Center of Mass

Chapter 12

KINE 3301Biomechanics of Human Movement

Segmental Method for Computing Center of Mass

Segment Segment Weight (N) CM Location (%) Proximal End Head 0.032 x BW + 18.7066.3 Top of HeadTrunk 0.532 x BW – 6.93 52.2 1ST CervicalUpper Arm 0.022 x BW + 4.76 50.7 ShoulderForearm 0.013 x BW + 2.41 41.7 ElbowHand 0.005 x BW + 0.75 51.1 WristThigh 0.127 x BW – 14.8239.8 HipLower Leg 0.044 x BW – 1.75 41.3 KneeFoot 0.009 x BW + 2.48 40.0 Ankle

From: Chandler, R. F., C. E. Clauser, et al. (1975).

Computing the Location of a Segments CM

How to Use Segmental Method

1. Determine the X, Y location of the endpoints of all body segments.

2. Determine the weight of each segment.3. Determine the location of each segments center of mass.4. Multiply the segment weights by the x or y coordinates and

then divide by the total weight to determine the location of the body center of mass.

𝑥𝐶𝑀=𝑚1𝑥1+𝑚2𝑥2+𝑚3 𝑥3…

𝑚1+𝑚2+𝑚3…

𝑦𝐶𝑀=𝑚1 𝑦1+𝑚2 𝑦2+𝑚3 𝑦…

𝑚1+𝑚2+𝑚2…

Using Excel to Compute CM

Sagittal View Example

Segment Segment Weight (N) CM Location (%) Proximal End Head 0.032 x BW + 18.70 66.3 Top of HeadTrunk 0.532 x BW – 6.93 52.2 1ST CervicalThigh 0.127 x BW – 14.82 39.8 Hip

In the back handspring assignment we are assuming that the right and left limbs move symmetrically, so the weights must be doubled, in cell F5 enter the following:

=2*((0.127*$L$2)-14.82)