Anthropometry

ANTHROPOMETRY

CONTENT

• Scope of anthropometry in movement biomechanics

• Density, mass, and inertial properties

• Direct experimental measures

• Muscle anthropometry*

SCOPE

In the past:

The major emphasis of these studies has been evolutionary and historical

Today:

Ergonomy (basic linear, area, and volume measures)

Human movement analysis (masses, moments of inertia, and their locations)

SCOPE

Segment Dimensions:

Drillis and Contini (1966)

Body segment lengths expressed as a fraction of body height H.

DENSITY, MASS, AND INERTIAL PROPERTIES

Density, mass, and inertial properties

Kinematic and kinetic analyses require data regarding mass distributions, mass centers, moments of inertia...

The human body consists of many types of tissue,each with a different density

The average density is a function of body build, called somatotype


Total body density

(c-Ponderal index; h-body height; m-body

mass); Density: d = 0.69 + 0.9c kg/l

EXAMPLE:


Segment densities

Body segments: unique combination of bone, muscle, fat, and other tissue

Density within a given segment is not uniform


Segment densities


Segment mass and center of mass

Center of mass ≠ Center of gravity

Center of gravity (only in one direcition)

With the total body mass increase

Increase the mass of each individual segment

The mass of each segment could be expresed as a percentage of the total body mass


Location of the center of mass



The center of mass located at distance x from the left edge of the segment:

The compex could be represented by the single mass M located at the distance x from the one end of the segment



EXAMPLE:From the anthropometric data (See next slide) calculate the coordinates of the center of mass of the foot and the thigh given the following coordinates: ankle (84.9, 11.0), metatarsal (101.1, 1.3), greater trochanter (72.1, 92.8), and lateral femoral condyle (86.4, 54.9)



EXAMPLE:


Center of mass of a multisegment system


Center of mass of a multisegment system

WHERE:

o analysis of sporting events, especially jumping events

o in studies of body posture and balance


Mass moment of inertia and radius of gyration

o In analysis of translationalmovement through space we need to know the inertial resistance to such movements (F = m * a)

o In the rotational sense: M = I * α

o M –moment of force

o α – angular acceleration;

o I- moment of inertia



o The value of I depends on the point about which the rotation is taking place and is aminimum when the rotation takes place about its center of mass



The moment of inertia about the left end is:

Typeequationhere.



Radius of gyration of a limb segment relative to the location of the centerof mass of the original system

Moment of inertia of an object rotating about the axis crossing perpendicular trought the center of mass



Most objects does not rotate about their center of mass (Body segments rotate about their joints)

Moment of inertia of an object rotating about the axis paralel to the axis crossing perpendicular trought the center of mass



Example:

A prosthetic leg has a mass of 3 kg and a center of mass of 20 cm from the knee joint. The radius of gyration is 14.1 cm. Calculate I about the knee joint



Example:

If the distance between the knee and hip joints is 42 cm, calculate Ih for this prothesis about the hip joint as the amputee swings through with a locked knee.


Calculation of segment masses and centers ofmass

Example:

Calculate the mass of the foot, shank, thigh, and HAT and its location from the proximal or distal end, assuming that the body mass of the subject is 80 kg. Using the mass fractions for each segment


Calculation of total body center of mass



It is not always posible to measure the center of mass of every segment:

EXAMPLE:

If we have the data from the right side of HAT and right limb (thight, leg, foot) we can simulate the data of the left side



EXAMPLE:

Assuming the symmetry of gate:The data trajectory of the left limb is the same as that of the right limb, but out of phase by half a stride

We can use data for the right limb one‐half stride later in time and shift them back in space one‐half a stride length, we can simulate data for the left limb and left side of HAT.



EXAMPLE:

Calculate the total‐body center of mass at a given frame 15



EXAMPLE:

1 Stride - 68 frames 1 Step – 68/2 frames = 34 framesTo simulate data of left segment at the given frame: Take datadata from frame 15+34, keep y and sheeft x for step length



EXAMPLE:

If stride length = 1.414 m Step length = 0,707 cm



EXAMPLE:



A 21-marker, 14-segment model to estimate the 3D center of mass of the total body in balance control experiments. Four trunk segments were necessary to track the internal mass shifts of the thoracic/lumbar volumes

(Winter et al., 1998)


Calculation of moment of inertia

EXAMPLE:

Calculate the moment of inertia of the leg about its center of mass, its distal end, and its proximal end

Leg mass:


Calculation of moment of inertia

EXAMPLE:

Calculate the moment of inertia of the HAT about its proximal end and about its center of mass

HAT mass: 0.678*80 kg = 54.84 kg

HAT length = 0.295 m

Radius of gyration (about the proximal/segment lenght = 1.456

DIRECT EXPERIMENTAL MEASURES

For more exact kinematic and kinetic calculations, it is preferable to have directly measured anthropometric values

The equipment and techniques that have been developed have limited capability and sometimes are not much of an improvement over the values obtained from tables


Location of the anatomical center of mass of the body


Calculation of the mass of a distal segment

The decrease in the clockwise moment due to the leg movement is equal to the increase in the scale reaction forcemoment about the pivot point


Calculation of the mass of a distal segment

To get the mass of the total limb, thisexperiment can be repeated with the subject lying on his back and the limb flexed at an angle of 90◦. From the mass of the total limb, we can now subtract that of the leg and foot to get the thigh mass


Moment of inertia of a distal segment

Quick realese experiment –used to calculate I directly:


Joint axes of rotation

Ankle joint marker: The lateral malleolus

the articulation of the tibial/talus surfaces is such that the distal end of the tibia (and the fibula) move in a small arc over the talus

The true axis of rotation is actually a few centimeters distal of the lateral malleolus



Hip joint marker: The greater trohanter

That internal and external rotations of the thigh relative to the pelvis may cause considerable errors, as will abduction/adduction at that joint

Therefore The true axis of rotation is actually is actualy more medial than the marker position



It is important that the true axes of rotation be

identified relative to anatomical markers that we

have placed on the skin



1. They must be translated and rotated in space so that one segment is fixed in space and the second rotates as shown

2. At any instant of time the true axis of rotation is at (xc, yc) within the fixed segment

3. We are interested on the position of (xc, yc) relative to (x3, y3) and (x4, y4)

4. Markers (x1, y1) and (x2, y2) are located as shown;


5. (x1, y1) has an instantaneous tangential velocity V and is located at a radius R fromthe axis of rotation.

6. V could be calculated from marker data (x1, y1)7. From the line joining (x1, y1) to ((x2, y2), we

calculate the angular velocity of the rotating segment ω



From Vx, Vy and z , Rx, Ry can be calculatedFrom (x1, y1) and Rx, Ry (xc, yc) could be calculated

MUSCLE ANTHROPOMETRY

Cross‐sectional area of muscles

The functional or physiologic cross‐sectional area (PCA) of a muscle:

the number of sarcomeres in parallel with the angle of pull of the muscles



The functional or physiologic cross‐sectional area (PCA) of a paralel fibered muscle:



The functional or physiologic cross‐sectional area (PCA) of pennatemucles:


Percent PCA of Muscles Crossing Ankle, Knee, and Hip Joints


Change in Muscle Length during Movement

Grieve and colleagues (1978), in a study on eight cadavers, reported percentage length changes of the gastrocnemius muscle as a function of the knee and ankle angle:

Resting position: knee flexion 90 deg

Plantarflexion 40 deg – 8.5 % shortheningDorsiflexion 20 deg – lengthening linear to 4%

Knee flexion 150 deg 3% shortheningFull knee extension – lengthening linear 6.5%


Force per unit cross‐sectional area (stress)

Stress values measured during isometric conditions: from 20 to 100 N/cm2 (higher values in pennate muscles)

Haxton, 1944: gastrocs and soleus stresses up to 38 N/cm2

Maughan et al., 1983: dynamic stresses calculated in the quadriceps (running and jumping) ‐70 N/cm2

and about 100 N/cm2 in isometric maximum voluntary contractions (MVCs)


Mechanical advantage of muscle

The origin and insertion of each muscle defines the angle of pull of the tendon on the bone and, therefore, the mechanical leverage it has at the joint center.

Smidt, 1973: increase in the moment length as the knee was flexed, reaching a peak at 45 deg, then decreasing again as flexion increased to 90 deg.


Multijoint muscles

The hamstrings are extensors of the hip and flexorsof the knee;The rectus femoris is a combined hip flexor and knee extensor;The gastrocnemius are knee flexors and ankle plantar flexors;

The fiber length of many of these muscles may be insufficient to allow a complete range of movement of both joints involved


Multijoint muscles

The fiber length of many of these muscles may be insufficient to allow a complete range of movement of both joints involved

Rectus femoris shortens during early swing in running as a result of hip flexion and lengthens at the knee as the leg swings backward in preparation for swing

The tension in the rectus femoris simultaneously creates a flexor hip moment (positive work) and an extensor knee moment to decelerate the swinging leg (negative work) and start accelerating it forward


Multijoint muscles

the net change in muscle length is reduced compared with two equivalent single‐joint muscles, and excessive positive and negative work within the muscle can be reduced

In running during the critical push‐off phase, when the plantar flexors are generating energy at a high rate, the knee is continuing to extend:The gastrocnemii may be essentially isometric (they may appear to be shortening at the distal end and lengthening at the proximal end)


Multijoint muscles

the net change in muscle length is reduced compared with two equivalent single‐joint muscles, and excessive positive and negative work within the muscle can be reduced

Toward the end of swing in running, the knee is rapidly extending while the hip has reached full flexion and is beginning to reverse (i.e., it has an extensor velocity). Thus, the hamstrings appear to be rapidly lengthening at the distal end and shortening at the proximal end, with the net result that they may be lengthening at a slower rate than a single joint would


Multijoint muscles


Multijoint musclesThe triceps surae moment-arm:• at the ankle 5 cm

• at the knee 3.5 cmTheir contribution to the ankle extensor moment in the active phase of stance about 50% greater than their contribution to the knee flexor moment.

The net effect of these two contributions is to cause the leg to rotate posteriorly and prevent the knee from collapsing.


Multijoint musclesThe hamstrings moment-arm:• of the short head of the biceps femoris 3-5 cm

• at the hip 6-7 cmWhen active during stance, their contribution to hip extension is about twice their contribution to knee flexion

The net effect of these two actions is to cause the thigh to rotate posteriorly and prevent the knee from collapsing.


Multijoint musclesThe rectus femoris moment-arm (only head of the quadriceps is biarticular:• of the knee 4 cm

• at the hip 5 cmSince the quadriceps activate as a group (whereas the uniarticulate quadriceps comprise 84% of the their PCA; the dominant action is knee extension

Thus, the net effect of the major biarticulate muscles of the lower limb is extension at all three joints, and therefore they contribute, along with all the uniarticulate extensors, to defending against a gravity-induced collapse

LITERATURE

• D.A.Winter, Biomechanics and Motor Control ofHuman Movement, Fourth edition. John Wiley & Sons, Inc., Toronto, 2009

• Robertson, Gordon, et al. Research Methods in Biomechanics, 2e. Human Kinetics, 2013

EXTENDED READING:

http://msis.jsc.nasa.gov/sections/section03.htm

Anthropometry

Documents

Transcript of Anthropometry