Strengthening

Muscle anatomy

• Muscles are made up of fiber bundles called fascicles

• have nuclei and are striated

• each MF is composed of many sarcomeres (contractile unit)

Sarcomere structure

• made up of two myofibrils: thin and thick filaments

• Thin filament: actin, double stranded

• Thick filament: myosin, single stranded w/ heads

Muscle contraction- Sliding Filament Theory

Binding, sliding, binding, sliding

• Myosin heads pull the actin filament inward, shortening the sarcomere→ actin slides on myosin

• action potential reaches NM junction and triggers release of ACH→ causes release of calcium from sarcoplasmic reticulum

• Calcium binds with troponin on actin→ troponin rotates tropomyosin to expose site for myosin heads to attach

Muscle contraction: muscles

made up of multiple motor units, innervated by nerve fibers

Muscle contraction: motor unit

1 motor neuron innervates many # of muscle fibers (4 to over 100)

Muscle contraction: Intrinsic muscle

Few muscle fibers innervated by 1 motor neuron

MF1+MF2+MF3+MF4

Muscle contraction: Extrinsic muscle

1 to >100 MF

Need to be activated more because bigger muscle

All or none principle

All muscle fibers innervated by a single MN contract at the same time or none contract at all

Slow twitch (type I) fiber

• O2 for energy

• increased resistance to fatigue

• slow to reach max force

• long lasting, low intensity

• red color

• endurance activities, posture

Oxidative (type IIa) fibers

• O2 and glycogen for energy

• some resistance to fatigue

• quick muscle contractions

• upper and lower extremities

• power and endurance

• white color

• ex. 1 mile run, soccer, basketball

Glycolytic (type IIb) fibers

• glycogen for energy

• max force quick but easily fatigue

• rapid and powerful contractions

• upper and lower extremities

• power activities

• white color

• ex. 100m sprint

What determines the type of fibers we have?

• ratio of fibers varies

• determined by genetics

  • everyone has all 3 but ratio is different depending on body type and training

Motor unit and Muscle fiber type

• a motor unit has all 1 type of fiber, never a mix

• between motor units of the same muscle there can be a mix

  • MU1 can have type 1 and MU2 can have type IIa

Can a muscle fiber become a different type?

• the percentage of fiber type cannot be altered through resistance or endurance training

• BUT type IIb (glycolytic) can become more efficient like type IIa (oxidative) through repeated endurance exercise

• type IIa can become like IIb through power and strength training

  ^ but both are temporary

Muscle fiber type and Rehab

• diff athletes need diff exercises→ know their needs and physical features

• determine intensity and reps based on fiber/body type

Muscle performance

• muscles ability to do work (force x distance)

• strength, endurance, power

Strength

• max force generation (single output/ 1 rep)

• often includes external resistance

• essential for injury prevention/normal functional movement

• if decreased strength→ lead to dysfunction and decreased functional performance

To regain strength…

6-10 reps for 3+ sets

Endurance

• repeated over an extended period

• if increased strength → increased endurance

• can improve endurance by increased reps and decreased weight

• if decreased endurance→ decreased functional performance in ADL bc not using max force

to increase endurance…

10-15 reps for 3+ sets

<1 min rest b/t sets

Power

• work in a given time

• strength x distance/ time

• if decreased power, decreased athletic performance

To increase power…

1-5 reps for 4+ sets

1-2 min rest b/t sets

Less reps but increased weight

Isometric contraction

• contraction w/o length change

• common in early rehab

• only within pain free limits

Concentric contraction

• muscle shortening contraction

• use after some ROM recovery

Eccentric contraction

• muscle lengthening contraction

• use after some ROM recovery

Factors determining muscle performance

• muscle hypertrophy

• size of motor unit

• NM efficiency

• biomechanics

• gravity

Cross-sectional area of muscle

• area = L x W x Thickness

• increased area = increased strength

• more muscle fibers, more MN, more force

Atrophy

• decreased muscle mass = decreased strength

• inactivity due to injury/surgery (as little as 48 hrs)

• size of muscle fibers shrink, you don’t loose # of them

Hypertrophy

exercise = increased area and strength of muscles

Factors: # and type of muscle fibers

increased # of MF = increased area = increased strength

increased type II = increased strength

number and type of MF are…

inherent

Neuromuscular system

nervous system + muscle causing movement of the body

Increasing motor units does what?

Increase MUs = increased fibers = increased strength

fire more MUs = more fibers involved in contraction = increased strength

Resistance Exercise does what

• increased efficiency→ involve more MU during contraction

• increased firing rate→ faster MUs, activate quicker

• increased synchronization b/t MUs (one ends, another begins)

• initial rehab (4-6 wks)

  • increased strength by increasing NM efficiency

Lever arm length

• distance b/t joint and the force

• longer lever arm = greater force needed

• resistance far from joint→ harder to move→ more force

• early rehab: resistance should be close to jt

Degree of force application

• max force is in mid range

• least force = end range (beginning/end)

Biomechanics: length tension relationship

physiologically shortened or lengthened muscles result in decreased force production capabilities and greater chance for dysfunction

Factors: age

• Max strength gains occur in the early to mid twenties→ age 25 muscular force begins to decline 1% per year

• can slow down curve through strength exercise

  • also decreased risk of future injuries