Fatique and Excercise

8/6/2019 Fatique and Excercise

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What is Fatigue?

Temporary loss of strength and energy resulting

from hard physical or mental work; "growing

fatigue was apparent from the decline in theexecution of their athletic skills

Feeling of tiredness or weariness usually

associated with performance decrement


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What is Fatigue?

A feeling of tiredness or weariness resulting in a

decreased capacity for physical and mental work

A condition that results when the body cannot

provide enough energy for the muscles to

perform a task

Physical weariness resulting from exertion


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Fatigue

Fatigue is caused by:

- The type of activity

- Muscle Fibre type (White fast twitch/Red slow twitch)

- The type of muscle contraction

The intensity of exercise

The duration of exercise

The level of fitness


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Types of Fatigue

Local pain or heaviness at the muscle eg:

sore bicep from doing 100 bicep curls

General can be both physical and mentalfatigue, eg: exhausted from training

Long term over training and will lead to

injury


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Fatigue refers to the inability to continue

exercise at a given intensity

decrease in muscular performance usually seen as a

failure to maintain or develop a certain expected force

or power.


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Central versus Peripheral

Where does fatigue occur?

Central fatigue

Proximal to the motor unit

Peripheral fatigue

Residing within the motor unit


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Central Fatigue

Brain and spinal cord; CNS fatigue

Studies that used voluntary exhaustion and then

additional electrical stimulation

After voluntary exhaustion, electrical stimulation

evoked sizable force production

Central location of fatigue


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Peripheral Fatigue

Fatigue occurring within the local motor unit;

local fatigue

Studies that fatigued a muscle with electrical

stimulation to the point of no muscle twitch

Muscle action potentials were relatively unaffected

Peripheral location of fatigue (but not at the NMJ)


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So, where does fatigue occur?

In both central and peripheral locations. The location of fatigue is intensity-dependent

Lower-intensity, longer duration fatigue will primarily

occur centrally Higher-intensity, short duration fatigue will primarily

occur peripherally

Example Why do we slow down during the course

of a 1600 m race? Do we slow down?


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Causes of Fatigue

1. Fatigue of energy generating systems within

and external to muscle

2. Accumulation of metabolic by-products &failure of the muscular contractile mechanism

3. Disturbances to homeostasis

4. Central or peripheral nervous system

dysfunction


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1. Fatigue of energy generating

systems

within and external to muscle

Muscle glycogen depletion

Liver glycogen depletion

Depletion of fat stores


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Depletion of Fuels

CP and Glycogen is the dominate fuel used for high intensity activities.

Once these fuels run out your body can no longer work at high intensityand must resort to fats. This is not as efficient and causes the athlete toslow down or stop.

CP stores will last continually for 10 seconds.

Your body has enough Glycogen stores for 90 180 minutes of continualexercise.

Anaerobic glycolysis will last continually at high intensity for 30-100seconds or for as long as the individual can with stand the increasing byproducts

High intensity activities require fast twitch muscle fibre (white) thatfatigue faster than slow twitch (Red).


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2. Accumulation of metabolic by-

products & failure of the muscular

contractile mechanism

Lactic acid accumulation Phosphocreatine depletion and phosphate

accumulation

Hypoxia/impaired of oxygen delivery Disturbance to calcium metabolism


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Disturbance to calcium metabolism

Both mechanisms thought to

be important in developmentof fatigue during prolonged

exercise


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By-Products

ADP

Inorganic phosphate (Pi)

Pyruvic Acid

Lactic Acid (LA)

Hydrogen ions (H+)


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By-Products

ADP

Produced by the break down of ATP

By-ProductInorganic Phosphate (Pi)

Produced from the breakdown ofCP

Pi is leading cause of fatigue in muscles


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By-Product

Pyruvic Acid

Formed when the body creates ATP through

Anaerobic glycolysis.

Pyruvic Acid will not cause fatigue and canactually be used to create ATP when there is

plenty of oxygen present. Stage two of aerobic

system, Krebs Cycle


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By-Product

Lactic Acid

Lactic Acid is produced when Pyruvic Acid is not converted toATP through Krebs cycle, from high intensity anaerobicactivity.

Lactic Acid does not cause muscle fatigue but will increase pH. Increased pH will not cause muscle fatigue but will increase

recovery time.

LA will inhibit key enzymes from working producing slowerreaction times.

LA will inhibit calcium which is needed for musclecontractions.

LA can be used to produce ATP if oxygen is present throughKrebs cycle. LA can be good and produce ATP


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By-Product

Hydrogen ions (H+)

By-Product of Anaerobic Glycolysis

Inhibits muscular contractions.

Increases pH.

Inhibits enzymes that assist glycolysis


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3. Disturbances to homeostasis

Electrolyte concentrations and theircompartmentalisation

Concentrations of glucose in blood, muscle and

other tissues (e.g. brain) Muscle and systemic pH and osmolality

Temperature (especially muscle and brain)

C

oncentrations of FFA Blood and plasma volume

Hormone concentrations


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Dehydration

Loss of fluid from

- Sweat, the bodies natural response tothermoregulation

- vasodilation, the increase in size of capillaries toreduce heat.

Effected by

- Duration of exercise

- Environment eg. hot day, humid

- Athletes acclimatisation to conditions


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Dehydration will result in

Continual loss of water will increase body temperate.

An increase in body temperature will require the

body to increase sweat production and vasodilation.

This will result in more loss of water and higher

temperatures

Results in fatigue


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Effects of Dehydration

Cramps

Heat stress

Heat stroke

Fatigue


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Guidelines to avoid Dehydration

Be well hydrated before exercise up to several hours prior toexercise

Do not wait until you are thirsty as an indicator to dehydration

Cold water is absorbed faster

Drink at least 500ml 30 minutes before exercise Drink at least 200ml every 15 minutes while exercising

Drink at least 500ml to 1 litre of water after exercise

1 kilo of weight loss during exercise = 1 litre of water loss


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4. Central or peripheral nervous

systemdysfunction

Positive inputs External stimulation

Crowd

voice

Other competitors

Negative inputs Pain (e.g. muscles,joints)

Sensations of

breathlessness

Fatigue

Low brain glucoseinputs


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What factors affect the time to onset

of fatigue?

Intensity, duration and pattern of exercise

Fitness

Age

Body Condition

Environmental conditions

Heat, heat & humidity or cold

Altitude

Pollution


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Indicators of fatigue

Ataxia, stumbling, unwillingness to exercise

Pain

Weakness

Hyperthermia

Low blood glucose

Hypovolaemia

Low BP

Nerve dysfunction


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Indicators of fatigue

Hypoglycaemia

Muscle glycogen depletion

Liver glycogen depletion

Changes in muscle EMG output

Dehydration

Hypovolaemia

Electrolyte loss

Acid-base disturbance


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Fatigue versus Exhaustion

FATIGUE

Able to restart exercise

after a short restPhysiologically normal

Risk of pathology low

EXHAUSTION

Not able to continue to

exercise

Physiological extremes

Pathological changes


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Definitions of Exhaustion

Extreme fatigue

Serious weakening and loss of energy

The act of exhausting something entirely The depletion of energy stores resulting in

muscle fatigue to the point where physical

activity cannot be performed


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Recovery

The aim of recovery is to minimise the effects offatigue

It aims to

- Replenish CP and ATP stores

- Breakdown and remove LA

- Restore muscle and liver glycogen

- Rehydration replace lost water and electrolytes

- Repair damaged muscle tissue- Reduce oxygen debt


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Passive recovery

Athlete remains still or lies on the ground

Best for

- Replenishing muscle PC- Is the faster form of recovery

- 70% of PC restored in 30 seconds

- 95 % of PC restored in 120 seconds


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Active Recovery

Involves athlete moving walking after exercise.

This pumps oxygen to the working muscle

Oxygen is essential in:

- Breaking down and removing LA- Removing H+

- Removing Pi and removing

50% removal of LA takes 30 minutes with Passive recovery

50% removal of LA takes 15 minutes with Active Recovery

Fatique and Excercise

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