Human G & MD Exam 3

Postural control

maintaining body alignment

maintaining balance in the face of external disturbing forces such as gravity

maintaining balance in the face of self-generated forces during movment

Neonate posture control

completely dominated by gravity

can lift head momentarily

cannot maintain sitting position

cannot maintain head, trunk alignments while being moved

Development progressions

1. holding head steady while moving

2. sits without support

3. sits upright

4. gets to sitting

5. pulls to standing

6. stands alone

Holding head steady while moving

1-5 months

Sits without support

5-8 months

Sits upright

5-10 months

Gets to sitting

6-11 months

pulls to standing

5-12 months

Stands alone

9-16 months

Sway

movement or motion about a central equilibrium axis

3 main classes of sensors

vision

vestibular

somatosensors/body sensors

Vision sensors

what we can see

tells us what our eyes are looking at

Vestibular sensors

sense head position

Somatosensors

sense if skeletal muscles are moving

found throughout entire body

CNS uses a combination of the 3 sensors

to rapidly figure out why swaying, how much sway, and then what muscles need to contract to fix it

Postural control progresses from

head/shoulders (1 joint)

to sitting (2 joints)

to standing (many joints)

Brain needs to relearn

for each new stage it enters

Visual dominance during

stage 1 development of head control

Newborn in room with vertical stripes

stripes twist

neck muscles contract as if trying to follow the movement of the stripes

if visual info is blocked and body or head is twisted, don’t get the same response

no evidence of vestibular or somatosensory sensors until several months later

Early head/neck control

main limiting factor is the nervous system

not limited by inadequate strenght

3-4 months

child will exhibit an appropriate neck response to sway 40-60% of the time

6 months

infant reaches sloppy sitting milestone

sway control begins to appear 6-7 months

Sloppy sitting

ignoring body info

independent sitting is more complicated

2 joints to control

interaction torque

Sway control begins to appear 6-7 months

using sensory signals from the neck to control the head

not exclusively visually dominant for head control

by 5-8 months, neck muscle responses become progressively coordinated with trunk responses

Independent sitting

sitting requires head plus trunk control, plus the ability to control sway (motion about a vertical equilibrium)

sway control during upright sitting appears around 6-7 months

Sensory information for sitting

vision dominates early and gradually gives way to somatosensory information from the hips

Moving room sitting adult vs infant

Adult: usually not affected, can trust our sensors

Infant: will fall for ~3 months, rely on visual sensors first

Idenpendent stance

strength does not limit development

coordinated muscle responses to platform disturbances emerge

vision is first source of sensory info and lessens in dominance in experienced walkers

Somatosensory info to muscles controlling stance occurs

around 9 months and strengthens as walking experience accumulates

Moving room standing

child is upright and independently controlling sway ~11-12 months of age

put in room while standing, go back to visual sensors so they fall for ~3 months

Visually dominant first

at each stage

Each stage has a new

source of information, so it’s easiest for the NS to initially default back to visual info

Progression complicated because

with each stage, the center of mass becomes higher and base becomes smaller

Efficient sway control occurs

when the brain figures out what pattern of muscle control to use

Hydraulic platform

backward movement of platform causes the equivalent of forward sway

forward movement of platform causes the equivalent of backward sway

Ankle strategy used when

the disturbance is small

contact surface is broad and stable

Ankle strategy muscles are recruited

forward sway: posterior muscles (inferior to superior)

backward sway: anterior muscles (inferior to superior)

Ankle strategy head movements are

in phase with hips

Hip strategy used when

the disturbance is large

surface is narrow or unstable

Hip strategy muscles recruited

forward sway: anterior muscles, no activation below knee (superior to inferior)

backward sway: posterior muscles, no activation below knee (superior to inferior)

Hip strategy head movement is

out of phase with hips

As brain gets better at incorporating muscles into adult-like patterns

sway gets better

EMG responses to forward sway

early on: general sustained contraction

there is a point where certain muscles are targeted

Muscle responses must be present to allow

progression to next functional stage

Muscle activation patterns during backward sway

no co-contraction of antagonistic muscles as we age

Can adaptation to sway be accelerated with balance training?

improved responses with training

Other options with platform device

can attach canopy that moves when the ankles move

platform can rotate forward with ankle movement (eliminates feedback from the feet and ankles)

What sensory imput is most important for balance

somatosensors

The more senses taken away

the more falls that occur

Somatosensors have greater

falls when taken away

2 types of postural adjustments

reactive

anticipatory

Reactive adjustments

response to a disturbance

ex: responding to sway

Anticipatory adjustments

prior to predictable disturbance

ex” infant stabilizes core before the reach occurs

Biological maturation

important in age related studies: need to compare individuals of equivalent chronological age

Biological maturation measured via

physical maturity of different organs or tissues

Skeletal maturation

use radiograph

the most accepted method for defining biological age

Skeletal maturation indicators

how much cartilage has been replaced by bone

have primary ossification centers appeared, secondary

has the growth plate fused

Many groups have looked at the above changes from birth to 20 and have created atlases to

be able to determine if growth is advanced, typical, or delayed

Some researchers focus efforts only on hand and wrist development because

their maturation spans the entire growing period

Dental maturation

time or age of eruption of the deciduous and permanent teeth

calcification of permanent teeth (x-ray): various methods (cusps, roots)

Sexual maturation

difficult to characterize sexual age based on hormones or releasing factors because they are released sporadically

Tanner developed a series of qualitative measures based on the appearance of secondary sex characteristics

5 point qualitative scale assigned after examination of photos

stage 1 (preadolescent) up to stage 5 (adult)

sometimes given term SMR (sexual maturity rating)

Can also look at menarche as

an indicator of sexual maturation

Somatic maturation

• all measurements in males seem to be shifted 2 years later

  • age at onset of growth spurt (age at takeoff)

  • age at peak height velocity

  • peak height velocity

  • age at peak rate of strength development

• correlates well with skeletal maturation

Average age of take off (when the growth curve switches from deceleration to acceleration)

females: 8-9

males: 10.3

Age at peak height velocity

females: 11.4

males: 13.4

Peak height velocity (cm/year)

females: 7

males: 8.2

In most cases B2 and G2 are

the first overt signs of sexual maturity

Most girls are in B2 and B3 and PH2 and PH3 at

the time of PHV

Most boys are in PH3 and G2 at

the time of PHV

Menarche occurs

about 1 year of more after PHV and when most girls are in stages B4 and PH4

Stature PHV

females: 12

males: 14

Peak trunk velocity

females: 12.5

males: 14.5

Peak leg length velocity

females:11.5

males:13.5

usually ~1/2 year before PHV

Peak velocity for change in bone width

females:12

males:14

Peak velocity for change in arm muscle width

females:13

males:14

Peak velocity for change in calf muscle width

females:12

males:14

Peak weight velocity

usually occurs after PHV (~1/2 year after)

no body dimensions show growth spurts after peak weight velocity

occurs last

Thermoregulation goal

to prevent core body temperature from rising or falling excessively

Core

muscles and internal organs

deep structures

Periphery

everything superficial

skin, subcutaneous fat

Dangerous core body temps

39°C or higher: heat production> heat loss (increased core temp)

39°C or lower: heat production< heat loss (decreased core temp)

2 mechanisms for prevention of excessive build-up of body heat

sweat and vasodilation

Vasodilation

vessels become larger, bringing blood to surface of skin, letting heat out

2 mechanisms for prevention of excessive body cooling

shivering and vasoconstriction

Shivering

increases metabolic rate

Vasoconstriction

vessels become smaller, keeps blood at core, preventing heat loss to environment

Sweat rates increase with age due to

glands produce more sweat as we get older

We have less blood flow to surface as we age which means

younger individuals rely more on changes in blood vessel diameter than older adults

Acclimatization

physiological and perceptual changes that occur when heat + exercise occurs in a natural environment

Acclimation

physiological and perceptual changes when heat + exercise occurs in an artificial environment

Upon transition from a cool or temperate climate to a warmer climate

a reduction in physical performance occurs

temporary

repeated exercise in the new environment gradually improves physiological functions and physical performance

HR, core temp, skin temp, perception of intensity are all

higher in a warmer environment than a cooler environment

During acclimatization, body functions gradually return to normal with

7-10 exposures of 45-90 minutes

key to these changes is a gradual increase in sweating rate, which facilitates body cooling

Girls and boys who live in the tropics show

considerably higher sweating rates and lower body temps for a given physical task than age-matched children who live in more temperate or cold environments

Children and adolescents take

longer to acclimatize than adults

Adults have a higher

RPE than children in warmer environments

Team travel

need to allow longer time for acclimatization and possibly a lighter workout schedule during that time

Responses to cold in water

with age, cooling rate slows

younger children get colder faster