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Torque

German: Drehmoment

1 Physical Definition

The torque is considered as a force which can cause a movement of a body around of a rotary axis. Due to this fact, it is always referred to the distance in between of the point of attack of the force and the rotary axis (=lever). By appliance of a constant force, with greater distance results a greater torque. Regarded reversely, with a constant distance given, a greater torque can be achieved by greater force. This is corresponding to the principle of the "law of the lever", which can be applied in physics as well as in everyday life: The input force multiplied by the distance from the input force to the fulcrum equals the load, or "the weight moved" multiplied by the distance from the fulcrum to the output of force.

The calculaction can be carried out by the following multiplication: M = r * F

2 Medical Relevance

In fields of medicine, there is just a small number of cases in which muscles are operating in a rectilinear movement. In most cases, that is to say especially in case of operating and impacting force of the skeletal muscles, muscles primarily have an impact on the joints - which are from the physical point of view rotary axises - and therefore producing a torque. In this connection the main torque impacting the joint axis is to be distinguished from torques operating in other directions.

2.1 Torque of the joint axis

If in fields of medicine the function of a muscle get named, it primarily results from decleration of the joint's axis and thereby of the joint on which it has an impact on. The various decriptions like flexion, supination, aduktion etc. are describing the direction as well as the axis of the executed rotary movement. This axis can actually possess an absolute relation to one of the three body axises (e.g. external rotation of the thigh) or can be related to one extremeity (e.g. supination of the hand).

In the rarest cases the force of a muscle takes effect exactly vertically on the joint's axis. Hence, the produced torque decomposes into its vectors of the rotary axis of the joint and its two verticals. It is exclusively the part of the torque impacting directly on the joint's axis respectively on one of the joint's axises which is referred to if the main function of a muscle is mentioned.

2.2 Further torques

The majority of muscles are producing several torques. Just when they are acting together (synergy) or in the context of the effect of a oppositely directed muscle the actual movements respectively the actual effects of the forces on the external world are resulting. On the one hand, this is necessary due to the fact that the human body is no machine with solid, rigid rotary axises but instead posesses a plastic, elastic and deformable locomotor system. On the other hand it comes with a lot of problems which pathological effects are treated in fields of orthopaedics.

For instance, none of the four parts of the quadriceps femoris muscle (Musculus quadriceps femoris) takes effect exactly on the axis of flexion of the knee joint. If the sum of the operating shear forces is not equalling zero, a physical stress is resulting on the system, in this case affecting the contacting planes in between of patella and patella groove (Sulcus intercondylaris), in which the patella is moving in. Consequences can be: luxation of the patella and/or more severe abrasion of the contact planes.

2.3 Impact on the Genesis of Pathological Alteration

By the numerous, just bad controllable divergent subforces and other torques which are deviant from the main torque, there are various, unmanageable interactions in between of the skelettal muscles. Even by interaction of correcting foces they cannot be controlled. The consequences are besides of already named aspects of abrasion and luxation overall tension and blockades.

3 Further Information

Further information on this subject can be found in literature of orthopaedics, in specialist literature of physics and via examples in following sources of the internet (mainly definitions): http://en.wikipedia.org/wiki/Torque

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