Download What is torque? Net Joint Torque Answers

2/19/2014
Assume: d = 7 cm, θ = 30°, the
muscle can produce 60 N of force
per cm2, and the cross sectional
area of the muscle is 13.33 cm2…
What is torque?
Torque is the turning effect created by an
eccentric force, about an axis, expressed as
units of force × units of length (Nm).
Our muscles produce
joint torque that
enables our
segments to rotate
about our joints.
1. What is the compressive component
of the quadriceps force (FC)?
2. What is the rotary component of the
quadriceps force (FR)?
3. How much torque is created by the
quadriceps force (TQ)?
4. How does the patella increase the
mechanical capabilities of the
quadriceps?
5. How might internal (muscle) knee
extension torque be related to ACL
injury?
Fb
rb
FC
FQ
d
θ
FR
Net Joint Torque
d = 7 cm; θ = 30°; CSAQ = 13.33 cm2.
Create a free-body diagram representing the
upper extremity (upper arm, forearm, and hand)
in the following circumstances:
Solve for the following:
1. Compressive component of the
quadriceps force (FC)
2. Rotary component of the
quadriceps force (FR)
3. Torque created by the quadriceps
force (TQ)
4. Also, how does the patella
increase the mechanical
capabilities of the quadriceps?
5. How might the knee extension
torque be related to ACL injury?
upper
1. You are holding 3 gallons of water (Fww = 111 N) in your right
hand: shoulder abduction = 90°, with your wrist and elbow in
anatomical position
FC
FQ
3. Your deltoid is the only active muscle force (Fd): it inserts at an
angle of 15° above the humerus and at a horizontal distance of
0.15 m from your shoulder joint
d
θ
Answers: FC = 692 N; FR = 400 N; and
TQ = 28 Nm
2. Water weight acts at a horizontal distance that is 0.60 m from
your shoulder joint
4. Your arm weighs 40 N (Faw): this weight acts at a horizontal
distance of 0.30 m from the shoulder joint
FR
5. The bucket is in static equilibrium (ΣF = 0; ΣT = 0).
Calculate:
Answers
1. Torque produced by the deltoid in order to hold the water
in static equilibrium
1. Deltoid Torque = 78.6 Nm
2. Deltoid force, including the resultant, rotary, and
compressive components
2. Force produced by the deltoid = 2024 N
(rotary = 524 N; compressive = 1955 N)
3. Compressive (horizontal) shoulder joint reaction force
(JRFX)
3. Compressive (horizontal) shoulder joint reaction force =
1955 N
4. Shear (vertical) shoulder joint reaction force (JRFY)
4. Shear (vertical) shoulder joint reaction force = 373 N
5. Resultant shoulder joint reaction force (JRF)
6. How might you decrease the shoulder joint reaction
force?
5. Resultant shoulder joint reaction force = 1990 N, 10°
below the horizontal axis
6. How might you decrease the shoulder joint reaction
force? Adduct the humerus (lower the water)
1
2/19/2014
Some A 1.5-kg forearm is horizontal and flexed 90˚ relative to a vertical upperarm, while holding a 5-lb weight in the hand (the forearm center of mass is 13 cm
away from the elbow joint). Although not a perfect assumption, assume that the
biceps brachii is the only muscle force acting on the forearm. The angle of
insertion for the biceps brachii is 45˚, and the insertion point is 3 cm from the
elbow joint. If the 5-lb weight is 30 cm away from the elbow, calculate the
following:
1. Torque, due to the force that is produced by the biceps brachii.
Answer: 8.63 Nm.
2. Force (resultant, rotary, and compressive) that is produced by the biceps
brachii.
Answers: 407 N, 288 N, and 288 N.
3. Magnitude and direction of the joint reaction force, applied by the upper
arm to the forearm.
Answers: 382 N, ~41˚ below a
horizontal axis.
Torque, due to muscle force is influenced by
joint angle
F
×
r
=
Torque, due to muscle
force, is highly
dependent upon joint
angle. Notice how the
perpendicular
distance related to the
muscle force changes
as joint angle
changes.
Mechanical advantage
(ME), within a
biomechanical context:
T
Typeequationhere.
Mechanical advantage is
a ratio of perpendicular
distances, or moment
arms: internal over
external
ri
re
FE
2