.
Quantitative assessment is crucial for the evaluation of human postural balance. The force plate system is the critical quantitative balance assessment method. The force plate uses either a firm or a foam surface to measure the weight distribution between the patient’s feet and utilizes normative data to ensure evidence-based practice. We can attain quantification through pressure measurement platforms or smart insoles with many built-in pressure sensors that can be used to obtain the plantar Centre of Pressure displacement. The center of pressure (COP) on the plantar surface of the foot is defined as the point of location of the vertical ground reaction force. The embedded in-shoe system can measure this pressure between the foot and the shoe.
COM is the center of mass. If the COM changes position, the value, and position of COP also change. Balance is quantified by measuring how much the COP moves in a certain amount of time, but that isn’t the only parameter.
There exist multiple parameters in balance measurement based on the force plate. They are as follows –
- The COP Ellipse Area – First is the COP ellipse area, wherein the ellipse set of the data is used to quantify 90% or 95% of the total area formed by the COP trajectory covered by the AP and ML directions. It is regarded as an indicator of overall posture performance, and it is generally believed that the smaller the area, the better the postural balance.
- The COP Path Length – the COP path length is the total distance traveled by COP during the test time. The smaller the path length, the better the postural stability. It is an effective evaluation index in numerous populations and balance conditions.
- COP Amplitude – COP amplitude is the distance between the maximum and minimum COP peak points in the AP and ML directions. The large amplitude value is due to poor postural stability.
- Weight-Bearing Asymmetry – A measure of the weight distribution between the lower limbs. It is expressed as the percentage of the average vertical force under the limbs with greater force to the total weight.
- COP Speed – COP speed is calculated by dividing the COP path length by testing time. In addition to the total COP average velocity, the average COP velocity components in the AP and ML directions can also be calculated. COP speed is an indicator of the efficiency of the postural control system. The average COP speed value is small, which is considered a good performance of posture control.
Now that we understand the parameters and what they are, let’s look at what test is used to measure balance.
The name of the test is the Modified Clinical Test of Sensory Interaction on Balance (mCTSIB). This test is very simple to understand. This protocol allows the sway velocity measurement in a comfortable stance in four sensorial conditions: stable surface with eyes open, stable surface with eyes closed, unstable surface with eyes open, and unstable surface with eyes closed. Each condition has three trials of 10 seconds. Generally, the sway and velocity measurement changes from each surface. For each trial, all the parameters mentioned above are quantified, giving the therapist an accurate depiction of the client’s balance.
The force plate is currently a widely-used method and technology for quantitative
postural balance assessment in laboratories and clinics. It is important to understand that balance control can be accurately measured through the usage of force plates which helps clinicians understand the patient’s body a little better. Non-instrument tests in balance assessment cannot detect subtle changes in posture control and only provide a gross indicator. Such methods have a limited ability to provide potential mechanisms for balance control and biomechanical defects related to balance damage. Therefore, quantitative assessment of balance is essential, especially for technical methods that are convenient for clinical use. Objective and quantitative balance assessment is regarded as the key to disease tracking and therapeutic intervention. COG and COP are crucial parameters for balance assessment, which can be reflected and analyzed to assess body sway and postural sway, respectively