This document discusses factors that affect fatigue and performance in different types of exercise. For ultra-short term performances lasting 10 seconds or less, factors include muscle fiber recruitment and distribution, skill and technique. For short term performances from 10-180 seconds, accumulation of lactate and H+ leads to fatigue as anaerobic glycolysis provides most ATP. For moderate performances from 3-20 minutes, cardiovascular fitness and aerobic ATP production are key, while lactate accumulation also plays a role. Environmental and fuel factors become more important for longer performances.

1. • A variety of metabolites is generated by the
working muscles such as:
– H+
– Pi (inorganic phosphate)
• These metabolites are implicated in fatigue
because of their effect on:
– Force development on periphery
– Central fatigue
Dr. Misbah-ul-Qamar

2. • H+ competes with Ca2+ for binding sites on
troponin C
• Resulting in decreased Ca activated force &
decreased Ca sensitivity
• Maximum shortening velocity slows down &
relaxation is prolonged
• Produces burning sensation
Dr. Misbah-ul-Qamar

3. • Due to Pi accumulation, following effects are
seen
• Reduced maximum force generating capacity
• Reduced myofibrillar Ca2+ sensitivity
• Reduced Ca2+ release
Dr. Misbah-ul-Qamar

4. • As peripheral effect of metabolites, reduced
force is generated per cross bridge
• Information about contractile events at the
periphery is sent back to CNS at spinal &
supraspinal levels motor neuron activation
is modified accordingly
Dr. Misbah-ul-Qamar

5. • The decreased force and chemical stimulus of
presence of these metabolites has central
fatigue effect
• Skeletal muscle contain group III/IV affrent
(sensory) nerve fibers
• Ends of these fibers can sense both
mechanical & chemical stimuli
Dr. Misbah-ul-Qamar

6. • Under normal conditions, Type III/IV fibers are
crucial to have a normal cardiorespiratory &
hemodynamic response to exercise
• When concentration of various metabolites
increases to very high levels, feedback from
these fibers to CNS can lead to inhibition of
motor unit recruitment further reduction in
muscle force production & performance
Dr. Misbah-ul-Qamar

7. Factors affecting performance
Specific to type of performance
Dr. Misbah-ul-Qamar

8. • Success in athletic performance is due to a
complex interaction of many factors like
– Psychological
– Biochemical
– Neurological
– cardiopulmonary
Dr. Misbah-ul-Qamar

9. Factors limiting anaerobic
performances
• As exercise intensity increases, ATP supply
needed for tension development becomes
more & more dependent upon anaerobic
metabolism
• muscle fiber recruitment progresses from type
I type IIa type IIx.
• The progression moves from the most to the
least oxidative muscle fiber type
Dr. Misbah-ul-Qamar

10. • Successful power athletes (e.g., sprinters)
generally possess a large percentage of fast
muscle fibers
• Endurance athletes (e.g., marathoners)
possess a high percentage of slow muscle
fibers
Dr. Misbah-ul-Qamar

11. • Fatigue is specific to the type of task
undertaken & its duration
• Anaerobic energy sources are prominent in
– Ultra short term performance
– Short term performance
Dr. Misbah-ul-Qamar

12. Ultra short term performances
• These performances last 10 seconds or less.
• Type II muscle fibers must be recruited in such
performances
• Type II fibers are fast twitch muscles which are used in
powerful bursts of movements but they fatigue faster
• The events that fit into this category include
– Shot put
– High jump
– Long jump
– 50 & 100 meter sprints
• These events require tremendous amount of energy in
short period
Dr. Misbah-ul-Qamar

13. • Maximal performance in ultra short term
duration is limited by
– Distribution of type of muscle fiber (type II)
– Number of muscle fiber recruited (influenced by
level of motivation & arousal)
– Also affected by skill & technique (dependent on
practice)
Dr. Misbah-ul-Qamar

14. • Anaerobic sources of ATP
– ATP-PC system
– Glycolysis
• In ultra short events, energy release is
determined primarily by demand generated
via neuromuscular drive
• In such events energy release is not limited by
intra muscular energy supply
Dr. Misbah-ul-Qamar

15. In short
• The factors affecting fatigue in ultra short
term events are dependent on
– Muscular power
– Skill & technique
• Skill/ technique can be improved by practice
• Muscular power mainly depend upon
phosphocreatine & glycolysis for ATP
• Creatine supplementation may improve
performance
Dr. Misbah-ul-Qamar

16. Short term performance
• These events last from 10 to 180 seconds
• Maximal performances in 10-60 seconds range
are predominantly (> 70%) anaerobic
• Muscle fibers in action are high force- fast
twitch fibers
Dr. Misbah-ul-Qamar

17. • When maximal performance is extended to 3
minutes, there is a shift of energy source
• About 60% of energy comes from slower
aerobic fibers
• This shift causes a decrease in maximal
running speed as the duration increases from
10 to 180 seconds
Dr. Misbah-ul-Qamar

18. Energy source
• Vast majority of ATP will be derived from
anaerobic glycolysis
• Phosphocreatine system can supply ATP for
only several seconds
Dr. Misbah-ul-Qamar

19. Fatigue in short term events
• Anaerobic glycolysis will cause an
accumulation of H+ in muscle as well as
blood elevated lactate levels causing fatigue
• The elevated H+ concentrations also interferes
with continued production of ATP via
glycolysis slowing down of glycolysis
• Contractile machinery of muscle is also
adversely affected by H+ concentration
– Troponin’s ability to bind with Ca++ is interfered
Dr. Misbah-ul-Qamar

20. • In short term, all out performances in which
anaerobic energy sources provide the vast
majority of energy for muscle contraction, the
focus of attention shifts to buffering of H+
released from muscle
Dr. Misbah-ul-Qamar

21. Factors limiting aerobic performances
• As duration of maximal performance increases,
more demand is placed on aerobic sources of
energy
• Other factors which play a role in development of
fatigue are
– Environmental factors
• Heat
• Humidity
– Dietary factors
• Water intake
• Carbohydrate ingestion
Dr. Misbah-ul-Qamar

22. • Aerobic performances may include
– Moderate length performances
– Intermediate length performances
– Long term performances
Dr. Misbah-ul-Qamar

23. Moderate length performances
• Duration of these performances is 3-20
minutes
• It requires high maximal oxygen uptake
• In a 3-minute maximal effort, 60% of ATP
production is derived from aerobic processes
• In a 20 minute maximal effort, amount of ATP
from aerobic source becomes 90%
Dr. Misbah-ul-Qamar

24. • Factors limiting moderate length performance
include
• Cardiovascular system
– (delivering oxygen rich blood to the muscles)
– High cardiac output is required achieved through
maximal stroke volume+ max HR
– Stroke volume in turn is influenced by
• Genetics
• training
• Mitochondrial content
Dr. Misbah-ul-Qamar

25. • Arterial oxygen content & capillary density is
also important in moderate performance
• The arterial content is influenced by
– Arterial hemoglobin content (anemia can affect
VO2 max)
– The fraction of inspired oxygen
– PO2 of inspired air
• High altitude can affect VO2 max due to low
PO2
Dr. Misbah-ul-Qamar

26. Fibers involved in moderate
performance
• In races lasting fewer than 20 minutes, type IIa
fibers are involved in supplying ATP aerobically
• Advantage: these fibers are rich in mitochondria
• In addition to type II fibers, already recruited type
I fibers are also involved
• Type IIx fibers are also recruited that can
generate great power through anaerobic
processes
Dr. Misbah-ul-Qamar

27. • An athlete with the highest VO2 max has a
distinct advantage in moderate performances
• Reason: races lasting less than 20 minutes are
run at 90%-100% of maximal aerobic power
Dr. Misbah-ul-Qamar

28. Factor affecting moderate
performance
• Since type IIx are also recruited , lactate & H+
production are increased
• H+ accumulation also affect tension
development in exercising muscle
Dr. Misbah-ul-Qamar

29. Intermediate length performances
• Duration of these performances is 21-60
minutes
• Example: 1500m races
• Important factors in these races are
• Vo2 max
• Percentage of vo2 max
• Running economy
Dr. Misbah-ul-Qamar

30. • High VO2 max is a prerequisite for success in
these performances
• It is directly related to the rate of ATP
generation that can be maintained during a
distance race
• Athlete work at less than 90% VO2 max in
intermediate length performance
Dr. Misbah-ul-Qamar

31. • A person who can run at a high percentage of vo2
max would have an advantage
• High percentage of vo2 max ( that can be
maintained over the course of the run) is related
to concentration of lactate in the blood
• Lactate threshold is one of the best predictors of
race pace
• A high percentage of type I muscle fibers is
associated with greater lactate threshold &
higher mechanical efficiency
Dr. Misbah-ul-Qamar

32. Factors affecting percentage of vo2
max
– Heat load
– Environmental factors
• The heat load will require that a portion of CO
be directed to skin CVS is pushed to work at
maximum at any running speed
• Environmental factors include heat, humidity
& the state of hydration of runner
Dr. Misbah-ul-Qamar

33. • Other factor which come into play is running
economy
• An economical runner can move at higher speed
for same amount of oxygen than a non-
economical runner
• Better running economy may be associated with
a linear built of athlete
• Differences in running economy are due to
– Mechanical factors (muscle contraction based)
– Bioenergetic factors (ATP source based)
Dr. Misbah-ul-Qamar

34. Factors affecting intermediate
performance
• Main factors which affect fatigue in 21-60
minute run are
– Steady state vo2
– Running economy
• Steady state vo2 is in turn determined by both
vo2 max & the percentage of vo2 max
Dr. Misbah-ul-Qamar

35. Long term performances
• Duration: 1-4 hours
• These are aerobic performances which involve
little anaerobic energy production
• The longer the performance becomes, there
are greater chances that environmental
factors will play a role in the outcome
Dr. Misbah-ul-Qamar

36. • In addition to environmental aspect, fuel
(glucose) supply is crucial
• The supply is required for
– ATP generation for cross bridge cycling
– For protection of muscle membrane excitability ( by
preserving Na-K pump action)
• Glucose supply comes from
– Muscle source
– Liver carbohydrate stores
– Glucose supplementation with consumption of fluid
Dr. Misbah-ul-Qamar

37. • Fatty acids can also provide substantial fuel
during prolonged muscular work at exercise
intensity less than 60% vo2 max
• Endurance activities that are performed at
higher exercise intensities, muscle fibers must
have carbohydrate to oxidize
• In short, improvements in endurance
performance focus on the supply of
carbohydrates & oxygen to muscle
Dr. Misbah-ul-Qamar

38. Factors affecting fatigue in long
performance
– Steady state vo2
– Running economy
• Both biomechanical & bioenergetic factors for
determining running economy depend on
involvement of percentage of type I fibers also
• Diet, fluid ingestion & the ability of the athlete
to deal with heat & humidity all influence the
final outcome
Dr. Misbah-ul-Qamar

39. • In short, in case of aerobic performances, an
increased ability to transport O2 to the
muscles & a delay in the onset of lactate
production are related to improved
performance
Dr. Misbah-ul-Qamar

40. Muscle adaptation to space travel
• Changes which occur:
– There is a change in velocity of shortening of
muscle during contraction
– Reduced work capacity
• The changes are more pronounced after long
duration space flights
Dr. Misbah-ul-Qamar

41. Work capacity is reduced due to
• Fiber atrophy (more prominent in slow fibers)
– Due to selective loss of myofilaments causes myosin
cross bridge to detach sooner at the end of power
stroke
– Antigravity muscles of legs are more affected than
arm muscles
– Slow muscles (soleus) affected more than fast twitch
muscles(gastrocnemeus)
• More reliance on carbohydrate diet
• Less ability to oxidize fat
Dr. Misbah-ul-Qamar

42. • Suggested prevention of these changes during
space travel:
• High endurance exercise during space flight
Dr. Misbah-ul-Qamar

43. Age related changes during endurance
performance
• There is progressive reduction in vo2 max with
advancing age
• A decline in endurance performance is also
related to reduction in the velocity at same
lactate threshold compared to young athlete
Dr. Misbah-ul-Qamar