Efecto de la temperatura

Figure 3.1. Examples of the range of motion (ROM) at the ankle joint when dorsiflexing, plantar flexing, everting and inverting the foot. Image taken from [82].

The flexibility of joints is defined as the range of motion (ROM) allowed at a joint and

describes how much a joint can move. A joint usually rotates when it moves. Therefore, an

angular movement is produced that is measured in degrees and thus the range of motion of a

joint is usually measured in degrees. The range of motion of a joint is usually measured by the

number of degrees from the starting position of a segment to its position at the end of its full

range of movement (Figure 3.1). There are two types of ROM: i) active ROM, where a person

voluntarily contracts their muscles around a joint and ii) passive ROM where an external force

acts on a body around a joint and produces movement [83]. The most common way to measure

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constructed from a toughened clear plastic so that it does not break easily and is usually 12, 8

or 6 inches wide with 1 degree increments. There are centimetre and inch measurement readings

along the proximal/fixed arm and the distal arm of the goniometer and 360-degree measurement

readings around its circular disk. The stationary arm, which is the proximal/fixed arm of the

goniometer, is placed parallel to the stationary body segment and holds a protractor. The

circular disk, which is the protractor, has a pin in its centre which is the axis of the goniometer

and is placed over the joint whose ROM is measured. The mobile arm, which is the distal arm,

moves along the moving body segment. The angular degree between the endpoints of the

goniometer denotes the range on motion of the joint for a specific movement.

Figure 3.2. A double-armed goniometer. Demonstrating the circular disk, the distal arm and the proximal/fixed arm that are placed on joints and body segments in order to calculate the range of motion (ROM) at a joint.

In occupational and physical therapy, a goniometer is a very helpful instrument used to

measure the range of motion of different joints of the body. It is a clinical tool that helps the

doctor or the physician to obtain objective measurements and to accurately follow the progress

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measuring the knee joint, the pin of the circular disk (point of rotation) would be placed on the

lateral epicondyle of the femur. The proximal arm is lined up with the greater trochanter of the

femur and the distal arm of the goniometer is lined up with the lateral malleolus of the fibula.

A measurement is then taken using the degree scale on the circular disk of the goniometer [86].

Goniometers are very useful tools that can be easily used by scientists when some knowledge

of the anatomy, the joints and the muscles of a human body is attained. They are also relatively

inexpensive, portable and can be accessed very easily. Reliability studies have shown that the

goniometers present good overall intra-measure (i.e. between measures) and inter-tester (i.e.

between testers) reliability when the measurements are repeated several times in an experiment.

However, there are a few issues concerning the accuracy of the readings from a goniometer.

Some studies suggest that these errors lie between 5 and 10 degrees when completing repeated

measures [85, 86]. Whilst overall validity and reliability of the goniometer has been recounted

as good they can be affected by incorrect application of the device; the reliability varies

according to the joint and the range of movement that is measured. Concerns about the intra-

measure and inter-tester reliability appear to increase when the scientist using the goniometer

is not very experienced. Mistakes can be made when estimating the centre of rotation of the

joint studied and the location of the bony landmarks when locating and maintaining the centre

of the goniometer over the joint studied etc., thus all of these require consideration when using

a goniometer in order to acquire the ROM of a joint [86].

The goniometer seen in Figure 3.2 is the one used in the experiments performed to determine

angles between joints, bones and muscles. Angles θ1, θ2 and φ seen in Figures 4.6-4.9 in

Sections 4.2 and 4.2.1 were calculated with the hand-held goniometer seen in Figure 3.2. In all

sections in Chapters 4 and 5 when a goniometer is mentioned, it is referred to the one seen in

Figure 2.3. For example, in order to calculate angle θ1 which can be referred to as the heel angle,

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was lined with the surface of the foot and the distal arm was pointing at the ankle joint. Angle

θ2, that can be referred to as the ankle angle of the foot segment, was calculated by placing the

pin of the circular disk on the ankle joint where the ankle marker was, the proximal arm of the

goniometer was pointing at the heel marker and the distal arm was pointing at the toe marker.

Lastly, angle φ that can be referred to as the Achilles tendon angle, was calculated by placing

the pin of the circular disk on the heel where the heel marker was, the proximal arm of the

goniometer was lined with the surface of the foot and the distal arm was aligned with the

Achilles tendon and was pointing at the RAT marker (see Section 3.3.3.2 and especially Figure

3.16). These measurements were taken several times in order to find angles θ1, θ2 and φ for all

the different movements studied, i.e. static movements (Figure 4.7) and dynamic movements

(dorsiflexion and plantarflexion, Figures 4.8 and 4.9 respectively). Each angle was measured at

least three times for each movement needed and the differences in the values found were 1or 2

degrees. This showed a consistency in the calculation of the angles. Then the values of the

angles were compared to the ones found from the reconstruction of the marker trajectories of

the Vicon |Nexus system explained in Chapter 5. The values of the angles found with the

goniometer and those found from the Vicon Nexus showed good agreement with a difference

up to 5 degrees maximum. These results verified and validated that the values of the angles

found were correct. Further analysis on why the hand-held goniometer was used is given in

Chapters 5.

An electro-goniometer adds the capability of an instrumented measurement to the clinical

goniometer by using a rotary displacement-measuring device such as a rotary potentiometer

[87]. Electro-mechanical goniometers such as those provided by Biometrics Ltd (Figure 3.3)

allow the time history of the angle between two body segments to be measured. They provide

real-time measurements and instantaneous results of the measured angles without range limits.

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human body against the skeletal segments (i.e. the bones). The gradient of the surface of the

skin changes for different joint angles, during joint movement or interactions with other entities.

These errors are difficult to quantify. Moreover, when analysing body segment locations that

are connected in series, accumulated angle errors appear when multiple body segment locations

are derived. A good example is the error accumulated from the ankle joint, knee joint and hip

joint when the location of the foot relative to the trunk of the body is studied.

Figure 3.3. A Biometrics Ltd goniometer. Two green sections are attached to the upper and lower part of the knee with double sided tape. The flex of the metal braded connection measures the acute angle between the two green sections. Image taken from [88].