Muscle Physiology: Maximum Force and EMG

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Questions and Answers

What type of scale is used for measuring attributes that can be ordered but do not have a true zero point?

Nominal scale

Ordinal scale (correct)

Interval scale (correct)

Ratio scale

When measuring the accuracy of a cloth for aircraft pads, why might measuring in micrometers be necessary?

Only for aesthetic purposes

Precision is critical in specific applications (correct)

To ensure consistency in design

It is a standard practice for textiles

What defines a point in the context of basic concepts of space?

A surface with height and width

A finite area in 3D space

A location that occupies no volume (correct)

An object with mass

Which frame of reference maintains its position and does not move with the object being measured?

Absolute frame of reference Signup and view all the answers

How is temporal analysis defined in the context of time concepts?

The sequencing of events and their durations Signup and view all the answers

What is the relationship between mass and inertia?

Mass directly correlates with the resistance to change in motion Signup and view all the answers

In basic concepts of space, which of the following describes a line?

An infinite series of points that is straight with no width or depth Signup and view all the answers

In a right-handed Cartesian system, which direction is considered positive for rotation around an axis?

Counterclockwise rotation Signup and view all the answers

What is the primary goal of indirect movement analysis techniques?

To obtain x, y, z coordinates of a point in space Signup and view all the answers

Which of the following is NOT a source of systematic error in motion analysis?

Discrete pixel size Signup and view all the answers

What method can help reduce perspective error in 2-D imaging techniques?

Ensure the film plane is parallel with the movement plane Signup and view all the answers

What type of markers may be used in automated motion analysis systems?

Passive or active markers Signup and view all the answers

Which filtering technique is crucial in eliminating high frequency signals?

Low Pass Filtering Signup and view all the answers

Which factor does NOT affect the accuracy of automated motion analysis?

Marker color Signup and view all the answers

What is a common method used to reduce noise in time-varying signals?

Applying filtering techniques Signup and view all the answers

What is typically required after marking joint centers in indirect methods?

Manual identification of the markers Signup and view all the answers

What defines an absolute coordinate system?

Axes are fixed to the ground and remain stationary. Signup and view all the answers

Which component primarily contributes to joint reaction force (JRF)?

Force generated by muscle activity. Signup and view all the answers

What is the primary characteristic of muscle force exertion?

Muscles can only exert a pulling force. Signup and view all the answers

Which method is commonly used to measure muscle forces directly?

Implantation of buckle transducers on the tendon. Signup and view all the answers

What does a larger cross-sectional area (CSA) in a muscle indicate?

A higher number of force-generating units in parallel. Signup and view all the answers

What is the significance of the specific tension value of 30 N/cm²?

It relates maximal isometric force to cross-sectional area. Signup and view all the answers

How is maximum muscle force calculated?

Fm = specific tension x CSA Signup and view all the answers

Which of the following factors accounts for 50% of the variance in strength across individuals?

Cross-sectional area (CSA) of the muscle. Signup and view all the answers

What factor influences changes in specific tension in muscles?

Activity level of the individual Signup and view all the answers

The process of calculating joint reaction force can involve which approach to overcome measurement difficulties?

Inverse dynamics calculations. Signup and view all the answers

What does electromyography (EMG) primarily measure?

Electrical activity of skeletal muscles Signup and view all the answers

What does SOH CAH TOA represent in vector resolution?

A formula for resolving vectors into components. Signup and view all the answers

What does muscle architecture variation affect?

The maximum force exerted by a muscle. Signup and view all the answers

Which component is NOT part of signal processing in electromyography?

Transmission Signup and view all the answers

What does the normalization process in EMG help to measure?

Max activity related to max force Signup and view all the answers

What is the purpose of rectification in EMG signal processing?

Converting negative values to positive Signup and view all the answers

What type of wave characteristics can be represented in the power spectrum analysis of an EMG?

Sine wave characteristics Signup and view all the answers

How does aging affect the specific tension of type 2 muscle fibers?

Declines with age Signup and view all the answers

What does differentiation primarily provide in relation to a function?

The instantaneous rate of change Signup and view all the answers

Which of the following describes what integration calculates?

The total accumulation of a quantity Signup and view all the answers

What is a characteristic of angular acceleration?

It represents the rate of change of angular velocity Signup and view all the answers

When using kinematic derivatives, what is a significant problem that can arise?

They rely solely on historical data without real-time feedback Signup and view all the answers

What unit must be used for angular measurements before calculating angular velocity?

Radians Signup and view all the answers

In the context of differentiation, how is instantaneous velocity defined?

The rate of change of a position at that instant Signup and view all the answers

Which of the following represents the result of integration in kinematics?

Displacement from acceleration data Signup and view all the answers

What does taking the derivative of the position function yield?

Velocity Signup and view all the answers

Study Notes

Maximum Force

Maximum force generated by a muscle is calculated using cross-sectional area (CSA).
Formula: Fm = specific tension x CSA, with specific tension generally being 30 N/cm².
Specific tension indicates the number of myofibrils per unit of CSA and may change with activity.
Type 2 fibers experience a decline in specific tension with age.

Electromyography (EMG)

EMG estimates muscle force by measuring electrical activity in skeletal muscles.
Muscle force is regulated by electrical signals from motor neurons to fibers.
Action potentials (APs) are recorded with electrodes, reflecting the sum of signals in the muscle.
Signals are filtered, amplified, and analyzed by computers.

Signal Processing

Rectification: Converts negative signals to positive for averaged muscle activity representation.
Integration: Analyzes the area under the curve or root mean squared (RMS) for muscle activity evaluation.
Normalization: Utilizes power spectrum analysis to measure fatigue and correlate max activity with max force.
Power Spectrum: Sine wave characteristics are represented on frequency plots; square waves can be broken down into sine components.

Musculoskeletal Forces

Musculoskeletal forces involve magnitude and direction of internal forces influenced by Newton's laws of motion.
Joint reaction force has three components, mainly the normal component—which compresses the joint surface.

Muscle Force Measurement

Muscles can only exert pulling forces and require agonists and antagonists for controlled joint movement.
Directly measuring muscle force involves assessing the force on tendons using specialized transducers.

Cross-Sectional Area (CSA)

A linear relationship exists between maximal isometric force and CSA; it applies equally to men and women.
Normalized force or specific tension is 30 N/cm², where CSA x 30 = force area.
CSA accounts for only 50% variance in strength; several other factors also play a role:
- CSA variation along muscle length.
- Identification of all contributing muscles.
- Antagonist muscle silence to prevent force counteraction.
- Whole muscle activation assumption is incorrect as fibers alternate activation.
- Variability in muscle architecture.

Spatial and Temporal Analysis Concepts

Space consists of boundless 3D volume; commonly measured using tape measures, optoelectronics, etc.
A point in space is a zero-volume location, while lines are infinite series of points.
Temporal analysis studies the sequencing and duration between events, while event refers to a designated instant in time.

Mass and Coordinate Systems

Mass characterizes a body's resistance to motion change (inertia) and its gravitational potential.
Absolute coordinate systems have fixed axes; relative systems move as the body moves.
Vectors can be resolved into x and y components using trigonometric principles (SOH CAH TOA).

Kinematic Data Processing

Indirect movement analysis aims to obtain coordinates in space, with joint centers marked by contrasting markers.
Reduced error methods ensure accurate measurements in 2-D imaging through optimal camera positioning.
Automated motion analysis uses wired or reflective markers with multiple camera feedback for accurate data.
Systematic errors can come from calibration issues or marker misplacement, while random errors include marker shape changes and pixel definition inconsistencies.

Low Pass Filtering

Low pass filtering is essential for removing high-frequency noise from time-varying signals.
Differentiation measures instantaneous changes like velocity, while integration assesses accumulative changes over time.

Angular Kinematics

Angular velocity indicates the rate of change of angular position, and angular acceleration describes the change in angular velocity over time.
Angular measurements must be converted into radians for accurate calculations.

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Description

Explore the principles of maximum force generation in muscles, focusing on the role of Cross-Sectional Area (CSA) and specific tension. This quiz also delves into how specific tension varies with activity and age, as well as the application of electromyography (EMG) in estimating muscle force.