1. Chris Jones (St Leonard’s College 2016)
Fatigue and Recovery
Chapter 6
Chris Jones (St Leonard’s College 2016)

2. Fatigue may be defined as:
“the exercise-induced reduction in the power generating capacity
of a muscle and an inability to continue the activity”.
A summary of the fatigue/recovery considerations

3. Our response to exercise and the subsequent fatigue depends on:
The type of activity – intermittent vs continuous
The intensity and duration of the activity – aerobic vs anaerobic
The muscle fibre being used – fast vs slow twitch fibres
The types of muscular contraction occurring – isometric vs isotonic
The fitness level and training adaptations of the performer

4. Types of fatigue

5. Fatigue is caused by many factors = multifactorial

6. Fuel Depletion: ATP –PC energy system
ATP is an immediate energy source but very limited (2 seconds supply)
PC occurs in limited supply at the muscles (10-12 seconds supply)
These are quick to supply ATP but just as quickly depleted - then muscle glycogen and liver glycogen is used in larger amounts.

7. Anaerobic and aerobic glycolysis
Muscle glycogen is used first during aerobic activities and then liver glycogen
Once liver glycogen runs low, muscles increasingly use blood borne fats and then stored fats
The rate of ATP resynthesis decreases quickly (50 – 100% slower) once the body switches to fats as the main fuel source – this causes slowed performances
Proteins are called upon when fat stores run low and this leads to an ever greater slowing down
Muscle glycogen levels after sustained exercise

8. Metabolic by-products:
Inorganic phosphate - reduces the contraction force of muscles and slows the release of calcium ions which also slows neural control of contractions by affecting the sodium potassium balance
(associated with ATP-PC system dominance)
ADP – accumulates during explosive activities and reduces the shortening velocity of contractions and hence decreases the power muscles can exert
H+ ions – increased amounts cause muscle acidity which slows the actions of glycolytic enzymes and the rate of glycogen breakdown. Also prevent crossbridges connecting to actin therefore reducing contraction forces
(associated with anaerobic glycolysis dominance)

9. Neuromuscular factors:
Central Nervous System Inhibition
When the brain detects local fatigue it sends inhibitory signals to stop further
muscular output. Sending fewer electrical signals will result in less forceful and
less frequent muscle contractions. This is designed to save fuel for vital
functions such as respiration and heart contraction.
Neurotransmitter depletion
The neurotransmitter substance Acetylcholine (Ach) is required to convert the
electrical signal of the nervous system, into a chemical signal in the muscles.
As the intensity of exercise increases, there comes a point where Ach release
into the synaptic cleft is reduced. This results in less muscle stimulation fewer
and less forceful muscle contractions.

10. Elevated Body Temperature:
Normal core temperature = 36.5 – 37.5 degrees celcius (optimal)
80-90% of body heat comes from muscles contracting, thus during prolonged exercise, the body’s core temperature will rise. The body must maintain a constant core temperature (thermoregulation) and so initiates cooling mechanisms.
Heat loss from the body occurs mainly by evaporation/sweating. This becomes less effective in hot (temps above 36 deg celcius) and humid environments
Evaporative cooling caused by sweat is assisted by blood being shunted towards the skin’s surface – this takes with it important fuels & oxygen and reduces waste removal rate
Decreased plasma volumes
resulting from increased
sweating cause increased heart
rate to maintain adequate blood
supply to working muscles
(known as cardiovascular drift)
A loss of 2% of body weight (just 1 kg for a 50-kg person) causes an
increase in perceived effort and could reduce performance by %.

11. Fatigue and Recovery Summary
HOW DOES IT CAUSE FATIGUE?
Energy
System
RECOVERY
DEPLETION OF PC (fuel: ATP-PC System)
Once PC is depleted ↑ reliance on LA system to
supply ATP. ATP is supplied at a slower rate ↓
amount of speed, force, power that can be applied.
ATP-PC
PASSIVE RECOVERY –
the length of recovery
required dependant on
amt PC depleted.
30secs = % PC,
180 secs = 98% PC
ACCUMULATION OF ADP
↓ contraction velocity (speed) ↓ strength, power +
speed;
causing fatigue in very high intensity activities where
ADP accumulates quickly.
ATP-PC
ACTIVE RECOVERY
MASSAGE
HOT/COLD SHOWERS
ACCUMULATION OF Pi
Inhibits the action of the cross-bridges decreasing
the force at which muscles contract: causing
fatigue in very high intensity activities where Pi
accumulates at a fast rate.
ATP-PC
ACTIVE RECOVERY
MASSAGE
HOT/COLD SHOWERS

12. Accumulation of H+ ions in the blood (> than 4mMol) leads to:
HOW DOES IT CAUSE FATIGUE?
Energy
System
RECOVERY
H+ ION ACCUMULATION
Accumulation of H+ ions in the blood
(> than 4mMol) leads to:
↑ muscle acidity (↓ pH)
2. ↓ pH impedes action of glycolytic enzyme function, ↓ rate at which glycogen is broken down to form ATP ↓ force of musc. contractions (power / strength) and speed.
3. Cross-bridge coupling (myosin and actin binding) prevented by accumulation of H+
Anaerobic
glycolysis
ACTIVE RECOVERY
utilising same activity (muscle
groups) below 75% HR max to
maintain elevated heart rate and
oxygen delivery to the muscles to
remove metabolic by-products.
Prevents venous pooling and skeletal
muscle pump assists venous return.
MASSAGE:
↑ blood flow to remove LA and
metabolic by-products
HOT/COLD SHOWERS:
Vasoconstriction + vasodilation ↑
blood flow to remove LA and
NOTE:
LACTIC ACID DOES NOT CAUSE FATIGUE; however, the presence of lactic acid decreases
the athlete’s ability to recover. Levels of lactic acid are measured as they are an indirect
measure of levels of H+ and direct measure of rate of anaerobic glycolysis.

13. DEPLETION OF GLYCOGEN ↓ availability of glycogen, ↑ reliance on
HOW DOES IT
CAUSE FATIGUE?
PREVENTION
RECOVERY
↓ availability of
glycogen,
↑ reliance on
triglycerides to
produce ATP.
Fats require more
O2, thus athlete must
↓ intensity.
CHO Loading:
Consume grams CHO /
kg of body weight 48 – 72 hours
prior to event and reduce
exercise levels (taper).
2. Low GI pre-event meal.
3. High GI during event
(carbohydration):
Consume 250mL / 15mins of
isotonic fluid (8% CHO) during
event (eg- powerade)
Up to 24 to 48 hours
Consume 50g of High GI CHO (1gram/kg BM) and Protein (4:1 ratio) within 15mins of exercise finishing.
2. Continue to consume 25-50g CHO every 15mins. After this 50g CHO / 2hrs.

14. PREVENTION / RECOVERY STRATEGIES
DEHYDRATION
HOW DOES IT CAUSE FATIGUE?
PREVENTION / RECOVERY STRATEGIES
Occurs when fluid loss exceeds fluid
replenishment.
• Elevated body temperature leads to ↑ blood
redistributed to the skin in an effort to cool down
(capillaries to the skin vasoldilate).
• ↓ blood delivered to the muscle ↓ amount of
oxygen avail for aerobic production of ATP ↑
reliance on LA system and metabolic by-products
accumulate.
• Blood ‘thickens’ (plasma volume ↓) becoming
harder to pump and SV ↓ resulting in ↓ blood
delivered to the muscle ↓ amount of oxygen
available for aerobic production of ATP ↑ reliance
on anaerobic glycolysis and metabolic by-products
1. ADEQUATE HYDRATION BEFORE THE EVENT:
2. HYDRATE DURING EVENT
3. CONSUME 250mL OF SPORT SRINK DURING EVENT.
4. PERFORM PRE AND POST WEIGHING TO MONITOR FLUID LOSS (1kg = 1 litre)
5. USE ICE VESTS TO PREVENT OVERHEATING
6. AVOID TIGHT AND DARK COLTHING.

15. Complete the textbook Review questions p171 - 172
Answer the following:
1. An elite athlete completes the 1500m running race. After the race, the
athlete consumes a plate of pasta with tomato and vegetable sauce, an apple
and banana.
a) What is the athlete restoring in the muscle by eating this type of meal?
b) For the greatest benefit, when should this meal be eaten?
c) Explain one reason why it is important for athletes to include protein in their diet.
2a) Identify one physiological factor, other than glycogen depletion, which might
lead to exhaustion when running a marathon
b) State the approximate time taken to completely replenish muscle glycogen after
exhaustive exercise such as a marathon
c) Discuss the similarities and differences between the ‘skeletal muscluar pump’
and the ‘vascular pump’
3. Exercise physiologists believe skeletal muscle is a likely site of fatigue during
exercise. List three causes of fatigue found at the muscular level, explain how it is
linked to fatigue and identify the appropriate method for recovery.

16. Past Exam Questions 1
Which of the following would you expect to observe immediately after the conclusion of a 1500-metre running
race?
A. decrease in both body temperature and hydrogen ion concentration
B. decrease in blood lactate concentration and increase in oxygen levels
C. decrease in muscle glycogen and increase in blood lactate concentration
D. increase in muscle glycogen and decrease in respiratory carbon dioxide levels 2
Which of the following would be most likely to cause fatigue in an 800-metre running race?
A. depletion of liver glycogen stores
B. depletion of intramuscular fat stores
C. accumulation of lactate ions in the blood
D. accumulation of hydrogen ions in the blood 3
Which of the following is aided by a passive recovery?
A. liver glucose replenishment
B. blood glucose replenishment
C. muscle glycogen replenishment
D. muscle phosphagen replenishment

17. 4 One of the strategies used by the players in the diary above would lead to an increase in oxygen to working muscles, removal of waste products and assist in the prevention of delayed onset muscular soreness (DOMS). In which time period did this occur? A. 0–5 minutes post game B. 10–30 minutes post game C. 30 minutes–1 hour post game D. 1 hour–24 hours post game 5 The physiological benefit of using ice as part of their recovery strategy would be A. prevention of delayed onset muscular soreness. B. vasodilation of the blood vessels which leads to decreased swelling. C. vasoconstriction of the blood vessels which leads to decreased swelling. D. ‘blood shunting’ or vasodilation and vasoconstriction of the blood vessels.
Use this information to
answer questions 4 and 5

18. 6 During the Australian Open Tennis championships in January 2006, temperatures exceeded 40oC and players were susceptible to dehydration. Which of the following may result from a player becoming dehydrated? A vasodilation or peripheral blood vessels B increased electrolyte levels and heat stress C reduced blood volume and increase in core body temperature D increased blood volume and increase in core body temperature 7 Other than depletoio of muscle glycogen stores, what are the main causes of fatigue for endurance athletes? A PC depletion and lactic acid accumulation B dehydration and elevated body temperature C pyruvic acid accumulation and dehydration D increased levels of ADP and hydrogen ions 8 What are the main functions of nutrition during recovery? A restoring muscle glycogen, replacing lost fluids and electrolytes and manufacturing new muscle and red blood cells in the repair and adaptation process B restoring muscle glycogen, replacing lost fluids and electrolytes and relaxation of muscles through massage C replacing lost fluids and electrolytes, allowing the immune systems to handle any damage caused by the exercise bout and preventing delayed onset muscle soreness D replacing lost fluids and electrolytes, manufacturing new muscle and red blood cells in the repair and adaptation process and preventing delayed onset muscle soreness

19. 9
Researchers have recently demonstrated that lactic acid accumulation is unlikely to inhibit muscle contraction force. Which option is more likely to cause a decline in muscle force production in a climber attempting to sustain a near maximal muscle contraction?
A an increase in muscle calcium concentration
B an increase in muscle phosphate ion concentration
C a decrease in muscle hydrogen ion concentration
D an increase in muscle lactate ion concentration 10
At the Commonwealth Games, a VCE Physical Education student noticed that the long jumpers sat down and rested in between their jumps, but the 200m sprinters did an active recovery of stretching and light exercise after their heat. Evaluate the physiological benefits of these two types of recoveries to the athletes.
Rest Recovery
Active Recovery

20. 11
The graph below shows a recreational runner’s blood lactate concentration measured during a running treadmill
test until exhaustion. The speed was increased every minute and the lactate concentration was measured at the
end of each minute.
a. At what speed does the lactate inflection point occur? (1 mark)
b. Why does the lactate inflection point occur? (1 mark)
c. Explain the relevance of the lactate inflection point to an endurance athlete. (3 marks)
Lactate
(mmol)
Treadmill speed (km/h)

21. 12
On the graph provided above, shade the region of excess post exercise oxygen consumption (EPOC)
i. Identify what would happen to EPOC after 30 minutes of running at the same pace in an outside temperature of 35oC compared to 20oC.
ii. Outline why this occurs
What strategy could an athlete use to reduce EPOC? Give a practical example of how this could be achieved.
Strategy
Practical example

22. 13
a. A marathon covers a distance of 42.2 km. Typically, a marathon runner’s speed declines at the 35km point during a race. Identify the most likely cause of fatigue for the runner at the 35km point and briefly outline how it causes fatigue.
b. A 400m sprinter’s speed declines throughout the race. Other than hydrogen ion accumulation, explain two possible causes of speed decline.