Muscular Activity

1
Muscular Activity

• Metabolism
• Supplies the energy needed to slide the actin
  filaments over the myosin filaments. It is a
  chemical process of converting food into
  mechanical work and heat.
• Some mechanical work is consumed by the body
  while other is consumed by physical activity
• Basic source of energy for contraction of the
  muscle is glycogen or glucose which is abundant
  in the blood
• Sources of energy (next time)

2
Energy

• Metabolism - Sources of energy (see Figure 8-2
  Sanders McCormick (7th ed)
• First 3-5 secs
• adenosine triphosphate (ATP)-a high energy
  phosphate compound is mobilized. It breaks down
  to adenosine diphosphate (ADP) which releases
  energy.
• ATP ? ADP P (phosphate radical) free energy
• ATP Regenerated
• To continue muscular activity, ATP must be
  regenerated
• creatine phosphate ADP ? creatine ATP
• creatine phosphate is high energy existing in
  small amounts in muscles
• Depletion of creatine phosphate occurs in about
  15 sec
• Blood glucose or glycogen is mobilized. Glucose
  is a blood sugar which is converted by various
  stages first into pyruvic acid.

3
Energy

• Metabolism further breakdown may be
• Anaerobic work if O2 is not supplied to the
  muscle, pyruvic acid is converted into lactic
  acid while ATP is regenerated. Lactic acid
  accumulation causes muscle fatigue and pain
• glucose 2 phosphate 2 ADP ? 2 lactate 2 ATP
• Aerobic work if O2 is supplied, pyruvic acid is
  broken down into water and carbon dioxide,
  releasing large amounts of ATP
• glucose 38 phosphate 38 ADP 6 O2 ? 6 CO2
  44 H2O 38 ATP
• Oxidation of pyruvic acid in aerobic work
  involves enzymes, co-enzymes, and fatty acids
  (Krebs cycle, figure 3.4 Pulat)
• O2 is key to efficient work. Its supply requires
  more blood be pumped to muscle per unit time as
  well as heavier breathing to oxygenate blood
• Kilocalorie (kcal) most common measure of
  energy requirement for physical activity
• Resting energy ? 0.3 kcal per minute for man of
  about 154 lbs
• Resting male (laying down and no digestive
  activity) ? 1700 kcal/day
• Resting female (laying down and no digestive
  activity) ? 1400 kcal/day

4
Energy

• Metabolism
• Basal metabolic rate (BMR) amount of energy
  needed per unit of time to sustain life
• Total metabolism equals sum of
• Basal metabolism
• Activity metabolism
• Digestive metabolism (10 sum of basal
  activity)

5
Supporting Systems

• Respiratory Response
• Nose and mouth, pharynx, larynx, trachea, lungs
  (consisting of bronchi and bronchioles, alveolar
  ducts, alveolar sacs, and alveoli)
• Primary function is to expose a large volume of
  water-saturated air to a large volume of blood to
  facilitate exchange of gases between air and
  inhaled air
• Gas exchange 70-90 m2 for average adult (surface
  area)
• At rest, 250 ml of O2 is absorbed and 200 ml of
  CO2 expelled
• Lung capacity
• 7-8 L for tall athletic young male
• Women 10 less
• Untrained 60-80 of volume

6
Supporting Systems

• Circulation
• Heart acts as double pump blood vessels outside
  the heart can be categorized into 2 classes
• Pulmonary vessels transport blood from the
  right ventricle of the heart through the lungs
  and back to the left atrium of the heart
• Systemic vessels transport blood from the left
  ventricle of the heart to all the other parts of
  the body including the head and lower body back
  to the right atrium
• Pulmonary and systemic ? peripheral circulation
• Kidneys remove waste (toxic) from the blood
• Liver, lungs, skin intestines also eliminate
  waste
• Arteries carry blood away from the heart
• Veins carry blood to the heart
• Nutrition
• Ingestion, digestion, absorption, and utilization
  of nutrient substances
• Provides necessary fuel and chemicals for
  physical activity

7
Muscular Activity

• Dynamic activity characterized by rhythemic
  contraction and relaxation of the muscles
  involved
• Example turning a handwheel to open a valve
• Alternating tension and relaxation allows more
  blood to circulate
• Static activity characterized by a prolonged
  state of contraction, which restricts blood flow
  to muscles
• Example holding a box in static posture
• Since no glucose or oxygen are being received
  activity wont last long
• Design Element Dynamic vs. Static
• Compared to dynamic effort, static effort will
  require longer rest periods
• Static effort could result in employee complaints
  and turnover
• Designers should minimize job elements in a
  process with static loading

8
Energy Cost of Work

• Energy demands increase with the onset of
  physical work. Increase depends on
• Physical conditioning
• Intensity of activity
• Gender
• Body weight
• Cardiovascular response
• At rest
• Heart rate (HR) 60-85 beats per minute
• Normal resting blood leaves lungs 97 saturated
  ? breathing harder will not increase O2 in
  muscles alone
• At work
• Increase cardiac output to increase O2 to
  muscles, more blood must flow thereby increasing
  cardiac output
• Heart rate increases - pumping actions
• Stroke volume volume per beat (rest 5 L/min
  hard work 25 L/min or more)
• At 40 of a persons max capacity stroke volume
  stabilizes while HR increases

9
Energy Cost of Work

• Cardiovascular response
• Oxygen lag
• Fig 3.5, p. 34, Pulat
• O2 and heart rate are linear under submaximal
  work (fig 3.6, 3.7, 3.8 Pulat)
• Violated when
• Arms over head
• Hot environments
• Increased blood pressure (BP) consequence of
  increased cardiac output
• Adrenal glands release catecholamines (hormones)
  that strength HR and increase BP
• BP is necessary to fill heart (note _at_ 120
  beats/min, heart has ½ sec to fill between
  strokes)

10
Energy Cost of Work

• Redistribution of blood (Sanders McCormick, p.
  231)

Blood Flow Distribution () Blood Flow Distribution ()
Part of body Resting Heavy Work
Muscles 15-20 70-75
Skin 5 10
Brain 15 3-4
Bones 3-5 0.5-1
Kidneys 20 2-4
Digestive System 20-25 3-5
Heart muscle 4-5 4-5
11
Energy Cost of Work

• Physical work capacity workers capacity for
  energy output function of
• Food, oxygen, sum of energy provided by aerobic
  and anaerobic process
• Working at 30-40 of ones maximum aerobic power
  in 8 hour shift causes notable muscular fatigue
• Energy cost of specific activities
• O2 ? energy consumption have good relationship
• Indirect measure of energy consumption
• 1 L of O2 ? 4.8 kcal
• Table 3.2 different activities kcal
• Factors
• As rate of activity increases, energy cost
  increases
• Body weight increase energy cost
• Men ? 3000-3500 kcal/day
• Women ? 2500-3000 kcal/day
• At age 65 ? 75 calories expended compared to
  those at age 25

12
Energy Cost of Work

• Keeping energy cost of work at acceptable limits
• For men
• Maximum time-weighted average of 5 kcal/min due
  to activity energy cost of work
• Maximum time-weighted HR average of 100 beats/min
• For women
• 4 kcal/min
• 90 beat/min
• Table 3.3 is a classification of work
• Factors affecting energy consumption
• Method of work
• Work posture
• Work rate or pace
• Tool design

13
Energy Cost of Work

• Fatigue
• Manifested in slight tiredness to complete
  exhaustion
• Produce lactate - which can be a good predictor
  of fatigue
• One subjective measure is the Borg-RPE (rating of
  perceived exertion) scale similar to scale
  being used in MP 1
• Scale of 6-20 are linearly related to the HR
  expected for that level of exertion
• Intended to rate exertion during dynamic work
• Motivation highly motivated underrate their
  level
• Work-rest cycle
• If workload cannot be maintained within
  recommended limits (work standards) there must be
  rest
• Some charts have been developed to determine
  amount of rest required

14
Rest Allowance

• (Kodak, 1986)

Example Someone working 10 minutes _at_ VH level
get 80 rest or 8 minutes
L M H V EH
15
Rest Allowance

• Murrell (1965)
• Solve Problem 3 in Pulat
• Using Murrell and method in text book

16
Strength and Endurance

• Strength the maximum force that one can exert
  voluntarily (kilograms using dynamometer)
• Static measured standing or sitting posture
• Example Pushing a button on a cell phone
• Design so that 95 of population can exceed these
  forces
• Dynamic measured during work using dynamic or
  isokinetic strength testing devices that control
  for speed of movement
• Speed of movement affects lifting ability
• Characteristics of strength
• Strength peak by late 20s, gradual decline to 75
  at age 65
• Women on average have 2/3 strength of men
• Exercise can increase by as much as 50
• Maximum grip _at_ 135 degrees of elbow flex
• Endurance ability to maintain activity over
  time
• Research says that people can only maintain
  maximum effort only briefly
• 20 of peak static over time
• 30 of peak dynamic work

17
Nervous System

• Coordinates and regulates body activities
• Responsible for the initiation and control of
  muscular activity
• The basic element of the nervous system is the
  neuron. Neuron is composed of a nerve cell along
  with a minimum of two nerve fibers.
• Dendrite brings messages to the nerve cell
  multiple dendrites may be associated with a cell
  therefore multiple paths may send signals
• Axon takes messages to another cell a neuron may
  not have more than one axon.
• Myelin coats the nerve fibers which serves to
  protect one nerve fiber's messages from another
  short-circuiting is prevented
• Synapse is the gap between the dendrite of one
  neuron and the axon of another neuron.
• Chemical/electrical process allow an impulse of
  one neuron to be passed to a succeeding on
  unaltered in 1/1000 of a second.

18
Nervous System

• Three major parts to the nervous system
• Central Nervous system which includes the brain
  and spinal cord
• Peripheral Nervous system which controls the
  voluntary activity
• Automatic system which covers the balance of the
  nervous system
• Automatic Nervous System
• Controls involuntary body activity including
  function of glands, smooth muscle tissue, and the
  heart. Includes the
• Sympathetic or thoracolumbar division stimulating
  these fibers creates small amounts of thick
  saliva, depression of gastrointestinal activity,
  and increased heart rate and occur in emergencies
  such as freight and consume energy.
• parasympathetic or craniosacral division
• For example when people are in a health threat,
  parasympathetic affect blood pressure,
  constricting of the pupils, etc.
• An axon in hand controls 3 -6 muscle fibers An
  axon in leg controls 100 -200 muscle fibers

19
Nervous System

• Peripheral Nervous System
• Controls the voluntary activity of the body
• 2 major elements are the sensory and motor
  systems
• Sensory system is responsible for conveying
  information from your senses to the central
  mechanisms sensory neurons have one axon and one
  dendrite each
• Once a message is received and processed through
  the Central nervous system, signals are passed
  down the pathways to the appropriate muscles.
  Motor neurons lie in the central mechanisms, and
  their axons travel in groups called motor nerves
• Speed of transmission
• Motor fibers 70-120 m/s
• Others 12-70 m/s
• Considering the distance between the sensory
  organs and motor organs to the central mechanism,
  it is not uncommon to have reaction times in the
  300-500 millisecond range

20
Nervous System

• Central Nervous System
• Two parts spinal cord and brain
• They are connected by the brain stem
• Spinal cord is gray matter encased in a bony
  column called the spinal column.
• contain the reflex neurons
• contains the neurons of the sensory system
• The brain
• medulla - connects the spinal cord with the
  higher centers of the brain nuclei for the
  neurons of the automatic nervous system
• cerebral cortex is the part of the brain where
  information is processed where information is
  stored most important with respect to perception
  and processing of information
• Thalamus - relay station for the brain sorts out
  messages and directs them to correct motor
  channels