Gait analysis is an important skill that is used daily in medical offices to determine both diagnosis and treatment options for patients in many different disciplines. The languange that is used to discuss gait observation and analysis varies often times based on a clinical vs. research point of view. Two of the more commonly used terms are "center of pressure" and "center of mass." For many, these are used interchangeably, but they are not synonymous. To offer some clarification, the descriptions of each is detailed below:
Center of Mass(COM) is a point on the body that moves as a representative of the body's reaction to external forces.
Center of Pressure(COP) is a temporally influenced measurement recorded by a force plate.
During quiet standing, the anterior/posterior movement of the COP is largely influenced by the ankle joint moments, while the medial/lateral movment of the COP is influenced primarily by the hip joint motion. During gait, the COP reflects the body movements that occur as forces attempt to rebalance the position of the COM.
As practitioners, we often recognize abnormal gait patterns that are the result of abnormal movements that affect the COM. In certain gait disorders, dysfunction of the musculoskeletal or neurological system, lead to severely inefficient movement as the body is constantly battling to maintain postural stability which leads to a balanced COM.
Intervention for any type of disorder that affects gait, should attempt to help the body regain this balance in an effiecient and timely manner. Whether using shoes, braces, prefabricated orthotics, custom orthotics, taping, wedges or strengthening programs, consideration of this goal is important.
For further reading on the effect of orthotics on the Center of Mass during gait initiation, take a look at our EJournal summary from today:
Najafi B, Miller D, Jarrett BD:Does footwear type impact the number of steps required to reach gait steady state?: An innovative look at the impact of foot orthoses on gait initiation. Gait Posture, 32(1):29-33, 2010.