Changes

In a state of equilibrium, the torques about a pivot balance each other in all directions.  These torques usually include that produced by the force of gravity.  The torque of postural muscles opposes the gravitational torque.   

In a state of equilibrium, the torques about a pivot balance each other in all directions.  These torques usually include that produced by the force of gravity.  The torque of postural muscles opposes the gravitational torque.   

:::::'''Fig 5.5   The effect of the site of muscle attachments on the torque produced by muscles over the hip joint'''  

:::::'''Fig 5.5   The effect of the site of muscle attachments on the torque produced by muscles over the hip joint'''  

:::::The turning effect of a force about a pivot P, the torque, depends on the magnitude of the force and its perpendicular distance from the pivot d1, d2, d3 or l.  In the diagram, the middle gluteal and the semimembranosus muscles turn the femur about the hip bone. Assuming the forces to be equal, the magnitude of the torque is greatest for the superficial part of the semimembranosus muscle and least for the middle gluteal muscle since d2 > d3 > d1.  The torques of each of these muscles summate, and produce a propulsive force on the ground.  The perpendicular distance of the propulsive force on the ground from the pivot, l, is much greater than the perpendicular distance of any muscle from the hip.

:::::The turning effect of a force about a pivot P, the torque, depends on the magnitude of the force and its perpendicular distance from the pivot d1, d2, d3 or l.  In the diagram, the middle gluteal and the semimembranosus muscles turn the femur about the hip bone. Assuming the forces to be equal, the magnitude of the torque is greatest for the superficial part of the semimembranosus muscle and least for the middle gluteal muscle since d2 > d3 > d1.  The torques of each of these muscles summate, and produce a propulsive force on the ground.  The perpendicular distance of the propulsive force on the ground from the pivot, l, is much greater than the perpendicular distance of any muscle from the hip.

 

:::::In propulsion, the torque of certain muscles at a pivot results in a force where the foot contacts the ground (Fig. 5.5).  The propulsive force at the foot is less than the force of muscle contraction. The advantage is, however, that the range of movement at the foot will be greater than the range of contraction of any of the muscles.  The power for propulsion comes from a concentration of forces about the hip (Fig. 5.2).  Use the concept of torques to consider how limb design must optimise the muscular forces that accelerate hip extension, while optimising stride length.  The properties of limbs are discussed further in Chapter 8.   

In propulsion, the torque of certain muscles at a pivot results in a force where the foot contacts the ground (Fig. 5.5).  The propulsive force at the foot is less than the force of muscle contraction. The advantage is, however, that the range of movement at the foot will be greater than the range of contraction of any of the muscles.  The power for propulsion comes from a concentration of forces about the hip (Fig. 5.2).  Use the concept of torques to consider how limb design must optimise the muscular forces that accelerate hip extension, while optimising stride length.  The properties of limbs are discussed further in Chapter 8.   

:::::Diagrammatic representations of two muscles of similar mass but different shape.  Mechanical values are given for the muscles relative to 100 for the muscle a.  The “functional transverse area” is indicated by the dotted lines.  Tendons of origin and insertion must be related in thickness to the strength of the muscle in series with them.

:::::Diagrammatic representations of two muscles of similar mass but different shape.  Mechanical values are given for the muscles relative to 100 for the muscle a.  The “functional transverse area” is indicated by the dotted lines.  Tendons of origin and insertion must be related in thickness to the strength of the muscle in series with them.

==='''Fibrous architecture of muscles'''===  

==='''Fibrous architecture of muscles'''===