it describes about the factors that limits us to tolerate from the excessive exposures of heat and also tells us about how does our body system changes with the environment and also in high altitudes..

1. Limit of Tolerance of Heat
& Acclimatization
PRESENTED BY
DR. PALAS
MPT SPORTS PHYSIOTHERAPY- 2ND
YEAR

2. What is Heat Tolerance ?

3. Heat Tolerance is the ability of a person to
physiologically adjust to a heat stress exposure.
About 4% of the population can be described as
heat intolerant; that is they do not
thermoregulate well enough to work under most
extreme conditions of heat stress.

4. Physiological thermoregulation refers specifically to
the intricate bodily responses that filter fine
adjustments to maintain a core temperature about
36.8⁰C (+/-0.5⁰C).
When exposed to hot external environments, the
physiological component of thermoregulation is a
short term response, which when repeated over time
promotes the developmental of acclimatization,
whereby a person becomes physiologically
accommodate to their new climatic environment.

5. Normal Heat Tolerance in Humans
A wet bulb temperature of 35⁰C or
around 95⁰F is much the absolute
limit of heat tolerance.

6. Thermoregulation Model

8. Factors limiting Heat
Tolerance

9. 1. Medication :
. Allergy medications can inhibit your body’s ability to
cool itself by preventing sweating.
. Blood pressure medications and decongestants may
decrease the blood flow to your skin. This also inhibits
sweat production.
. Decongestants can cause increased muscle activity,
which can raise your body’s temperature.

10. 2. Caffeine
. Caffeine is a stimulant that can increase
your heart rate and speed up your
metabolism. This can cause your body
temperature to rise and lead to heat
intolerance.

11. 3. Hyperthyroidism
. Hyperthyroidism occurs when your thyroid produces
too much of the hormone thyroxine.
.Thyroxine affects the regulation of your body’s
metabolism.
. An excess of this hormone can cause your body’s
metabolism to increase, which leads to a rising body
temperature.

12. 4. Acclimatization
. Heat acclimatization refers to the physiologic adaptive changes that
improve heat tolerance.
. Repeated exposure to hot environments, when combined with
exercise, improves the capacity for exercise with less discomfort during
heat stress.
. For an acclimatized individual, increased sweat loss increases the need
to rehydrate during and after exercise.
. A heat-acclimatized person exercises with a lower skin and core
temperature and heart rate than an unacclimatized individual because of
adjustments in circulatory function and evaporative cooling.
Unfortunately, major benefits of acclimatization to hot environments
dissipate within 2 to 3 weeks after a return to more temperate climates.

13. 5. Exercise Training
. The normal exercise-induced “internal” heat stress from
strenuous physical activity in a cool environment adjusts
peripheral circulation and evaporative cooling in a manner
qualitatively similar to hot ambient temperature acclimatization.
. Exercise training alone increases sweating response
sensitivity and capacity so sweating begins at a lower core
temperature.
. Full heat acclimatization does not occur without exposure to
environmental heat stress. Athletes who train and compete in
hot weather have a distinct thermoregulatory advantage over
those who train in cooler climates but periodically compete in
hot weather.

14. 6. Age
. Studies that consider body size and composition,
aerobic fitness level, hydration level, and degree of
acclimatization show little age-related effects on
thermoregulatory capacity or acclimatization to heat
stress.
. For example, in comparing young and middle aged
competitive runners, no age-related decrements
emerged in thermoregulatory ability during marathon
running.

15. 7. Gender
. Women and men equally tolerate the physiologic and thermal
stress of exercise when matched for fitness and
acclimatization levels. Gender differences occur for the
following four thermoregulatory mechanisms:
1. Sweating
2. Evaporative versus circulatory cooling
3. Body surface area-to-mass ratio
4. Menstruation

16. 8. Excess Body Fat
. Excess body fat negatively impacts exercise performance in
hot environments.
. Fat’s specific heat exceeds that of muscle tissue and
subsequently insulates the body’s shell to retard heat
conduction to the periphery.
When these effects are compounded by evaporation-retarding
characteristics; the added weight of sports equipment (e.g.,
football uniforms and pads); intense competition; and a hot,
humid environment, overfat athletes experience considerable
difficult regulating their body temperature.

17. What is Acclimatization ?

18. . It is the process in which an individual organism
adjusts to change in its environment (such as, change in
altitude, temperature, humidity) allowing it to maintain
fitness across a range of environmental conditions.
. Acclimatization involves a complex multi-organ
response delivering a suite of neurological and
endocrine responses.
. For people exposed to a hotter climate,
acclimatization requires active exposure comprising
two to six weeks of daily exercise for about 2hrs (or
more) in that novel climate.

19. . Proper acclimatization will help an athlete minimize
the potential for heat related problems.
. A proper acclimatization program will take 10 to 14
days and will involve gradually increasing the
exercise intensity and duration.
. A variety of physiological changes occur during the
acclimatization process, including increased sweat
rate, increased plasma volume, decreased salt content
of the sweat, lower heart rate and core temperature at
a given exercise intensity, and increased blood flow to
the skin.

20. . An athlete who is unable to be at a race site long enough to
acclimate can mimic race conditions by dressing in layers,
which acts to create a microenvironment.
. The Wet Bulb Global Temperature (WBGT) is a popular heat
stress index. The following equation is used to determine the
WBGT :
WBGT = (0.7 Twb) + (0.2 Tg) + (0.1 Tdb)
Twb - wet bulb temperature
Tg - black globe temperature
Tdb - shaded dry bulb temperature

21. . The WBGT equation is a more accurate measure of
heat stress than ambient temperature.
. The WBGT takes into account the radiant heat from
the sun (Tg) as well as the relationship of
environmental humidity (Twb) on heat stress.
. This is because the main way the body cools itself is
via sweat evaporation. The greater the environmental
humidity the more difficult it is for sweat to
evaporate.

22. Levels of Acclimatization

23. Acclimatization Continuum showing population
distribution through three levels

24. 1. Low Acclimatization
. Sedentary people, who are usually able to avoid heat exposure,
are likely to achieve relatively low levels of acclimatization for
their region.
. By predominantly spending time indoors, people in cool or air-
conditioned environments with minimal engagement in exertional
outdoor activities, will rarely have their thermoregulatory systems
challenged.
. Their consequent lack of acclimatization will render these
people at extreme risk of heat stress during heat waves when
they cannot effectively escape the heat, such as during power
failures or transport interruptions.

25. 2. Partial Acclimatization
. School children, and those who predominantly work
indoors, yet routinely undertake occasional and varying
activities in the heat, for example sport, shopping, gardening
and commuting are likely to achieve partial acclimatization.
. As the planet continues to warm and summers become
hotter, seasonal partial acclimatization will continue to
occur, and population level heat tolerance is likely to
incrementally improve, and continue to deliver partial
protection, if exposure increase is gradual.

26. 3. High Acclimatization
. At the upper end of the Acclimatization Level spectrum are,
for example, outdoor workers, and emergency and essential
service (EES) delivery staff whose activities or occupations
offer limited discretion about their heat exposure.
. In a warming climate, full acclimatization will be a vital
component to safe heat adaptation responses, and will determine
human capacity to continue functioning, particularly at high
physical intensity levels on hot days.
. Those whose leisure pursuits entail regular activity in the heat,
such as amateur sports people, are also likely to attain high levels
of acclimatization, according to the combination of their exercise
regularity and intensity, and intensity of heat exposure.

27. Acclimatization in Sports

28. Heat Acclimatization

29. Heat Acclimatization

30. . Heat acclimatization (or acclimation) confers biological
adaptations that reduce physiological strain (e.g., heart rate and
body temperature) improve comfort, improve exercise capacity
and reduce the risks of serious heat illness during exposure to heat
stress.
. The biological adaptations include integrated thermoregulatory,
cardiovascular, fluid-electrolyte, metabolic and molecular
responses.
. Heat acclimatization occurs when repeated exercise-heat
exposures are sufficiently stressful to invoke profuse sweating and
elevate whole-body temperatures.
. Generally, about 1-2 wk of ~90 min daily heat exposures are
required; but highly aerobic fit athletes can heat acclimatize.

31. . The benefits of heat acclimatization are retained for
~1 wk and then decay with about 75% lost by ~3 wk,
once heat exposure ends.
. During this period, re-acclimatization occurs more
rapidly than the initial acclimatization when re-exposed
to heat.
. A day or two of intervening cool weather will not
interfere with acclimatization to hot weather. In
addition, after achieving heat acclimatization, training
and heat acclimatization can be interspersed by every
second or third day.

32. . Aerobically trained athletes can induce heat
acclimatization more rapidly (as much as 50%)
and retain its benefits longer than athletes with
low aerobic fitness.
. Aerobic exercise training in temperate climates
can reduce physiological strain and modestly
improve exercise capabilities in the warm-hot
climates.

33. Physiological Adaptations to
Heat Acclimatization

34. . Heat acclimatization improves thermal comfort and
submaximal and maximal aerobic exercise capabilities
in warm-hot weather.
. The benefits of heat acclimatization are achieved by
improved sweating and skin blood flow responses,
improved cardiovascular stability (ability to sustain
blood pressure and cardiac output), better fluid-
electrolyte balance and a lowered metabolic rate.
. The three classic signs of heat acclimatization are
lower heart rate , lower core temperature and higher
sweat rate during exercise-heat stress.

35. Physiological
Adaptations to
Heat
Acclimatization

36. . An unacclimatized person may secrete sweat
with a sodium concentration of 60 mmol.L-1 or
higher and, if sweating profusely, can lose large
amounts of sodium.
. Athletes need to ensure that they consume
adequate amounts of sodium (via food and
beverage), particularly early in the
acclimatization process, as salt deficits can lead
to dehydration despite consuming plenty of fluids.

37. Heat Acclimatization
Strategies for Sports
persons

38. Strategies of Heat
Acclimatization
for athletes
preparing for
competition in hot
weather.

39. . Heat acclimatization in a dry environment confers a
substantial advantage in humid heat, but the
physiological and biophysical differences between dry
and humid heat lead one to expect that humid heat
acclimation would produce somewhat different
physiological adaptations from dry heat acclimation.
. If heat acclimatization needs to be induced for both dry and
humid heat, and if rapidity of induction is important, then we
postulate that first acclimatizing athletes to dry heat
(producing adaptations to sweating with some
cardiovascular benefits) and secondly acclimatizing
athletes to humid heat (likely inducing greater fluid
regulatory and cardiovascular adaptations) might be most
efficacious.

40. Altitude Acclimatization

41. . Altitude acclimatization consists of physiologic adaptations
that develop in a time-dependent manner during repeated or
continuous exposures to moderate or high altitudes.
. In addition to achieving acclimatization by residing
continuously at a given target altitude, at least partial altitude
acclimatization can develop by living at a moderate
elevation, termed staging, before ascending to a higher target
elevation.
. The goal of staged ascents is to gradually promote
development of altitude acclimatization while averting the
adverse consequences (e.g., altitude sickness) of rapid ascent
to high altitudes.

42. . Breathing low concentrations of oxygen using masks,
hoods, or rooms (i.e., normobaric hypoxia) is not as
effective as being exposed to the natural altitude
environment (i.e., hypobaric hypoxia) for inducing
functionally useful altitude acclimatization.
. For individuals ascending from low altitude, the first
stage of all staged ascent protocols should be ≥3 d of
residence at moderate altitude.
. At this altitude, individuals will experience small
decrements in physical performance and a low
incidence of altitude sickness.

43. . Short stays of 3–7 d at moderate altitudes will
decrease susceptibility to altitude sickness at
higher altitudes. Stays of 6–12 d are required to
improve physical work performance.
. The magnitude of the acclimatization response is
increased with additional higher staging
elevations or a longer duration at a given staging
elevation.

44. Physiological changes in High
Altitude Acclimatization

45. Exercise Prescription for
Altitude Acclimatization
Individuals

46. . During the first few days at high altitudes,
individuals should minimize their exercise/PA to
reduce susceptibility to altitude illness.
. After this period, if the Ex Rx specifies a target heart
rate (THR), the individual should maintain the same
exercise HR at higher altitudes.
. The personalized number of weekly training sessions
and the duration of each session at altitude can remain
similar to those used at sea level for a given
individual.

47. . This approach reduces the risk of altitude illness
and excessive physiologic strain.
. For example, at high altitudes, reduced speed,
distance, or resistance will achieve the same THR
as at lower altitudes. As altitude acclimatization
develops, the THR will be achieved at a
progressively higher exercise intensity.

48. Staging Guidelines for
Exercise at High Altitudes

49. The general staging guideline is as follows:
For every day spent >1,200 m (3,937 ft), an individual is
prepared for a subsequent rapid ascent to a higher altitude equal
to the number of days at that altitude times 305 m (1,000 ft). For
example, if an individual stages at 1,829 m (6,000 ft) for 6 d,
physical performance will be improved, and altitude sickness
will be reduced at altitudes to 3,657 m (12,000 ft). This
guideline applies to altitudes up to 4,267 m (14,000 ft).

50. Medical Considerations
for Amateur Athletes

51. . Children are not at greater risk of altitude illness than
adults and may actually be at lower risk.
. Male children and children with a greater body mass index
may be at greater risk for altitude illness compared with
other children ,though there is no correlation between
altitude illness and physical fitness.
. Certain underlying medical conditions including a history
of prematurity with respiratory distress syndrome,
pulmonary hypertension, congenital cardiovascular or
pulmonary abnormalities, current respiratory infection,
trisomy 21, and obstructive sleep apnea.

52. Medical Considerations for
Older Athletes

53. . Adults with controlled, stable chronic lung
disease can do well at high altitude but should be
prepared for exacerbation.
. Individuals with unstable cardiovascular disease
should be cautious at altitude, while those with
well-controlled disease usually do well.
. An older adult’s prognosis related to high
altitude is based on his or her medical conditions
and general physical fitness.

54. Concerns for Athletic Teams
Traveling to High Altitude

55. . Altitude training has emerged as a way to gain a tactical
advantage over the competitor.
. It entails breathing in a reduced percentage of oxygen
(hypoxia), either natural or simulated, with a goal of improved
athletic performance.
. The optimal altitude for this type of training is unknown;
however, most research studies have been conducted at
moderate altitudes (2000-3000 m).
. Altitude training can be simulated (normorbaric hypoxia)
through an altitude simulation room, tent, or hypobaric
chamber.

56. High Altitude Acclimatization
Training

57. 1. Live High, Train High
. Some team sports also have facilities at altitudes in the 1800- to 2500 m
range.
. However, there is concern that elevations higher than 3000 m can result in
loss of training intensity and subsequent muscle wasting, excess ventilatory
work, and increased likelihood of acute mountain sickness.
. While training at altitude does allow for acclimatization, endurance athletes
often are not able to train at the same intensity as compared with sea level
training.
. Another drawback of living at persistently high altitudes and returning to
sea level is the challenge of heat acclimatization back at sea level after being
at a cooler high altitude temperature.

58. 2. Live Low, Train High
. LLTH is a model of altitude training where athletes live in a
natural environment (normobaric normoxic) and are exposed
to short intervals (5-180 minutes) of simulated normobaric
hypoxia or hypobaric hypoxia.
. Intermittent hypoxic exposures are effective in pre-
acclimatization in athletes before ascending to high altitude.
. However, the effect seen on performance has been mixed,
and this strategy does not seem to improve endurance capacity
any more than training in the natural environment.

59. 3. Live High, Train Low
. With LHTL, athletes either live/recover at moderate altitude
(2000 to 3000 m; hypobaric hypoxia) or use simulated altitude
(normobaric hypoxia) and train at lower altitude or sea level.
. In addition to acclimatization, LHTL methods enhance exercise
performance at altitude and sea level as athletes gain physiological
benefits at altitude while maintaining workout volume and
intensity training at a lower altitude.
. To sustain a hypoxic erythropoietic effect with altitude
training, the athlete must accumulate approximately 300 to
400 hours by living at a minimum altitude of 2000 m for more
than 14 to 16 hours per day for at least 19 to 20 days.

60. . The optimal altitude for an athlete depends on the athlete’s sport,
current residing altitude, and altitude of the event.
. Athletes that may derive the most benefit from altitude training
are those that cover long distances with repeated high-intensity
effort.
. Hypobaric hypoxia LHTL currently provides the best
protocol for enhancing endurance performance in elite and
sub-elite athletes, while some normobaric hypoxia protocols
are effective in sub-elite athletes.
. There is some evidence that suggests nitrogen dilution
may enhance sea level performance in elite athletes,
provided a sufficient dose of simulated altitude is applied
(12-16 hours for 4 weeks at an elevation of 2500-3000 m).

61. Thank You