EXS 410 Ch. 2
The patella and mechanical advantage:
(a) The patella increases the mechanical advantage of the quadriceps muscle group by maintaining the quadriceps tendon's distance from the knee's axis of rotation. (a) Absence of the patella allows the tendon to fall closer to the knee's center of rotation, shortening the moment arm through which the muscle force acts (MM) and thereby reducing the muscle's mechanical advantage.
Other factors that influence the torque-joint angle relationship include:
Types of exercise (isotonic, isometric) --generate more force during isometric contractions—more time to generate force with cross bridge connections Which joint (e.g. single arm row - elbow versus shoulder) o Which joint/muscle moment arm are you focusing on Which muscle are used Speed of contraction --Faster you go, less force you can generate
Human movement technique example than generates great force:
Vertical jump-arms swing upwards exerting downward force on the body and the shoulders, slowing the upward movement of the body and forcing the hip and knee extensor muscles to contract more slowly than they otherwise would--> greater force development
Power measure in:
Watts
Strength to mass ratio: **Could be a HUGE strong guy but strength to mass ratio may be much smaller than a tiny gymnast
When body size increases, muscle volume (and mass) increases proportionally more than muscle CSA-- -increasing muscle volume does not= an equivalent increase in strength. -In sprinting and jumping, the ratio directly reflects an athlete's ability to accelerate his or her body. -Getting bigger does not help in sports involving weight classification, the ratio helps determine when strength is highest relative to that of other athletes in the weight class. • Optimal weight class
Isometric contraction velocity:
Where the muscle contracts and stays the same length (there is no velocity)
Fulcrum/axis: A
pivot point of a lever
Body movements directly involved in sport and exercise primarily act through:
the bony levers of the skeleton
As muscle mass/volume increases, CSA (strength) only increases by a factor of:
~ 2/3 -for every one unit of increased muscle mass, only 0.66 increases in CSA strength occurs -Iimit to how big you want to be
What is the relationship between power and strength?
• All applied strength (force) will result in power output, and all power output requires a strength component. -Power and strength are different but interdependent. ***Greater strength does NOT always equal greater power output Power has a time component to it, whereas strength does not
Body size:
Absolute strength (assuming larger csa) is generally greater in a bigger person ---But, relative (pound for pound) strength of a smaller person is generally greater. o Relative to body mass-strength
Difference between torque and work:
Distance component of torque unit refers to the length of the moment arm perpendicular to the line of action of the force, while the distance component of the work unit refers to the distance moved along the line of action of the force.
MAF=
Moment arm of the applied force
FR=
Moment arm of the resistive force ***The lever applies a force on the object equal in magnitude to but opposite in direction from FR.
Isokinetic contractions:
**isokinetic (constant-speed) contraction velocity ↑, force ↓
Risk of Back injury during RT:
-Back in more vulnerable to injury -normal/flat back>> rounded back for preventing injury -Most (85-90%) vertebral injuries occur between L4-L5 and L5-S1 (these are the largest vertebrae)
Why do pennate muscles have greater force but lower speed?
-Greater force because more sarcomeres in parallel and fewer in in series, but have a lower maximal shortening velocity than non-pennate so therefore decreased SPEED
Fluid ball when lifting:
-Intra-abdominal pressure can be increased by contracting the diaphragm and deep muscles of the torso to create a "fluid ball" that supports the vertebral column. **refrain from using the valsalva maneuver
Frontal Plane:
-Slices the body front to back Examples: wrist ulnar deviation, neck tilt, shoulder adduction/abduction, hip adduction/abduction, ankle inversion/eversion, lower back left/right tilt shoulder press
Arrangement of muscle fibers-
-The arrangement and alignment of fibers in relation to the long-axis of the muscle influences strength. -Wide range of muscle contraction force due to the angle of pennation of muscle (arrangement of sarcomeres) relative to the long axis of the muscle.
Does mechanical advantage change as a joint changes position during a movement?
-YES, mechanical advantage often changes continuously during real-world activities. -When you extend your arm down, the moment arm is shorter muscle has less force. In a flexed position, the moment arm is also shorter and therefore the muscle has less force. The 90 degree position has the greatest moment arm and therefore greatest force. -The force development capability changes through the range of motion ***always consider the HORIZONTAL distance
Inertia early in the ROM
-acts in any direction -When initially lifting and accelerating a bar off the ground, the agonist muscle receives resistance in excess of the bar weight alone due to the demands of acceleration. **Need to accelerate the weight up which means need to create more force
Fleshy attachments:
-most often found at the proximal end of a muscle -Directly affixed to the bone usually over a wide area so that force is distributed rather than localized
Inertia later in the ROM
-resistive forces experienced by the agonist will be less than the bar weight toward the end of the ROM as the bar decelerates.
Transverse plane:
-slices body top to bottom Example: shoulder internal/external rotation, neck rotation, peck flyes, lower back rotation
Sagittal plane
-slices the body left to right Examples: wrist flexion/extension, elbow flexion/extension, shoulder flexion/extension, neck flexion/extension, ankle dorsiflexion/planter flexion barbell curl
Local acceleration due to gravity:
9.8 m/s^2
Sticking point:
: the point at which the moment arm of the resistive force is fairly large and the muscle moment arm is almost at its fullest moment arm—but needs to overcome the resistive force to overcome the movement.
What is negative work?
=Work performed ON, rather than by, a muscle. When a weight is lowered, its potential energy is used to perform an equal amount of work on the athlete. **2 m/s^2 downward--controlled the downward acceleration **While lifting, muscle works on the weight, increasing its potential energy -->While lowering the weight, the potential energy works on the athlete. Occurs during eccentric muscle action ---The lowering is the negative work
Class 3 lever: Mechanical disadvantage
A lever for which the muscle force and RF act on the same side of the fulcrum with the muscle force acting through a moment arm shorter than that of the RF. Mechanical advantage= less than 1 and therefore a disadvantage for the MF. F force is in the middle (muscle) EX: Bicep curl- the muscle is in the middle of the axis (elbow) and the weight
First class lever
A lever for which the muscle force and resistive force act on opposite sides of the fulcrum A-axis is in the middle EXAMPLE: tricep pushdown Mechanical disadvantage
Second class lever:
A lever for which the muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm longer than which the RF acts. R is in the middle EXAMPLE: Calf raise- the resistive force of the body weight is in the middle of the axis (toes) and the muscle MECHANICAL ADVANTAGE FOR MUSCLE
What is a lever?
A lever is a rigid or semi-rigid body that, when subjected to a force whose line of action does not pass through its pivot point, exerts force on any object impeding its tendency to rotate.
Isometric muscle action:
A muscle action in which the muscle length does not change, because the contractile force is equal to the resistive force. The forces generated within the muscle and acting to shorten it are equal to the external forces acting at its tendons to stretch it. **trunk during a sit up is isometric
Eccentric muscle action:
A muscle action in which the muscle lengthens because the contractile force is less than the resistive force. The forces generated within the muscle and acting to shorten it are less than the external forces acting at its tendons to stretch it. **the downward movement of a weight during RT in which the muscle keeps the weight from being accelerated downward by gravity
Concentric muscle action:
A muscle action in which the muscle shortens because the contractile force is greater than the resistive force. The forces generated within the muscle and acting to shorten it are greater than the external forces acting at its tendons to stretch it. **swimming and cycling=exclusive concentric muscle action
Muscle insertion affects on speed:
A muscle insertion further from the axis places the muscle in a mechanical advantage, however there is LESS movement in degrees for the same amount of movement compared to a closer muscle attachment. Therefore someone with a closer muscle attachment are at a disadvantage but are much faster
Pennate muscle:
A pennate muscle has fibers that run obliquely (at an angle) to the long axis, resulting in more sarcomeres in parallel, and fewer in series. -Angle of pennation is defined as the angle between the muscle fibers and an imaginary line between the muscles origin and insertion (0 degrees= no pennation) -Many muscles are pennated but few in excess of 15 degrees -More sarcomeres greater force but you lose some speed because the line of pull is oblique rather than direct. -GREATER CSA so more force but decreased speed -Heritable and modifiable
Agonist and antagonist of: Calf Raises
Agonist: Gastrocnemius (plantar flexion) Antagonist: Tibialis anterior (dorsiflexion)
Agonist and antagonist of: Bench press
Agonist: Pec major (arm flexion, medial rotation) Antagonist: lats (extension/adduction)
Agonist and antagonist of: Military press:
Agonist: deltoids (abduction) Antagonist: lats/teres major (adduction)
Agonist and antagonist of: Kicking soccer ball
Agonist: rectus femoris/quads (leg extension) Antagonist: biceps femoris/glutes (leg flexion)
Agonist and antagonist of: Shooting free throw
Agonist: triceps (humeral extension) Antagonist: biceps brachii humeral flexion
Muscle cross-sectional area:
All else being equal, the force a muscle can exert is related to its cross-sectional (csa) rather than its volume. **No matter height, length, volume, if the CSA of a muscle is the same, force output will be the same **want to maximize CSA
Strength vs. power:
Although the word strength is often associated with slow speeds, and the word power with high velocities of movement, both variables reflect the ability to exert force at a given velocity The sport of weightlifting (Olympic lifting) has a much higher power component than the sport of powerlifting, due to the higher movement velocities with heavy weights of the weightlifting movements (explosive) Strength: capacity to exert force at any given velocity Power: mathematical product of force and velocity at a particular speed
Angular displacement &angular velocity:
Angular displacement: the angle through which an object rotates Angular velocity: the objects rotational speed
Joint angle affecting force/torque development: **all body movements take place by means of rotation about an axis
As a joint rotates maximum torque (rotational force) changes as a result of changes in; • muscle length and • mechanical advantage (moment arm length changes)
How is movement created?
Muscles shorten and then "pull" against bones that rotate around joints and transmit through the skin to the environment.
Lifting belts:
Belts also create a "fluid ball", but should only be used in maximal or near maximal lifts that directly stress the lower back, to ensure proper training stimulus for deep abdominal muscles--want to stimulate and train abdominal muscles **only use them when really needed
Fibrous attachments (tendons):
Blend in and are continuous with both the muscle sheaths and the CT surrounding the bone -Have additional fibers that extend into the one-very strong union
Acceleration:
Change in velocity per unit time -velocity has a vector/directionality -in a linear path, speed and velocity are the same -Direction is critical
The quadriceps muscle group functions as a decelerator to knee joint flexion in weight-bearing movements by contracting concentrically to prevent too rapid of a downward movement. T/F
False **The quads would be eccentrically contracting
When performing a "squat" exercise the hip is extended during the lowering phase T/F
False-hip is flexing (but not controlled by iliopsoas but rather the hamstrings are controlling)
Failures in CAM of machines?
For a CAM to work as perfectly planned, the athlete has to move at a constant, slow angular velocity which is usually hard to maintain.
FA=
Force applied to the lever
Resistive force (R)-resistance:
Force generated by a source external to the body that acts contrary to the muscle force
Muscle force (F):
Force generated by biochemical activity or stretching of non-contractile tissue, that tends to draw the opposite ends of a muscle towards each other.
Newton's 2nd law, Force=
Force= Mass x Acceleration
Inertia related to real-life situations:
Inertia and acceleration allow for explosive exercises to exert greater force than originally possible *Greater resistance in earlier stages of motion and less resistance in later stages of motion
What is a synergist?
It is a muscle that indirectly assits a movement. Can also be a stabilizer. ** Synergists are also required to control body motion when the agonist is biarticulate!
Agonist:
It is a muscle that is most directly involved in causing (controlling) the movement. It is also known as the "prime mover". ***Can cause a movement UP and control it on the way DOWN
Mechanical advantage definition:
It is the ratio of the force that performs the useful work of a "machine" to the force that is applied to the machine. = F/R Force / resistance **Often changes during real world activities
Bracketing technique
It is where the athlete performs the sport movement with less than normal resistance and greater than normal resistance. **Higher resistance trains force during the acceleration phase **less resistance trains greater velocity during the acceleration phase
What does the term Biomechanics mean?
It refers to the mechanisms through which anatomical structures interact to create movement.
Work measured in:
Joules
Avoid valsalva?
Keep glottis open and create the fluid ball--though experience athletes may utilize the valsalva at necessary times of a lift if they avoid the risks
Do all muscles in the body act through levers?
NO- face/tongue/heart
Do all joints move in the same direction?
No. Some are uniaxial axial (elbow), biaxial axial (ankle), or multiaxial axial (shoulder)
Which end of the muscle is the origin and which is the insertion?
ORIGIN- proximal end (towards the center of the body) INSERTION- distal end (away from the center of the body)
What fitness parameter has gained popularity as a measure of the ability to exert force at high speed?
POWER rate-force development
Power is:
Power is the product of force being applied at a given speed. -explosive strength
When choosing exercises to develop high-speed strength:
Resistance levels must be adapted downward to accommodate this force-velocity curve. • Don't want weight to be TOO heavy or else it will compromise force/power
Why are the body's levers typically at a disadvantage?
SPEED -Muscle tendon insertion points vary considerably -A muscle insertion further away from the joint (↑MM), results in more force, but less maximum speed, and reduces the muscle's force capability during faster movements. -Longer limbs—may make the moment arm of the resistance greater and harder to overcome
Advantages in slower movements vs. faster movements:
Slower movements (power lifting)-further insertions are advantageous because they provide greater force development. Faster movements (sports) are easier with closer muscle insertions.
What kind of joint is primary in most sport and exercise activities? Why?
Synovial, because they have a large ROM and low friction:
Each person has a unique distance from the muscle insertion to where the weight/resistance is location, where greater distance equals greater resistive torque. T/F
TRUE
Muscles can be both agonists and synergists T/F?
TRUE Ex:rectus femoris—on the way up from a squat the r.f. is contracting concentrically and extending the leg at the knee. The gluteus is acting during this motion to keep your torso upright to fight against the torso from bending forward (gluteus max is a synergist to the r.f. but also a prime mover-agonist to extend the hips).
Torque: AKA moment
The degree to which a force tends to rotate an object about a specified fulcrum. Magnitude of force x length of moment arm
Mechanical advantage of back muscles:
The distance from the intervertebral column is much shorter to the erector spinae muscles than to the weight being lifted (say in a back squat) which places the back at a very large disadvantage (the moment arm is much shorter)
Valsalva maneuver
The glottis is closed, thus keeping air from escaping the lungs, and the muscles of the abdomen and rib cage contract, creating rigid compartments of liquid in the lower torso and air in the upper torso. **increases the rigidity of the torso, making it easier to lift heavier loads -raises blood pressure and makes it harder for blood to return to the heart
How does the location of the weight relative to the axis of the participating joint(s) influence torque demands and thus force output?
The greater the horizontal distance a weight is from the joint's axis, the •greater the resistive torque •the greater need for muscle torque to achieve the same work. (vice versa) **example: during a bicep curl, when the forearm is horizontal, the moment arm of the resistive force is at its longest horizontal distance, therefore the greatest muscle exertion needs to occur at this point to overcome the resistive force.
Definition of strength:
The maximum force a muscle or muscle group can be generated with a single effort-independent of the speed its done.
What does our textbook suggest the definition of strength should be changed to?
The maximum force that a muscle or muscle group can generate at a specific velocity. -More relevance Because: Strength scores obtained from static (handgrip dynamometer) or low-speed (1RM) tests have limited value in predicting performance in sports when force must be exerted rapidly.
Moment arm: aka force arm, lever arm or torque arm
The perpendicular distance from the line of action of the force to the fulcrum
Mechanical advantage:
The ratio of the moment arm through which an applied force acts to that through which the resistive force acts.. Equilibrium~the product of the muscle force and the moment arm through which it acts must equal the product of the resistive force and the moment arm through which it acts.
Risk of RT:
The risk of injury from resistance training is low compared to that with other sport and physical conditioning activities There are still very real risks.
Contraction velocity:
The type of "Muscle action" influences force at various joint angular velocities.
Calculating work (force x displacement) ~~the displacement can be measured by:
The vertical travel of the bar during the exercise multiplied by the number of reps.
How should the fact of changing mechanical advantage be accommodated during training?
To ensure maximum overload throughout a full ROM; -maximally stimulate all muscle groups •loads should be increased at points of high mechanical advantage, and decreased at points of mechanical disadvantage **ex: chain to a bench press
Concentric muscle actions are the shortening contraction of muscles against gravity or a resistance. T/F
True
Eccentric actions occur when muscles lengthen under tension to control the joints moving with gravity or a resistance. T/F
True
Muscles may shorten or lengthen in the absence of a contraction through passive movement caused by other contracting muscles. T/F
True
Quantitatively work= & power=
Work= Force x Displacement Power= Work/Time W= work (force [mass • acceleration] x distancedisplacement) Force= mass x acceleration
Does the horizontal distance of the load from the joint axis change during an exercise?
Yes, constantly changes Where the weight is relative to the joint line of pull
Can one deliberately manipulate the distance a load is from the axis to shift stress among muscle groups?
Yes. Compare front versus back squat, and high versus low bar positions in the back squat --can change the resistive torque on specified body parts to change stress and muscle activation
Mechanical advantage=
a ratio greater than 1 -allows the applied muscle force to be less than the resistive force to create an EQUAL amount of torque
Mechanical disadvantage=
a ratio less than 1 -One must apply greater muscle force than the amount of resistive force present
Neural control-greatest muscle force:
a) More MU's are involved b) the MU's bigger and c) the rate of MU firing is faster (rate coding), and d) when there is greater MU synchronization (contracting at the same time) • These neural adaptations are the primary reason strength is increased in the first few weeks of RT.
Most human joints operate in a mechanical:
disadvantage: extremely high forced experienced by muscles and tendons--> high injury rate
What is the difference between the mass and the weight of an object?
• Remember- mass is the property of an object that is a measure of its inertia, and the amount of matter it contains. •Mass remains constant •Weight = the weight of an object times (x) the- local acceleration due to gravity. •Weight changes depending on terrestrial location. (a 160 lb. person would weigh ~26.4 lbs. on the moon)
What are the advantages of stack machine weights?
• Safety - objects fixed in place • Some design flexibility - lat pull-down, hip adduction and abduction, leg curl -Hard to do the same exercises with free weights -Ham curl?? • Ease of use- less skill needed, and less time to change load --Cam machines attempt to create more resistance where the muscle can exert greater torque, and less resistance where the muscle can provide less torque--better for activating full range of muscle action
Shoulder injury:
• The forces, structure and mobility of the shoulder joint makes it vulnerable to injury • Warm-up shoulders with light weights • Exercise shoulders in a balanced way • Avoid rapid transitions from eccentric to conccentric movements
Does the moment arm of the resistive force change throughout a ROM?
• The moment arm of the resistive force also changes through range of motion in extended and flexed arm positions, the moment arm of the resistance force gets smaller and therefore less force as well (the weight will be easier to lift at the point with a smaller moment arm). •The longer the MR, the greater force needed to overcome the resistance **Consider the horizontal distance from the resistive force to the primary mover muscle groups
Concentric contraction velocity:
• Where the muscle contracts and shortens (as velocity ↑, force ↓ )OR (as force ↑, velocity↓) o Inverse relationship
Fluid resistance:
•Fluid resistance is the 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 opening. •For example: pool based activities **Most all motions in fluid resistance are concentric contractions
Friction:
•Friction is the resistive force encountered when one attempts to move an object while it is pressed against another object. •For example, run pulling a sled
Muscle length affecting
•Potential cross-bridge totals are optimal at resting to slightly contracted muscle lengths. ---Most optimal for cross-bridging • Muscles shorter or longer than resting lengths have fewer shortening and, cross-bridge options, therefore decreased force potential
What is angular work and power?
•The angle through which an object rotates Rotational work = Torque × Angular displacement Rotational power: work/time
Elasticity:
•The more an elastic component is stretched, the greater the resistance. • For example: bands --When using a resistance band, the resistive force increases during the highest mechanical advantage of the muscle (not the same as real life where the resistance gets less) which is not ideal
Elbow and wrist injury:
•The primary concern involves overheard lifts. **more common injuries occur during overhead sports such as throwing or tennis serves --low elbow and write injury during weight lifting
Eccentric contraction velocity:
•Where the muscle contracts and lengthens [as velocity ↑(up to 90º/s) force↑, then force ↓thereafter] o 90 degrees per second
What are the advantages of free weights?
•Whole body training •Simulation of real-life activities •Potentially faster strength gains (extra neurological flow) More taxing and greater bone mineralization
Knee injury:
♣ The knee is prone to injury because of its location between two long levers ♣ The patella and surrounding soft tissues are most susceptible to injuries ♣ Knee wraps can actually help extend the knee, but use should be limited to the hardest lifts, due to potential to increase wear and tear of the knee and lack of evidence supporting their usefullness
