health practices chapter 3

The Muscular System

Skeletal Muscle

·      40-45% of average adults body weight

·      Cells are long narrow cylindrical with many cross striations and many nuclei

·      Voluntary

·      Irritability= ability to receive and respond to a stimulus

Muscle Properties

·      Muscles contract due to protein structures

o   Contractile component

o   Elastic component

·      Extensibility- ability if muscle to be stretched or to increase in length resting ability

·      Elasticity- ability of a muscle to return to its resting length after being stretched

·      Viscous- resistance to elongation increases with the rate of stretch, protects against over stretching

·      The viscous elements are influenced by temperature, rate and duration of applied forces

o   The slow, lower force, longer duration stretches to warm up muscles= less tendency of strains/brakeage

Muscle Cells

·      Or muscle fibers

·      Long and thin

·      Fibers grow in length and diameter from birth to adulthood

·      Strength training with heavy weights and low reps can cause increase in muscle cell diameter termed hypertrophy

Sliding filament theory

·      Describes how muscle cells contract

·      Myosin and actin filaments bind and pull on each other in cross bridges to shorten the muscle

·      Molecules involved CA2+ (Calcium) and ATP

Muscle fiber types

Type 1- Slow twitch

·      Aerobic (needs oxygen)

·      Prolonged periods/endurance activities

·      Slower contraction

·      Smaller cross section

·      Higher resistance to fatigue- can work longer

·      Sustained contractions

·      Repetitive low intensity

o   Slow controlled movements

o   Balance movements for long periods of time

o   Core/ postural muscles

Type 2- Fast twitch

·      Anaerobic

·      Fastest contractions

·      Largest diameter

·      Greatest force produced

·      Fatigues quicker

·      Short duration

·      High intensity

o   Jumping

o   Fast movements

o   Running/ sprinting

Muscle Cross-sectional area

·      A muscle with more muscle fibers will be capable of producing more force than on with fewer fibers

·      The bigger the muscles the greater the force

Attachments to bone

·      Muscle belly- central thicker part

·      Tendon- strong cordlike or flat band attaching muscle to bone

·      Origin- generally stays stationary; proximal attachment usually stabilized due to greater mass

·      Insertion- generally moves; distal attachment usually moving

Muscles and bones as a lever system

·      Force arm=moment arm

o   Perpendicular distance from the line of force to the axis of rotation

o   The farther the load is from the body the more difficult to lift

·      Magnitude and distance from axis determine force

o   Develope vs brush? Which is easier?

Dynamic muscle contractions

·      Tension occurs when there is a change in length of the involved muscle and an observable joint movement

·      Isotonic (dynamic contractions)

Concentric contractions

·      Shortening

o   Visible movement toward the action of primary muscle (center)

·      Force from muscle is greater than that of the resistance (so limb moves)

·      Up phase of movements in dance

o   Rising from plie, takeoff phase

Eccentric Contractions

·      Lengthening of the muscle and distance between origin and insertion gets greater away from center

·      The muscle is contracting to control the effect of the resistance

o   Gradually decreasing the degree of contraction

·      Down phase

o   Plie, landing from jump, lowering arms/legs

Static (Isometric) Contraction

·      Contraction of the muscle where no visible joint movement occurs

·      Resistance form

o   Internal forces: contraction muscles with opposite actions

o   External forces: another person, a weight, or gravity

·      Hold phase

o   Postural alignment, plank, lift, balance

“Pull up on your knees” technique

·      Some instructors encourage the use of a slight contraction in the quadriceps in standing positions

o   This pulls up the patella

·      Use of the quadriceps stabilizes the standing leg

Muscle Roles

Agonist (mover)

·      A muscle whose contraction produces the desired joint movement

·      Prime mover- muscles that are most important or effective in producing the movement

·      Arabesque agonist= hamstrings

Antagonist

·      Muscle with an opposite action to that of the prime mover

·      Side of the joint opposite to the agonist (hamstrings vs quads)

·      Relax while the prime movers contract

·      Arabesque antagonist: quadriceps (rectus femoris)

Synergist

·      A muscle that works together with the agonist to help achieve the movement goal

·      Neutralize undesired secondary actions of the prime movers

·      Arabesque synergist:  biceps femoris

Stabilizer (fixator)

·      A muscle that contracts isometrically to support or steady a body part against forces

o   Muscle contraction

o   Gravity

o   Soft tissue constraints

o   Momentum

·      Arabesque stabilizer: abdominals

o   Stabilize the pelvis by pulling up on the pubic bone

Stretch-shortening Cycle

·      A muscle used eccentrically immediately preceding use of the same muscle concentrically – pre stretch

·      Mechanical energy is stored in the elastic component of the muscle

·      Then released during following shortening contraction

o   Resulting in greater force production

·      Example quick demi plie prior to jump