Determining Centre of Mass

As part of the 'timed up and go' test participants will have a marker attached to their centre of mass in order to collect data on factors such as jerk and postural sway. The centre of mass is described as a balance point of an object (Gambino et al, 2006). However before we can do this we need to determine where abouts on the body the centre of mass will be. According to Gambino et al (2006) a person's centre of mass is just below the belly button, which is nearly the geometric centre of a person. In a trial run of our experiment we were placing the marker slightly above the participant's belly button so it is possible that the data we collected maybe be inaccurate as this could have been the wrong positioning for their centre of mass.

Gambino et al (2006) concluded that a female's centre of mass is slightly lower than a males centre of mass. Unfortunately we would not be able to perform the test they did to collect these results as we are working with the frail elderly. The test they completed involved lying on beams in order to record the weight and height of each participant. There is the possibility of an injury and this involves the use of a large amount of equipment.

According to McGinnis (2005) a person's centre of mass is estimated at between 55 and 57% of their height in the anatomical position. Similarly, McGinnis (2005) identifies that a females centre of mass will be slightly lower than a males centre of mass as a result of larger pelvic girdles and narrower shoulders. This way of calculating the centre of mass would be easier to carry out as it requires little of the participants and only a small amount of equipment. If the measurements are not carried out then at least we now have a better understanding of where the centre of mass is on the human body.

References

Gambino,S, Mirochnik, M and Schechter S. (2006) The Physics Factbook.
McGinnis, P.M. (2005) Biomechanics of sport and exercise. Human Kinetics. pp 133.