Test 1 Mechanical Analysis of Human Movement

Biomechanics

The study of the structure and function of biological systems by means of the methods of mechanics

Biomechanics

Application of mechanical principles to the study of biological systems

Why study biomechanics?

Improve a person's performance

Reduce a person's risk of injury

Human Performance

Is not limited to high-achieving athletic competitions

Performance

Occurs during any human activity

Mechanopathology

The mechanics that result in injury

Example of Mechanopathology

An incorrect landing that leads to an ankle injury

Pathomechanics

The mechanics that are a result of an injury

Example of Pathomechanics

Changing your gait due to an ankle injury

In order to understand injury mechanics

You must understand the interactions of both internal and external factors

The rules of human movement can be grouped into 3 basic sets of principles

Mechanical

Multisegment

Biological

Mechanics

"Classical" study of forces and their effects

Based on the work of Sir Isaac Newton

Mechanics

Types of Dynamic Movement

Kinematics

Kinetics

Types of Static Movement

Loads

Response to loads

Dynamics

Interested in changing systems

Broken into two major areas:

Kinetics and Kinematics

Kinematics

The study of motion without consideration of the cause.

Describing how we are moving

Kinetics

The study of the causes of motion.

Forces that cause motion

Statics

Interested in unchanging systems

No acceleration of systems

Often used in material science, which includes:

Material properties

Response to loads

in a biomechanics setting, these analyses are often referred to as "tissue mechanics"

Multisegment Principles

the body is not a single element.

Composed of connected segments

Requires coordination of activities of segments

Examples of Multisegment Principles

Throwing

Reaching and grasping

Walking

Running

Jumping

Biological Principles

Humans are animate and not machines

This principle is the "bio" of biomechanics

Due to the amount of varying anatomical and physiological properties of humans, biological principles will always influence the mechanics analyzed

Human movement is non-linear

Mathematics

The common language of the world

Allows for a large amount of information to be concisely represented

Symbols

Compose the language of math

Symbol

Has four parts

Variable

Leading superscript

Following subscript

Following superscript

Variable

Main part

Leading Superscript

Direction

Following Subscript

Body

Used when more than one person is being observed to differentiate between people

Following Superscript

Change in time

Hierarchical Model

An aid to assist you with keeping track of multiple variables

Often called a "deterministic model"

An outline approach is very similar and just as effective

Top Level

Performance measure/result

Second Level

Factors that determine the top level variable

Third Level

Factors that determine second level variables

Rules of Hierarchical Modeling

Factors included in the model SHOULD be mechanical quantities. (Can also include anatomical/neural factors).

Each of the factors in the model should be completely determined by those factors linked in the level below.

Annotate (or mark) those boxes that you can not control.

No matter what approach, there are four basic levels

Whole Body (COM)

Total Limb

Joint

Tissue

Top Down Approach

Most often recommended type of analysis

Many examples of this type

Bottom Up Approach

Opposite order

Useful when studying Pathomechanics (what happens after the injury), the mechanics that are the result of an injury or illness

Also useful when analyzing an intervention

You cannot understand the mechanics of the movement without understanding the

purpose of the movement

Proficiency

How well a person performs a movement and achieves the goal of the task

Classes of Movement

Discrete

Serial

Cyclic

Discrete

Distinct beginning and end, without movement repeating

Ex: Vertical jump

Serial

Distinct beginning and end, but links at least two discrete movements

Ex: Tripe jump

Cyclic

Involves repeating a pattern over and over again

Ex: Walking, running, cycling

Can be separated into three distinct phases

Movement

Preparation

Countermovement: the opposite direction before you do your movement

Propulsion

Action: move in the direction of the movement

Braking

Recovery: unloading, landing phase

Three things about preparation

Put the body in an advantageous position

Maximize the displacement

Initiate the stretch-shortening cycle

Key characteristic of Propulsion

MTCs generate energy and deliver it to the segments

Key characteristic of Braking

Energy that was not transferred to an external object is absorbed

Critical Elements

Aspects of a movement that are necessary for optimal performance

The magnitude are generally not discrete values, but fall in a range of acceptable values

The timing is as important (or more important) as the critical elements themselves

Three types of Constraints

Organismic

Environmental

Task

Organismic

Intrinsic dynamics

The kinematic (range of motion) and kinetic (strength, power, endurance) capacities of each degree of freedom involved in a task

Environmental

Due to the physical surroundings

Walking on ice or uneven terrain

Task

Due to the nature of the performance

Landing

A softer landing is safer to perform because it decreases the magnitude of ground reaction force, yet it is more demanding because it increases the torque demand at each joint.

Identifying Faults

Determination of what the person is doing wrong

- Must be evaluated against some criteria

- Exemplary performance or guiding principles

Generalized Principles of Identifying Faults

Use of stretch-shortening cycle

Sequencing of movements

Maximizing the distance/time over which a force is applied

Minimizing external torque

Walking

No universally accepted criterion

Simplest way to differentiate phases:

Stance

Swing

Stance

Periods where the foot is in contact with the ground

Swing

Foot is in the air

Periods when the foot is not in contact with the ground

Functional Tasks of Walking

Weight acceptance

Single-limb support

Swing-limb advancement

Running

Can be analyzed in two ways:

- Macrocosm

- Microcosm

Macrocosm

Entire length of the race

- Top Speed

- Acceleration

- How long top speed was held

Difference in top speed and final speed

Microcosm

One stride

- Compare and contrast walking

- Walking:

- No period of non-support

- Period of double support

Movements are considered to be dysfunctional for two reasons:

- Take away from performance

- Expose the body to potential injurious stresses

Valgus Collapse

During landing, an excessive motion at:

- Subtalar joint

- Hip joint

Causes:

- Lack of strength/power/endurance

- Restricted inversion of the subtalar

- Restricted external rotation of the hip

Impairment in the sagittal plane

Places increased demand at the knee

- ACL Tears

- Iliotibial band syndrome

- Patellofemoral pain syndrome

Lifting Mechanics

Two guiding principles

- Minimize the torque on the lumbar spine

- Hold the object as close to the trunk as possible

- Maximize the ability of the lumbar musculature to create a posterior shear force to counteract the anterior shear created by the load

- Avoid full flexion

Kinematics

The study of motion without considering what is causing the motion

The Geometry of motion

Includes both spatial and temporal characteristics of motion

Body

The object of analysis

System

The object of analysis that is made up of two or more bodies

Point

A way of representing a body that has no dimensions

Frame of Reference

The perspective from which movement is described

-Must include:

Origin

Direction

The finish line of the 100 m sprint is 100 m away from the starting line

Origin

The place where the frame of reference begins

Direction

A pointing toward something, determined by its orientation and sense

Direction

Specified by:

- Axes

- Orientation

-Sense

Axes

A straight line running through the origin specifying a direction from the origin

Orientation

A particular reference line (horizontal, vertical, north, south, east, west)

Sense

Specified by: two points (what direction you are moving in)

Establishing a Frame of Reference

1. Locate an origin that is fixed and memorable

2. Define an axis

3. Specify a positive and negative direction

Position

An object's location (p) in the frame of reference

- The object's physical location in space

Includes: magnitude and direction

Scalar quantity

Magnitude only

Examples: distance, speed, mass

Should never be negative numbers

Vector quantities

Magnitude and direction

Examples: displacement, velocity, force

Displacement

A change in position

Denoted as ∆p

Measured as a length or the difference in position between two instances in time

Typical unit: meters

Quantity: Vector

∆p = p' - p

Abscissa axis

X-axis (usually time)

Ordinate axis

y-axis (usually the remaining variable)

Speed

How fast a body is moving with no regard to direction

Measured as the rate of change of distance

Quantity: Scalar

Typical unit: m/s or mi/hr

distance/change in time = d/∆t

Velocity (v)

How fast a body is moving in a particular direction

Measured as the time rate of change in position

∆position/∆time = p'-p/t'-t

Quantity: Vector

Typical unit: m/s or ft/sec

Slope

The incline of a line on graph from the horizontal axis

(position/time) gives you velocity

Average

A number representing the value of a quantity that did not change (was constant) throughout the period of interest

- Assumes the velocity was constant throughout the entire race

Instantaneous

The value of a quantity at a particular moment in time

- Allows for a clearer picture of the outcome and the activity during the event

Chords

Straight line drawn from the start to the finish of the period of interest

-Graphically, it is the slope of the average velocity

Tangent

Straight line just touching the curve at a single point

- Graphically the slope of the instantaneous velocity

- If velocity is constant, the tangent and chord are identical

Acceleration (a)

How rapidly something is changing velocity

Measure of how something is speeding up or slowing down

∆v/∆t = v'/t = m/s^2

Quantity: Vector

Acceleration

Typically thought of as an increase in the speed or velocity of a person/object

However, persons/objects also accelerate when they slow down

Anytime velocity changes, there is an ________________

(+) acceleration

(+) slope = (?) acceleration

(-) acceleration

(-) slope = (?) acceleration

Relative Velocity

How fast one body is moving in relation to another body

If two bodies are moving at the same rate, their relative velocity = 0 m/s

Absolute Velocity

How fast one body is moving in relation to the (fixed) earth

Displacement (∆p)

Vector Quantity

Allows for a "net" value

- The total value after summing all the individual values

∆p = p' - p