Chapter 2 - Biomechanics of Resistance Exercise

Question 1

Origin and Insertion

Answer 1

O: proximal (doesn’t move; closer to body).
I: distal (moves; further from body)

Question 2

Agonist

Answer 2

muscle most directly involved

aka Prime Mover

Question 3

Antagonist

Answer 3

muscle that can slow down or stop a movement (opposite)

Question 4

Synergist

Answer 4

muscle that assists indirectly in a movement.

Question 5

Mechanical Advantage

Answer 5

Ratio of moment arm through which an applied muscle force acts to that through which a resistive force acts.

1. 0+ = Fm < Fr to produce equal torque; advantage.
   - 1.0= Fm > Fr to produce equal torque; disadvantage.

Question 6

First Class Lever

Answer 6

MF and resistive force act on opposite sides of the fulcrum.

Ex. triceps ext.

Question 7

Second Class Lever

Answer 7

MF and Fr act on same side of fulcrum, with MF acting through a moment arm longer than that of Fr.
Mechanical Advantage.
Ex. Calf Raise

Question 8

Third Class Lever

Answer 8

MF and Fr act on same side of fulcrum, with MF acting through a moment arm shorter than that of Fr. Mechanical Disadvantage.
Ex. Bicep Curls

Question 9

Patella and Mechanical Advantage

Answer 9

Patella increases MA of quads by maintain the quads tendon’s distance from the knee’s axis of rotation.
Absence of patella allows tendon to fall closer to knee’s center of rotation, shorting the moment arm

Question 10

Moment Arm and Mechanical Advantage

Answer 10

Longer moment arm = more MA
Shorter moment arm = less MA

Ex. Biceps curl; moment arm length changes during the ROM. Shorter at full ext., longest at middle, and shortest at full curl.

Question 11

Variations in Tendon Insertion

Answer 11

Tendons attach to bones.
Insertion further from joint = ability to lift heavier weights, but loss of max speed and reduced MF capability during faster movements.

Question 12

Anatomical Planes

Answer 12

Sagittal (L,R)
Frontal (F,B,
Transverse (U,L)

Question 13

Strength

Answer 13

Capacity to exert force

Question 14

Positive Power

Answer 14

Precisely defined as the time rate of doing work.

Power (watts) = Work/Time (seconds)

Question 15

Positive Work

Answer 15

Product of the force exerted on an object and the distance the object moves in the direction in which the force is exerted.
Work (Joules) = Force x Displacement (meters)

Question 16

Negative Work and Power

Answer 16

All such “negative” power and work occur during eccentric muscle action (i.e. lowering weight or decelerating at the end of a rapid movement.

Question 17

Angular Work and Power

Answer 17

Required for objects rotating about an axis or to change rotational velocity.

Question 18

Angular Displacement

Answer 18

Angle in which an object rotates on a circular path.
Angle between starting ands final position.
Measured in radian (rad).

Question 19

Angular Velocity

Answer 19

Object’s rotational speed. Measured in radians per second (rad/s).

Question 20

Torque

Answer 20

Degree to which a force tends to rotate an object about a specified fulcrum, aka moment. Measured in newton-meters (N-m)

Question 21

Rotational (Angular) Work and Power

Answer 21

Rotational Work = Torque x Angular Displacement

Rotation Power is same as linear power.

Question 22

Strength v. Power

Answer 22

Although STR is associated wit slow and PWR with high velocities of movement, both reflect ability to exert force at a given velocity. (i.e. weightlifting has higher power component than powerlifting b/c of higher movement velocities with heavy weights.
Power is direct mathematical function of force and velocity.

Question 23

Biomechanical Factors in Human Strength (8)

Answer 23

Neural Control
Muscle Cross-Sectional Area
Arrangement of Muscle Fibers
Muscle Length
Joint Angle
Muscle Contraction Velocity
Joint Angular Velocity
Strength-to-Mass Ratio
Body Size

Question 24

Neural Control

Answer 24

MF is greater when: (a) more motor units are involved ini a contraction (recruitment), (b) the motor units are greater in size, or (c) the rate of firing is faster (rate coding).

Question 25

Muscle Cross-Sectional Area

Answer 25

Force a muscle can exert is related to its cross-sectional area rather than to its volume.

Question 26

Arrangement of Muscle fibers

Answer 26

Varation exists in the arrangement and alignment of sarcomeres in relation to the long axis of the muscle.

Question 27

Pennate Muscle and Angle of Pennation

Answer 27

Pennate Muscle: muscle with fibers that align obliquely with the tendon, creating a featherlike arrangement.
Angle of Pennation: angle between the muscle fibers and an imaginary line between muscle’s origin and insertion; 0 degrees corresponds to no pinnation.

Question 28

Muscle Length

Answer 28

Resting: actin and myosin lie next to each other; max number of potential cross-bridge sites are available; muscle can generate greatest force.
Stretched: smaller proportion of actin and myosin lie next to each other; fewer cross bridge sites, can’t generate as much force.
Contracted: actin overlaps myosin; number of cross-bridge sets reduced; decreased force generation capability.

Question 29

Joint Angle

Answer 29

Amount of torque that can be exerted about a given body joint varies throughout the joint’s ROM, largely bc of its relationship of force v. muscle length, as well as the ever-changing leverage of brought about by the dynamic geometry of muscles, tendons, and internal joint structures.
Additional factors are: the body joint in question, the muscles used at that joint, and speed of contraction.

Question 30

Muscle Contraction Velocity

Answer 30

Nonlinear, but in general, the force capability of muscle declines as the velocity of contraction increases.
i.e. vert jump: arms swing up causing downward force on body at shoulders, slowing the upward movement and forcing hip and knee extensors to contract slower, enabling them to generate higher force for longer times.

Question 31

Joint Angular Velocity

Answer 31

Concentric action: shortens; contractile force > resistive force (weight).
Eccentric action: lengthens; contractile force < resistive force.
Isometric: stays the same; contractile force = resistive force.

During isokinetic concentric exercise, torque capability decreases as joint angular velocity increase.
In contrast, during eccentric exercise, as joint angular velocity increases, maximal torque capability increases until about 90 degrees/s

Question 32

Strength-to-Mass Ratio

Answer 32

Directly reflects athlete’s ability to accelerate body when sprinting or jumping.
Helps to determine when strength is highest relative to that of other athletes in same weight class.

Question 33

Body Size

Answer 33

As size increases, body mass increases more rapidly than muscle strength.
Given constant body proportions, the smaller athlete has a higher strength-to-mass ratio than the larger athlete.

Question 34

Sources of Resistance to Muscle Contraction

Answer 34

Gravity
Inertia
Friction
Fluid Resistance
Elasticity

Question 35

Gravity

Answer 35

When weight is horizontally closer to the joint, it exerts less resistive torque. When further from joints, t exerts more resistive torque.
Ex. front squat produces more torque than high or low back squats bc the distance from bar to knee joint is greater.

Question 36

Inertia

Answer 36

When a weight is held in a static position or when it is moved at a constant velocity, it exerts constant resistance only in the downward direction.
However, upward or lateral acceleration of the weight requires additional force.
Ex. back squat; accelerating the bar upward.

Question 37

Friction

Answer 37

the resistive force encountered when one attempts to move an object while it is pressed against another object.

Question 38

Fluid Resistance

Answer 38

resistive force encountered by an object moving through a fluid (liquid or gas), or by a fluid moving past or around an object or through an orifice.
ex. water and air resistance; swimming/rowing (water), sprinting/pitching (air).

Question 39

Elasticity

Answer 39

the more an elastic component is stretched, the greater the resistance. Begins with low resistance and ends with high resistance. Limited adjustability.

Question 40

Back Injuries

Answer 40

Low back is particularly vulnerable.

Resistance training exercises should generally be performed with low back in a moderately arched position.

Question 41

Intra-Abdominal Pressure and Lifting Belts

Answer 41

Abdominal “fluid ball” and tissues aid in supporting vertebral common during resistance training.
Valsalva maneuver: glottis is closed, thus keeping air from escaping the lungs, and the muscles of the abdomen and rib cage.
Weightlifting belts: improve safety. Not needed for non-low back exercises. Refrain from using during lighter sets.

Question 42

Shoulder Injuries

Answer 42

Prone to injury during weight training b/c of its structure and forces to which it is subjected. Warm up with light weights.

Question 43

Knee Injuries

Answer 43

Prone to injury b/c located between two long levers. Minimize use of wraps.

Question 44

Elbow and Wrist Injuries

Answer 44

Primarily concern is during overhead lifts. Lower risk of injury during resistance training than during actually sport competition. In young athletes, primary concern is epiphyseal growth plate damage or overuse in posture aspect of elbow or in the distal radius.

Question 45

Reducing Risk of Resistance Training Injuries

Answer 45

Warm up sets with using relatively light weights, especially for knee and shoulder exercises.
Perform exercises through full ROM.
use lighter weight for new exercises or resuming training after layoff of 2+ weeks.
Do not ignore pain around joints.
Never attempt max loads without proper prep.
Performing several variations of an exercise = more complete muscle development and joint stability.
Safely integrate plyometrics into a training program.

Question 46

Acceleration

Answer 46

Change in velocity per unit of time.

Force (Newtons) = Mass x Acceleration