Muscles & Joint Rotations

• Important Info about Torque:

  • Torque is influenced by:
  • Magnitude of the force
  • Line of action of the Force (direction)
  • Point of application of the force
  • Ƭ = Fr
  • The distance r is always measured perpendicular - ie at right angles or 90° - to the line of action of the force
• Important Info about Torque:

  • The axis of rotation can be fixed
  • The hinges on a door
  • Your forearm is fixed to your elbow axis
  • The axis of rotation can be free
  • Centre of mass (CoM)
• Sum of Torques:

  • The net turning effect on an object is equal to the sum of the Torques
  • 𝚃 = Fr
  • Σ𝚃 = ΣFr
• Sum of Torques:

  • Just like the force is the sum of them that cause the movement
  • Equation can be used to gain understanding about other components of effectiveness of the torque & balance
• Which force has the greatest advantage?

  • 𝚃 = Fr
  • Insertion point of muscle = rm = 0.06
  • Wr = weight holding = 30 kg
  • rR = 0.4 m = length of forearm
  • Fm = 300 N = force applies
• Which force has the greatest advantage?

  • 𝚃 = Fr
  • Sum of torques acting
  • ∑T = Fm x rm (CCW) + Fw x rw (CW)
  • ∑T = 18 N/m + ∑117.7 N/m
  • ∑T = - 99 N/m CW
• Which force has the greatest advantage?

  • 𝚃 = Fr
  • What is the torque of the weight
  • 117.7 N/m
  • Torque of muscle
  • 18 N/m
  • Direction = vertical = y axis
• What is the net torque?

  • CCW = +
  • ∑T = Fr
  • ∑T = F1r1 + F2r2
  • ∑T = (150 x 2) + (100 x 2)
  • ∑T = - 100 N CW
  • Distance from axis has more effect
• Torque (moment) as scalar quantity:

  • Tm = Fm rm
  • Tw = -Fw rw
  • TJ = Fw rw + Fm rm
• Torque (moment) as scalar quantity:

  • Direct as is a downward/CW force
  • Moment as scapulae as no calculating torque by components are calculating resultant
• How much muscle force is required to hold this mass?

  • We are static when the sum of the torques acting on a joint are equal to 0
  • What muscle force is required to hold this resistance
  • Fm = 117.7 / 0.06 = 1962 N
• Important Info about Torque:

  • The net effect of the force is equal to the sum of the torques on the axis
  • If there is no rotation occurring then the sum of the Torques must be equal to 0