Biomechanics

Biomechanics

• mechanisms through which musculoskeletal components interact to create movement

• skeletal musculature- a system of muscle enables the skeleton to move

• origin-proximal attachment

• insertion-distal attachment

• types of attachment

  • fleshy attachment-occurs at the origin, where muscle fibers directly affix to the bone

  • fibrous attachments-the muscle blends into and with muscle sheaths (tendon)

• movement

  • agonist-most directly involved is bringing about a movement; prime mover

  • antagonist-acts opposite to the agonist; can slow or stop a movement; assists in joint stabilization

  • synergists- muscle that aid directly in the movement

• levers

  • bony levers

  • fulcrum-pivot point of lever

  • lever-rigid or semi-rigid body, excerpts force on an object impeding the tendency to rotate if the force line of action does not pass through pivot point

  • moment arm-perpendicular distance from the line of action to the fulcrum

  • mechanical advantage- ratio between moment arm of applied force (muscle force) to moment arm of resistance force (force we try to overcome)

  • if the ratio is greater than 1, there’s a mechanical advantage

    • you can apply less muscle force than resistive force to produce an equal amount of torque

  • if the ratio is less than 1, there’s a mechanical disadvantage

    • you must apply greater muscle force than resistive force to produce an equal amount of torque

• elbow extension is a first class lever because the muscle and resistive force are on opposite sides of the fulcrum

• plantar flexion is a second class lever because the muscle and resistive force act on the same side of the fulcrum

  • moment arm of the muscle force is longer than that of resistive force

  • works at mechanical advantage

• elbow flexion is a third class lever because the moment arm of the resistive force is shorter than the moment arm of muscle force

  • work at mechanical disadvantage

  • both forces act on the same side of the fulcrum

1st class-opposite sides of the fulcrum

length of moment arm of muscle and resistance varies

mechanical advantage and disadvantage varies

2nd class-same side of fulcrum

moment arm of muscle is greater than that of resistance

mechanical advantage

3rd class lever-same side of fulcrum

moment arm of resistance is greater than that of muscle

mechanical disadvantage

• perpendicular distance from joint axis changes throughout movement

  • shorter moment arm of muscle force leads to less mechanical advantage

  • also subject to change for resistance arm

• most skeletal muscles operate at a mechanical disadvantage

Anatomical Planes

• saggital- left and right

• frontal- front and back

• transverse- up and down

Human Strength and Power

• strength-the capacity to excerpt force at any velocity

• acceleration-change in velocity per unit time

  • force=mass x acceleration

• power-explosive strength

  • force x velocity or work/time

• work=force x displacement

• “negative work”-force exerted in opposite direction of weight movement

• angular work and power-angular displacement-angle through which an object rotates

  • rotational work-torque x angular displacement

• it is not correct to associate strength with low speed and power with high speed

• neural control- impacts maximum force output by recruitment (motor unit number and size)

  • rate coding-rate at which motor units are being recruited

• strength improvements in the first two weeks are mostly due to neural adaptations

• muscle cross-sectional area-related to force

• arrangement of muscle fibers

  • pennate-fibers align obliquely with tendon; angle of pennation-angle between muscle fiber and imaginary line between origin and insertion

  • more pennation leads to generation of better force; less maximal shortening velocity

• less pennation leads to greater maximum shortening velocity

Muscle length

• at rest-actin and myosin filaments lie next to each other

  • potential crossbridge sites greater; greatest force potential

• when contracted- actin filaments overlap

  • potential crossbridge site are fewer than at rest; less force potential

• when stretched- actin and myosin filaments are farther away

  • potential crossbridge sites are fewer; less force potential

• joint angle- torque generated varies through range of motion

• muscle contraction velocity- increase velocity and decreased force capability

• concentric- contractile force is greater than resistive; muscle shortening

• eccentric- resistive force is greater than contractile force; muscle lengthening ; prone to leading to muscle soreness

• isometric- contractile force equals resistive force; no change in muscle length

• strength to mass ratio-ratio of muscle strength to the mass of accelerating body parts

  • reflects the ability to accelerate the body

• increased body size leads to increased muscle volume but not necessarily cross sectional area

Sources of Resistance

• gravity-applies a downward force on an object; force will always be horizontal

  • i.e. weight’s object

  • e.g. weight stacked machines (can provide greater control of direction and pattern of resistance)

• weight horizontally closer to the joint provides less resistive force

• weight horizontally further from the joint provides more resistive force

• exercise technique can affect resistive torque patter and shift stress among muscle groups

• inertia- barbell or weight stack exerts force

  • inertia can act in any direction, while gravity only acts downward

  • upward or lateral acceleration of weight exerts inertial force on athlete and alters required force

• friction provides resistive force; e.g. cyclogometers

• fluid resistance-resistive force from moving through a fluid, liquid or gas

  • e.g. swimming, rowing, baseball pitching

• elasticity- the stretch of an elastic components

  • greater stretch→ the greater resistance applied

  • e.g. resistance bands

Concerns in Resistance Training

• back injury is very vulnerable and likely

  • disk herniations→ spinal disk puts pressure on your nerve→ occur between L4 and L5 or L5 and S1

  • decrease injury risk by using proper alignment→ neutral spine-slightly arched position

• supporting back during exercise

  • valsalva maneuver-you force expiration against the glottis→ internal pressure and support to the vertebral column→ negative side effects- increase blood pressure leading to pass out, increase compressive forces on the heart

  • weight lifting belt- side effects→ do not stabilize core muscles

• shoulders-prone to injury due to the structure and range of motion

• knees are prone to injury as they’re between two long levers

• elbows and wrists- primary concern→ overhead lifts