Determine if an object is in static equilibrium when the forces and torques acting on the object are known
Determine an unknown force or torque acting on an object, if all the other forces and torques acting on the object are known and the object is in static equilibrium
Define center of gravity
Estimate the location of the center of gravity of an object or body
Is there a benefit to having the joint position that maximizes the effort arm being a different position than the joint position that maximizes muscle force?
The following tables are excerpted from Plagenhoef et al., 1983. They describe body segment mass as a proportion of total body mass and the location of each segment's center of mass as a proportion of segment length.
Segment Mass Percents:
Segment
Males
Females
Head & Neck
8.96
8.20
Trunk
46.84
45.00
Upper Arm
3.25
2.90
Forearm
1.87
1.57
Hand
0.65
0.50
Thigh
10.50
11.75
Shank
4.75
5.35
Foot
1.43
1.33
Segment Length Percents (from proximal):
Segment
Males
Females
Head & Neck
55.0
55.0
Trunk*
50.0*
50.0*
Upper Arm
43.6
45.8
Forearm
43.0
43.4
Hand
46.8
46.8
Thigh
43.3
42.8
Shank
43.4
41.9
Foot
50.0
50.0
* Estimates for trunk are from Winter (1990) and are calculated from Dempster data (1955) but adapted for the torso alone (without including head & neck). Segment endpoints are from mid-shoulders to mid-hips.
Calculating center of mass in a body
The shoulder of a tennis player is 1.60m above the ground while the elbow is 1.77m above the ground. Where is the center of mass of the upper arm (the length percent for the upper arm is 43.6%)?
Emma Coburn jumps off the steeplechase barrier with her right leg in the following position from a side view in meters relative to the ground vertically and from the front edge of the barrier horizontally:
Hip (0.84, 1.44)
Knee (0.65, 1.12)
Ankle (0.31, 0.92)
Heel (0.29, 0.95)
Toe (0.25, 0.72)
Where is the center of mass of the leg if the body segment parameters are as follows:
