Chapter 2 P20 biomechanics Flashcards
biomechanics def
the mechanisms through which the musculoskeletal components interact to create movement.
origin and insertion
origin= proximal attachment, insertion= distal attachment
fleshy attachments
muscle fibers directly attached to bone; usually at proximal end of a muscle over a wide area
fibrous attachments
ie tendons, continuous with muscle and CT around bone and have fibers extending into the bone.
prime mover/ agonist
the muscle most directly involved in bringing about a movement.
antagonist
a muscle that can slow down or stop the movement of the agonist.
antagonist role
to assist in joint mobilization, slow down movement toward end range for protection
synergist muscles
muscles that assist the prime mover or agonist INDIRECTLY
first class lever
a lever where the muscle force and resistance act on opposite sides of the fulcrum. (teeter totter, triceps)
mechanical advantage def
the ratio of the moment arm through which an applied force acts to that through which a resistive force acts.
mechanical advantage >1
allows the applied (muscle) force to be less than the resistive force to produce an equal amount of torque.
mechanical advantage <1
on must apply greater muscle force than the amount of resistive force present, creating a disadvantage
moment arm, force arm, lever arm, torque arm
the perpendicular distance from the line of action of the force to the fulcrum (p 21)
mechanical advantage ratio calculation
moment arm of muscle force/ moment arm of resistive force
muscle force
force generated by biomechanical activity, or the stretching of non-contractile tissue, that tends to draw the opposite ends of a muscle toward eachother
resistive force
force generated by a source external to the body (eg gravity, inertia, friction) that acts contrary to muscle force
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 that through which the resistive force acts (calf, wheelbarrow). High mechanical advantage requiring smaller muscle force.
third-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 shorter than that through which the resistive force acts. Mechanical advantage is less than 1. (biceps)
torque, moment
the degree to which a force tends to rotate an object about a specified fulcrum. The magnitude of a force times the length of its moment arm.
Mechanical advantage of limbs
most operate at a mechanical advantage of < 1
moment arm variation
during resistance exercise, the moment arm through which the weight acts = the horizontal distance from a line through the center of mass of the barbell or DB to the body joint where rotation occurs, so the RESISTIVE MOMENT ARM varies through the movement
Variation in anatomy and moment arm/ strength
variation in human anatomical structure exists, including the points at which tendons are attached to bone. a person whose tendons are inserted on the bone farther from the joint center should be able to lift heavier weights because the muscle force acts through a longer moment arm, producing greater torque.
variation in anatomy and moment arm/ speed
a person whose tendons are inserted on the bone farther from the joint center should be able to lift more weight, but at the cost of a loss in maximum speed because, with the tendon inserted farther from the joint, center, the muscle has to contract more to make the joint move through a given ROM. This results in less rotation of a body segment around a joint, which translates in to a loss in movement speed.
anatomical position
body erect, arms at sides with palms forward
Sagittal plane
divides body in to L and R halves
frontal plane
divides body in to front and back halves
transverse plane
divides body in to inferior and superior planes
strength def
the ability to exert force
acceleration
change in velocity per unit of time
Newton’s second law
F= Mass x acceleration
power def
“explosive strength”, time rate of doing work…where work is the product of the force exerted on an object and the distance the object moves in the direction in which the force is exerted.
work formula
work = force x displacement
power formula
power= work / time
International system of units (SI)
worldwide standard
force is measured in
newtons (N)
distance is measured in
meters (m)
work is measured in
joules ( J) or neton meters (work= F x D
time is measured in
seconds (s)
power is measured in
watts (W) or joules per second J/S
work involved with lifting 100kg bar 2 meters per rep for 10 reps
P28, 29 revisit
Negative work and power
because power equals the product of force and velocity, when force is exerted on a weight in the direction opposite to the one in which the weight is moving (eccentrically), calculated power has a negative sign
angular displacement
the angle through which an object rotates
SI unit for angular displacement
radian (rad), 1 rad = 180 degrees/ pie = 57.3 degrees
angular velocity
the objects rotational speed
angular velocity measured
radians per second ( rad/s)
torque measurement
newton-meters (Nm) (not to be confused with work which is also measured in Nm)
Rotational work equation
work= torque x angular displacement
strength
the capacity to produce force at any given velocity
power
the mathematical product of force and velocity at whatever speed
biomechanical factors in human strength
neural control, muscle cross section area, muscle fiber arrangement, muscle length, joint angle, muscle contraction velocity, joint angular velocity, body size
neural control affect on strength
affects the maximal force output of a muscle: determines how many motor units are involved in muscle contraction (recruitment) and the rate at which the motor units are fired (rate coding)
muscle cross section area affect on strength
force a muscle can exert is related to its cross-section area, not its volume. taller person has more muscle volume, but with everything else equal, strength should be the same
arrangement of muscle fibers affect on strength
variation of arrangement in sarcomeres in relation to the long axis of the muscle. PENNATE MUSCLE has fibers that align obliquely with the tendon, creating a feather-like arrangement. More pennation = greater strength, less pennation = greater velocity.
maximally contracting muscles can generate forces of
23-145 psi or 16-100 N/cm2
Angle of pennation is modifiable
through training
muscle length affect on strength
When a muscle is at its resting length, the actin and myosin filaments lie next to each other, so that a maximum number of potential cross-bridges are available - so, greatest force is produced at resting length. Stretching muscle reduces the number of potential cross-bridge sites.
joint angle affect on strength
movement about a joint is manifested as torque, changes through the movement
muscle contraction velocity affect on strength
force capability of muscle decreases as velocity of contraction increases
joint angular velocity affect on strength
concentric m action, eccentric muscle action, isometric muscle action
muscle torque varies with
joint angular velocity according to the type of muscular action
greatest force can be produced by muscle during which type of muscle action?
eccentric
strength to mass ratio affect on strength
if mass and strength increase or decrease disproportionately, it lowers or increases ability to accelerate (for runners).
a low strength to mass ratio is important in
sports with weight classes
classic formula for strength to mass ratio
weight lifted/ body weight to the 2/3 power
sources of resistance to muscle contraction -gravity
gravity = mass x local acceleration due to gravity
weight of a barbell
in pounds measures force and changes with local gravity, in KG is measured in mass and stays the same
Inertia and lifting weights
initial acceleration of weight provides inertia producing less resistance later in the movement (clean)
sources of resistance to muscle contraction- friction
sled, airdyne - more force to begin movement, and constant force to keep motion. Friction coefficient does not change with speed.
sources of resistance to muscle contraction-fluid resistance def
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
fluid resistance machines act
concentrically only
sources of resistance to muscle contraction- elasticity
bands: force is proportional to length band is stretched, so force increases at end of motion where there is less potential for force production from muscle and is force is low at beginning of movement where force potential is greatest.
resistance training and injuries- back
back muscles act with a severe mechanical disadvantage; deep squatting positions are not necessarily associated with back injury; a normal lordotic lumbar position is safest (moderately arched)
85-90% of dsk herniations occur at
L4-5
intra-abdominal pressure and lifting belts
fluid around abdominal muscles helps to stabilize torso during contraction. wight lifting belts have been shown to increase intra-abdominal pressure, should only be used for heavy sets or may weaken intra-abdominal musculature.
the valsalva maneuver
is not necessary for increasing intra-abdominal pressure compressive force in thoracic cavity can place stress on hear during valsalva and make blood return to the heart difficult, valsalva can transiently slightly raise blood pressure
shoulder injuries
shoulder joint is prone to injury, warm up well and exercise the shoulder in a balanced way
knee inuries
patella is most prone with resistance training due to too much volume/intensity producing tendonitis, no evidence knee wraps help and may cause chondromalacia
elbows and wrists injuries
lifting overhead is primary incident of injury, but it’s pretty small. Most injuries from sports.
muscle recruitment
recruitment of motor units for contraction
rate coding
rate at which motor units fire
muscle force is greater when
more motor units are involved
the motor units are larger in size
the rate coding is fast
most of the improvement in the first few weeks of resistance training is
neural adaptation
muscle cross section area vs volume
force a muscle can exert is related to muscle cross section area, not volume
actin and myosin positioning at resting length
A and M lie next to each other so the max # of potential cross-bridge sites are available
muscle can generate greatest force at
resting length
joint angle and body movements
all body movements- even in a straight line- occur by means of rotation about a joint or joints
forces that muscles produce must be manifested as
torques
force capability of a muscle declines as
the velocity of contraction increases
3 types of muscle action
concentric, eccentric, isometric
greatest muscle force can happen with
eccentric muscle action
most common sources of resistance for strength training are
gravity, inertia, friction, fluid resistance, elasticity
gravity def
downward force on an object/weight
weight formula
mass x local gravity : F=MA
the pound is a unit of
force
the mass of a weight stays
constant
the moment arm is always____to the line of action of the force
perpendicular
the torque due to an object’s weight is is the product of:
the weight and the horizontal distance from the weight to the pivot point
advantages of weight machines
safety, design flexibility(hip rotation), ease of use
advantages of free weights
whole body training, simulation of real life activities
when weights are accelerated they have ____
inertia / inertial force which must be decelerated to stop
an exercise involving higher acceleration (explosive) provides greater____
resistance to the muscle early in the lift and less resistance later in the lift
because of inertia, heavier weights can be handled in
accelerative exercises than in slow exercises
Bracketing Technique
an athlete performs the sport movement with less than normal and greater than normal resistance ( a form of acceleration training)
friction def
the resistive force encountered when one attempts to move an object while it is pressed against another object
exercise devices that use friction
belt or break pad cycles, weighted sled
it takes more force to ____movement between two surfaces in contact than to _____
initiate than to maintain movement
friction resistance ___ change as speed increases
does not
fluid resistance def
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
fluid resistance is a significant factor in
swimming, rowing, golf, sprinting, discus throwing, rowing
two sources of fluid resistance
surface drag, form drag
surface drag def
friction of fluid passing along the surface of an object
form drag
resistance resulting from the way in which a fluid passes against the front or rear of an object when passing through it
cross sectional (frontal) area has a major effect on
form drag
fluid resistance machines and muscle action
muscle action is concentric of agonist and concentric of antagonist
elasticity in resistance training
devices that have elastic components such as springs, bands, bows, or rods often used at home
the resistance provided by a standard elastic component is proportional to
the distance it is stretched
the problem with elastic components for resistance training
every exercise movement begins with lower resistance and ends with high resistance which is contrary to the force capability pattern
muscle groups show a drop off in force capability towards …
the end of the range of motion
the problem with band training for vertical jumping
least resistance at start where force is applied, most resistance after muscle has contracted, risk for injury with being pulled to the floor
activity with high injury risk
team sports
activities with intermediate injury risk
running, aeroics
activities with low injury risk
cycling, walking, resistance training
resistance training injuries per 1,000
4/1,000
the back muscles act at a great
mechanical disadvantage
deep squatting positions are not necessarily associated with
back injury
85-90% of all intervertebral disk herniations occur at
between L4-5 or L5-S1
the valsalva maneuver is not necessary for generation of
intra-abdominal pressure
an advantage of the valsalva maneuver is
it increases the rigidity of the entire torso, making it easier to support heavy loads
a disadvantage of the valsalva maneuver is
it can put pressure on the heart, making it more difficult for blood to return to the heart
valsalva maneuver can transiently, slightly raise
blood pressure
the glottis and ab muscles can contract without the valsalva maneuver and this must be regarded as
safer than using the valsalva and used for most resistance training
a weight belt is not needed for exercises that
do not directly affect the lower back
lifting belts should not be worn while performing
lighter sets
the shoulder joint is particularly prone to injury during resistance training because…
of its structure and the forces it is subjected to. It is not a true socket
the shoulder joint has the greatest
ROM of any joint in the body
the knee is prone to injury because
of its location between two long levers
the patella’s main function is to
hold the quadiceps tendon away from the knee’s axis of rotation, thereby increasing the moment arm of the quadriceps
