Chapter 2 Flashcards
List the characteristics of fleshy and fibrous attachments.
The two main attachment categories of muscle to bone are fleshy attachments, fibrous
attachments.
Fleshy Attachments
• Muscles fibers affixed directly to bone
• Usually attach over a wide area to distribute force
• Often found at the proximal end of the muscle
Fibrous Attachments
• Contiguous with muscle sheaths and connective tissues around the bone
• Additional fibers extend into the bone itself
• Very strong
• Example: tendons
List the roles agonist, antagonist, and synergist muscles play during a given
motion
Agonist
• Muscle most directly involved in bring about the movement
• Also called the “prime mover”
• Example: triceps extending the elbow during throwing
Antagonist
• Muscles that can slow down or stop the movement
• Assists in joint stabilization and braking
• Protects joint structure from damage during fast motions
• Example: biceps slowing down elbow extension at the end of a throwing motion
Synergist
• Muscles that assist indirectly in a movement - i.e. scapular stabilizers during upper
arm movement
• Required to control body motion when agonist crosses two joints - i.e. gluteus
maximus synergizes with the rectus femoris during combined knee and hip
extension in a low squat
Define levers and explain how torque and mechanical advantage is calculated
A lever is defined as a rigid or semirigid body that can transmit force tangential to its arc of
rotation around a fulcrum.
The force applied to one contact point will be equal in magnitude but opposite in direction than
the resulting force on the other point of contact.
The perpendicular distance from the force’s line of action to the fulcrum on the lever is called
the moment arm.
Torque is calculated by multiplying the magnitude of a force by the length of its moment arm.
Torque physically represents the degree to which the force will tend to rotate an object around
the fulcrum.
Torque = Magnitude of Force (F) x Length of Moment Arm (M)
The torque generated by the applied force (A) must always equal the torque generated by the
resisting force (R).
FA * MA = FR * MR
Therefore, a smaller force acting through a longer moment arm can lift a heavier object with a
shorter moment arm.
This is known as mechanical advantage and is numerically defined as the ratio of the applied
force moment arm to the resistive force moment arm.
Mechanical Advantage = MA / MR
A mechanical advantage greater than 1.0 means that the applied force can be less than the
resistive force.
A mechanical advantage less than 1.0 means that the applied force must be greater than the
resistive force to generate equal torque. This is known as mechanical disadvantage.
Describe the difference between a first, second, and third-class lever. Specify which levers act at mechanical advantage or disadvantage. Give an example of each in the human body. Discuss the implications of mechanical advantage and disadvantage in human movement
First-Class Lever
• Muscle force and resistive force on opposite sides of the fulcrum
• Can act at mechanical advantage or disadvantage
• Example: forearm acts as a first-class lever during tricep extensions
Second-Class Lever
• Resistive force acts the same side of the fulcrum as the muscle force
• Muscle force acting through a longer moment arm than the restive force
• By definition operate at a mechanical advantage
• Example: the foot when calf muscles raise the body onto the balls of the feet
Third-Class Lever
• Resistive force and muscle force act on the same side of the fulcrum
• Muscle force acts through a shorter moment arm than the resistance
• By definition operate at a mechanical disadvantage
• Example: the forearm during the bicep curl exercise.
Most muscles operate at mechanical disadvantage.
This means that during many sporting activities, the forces in the muscles and tendons are far
greater than those exerted by the hands and feet on external objects.
How do variations in tendon insertion affect the strength and speed of athletes?
Which sport types are favored by a given tendon insertion distance?
Due to the principle of mechanical advantage, the location where a muscle attaches to the
bone will affect the relative strength and speed of athletes with identical muscle size and neural
control.
Attachments Further from The Joint:
• Greater mechanical advantage compared to attachments closer to the joint
• Ability to lift heavier weights relative to muscle strength
• Longer moment arm means that the resistance will move slower for a given muscle
contraction velocity
• Provides advantage in strength sports such as powerlifting
Attachments Closer to The Joint:
• Able to accelerate the resistance more quickly
• Less mechanical advantage than further attachments
• Less ability to move heavier weights
Provides advantage in speed-dependent sports
Define the anatomical position as a reference for the major planes of motion.
Discuss the general movements for each plane. Give an example for each.
Human movement is categorized based on the direction of the movement in the planes that
define three-dimensional space.
The reference point for human movement is the anatomical position.
Anatomical Position
• Body Erect
• Arms Down at the Sides
• Palms face forward
Sagittal Plane
• Slices body into right and left halves
• Flexion and extension are the primary movements
• Movement example: Hip and knee extension during squat
Frontal Plane
• Slices body into front and back
• Abduction and adduction are the primary movements
• Movement example: Shoulder abduction during lateral raise
Transverse Plane
• Slices body into upper and lower sections
• Internal and external rotation are the primary movements
• Movement example: trunk rotation when swinging a bat
Define the relationships between human strength and power and the factors
relevant to each.
Strength and power are important abilities that contribute to maximal effort in sports and other
physical activities.
The concepts of force, mass, work, displacement, and time must be understood to properly
define these relationships.
Strength
• Ability to exert force
• Disagreement as to best way to measure
• Maximum weight one quantitative measure of strength
• Isometric and isokinetic testing used as well
Acceleration
• Change in velocity per unit of time
• Associated with resistive force according to Isaac Newton’s Second Law:
Force = Mass * Acceleration
• Local acceleration of gravity needed for calculation
➢ 9.8m/s2
can be used to approximate gravitational acceleration
Power
• Time rate of doing work
• Work = Force * Displacement
• Power = Work/Time
Units used
• Force = Newtons (N)
• Displacement = Distance in meters (D) - For calculating work performed during
lifting, the upward displacement against gravity must be calculated
• Angle between force vector and displacement vector (𝛳)= Radians
➢ The cos(𝛳) is used to calculate the vertical displacement
• Work = Joules (J)
• Power = Watts (W)
Calculate the positive work performed and the power output when weight
lifting using the following numbers
Barbell weight = 100kg
Vertical Displacement = 2 meters
Desired Acceleration rate = 2 m/s
Time needed to fully lift bar = 4 seconds
1. Determine weight of bar in newtons and take the angle into consideration. In this
case, 𝛳 = 0 degrees
➢ Weight of bar in N = 9.8m/s2 * 100kg = 980N
2. Calculate additional force needed to accelerate the bar upward
➢ Force = 2m/s2 * 100kg * cos(0) = 200N
3. Apply work equation to calculate work needed for one repetition
➢ Work (J) = (980N + 200N) * 2m = 2,360 J
4. Power output = 2,360 J / 4 seconds (time required to lift bar) = 5.9 Watts
Calculate the negative work performed when lowering a barbell with the
following numbers
Barbell weight = 100kg Vertical Displacement = -2 meters Desired Acceleration rate = -2 m/s2 Time required to lower bar = 4 seconds 1. Calculate the force that must be removed to lower the bar at 2 m/s2 2 m/s2 * 100kg *cos(0) = 200N 2. Use work equation to calculate work for 1 repetition Work = (980N - 200N) * (-2m) = -1,560 J 3. Calculate power output -1,560 J/4 seconds = -3.9W In this case, the negative sign means that technically, the work is being performed on the athlete by the bar.
Discuss the equation needed to calculate rotational work
When a weight is not moving straight up and down but is instead rotating, the calculations must be modified to account for the rotational work performed. Units • Angular displacement = the angle through which an object rotates (Radians) • Angular velocity = the rate at which an object rotates in Radians/second • Torque = Force * moment arm - expressed as Newton-meters Rotational work (J) = Torque * angular displacement Rotational power (W) = rotational work/time
What are the implications of the strength-power relationship for strength and
conditioning?
Power is a crucial factor in sport performance.
Each sport has a characteristic velocity needed for maximum performance.
Since power is a function of work and time, increasing strength or reducing the time to perform
the work will both improve power.
Depending on the sport, it may be more beneficial to develop maximum strength (i.e. football
linemen) or decrease the time needed to perform the given work (i.e. tennis players). Both
reflect increases in power but differ in performance outcomes.
List the Biomechanical factors in human strength. Define each.
The following biomechanical factors affect the body’s ability to generate force:
1. Neural control
• The ability of the nervous system to recruit more motor units and increase
speed of recruitment
2. Muscle cross-sectional area
• The cross section size of a given muscle
3. Arrangement of muscle fibers
• The angle between muscle fibers and the imaginary line between the muscle
origin and insertion
• Referred to as the angle of pennation
• Angle of pennation varies muscle-to-muscle and changes during contraction
4. Muscle length
• Resting, stretched, or contracted state of muscle affects force production
capability at any moment in time
5. Joint angle
• Torque changes as joint rotates about its axis, affecting the force exerted on
the resistance
6. Muscle contraction velocity
• Slower contraction speeds allow greater force production over a longer time
7. Joint angular velocity
• The speed of rotation occurring in a given joint
8. Strength-to-mass ratio
• The relative strength of an athlete compared to their body size
9. Body size
• The overall height and weight of an athlete
How does muscle cross-sectional area affect force production capability? What
is the implication for athletic performance in terms of body size? Define the
classic formula.
The maximum force capability is directly related to the cross-section area of the muscle.
All else being equal, greater muscle cross-section means greater force production capability.
Muscle force capability is not directly related to muscle volume.
Implication:
• Smaller athletes are pound-for-pound stronger than larger athletes
• Taller athletes will not be stronger than smaller athletes with the same muscle crosssection
• Optimal strength-to-mass ratio important for weight-class athletes
• Strength-to-mass ratio affects acceleration ability
• Athletes can experiment to find the optimal-strength-to-mass ratio
The classic formula is used to compare the strength of different sized athletes.
• Most effective for athletes in the middle of the bodyweight range
• Designed to account for the relationship of cross-section and muscle volume
Classic formula = load lifted / bodyweight^2/3
How does neural control affect a muscle’s ability to produce force?
Neural control is a big factor in the maximal force output of a muscle.
The number of motor units involved in contraction (recruitment) and the rate at which motor
units fire (rate coding) greatly affect the force production capability of a muscle.
More motor units and faster rate coding improve maximum force capability in muscle.
Neural Control:
• Adaptations in the brain that increase muscle force through:
➢ Greater recruitment - more motor units involved in contraction
➢ Faster rate coding - muscles contract at a faster rate
➢ Both factors responsible for early strength gains
Once an athlete has developed neural control, strength gains will begin to slow and become
increasingly dependent on other adaptations such as muscle hypertrophy
Describe the three types of muscle action. List an example of each in sports or
movement. What is the effect of joint angular velocity on force production
during each muscle action
Concentric Muscle Action
• Contractile force greater than resistive force
• Muscle shortens
• Responsible for moving objects
• Swimming, biceps during raising phase of a curl
• Torque capability decreases as joint angular velocity increases
Eccentric Muscle Action
• Contractile force less than resistive force
• Muscle lengthens
• Resists gravitational force during lowering of resistance
• Slows weight during descent
• Quadriceps during lowering phase of a squat
• Torque capability increases as joint angular velocity increases until around 90
radians/second
Isometric Muscle Action
• Contractile force equals resistive force
• Muscle length does not change
• Occurs in static holds and stabilization
• Example: Holding trunk straight during sit up exercises
• Joint angular velocity = zero (0) during isometric action
