Exam 1 Study Guide - Summary Biomechanics and Kinesiology PDF

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Anthropometrics: It concerns the measurement of the size, shape, and proportion of the human body and its segments Overall Body Size  Standing Height (Stature) o Overall length of the body  Body Weight o Measure of body mass Segment Lengths  Sitting Height o Measured from sitting surface to top of head o A measure of trunk length  Arm Length o Measured from fingertips to acromion process  Forearm Length o Measured from fingertips to lateral epicondyle  Leg Length o Measured from the sole of the foot to the greater trochanter  Knee Height o Measured from the sole of the foot to the knee joint o A measure of shank length Derived Lengths  Upper Arm Length o Arm length minus forearm length  Thigh Length o Leg length minus knee height Limb Circumferences  Arm Girth o Taken around widest part (flexed) or middle of upper arm  Thigh Girth o Taken around middle of thigh  Calf Girth o Taken around widest part of calf

Breadth Measurements  Shoulder Width o Biacromial breadth 

Hip Width o Bicristal breadth

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Elbow Width o Biepicondylar breadth

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Knee Width o Bicondylar breadth

Body Proportions  Hip/Shoulder Ratio o Hip width relative to shoulder width o  Sitting Height/Standing Height Ratio o Trunk length relative to leg length o Studied to see if you have higher/smaller ratio do you have a better performance

Body Composition: the relative make up of the body in terms of its basic components Five Levels of Body Composition  Atomic (Elemental) o C, H, O, N = 95% of body mass o Na, K, P, Cl, Ca, Mg, S = 4.5% body mass 

Molecular (looking at more complex molecules) o Water, fat, essential lipids, protein, bone mineral, soft tissue minerals, CHO, residual

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Cellular (identifying the cells in body composition) o Adipocytes, other cells, intracellular fluid, extracellular fluid and solids

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Tissue/Organ o Adipose (subcutaneous and visceral), skeletal muscle, bone, visceral organs, brain, liver

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Whole Body o Head and neck, trunk, upper and lower limbs o Assessed by (whole body methods)  Anthropometrics  Body Mass Index (BMI)  Skinfolds  Body volume and density

Models of Body Composition- Consist of two or more components Quantifying components: C = f (Q) 

Q may be a measurable property (ex: body volume, electrical resistance, skinfolds) or a known component (ex: FFM derived from FM)

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f may be empirical (regression equation) or based on a model (ratios or proportions)

Two-Component Model (Behnke) Consists of fat mass and fat-free mass   

BM = FM + FFM BV = FM/0.9007 g/cm3 + FFM/1.100 g/cm3 FM = BV(4.971) – BM(4.519)

Assumes that proportions of water, protein, and mineral in FFM are constant

Three-Component Model (Siri) Consists of fat mass, fat-free dry mass, & total body water  BM = FM + FFDM + TBW  FM = BV (2.057) – TBW(0.786) – BM(1.286)

Assumes a constant ratio of protein to mineral in FFDM

Common Methods Used in Estimating Body Composition BMI, Densitometry (Hydrostatic weighing “underwater weighing” & Air displacement plethysmography “bod pod”), Bioelectrical impedance analysis, Dual-energy x-ray absorptiometry, Skinfold (most common) Body Mass Index: BMI = mass (kg) / height (m)2 Problems with BMI  Overprediction of fat mass in muscular individuals Densitometry: Techniques involve measuring body volume and then, using body mass, calculating body density (Db): o Db = BM / [BV – RV – VGI] o Hydrostatic weighing BV = (MA–MW)/DW o RV is measured indirectly or estimated o VGI is typically estimated to be 100 ml  Hydrostatic Weighing  Air Displacement Plethysmography Calculating Body Fat  Using the Two-Component Model o One of the most used formulas o %BF = 4.950/Db – 4.500 (Siri) Bioelectrical Impedance Analysis: Based on differences in electrolyte and water content between lean tissue and fat  FFM can be estimated from impedance to a low electrical current DEXA: Dual Energy X-Ray Absorptiometry  Based on three component model  Uses two X-ray energies to measure fat, bone-free lean tissue, and bone mineral Skinfold Thicknesses Triceps, Subscapular, Chest, Abdominal, Suprailiac, Thigh, Medial Calf Variation in Body Composition Among Individuals  Males vs. Females o Reference Male: 12-15% Body fat o Reference Female: 25-28% Body fat 

Differences are due to: o Ref. female has a greater % of body mass as storage fat (15% vs. 12%) o Ref. females has a greater amount of essential fat (12% vs. 3%)

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Among Athletes o Athletes have lower body fat than the avg. male or female (esp. for females) o Lowest body fat values are found in distance running, rowing, xc skiing, & gymnastics

o Highest body fat values are found in football & the weight events in track/field Physique: refers to the overall form and structure of the body May be described in descriptive terms: lanky vs. stocky, slender, short leg vs. broad shoulders May be based on anthropometric measurements Sheldonian Somatotypes: Three components of physique

Ectomorphy: Endomorphy: predominance of

Adipose tissue and Roundness of body contours

predominance of

Surface area over body mass, Limited muscular development, and Linearity Mesomorphy: predominance of

Muscle, Bone, and CT Physique of  Most mesomorphs  Most sports tend to favor a particular physique  A great deal of variation exists within any given sport

Athletes athletes are

Linear Motion (a.k.a. linear movement or translation) In linear motion a body is moved (translated) from one position to another along a particular path Types of Linear Motion  Rectilinear motion o The body moves in a straight line 

Curvilinear motion o The body moves along a curved path

Descriptions of Linear Motion  Displacement ( d or s ) o The distance that the body is from some reference point (vectors), and includes both magnitude and direction 

Distance: the magnitude of displacement Displacement vs. Distance

Velocity ( v ) is the amount of displacement per unit time, or the rate of change in displacement; it is a vector quantity  Speed is simply the magnitude of velocity, or the rate of change in distance Measuring Velocity  Average Velocity o Average velocity over a given time period  Instantaneous Velocity o Velocity at any given instant in time  Acceleration o The amount of velocity per unit time, or the rate of change in velocity o It is a vector quantity  Constant velocity o Implies that for every unit of time there is the same change in displacement  Constant acceleration o Implies that for every unit of time there is the same change in velocity o The acceleration due to gravity is a constant acceleration of 9.81 m/s2 The Relationship of Force, Mass, and Acceleration  Newton’s Second Law of Motion states: o Acceleration of a body is:  Directly proportional to the force causing it  Inversely proportional to the mass of the body 

A related concept is momentum o Which is the product of mass and velocity (mv)

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Newton’s Second Law can be rewritten as: o F = D(mv)/t or F = m(Dv/t)

a = F/m (or)

F = ma

Momentum= Mass x Velocity

Force = Displacement (Mass x Velocity) / Time (or)

Force = Mass (Displacement x Velocity) / Time 

This last equation is related to the concept of impulse*: o Ft = m(Dv) Impulse: Force x Time = Mass x (∆ Velocity)

Impulse in Physical Activity  The larger the impulse (Ft) the larger the change in velocity (Dv)  The larger the change in velocity (Dv) the larger the impulse required (Ft) Angular Motion (a.k.a. angular movement or rotation) In angular motion a body rotates around a fixed point: the axis

Descriptions of Angular Motion  Angular displacement ( Ø ) o Change in angular position o Unit: Degrees 

Angular velocity ( w ) o Rate of change in angular displacement o Unit: Degrees per second

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Angular acceleration ( a ) o Rate of change in angular velocity o Unit: Degrees^2 (squared)

The Relationship Between Linear and Angular Motion  An angle point farther from the axis = a greater linear displacement (than points closer to the axis)  An angular velocity points farther from the axis = a greater linear velocity (than points closer to the axis)  These relationships can be expressed as follows:  d=Ør Displacement = Angular displacement x Radius  v=wr Velocity = Angular velocity x Radius (Constant w) Increase radius = increase velocity @ end of radius, but longer lever requires more T

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The Moment of Inertia ( I ) In linear motion the inertia of a body is related only to its mass

In angular motion inertia is related to mass as well as the distance the mass is from the axis of rotation o This relationship is expressed as the body’s moment of inertia : I = mr2 o Example: twisting vs. flipping a water bottle. Flipping it will have a larger Inertia = Mass of whatever is rotating x Radius^2 inertia o The Acceleration of Rotating Bodies  Newton’s Second Law also applies to rotating bodies, but in angular terms: o Angular momentum is expressed as Iw (as opposed to mv for linear momentum). o F = ma becomes T = Ia. 

The Conservation of Angular Momentum States that the angular momentum of a body will not change unless acted upon by an external torque.

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This is important in sports: during the course of rotating the body experiences minimal external forces. Example of a figure skater: o In performing a spin the skater can increase his or her moment of inertia by extending the arms, which in turn will cause the angular velocity to decrease. o Conversely, if the arms are brought closer to the body the moment of inertia will decrease and the angular velocity will in turn increase.

Centripetal and Centrifugal Force The force that tends to pull a rotating body towards its axis of rotation  Centrifugal force: force that tends to pull a rotating body away from its axis of rotation.  Centripetal force and centrifugal force are always equal but opposite. 

The centripetal (or centrifugal) force is equal to the mass of the body times the square of its velocity, divided by its distance from the axis of rotation:

Fc = mv2/r

Force Pushes or pulls through direct mechanical contact (or force of gravity) to alter the motion of an object. All forces have 4 properties:  Magnitude (measured in Newton’s: N)  Direction  Point of application  Line of action Torque (Know the relationships among force, moment arm, and torque) Rotation of an object caused a force. The turning effect of a force is called the torque or moment.  The torque equals the magnitude of the force times its moment arm:  Moment arm: T=Fxd o The perpendicular distance between the line of action of the force and the axis of rotation:

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The units for Torque are Newton-meters (N-m) Only get a torque if the line of action of the force does not pass through the axis of rotation

Levers A lever is a simple machine that operates according to the principle of torques

Three functions depending on their arrangement:  Magnify a force  Increase the speed and range of motion of a point on the lever  Balance two or more opposing forces Four basic parts to every lever:  Rigid bar  Axis of rotation (A; aka, fulcrum)  Effort force(s) (E)  Resistance force(s) (R) Classes of Levers  First-Class Levers o The axis is located between the effort force and the resistance force: o First-class levers can serve any of the three functions of levers depending on where the forces are relative to the axis  Examples: teeter-totter, scissors 

Second-Class Levers o The resistance force lies between the axis and the effort force: o Second-class levers always serve to magnify the effort force  Examples: wheelbarrow

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Third-class Levers o The effort force lies between the axis and the resistance force: o Third-class levers always serve to increase the speed and range of motion of a point at the end of the lever  Examples: shoveling, canoeing

Levers in the Human Body  The human musculoskeletal system operates as a series of levers: o Bones act as rigid bars o Joints are the axes o Muscles provide the effort force o Weight of the body along with additional external forces provide the resistance force Examples 

Center of Gravity (C of G or CG) The single point at which all of the body’s mass would be located

Stated differently, The CG is the point of application of the force of gravity Location of the CG  Remains fixed as long as the object does not change shape or mass distribution o But, not the human body: changing our body position changes our center of gravity.

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Location of the CG in the Human Body When standing erect in anatomical position, the location of the CG varies depending on: o Body composition o Body physique (somatotype) o Age o Sex On average, the CG is located between 55 and 60% of an individual’s standing height.

 Stability and Equilibrium  Equilibrium: any object that is not changing its speed or direction o Static equilibrium: when a body is at rest

o Dynamic equilibrium: moving with a constant velocity Equilibrium can also be described as being stable or unstable.  Stable vs. Unstable Equilibrium o In stable equilibrium a body will tend to return to its original state if perturbed o In unstable equilibrium a body will tend to lose equilibrium if perturbed 

Stability and Balance o Stability: a body’s resistance to losing equilibrium.

o Balance: the process by which the body’s state of equilibrium is controlled for a given purpose. Primary Factors Influencing Stability  Size and shape of the base of support o The base of support is the surface area of the body in contact with the supporting surface plus the area in between o General Rule: The larger the base of support in the direction of the perturbing force, the greater the stability.  Height of CG o General Rule: The lower the center of gravity, the greater the stability. Secondary Factors Influencing Stability  Mass of the body

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Relation of the line of gravity to the base of support o Line of gravity: the line of action of the force of gravity acting at the center of gravity of the body. o A body will only be in equilibrium if the line of gravity falls within the base of support. o General Rule: The closer the line of gravity is to the center of the base of support, the greater the stability.

o Mass is a measure of a body’s inertia: its resistance to a change in velocity. o General Rule: The greater the mass of the body, the greater its stability. 

Friction at the base of support o General Rule: The greater the friction between the supporting surface and the parts of the body in contact with it, the greater the stability.

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Segmental alignment o General Rule: Maximal stability is achieved when the center of gravity of each weightbearing segment lies in a vertical line centered over the base of support.

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Visual and psychological factors o General Rule: Visual distractions or an impaired emotional or psychological state can have a negative impact on stability.

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Physiological factors o General Rule: A physiological condition that affects proprioception can have a negative impact on stability.

Stability vs. Mobility Just as for the joints, there is an inverse relationship between stability and mobility:  The more stable the body = the more difficult to change speed or direction (starting & stopping)  But, the more mobile the body is = the less stability it has. o Example: when starting we generally put the body into a state of unstable equilibrium by moving the line of gravity close to the forward edge of the base of support. (This is seen in the starting positions in swimming and track-and-field sprinting.)

Part III: Applied Questions 1) Discuss the potential problems associated with the use of BMI with athletes. 2) Define the mechanical concept of impulse and explain how it applies to the following sports situations: (a) "sticking" a landing from a dismount in gymnastics vs. "giving" as you land from a jump, (b) catching a 100-mph fast ball, and (c) the wind-up or preparatory phase of a throw-like activity. 3) Define the mechanical concept of the conservation of angular momentum and explain how it applies to a sport like figure skating or diving. 4) Discuss the mechanical factors that influence the choice of bat length for a particular batter. 5) You are asked to assume a standing position in which you will have maximal stability. Describe the position you assume and the reasons for adopting this position....