EXSI 420 ch 2 Biomech of Resistence

Biomechanics

mechanisms through which components interact to create movement

Origin

proximal

Insertion

distal

Agonist

muscle most directly involved; prime mover

antagonist

muscle slow down or stop movement

synergist

muscle asisst indirectly in a movement

Levers

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.

Fa

force applied to lever

Maf

moment arm of the applied force

Fr

force resisting the lever’s rotation

Mrf

moment arm of resistetive force; equal force in mag but oppisite direction

Mechanical advantage

ratio of moment arm through force is applied acts to resistive force; if resistive moment arm is shorter —> less, if longer —→ greater

Greater than 1 = less muscle force than resistive force for equal amount of torque

Less than 1 person must apply greater muscle force than the amount of resitve force

first-class lever

muscle force and resistive force act on oppisite sides

second-class lever

muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm longer

required muscle force is smaller than the resistive 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

MA less than 1 so muscle force greater

Patella mechanical advantage

• 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.

• 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
  and thereby reducing the muscle’s mechanical
  advantage.

Are forces in the muscles and tendons higher than hands or feet on external objects?

yes

Tendon insertion variation

further away from the joint center = ability to llift heavier weights

results in loss of max speed and force capibility during faster movements

Strength

capacity to exert force at any given speed

Accleration

change in velcocity per unit of time (force= mass x accleration)

Power

explosive strength

rate of time doing work (power= work/time)

Work

product of force exerted on an object and the distance the object moves in the direction the force is exerted (work = force x displacement)

Negative work

work performed on, rather than by a muscle

eccentric muscle contractions

Angular work and power

angle which an object rotates

rotational work = torque x angular displacement

Commonality between strenth and power

reflect the ability to exert force at a given velocity

Biomechanical factors in human strength

• Neural control-which and how many motor units (rate coding)'

• muscle cross-sectional area

• arrangement of muscle fibers- pennate (align obliquely)

• muscle length (resting)- muscle can generate greatest force

• muscle length (contracted)- decreased force generation capability

• joint angle-force v muscle length (torque)

• muscle contraction velocity- force dec as velocity inc

• joint angular velocity (3 type)

• body size- body size inc, body mass inc more rapidly than muscle strength; smaller athlete has high strength to mass ratio

Concentric action

muscle shortens bc contractile force greater than resitive force. Forces generated within muscle and acting to shorten it are greater than external forces acting at tendons to stretch it

eccentric action

muscle lengthens bc the contractile force is less than the resistive force. Forces generated within muscle to shorten are less than the external forces to stretch it

Isometric acton

muscle length does not change. Contraction equal to the resitive force

Force-velocity curve

inverse relationship between speed and the amount of external force or resistence a muscle can produce

Eccentric flexors and extensors more torque with - joint angle

Strength to mass ratio

Directly reflects an athlete’s ability to acclerate his or her body when dealing with sprinting or jumping

Gravity application to resistence training

• When weight is horizontally closer to a joint, less resitive torque

• weight horizontally farther, more resistive torque

• exercise tech can affect resistive torque pattern and shift stress among muscle groups

Back injury

resistence training, the back should be in a moderately arched position

fluid ball aids in support (lifting belt)

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.

Shoulder injury

• warm up w light weights

• exercise shoulders in a balanced way

• exercise at controlled speed

  • prone to injury during weight training

Knee injury

• prone to injury because of location between two levers

• minimize use of wraps