Chapter 2: Biomechanics of Resistance Exercise Flashcards
1
Q
What does biomechanics focus on?
A
Biomechanics focuses on the mechanisms through which the musculoskeletal components interact to create movement.
2
Q
What is the origin of a muscle?
A
The proximal attachment (towards the center of the body) or the more stationary structure.
3
Q
What is the insertion of a muscle?
A
The distal attachment (away from the center of the body) or the more mobile structure.
4
Q
How does the origin and insertion reverse in certain movements?
A
Straight-leg sit-up: Origin of iliacus is the femur (immobile), insertion is the pelvis (mobile). Leg raise: Origin is the pelvis (immobile), insertion is the femur (mobile).
5
Q
What are fleshy muscle attachments?
A
Muscle fibers are directly affixed to the bone, typically at the proximal end, distributing force over a wide area.
6
Q
What are fibrous muscle attachments (tendons)?
A
Tendons blend into the muscle sheaths and surrounding bone tissue, with additional fibers extending into the bone for a strong bond.
7
Q
What is a prime mover (agonist)?
A
The muscle directly involved in generating movement.
8
Q
What is an antagonist muscle?
A
A muscle that slows down or stops a movement, stabilizing joints and preventing excessive force.
9
Q
What is an example of an agonist-antagonist relationship?
A
In throwing, the triceps (agonist) extends the elbow, while the biceps (antagonist) slows and stops the extension.
10
Q
What is a synergist muscle?
A
A muscle that assists movement indirectly by stabilizing joints or supporting other muscles.
11
Q
How do synergists function in multi-joint movements?
A
They help control body motion when a muscle crosses multiple joints.
Example: Rectus femoris crosses the hip and knee—gluteus maximus counteracts hip flexion during a squat rise.
12
Q
How do muscles act as levers in the body?
A
Muscles use the skeletal system’s levers to produce movement in sports and exercise.
13
Q
What is a lever?
A
A rigid or semirigid body that rotates around a fulcrum when force is applied.
14
Q
What is a fulcrum?
A
The pivot point of a lever.
15
Q
What is a first-class lever?
A
A lever where the muscle force and resistive force act on opposite sides of the fulcrum.
16
Q
What is mechanical advantage?
A
The ratio of the moment arm of applied force to the moment arm of resistive force.
17
Q
What is the formula for equilibrium in levers?
A
(Muscle Force × Muscle Moment Arm) = (Resistive Force × Resistive Moment Arm).
18
Q
What does it mean if mechanical advantage is greater than 1.0?
A
Less muscle force is needed to overcome resistance.
19
Q
What does it mean if mechanical advantage is less than 1.0?
A
More muscle force is required to overcome resistance, creating a disadvantage.
20
Q
What is the moment arm (force arm, lever arm, torque arm)?
A
The perpendicular distance from the force’s line of action to the fulcrum.
21
Q
What is the line of action?
A
An infinitely long line passing through the force application point, indicating force direction.
22
Q
What is muscle force?
A
Force generated by muscle contraction or passive tissue stretch, drawing muscle ends together.
23
Q
What is resistive force?
A
An external force (e.g., gravity, inertia, friction) that opposes muscle force.
24
Q
What is a second-class lever?
A
A lever where muscle force and resistive force act on the same side of the fulcrum, with the muscle force having a longer moment arm than the resistive force (e.g., calf raise).
25
What is the mechanical advantage of a second-class lever?
Greater than 1.0, meaning less muscle force is needed to lift a load.
26
What is a third-class lever?
A lever where muscle force and resistive force act on the same side of the fulcrum, but the muscle force has a shorter moment arm than the resistive force.
27
What is the mechanical disadvantage of a third-class lever?
Less than 1.0, meaning muscle force must be greater than the resistive force.
28
What is torque (moment)?
The extent to which a force causes an object to rotate around a fulcrum.
29
What is the formula for torque?
Torque = Force × Moment Arm.
30
What is an example of a first-class lever in the body?
A lever where muscle force and resistive force act on opposite sides of the fulcrum, often requiring a greater muscle force due to a shorter muscle moment arm.
31
Why are most human muscles at a mechanical disadvantage?
Most muscles that rotate the limbs operate at a mechanical advantage of <1.0, meaning they require internal muscle forces much greater than external forces.
32
What is an example of mechanical disadvantage in human muscles?
If the resistance moment arm is 8× longer than the muscle moment arm, the muscle force must be 8× greater than the resistive force.
33
How does mechanical disadvantage contribute to injury?
High internal forces required for movement increase the risk of muscle and tendon injuries.
34
Why is lever classification sometimes arbitrary?
The classification of first-, second-, or third-class levers depends on fulcrum positioning, making mechanical advantage more important than lever classification.
35
Why is understanding mechanical advantage more important than classifying levers?
Mechanical advantage determines the force required for movement, while lever classification can vary depending on fulcrum positioning.
36
How does the knee joint affect mechanical advantage?
The knee joint is not a true hinge, so its axis of rotation shifts throughout movement.
37
What role does the patella play in mechanical advantage?
The patella stabilizes mechanical advantage by preventing the quadriceps tendon from moving too close to the axis of rotation.
38
How does elbow movement differ from knee movement in terms of mechanical advantage?
Unlike the knee, the elbow lacks a patella-like structure to stabilize the tendon’s perpendicular distance from the joint axis.
39
How does the absence of a patella-like structure in the elbow affect mechanical advantage?
It leads to greater variation in mechanical advantage throughout elbow movement.
40
How does variation in tendon insertion affect strength and movement efficiency?
Variation in tendon insertion points affects strength and movement efficiency by influencing the moment arm, torque production, and the ability to lift heavier weights.
41
What happens when the tendon insertion is farther from the joint center?
A farther tendon insertion increases the moment arm, allowing greater torque production and enhancing mechanical advantage.
42
What is the trade-off between strength and speed with tendon insertion variation?
Greater mechanical advantage from farther tendon insertion improves strength but reduces movement speed because the muscle contraction must be greater to move the joint through the same range of motion.
43
How does tendon insertion affect joint rotation per unit of muscle shortening?
If the tendon is inserted farther, the same muscle shortening results in less joint rotation.
## Footnote
For example, 37° of rotation with normal insertion becomes only 34° with farther insertion.
44
How do muscles with farther tendon insertion maintain joint rotational velocity?
Muscles with farther tendon insertion must contract at higher speeds to maintain joint rotational velocity, but the inverse force-velocity relationship reduces their force production at high speeds.
45
What is the advantage of farther tendon insertion for slower movements?
Farther tendon insertion increases force production, making it advantageous for slower movements like powerlifting.
46
Why is farther tendon insertion disadvantageous for fast movements?
Farther tendon insertion reduces movement speed, making it disadvantageous for fast movements like hitting a tennis ball.
47
How can understanding tendon insertion variation optimize performance?
Understanding tendon insertion differences helps optimize performance based on the movement demands, as skeletal structures are non-modifiable but their impact can be managed.
48
What is the standard anatomical position?
The body is in an erect position, arms down at the sides, and palms facing forward.
49
What are the three anatomical planes?
Sagittal plane: Divides the body into left and right sections. Frontal plane: Divides the body into front and back sections. Transverse plane: Divides the body into upper and lower sections.
50
What is an example of an exercise in the sagittal plane?
Standing barbell curl.
51
What is an example of an exercise in the frontal plane?
Standing lateral dumbbell raise.
52
What is an example of an exercise in the transverse plane?
Dumbbell fly.
53
What is biomechanical analysis of movement?
Biomechanical analysis is used to quantitatively assess sport movements, and can involve visual observation, slow-motion video, and commercial software for detailed movement analysis.
54
What are the key movement planes for body movements?
Frontal, sagittal, and transverse.
55
How do exercising muscles in different planes affect movement?
Exercising muscles in these planes strengthens them for movements between planes, helping to improve overall movement capabilities.
56
What are some commonly omitted movements in training?
Shoulder internal and external rotation (e.g., throwing, tennis), Knee flexion (e.g., sprinting), Hip flexion (e.g., kicking, sprinting), Ankle dorsiflexion (e.g., running), Hip internal and external rotation (e.g., pivoting), Hip adduction and abduction (e.g., lateral cutting), Torso rotation (e.g., throwing, batting), Neck movements (e.g., boxing, wrestling).
57
What should a comprehensive exercise program include to ensure balanced training?
A comprehensive exercise program should ideally include resistance exercises for all the movements listed (e.g., shoulder rotation, hip flexion, knee flexion) to ensure balanced training.
58
What is the definition of strength?
Strength is the ability to exert force. Traditionally measured by the weight a person can lift.
59
What are the two main types of strength testing?
Isometric strength testing: Measures strength at a fixed position (no joint movement). Isokinetic strength testing: Measures strength at a constant velocity throughout the range of motion.
60
What is acceleration and how does it relate to force?
Acceleration is the change in velocity per unit of time. According to Newton’s Second Law, Force = Mass × Acceleration.
61
Why is acceleration important in sports?
Acceleration is crucial in sports involving movement of the body or an implement, such as swinging a baseball bat, throwing a javelin, or using a tennis racket.
62
How does velocity affect an individual’s ability to exert force?
Individuals vary in their ability to exert force at different velocities. Low-speed strength tests may not accurately predict high-velocity force capabilities.
63
What is the benefit of sport-specific strength testing?
Strength testing at various loads and velocities provides better insight into an athlete’s specific capabilities and weaknesses.
64
How is power defined in physics and training?
Power in physics: The time rate of doing work. In training: The ability to exert force at higher speeds (explosive strength).
65
What are the formulas for work and power?
Work = Force × Displacement.
66
What are the SI units for force, work, and power?
Force: Newtons (N), Work: Joules (J) = Newton-meters (Nm), Power: Watts (W) = Joules per second (J/s).
67
How do you calculate power output in a workout?
Calculate work: (Force × Displacement × Reps). Divide by time: Power = Work / Time.
## Footnote
Example: Lifting 100 kg barbell 2m for 10 reps in 40s → Power = 590 W.
68
What is negative work and when does it occur?
Negative work occurs when force is exerted in the opposite direction of movement, such as lowering a weight or decelerating at the end of rapid movements.
69
How do you calculate power output in a workout?
Calculate work: (Force × Displacement × Reps)
Divide by time: Power = Work / Time
## Footnote
Example: Lifting 100 kg barbell 2m for 10 reps in 40s → Power = 590 W.
70
What type of muscle action is responsible for negative work?
Eccentric muscle actions (e.g., lowering a weight, decelerating movement).
71
What happens during the lifting and lowering phases of an exercise in terms of energy?
Lifting phase: Muscles perform work on the weight, increasing its potential energy.
Lowering phase: The weight’s potential energy performs an equal amount of work on the athlete.
72
How do repetitions affect power output?
The rate of repetitions determines power output; faster repetitions increase power.
73
How is negative work calculated?
Negative work formula: Work = (Force × Displacement × Reps), but with force applied in the opposite direction.
74
What is angular displacement?
The angle through which an object rotates, measured in radians (rad). 1 rad = 57.3°.
75
What is the formula for rotational work?
Rotational Work = Torque × Angular Displacement (Joules, J).
76
What is the difference between torque and work?
Torque (N·m): Force applied at a perpendicular distance from an axis.
Work (Joules, N·m): Force applied along the direction of movement.
77
What is the formula for rotational power?
Rotational Power = Work / Time (Watts, W).
78
Why is powerlifting misleading in terms of power output?
Powerlifting involves high forces but low movement speeds, producing less mechanical power than Olympic lifting, despite its name.
79
How does strength relate to power and velocity?
Strength: Ability to exert force at any velocity.
Power: Product of force and velocity (Power = Force × Velocity).
Velocity-specific strength: Important for different sports demands.
80
How do strength demands differ between sports?
Low-velocity strength: Important for high-resistance movements (e.g., football linemen).
High-velocity strength: Important for fast, low-resistance movements (e.g., badminton strokes).
81
What are the main biomechanical factors that affect human strength?
Neural control, Muscle cross-sectional area, Muscle fiber arrangement, Muscle length, Joint angle, Muscle contraction velocity, Joint angular velocity, Body size.
82
How does neural control affect force output?
Motor unit recruitment: Determines which and how many motor units are activated.
Rate coding: The rate at which motor units fire influences force production.
Higher force output occurs with: More motor units recruited, Larger motor units activated, Faster motor unit firing rate.
83
What role do neural adaptations play in strength training?
Initial strength gains come from neural adaptations, not muscle growth.
The brain learns to use existing muscle more efficiently.
Novice trainees experience rapid early gains followed by a plateau.
Long-term improvements shift toward muscle hypertrophy.
84
How does muscle cross-sectional area (CSA) relate to strength?
Force is related to CSA, not muscle volume.
Two athletes with the same biceps CSA have similar biceps strength, even if one is taller.
Heavier athletes tend to have lower relative strength (strength-to-weight ratio).
Resistance training increases both CSA and strength.
85
What is muscle pennation and how does it affect strength?
Pennation angle: The angle between muscle fibers and the tendon.
Greater pennation = More sarcomeres in parallel → Higher force, lower velocity.
Smaller pennation = More sarcomeres in series → Higher velocity, lower force.
Most human muscles have ≤ 15° pennation, which increases with training.
86
How does training affect pennation angle?
Training can increase pennation angle, improving strength but reducing speed.
Individuals with similar muscle size may have different strengths due to pennation angle variations.
87
How does muscle length affect force production?
Resting length = optimal force production (best actin-myosin crossbridge formation).
Overstretched muscles = fewer actin-myosin overlaps → reduced force.
Overly contracted muscles = excessive overlap → fewer crossbridge sites.
88
Why does torque change with joint angle?
Muscle length changes affect force generation.
Leverage changes with joint position.
Contraction speed varies with movement type (e.g., isometric vs. isotonic).
89
What is an example of torque variation in an exercise?
In a biceps curl, torque is highest at the mid-range due to optimal leverage and muscle length.
90
What is the force-velocity relationship in muscle contraction?
Higher contraction velocity → Lower force output (A.V. Hill’s research).
## Footnote
Example: Slowing contraction speed in a vertical jump allows greater force production.
91
How does torque vary with muscle action types?
Concentric: Torque decreases as velocity increases.
Eccentric: Torque increases up to 90°/s, then declines.
Isometric: Torque remains constant.
92
Why is eccentric training beneficial for strength?
Eccentric training produces the highest forces.
Negative repetitions (slow lowering) can improve strength.
93
Why is the strength-to-mass ratio important in sports?
Higher strength-to-mass ratio improves acceleration in sprinting and jumping.
In weight-class sports, athletes must balance muscle mass and strength.
94
How does increasing body mass affect acceleration?
If mass increases by 15%, but force output increases only by 10%, acceleration potential decreases.
95
Why do smaller athletes have a higher strength-to-mass ratio?
Strength scales with CSA (squared).
Mass scales with volume (cubed).
As size increases, mass grows faster than strength, reducing strength-to-mass ratio.
96
What formula adjusts for strength-to-mass differences?
Load lifted ÷ body weight^(2/3) helps compare athletes fairly.
97
Why do middle-weight athletes often perform best in strength-to-weight comparisons?
The bell curve of human body weight distribution favors middle-weight athletes.
98
What is the formula for frictional resistance?
FR = k • FN
Where:
FR = Resistive force
k = Coefficient of friction between surfaces
FN = Normal force (force pressing objects together)
99
What are the two types of friction?
- Static friction: The force required to initiate movement (greater than sliding friction).
Sliding friction: The force required to maintain movement (remains constant after initiation).
100
How does friction-based resistance affect exercise?
More force is required to start movement, but once in motion, the resistance remains constant regardless of speed.
101
How does surface type affect frictional resistance in sled training?
Different surfaces (e.g., dry grass, sand, wet turf) change the coefficient of friction, altering resistance.
102
Why does a sled require more force to start moving than to keep moving?
Static friction is greater than sliding friction, meaning initial movement requires more force.
103
What is fluid resistance?
The resistive force encountered when an object moves through a fluid (liquid or gas) or when a fluid moves around an object.
104
What are the two types of fluid resistance?
- Surface drag: Friction of fluid moving along the object's surface.
Form drag: The resistance caused by the shape of an object moving through fluid.
105
How do fluid-resisted exercise machines work?
They use hydraulic (liquid) or pneumatic (gas) cylinders, where resistance increases as movement speed increases.
106
What is the formula for fluid resistance?
(FR = k • v) where:
FR = Resistive force
k = Constant reflecting the physical characteristics of the cylinder, piston, fluid viscosity, and opening properties
v = Piston velocity relative to the cylinder
107
Why are fluid-resisted machines not truly isokinetic?
Resistance increases with speed, making it difficult to maintain a constant movement velocity.
108
How do fluid-resisted machines differ from free weights in terms of eccentric movement?
Free weights involve both concentric and eccentric phases, while fluid-resisted machines typically lack an eccentric phase unless an internal pump is used.
109
Why might fluid-resisted machines be less effective for sports training?
Many sports require eccentric muscle actions (e.g., running, jumping), which fluid resistance does not adequately train.
110
What is elastic resistance?
Resistance provided by elastic components such as bands, springs, or rods, which increases as they are stretched.
111
What is the formula for elastic resistance?
FR = k • x
FR = Resistive force
k = Constant that reflects the physical characteristics of the elastic component
x = Distance the elastic component is stretched beyond its resting length
112
Why is elastic resistance often inconsistent with human muscle force capabilities?
Resistance starts low and increases at the end of the movement, while muscles are typically strongest at the beginning and weaker at the end.
113
What is a major limitation of elastic resistance training?
Limited adjustability, as resistance is determined by the elasticity of the material, restricting progression and variation.
114
How does elastic resistance affect vertical jump training?
Bands provide minimal resistance at the start (when muscles are strongest) and maximum resistance at the peak, which can increase landing impact and injury risk.
115
Why might elastic resistance be less effective for strength training?
The resistance pattern does not match natural force curves, making it difficult to achieve consistent overload throughout the range of motion.
116
Why is the back particularly vulnerable to injury in resistance training?
The upright posture of humans increases compressive forces on the spine during activities, making the back prone to injury, especially during lifting.
117
What is the most common site for intervertebral disk herniations?
The L4-L5 and L5-S1 vertebrae, as they experience the highest compressive forces during lifting.
118
How does trunk inclination affect torque on the lower back?
When weight is held with a forward-leaning trunk, the horizontal distance from the weight to the lower back increases, creating greater torque and stress on the intervertebral disks.
119
Why is a neutral (lordotic) lumbar spine preferred for lifting?
A neutral spine minimizes compressive forces on the L5/S1 disk, reduces ligament strain, and allows the low back muscles to generate higher forces safely.
120
How does the natural S-shape of the spine affect disk compression?
When the spine maintains its natural curve, the intervertebral disks are evenly compressed. Rounding or excessive arching can cause uneven pressure, increasing the risk of disk rupture.
121
What is intra-abdominal pressure, and how does it support the spine?
Intra-abdominal pressure is created by the diaphragm and deep abdominal muscles contracting to form a 'fluid ball,' reducing spinal compression and injury risk.
122
What is the Valsalva maneuver, and what are its pros and cons?
The Valsalva maneuver involves closing the glottis while contracting the torso muscles. It increases spinal stability but can also raise blood pressure and compress the heart.
123
Why should lifters avoid over-reliance on weightlifting belts?
Frequent belt use can weaken the abdominal muscles responsible for generating intra-abdominal pressure, increasing injury risk when lifting without one.
124
When should a weightlifting belt be used?
Only for near-maximal and maximal lifts that stress the lower back, while avoiding use during lighter sets to maintain abdominal muscle strength.
125
Why is the shoulder more vulnerable to injury than the hip?
The shoulder has greater mobility but less stability, relying on the rotator cuff and other soft tissues for support.
126
What is the function of the rotator cuff in the shoulder?
The rotator cuff stabilizes the humerus in the glenoid cavity and assists with shoulder movement.
127
What is shoulder impingement?
A condition where shoulder structures rub against each other, leading to pain and potential injuries such as tendinitis or muscle tears.
128
What training precautions can help prevent shoulder injuries?
Proper warm-ups, balanced training for all shoulder movements, and avoiding excessive overhead loading can reduce injury risk.
129
What role does the patella play in knee function?
The patella increases the mechanical advantage of the quadriceps by holding the tendon away from the knee joint axis, enhancing force production.
130
What is patellar tendinitis, and what causes it?
An overuse injury characterized by inflammation and tenderness of the patellar tendon, often caused by excessive training volume or intensity.
131
What are the potential downsides of knee wraps in resistance training?
While they may enhance lifting performance, knee wraps can cause skin damage and contribute to chondromalacia patellae (worn cartilage).
132
What is chondromalacia patellae?
The roughening and deterioration of the patella’s posterior surface, often caused by improper knee mechanics or excessive stress.
133
Why are elbow and wrist injuries relatively rare in resistance training?
Resistance training poses a lower risk compared to overhead sports like tennis or throwing events, where joint stress is higher.
134
What is traction apophysitis, and which athletes are most at risk?
An overuse injury caused by repetitive tendon pulling on a growth plate, commonly seen in young athletes in sports like diving and wrestling.
135
What are the concerns regarding growth plates in youth resistance training?
Excessive loading on the elbow or wrist in young athletes could potentially damage the epiphyseal growth plates, but evidence suggests that resistance training is safe with proper supervision.
136
What is physeal closure, and why is it important for young athletes?
Physeal closure is the process of growth plate fusion after puberty. Resistance training does not negatively impact this process when performed safely.
