EXPH 387: Chapter 25; Exercise and Thermal Stress

Muscular activity: exercise maintains a constant core temperature in areas as cold as ______?

-30 C

The sweat loss for moderate-intensity exercise lasting more than one hour is between ____ and ____ L

.5 and 1.0 L

a CLO unit of ___ maintains a sedentary person at ____ Met indefinitely in an environment of ___ C and ____ % humidity

1,1 Met, 21 C, 50%

at 38-40C

1. Higher brain temps decrease central drive to exercise 2. impaired muscle activation/depressed neuromuscular drive 3. depressed GI blood flow and increased permeability of toxins

What is evaporation from skin and pulmonary surfaces influenced by?

1. SA exposed to the environment 2. temp and relative humidity of the ambient air 3. convective air currents about the body

How is exercising in the heat resulting in increased lactate accumulation

1. decrease uptake at the liver because of vasoconstriction 2. reduced muscle catabolism because increase in diverting to the periphery

Evaporation and sweating:

1. during heat loss: eccrine sweat glans secrete large quantities of sweat 2. evaporation of sweat from the skin creates a cooling effect 3. the cooled skin in turn cools the blood diverted from interior tissues to the surface

Exertional Heat Stress compared to cooler conditions

1. earlier accumulation of lactate 2. encroachment on glycogen reserves 3. premature fatigue during prolonged moderate exercise

what are the features of the peripheral thermal receptors?

1. early warning system 2. free nerve endings in the skin 3. responsive to rapid changes in heat and cold 4. cold receptors

there is a compensatory vasoconstriction in splanchnic and renal vascular beds:

1. exercise and blood flow increases 2. GI & Kidney blood flow decrease

what two ways is body temperature regulated:

1. keeps temp between 37 C +/- 1 C 2. can not turn off- only can protect the body from heat buildup or heat loss

during exercise in the heat, a competition exists between:

1. mechanisms that maintain a large muscle blood flow 2. thermoregulatory mechanisms

what are the features of the cold receptors of the peripheral thermal receptors?

1. more numerous 2. exist near the skin surface 3. initiate regulatory response to cold

two competing dements when one exercises in heat:

1. muscle requires blood to sustain energy metabolism 2. arterial blood (diverts to the periphery to transport metabolic heat for cooling at skin surface)

what are the four physical processes that facilitate heat loss:

1. radiation 2. conduction 3. convection 4. evaporation

Fluid deficits:

1. reduce the ability to dissipate heat 2. increase the rate of heat storage and CV strain

what are the early warning signs of Peripheral Thermal Receptors:

1. sends sensory information to the hypothalamus and cortex 2. evokes appropriate physiological adjustments

what are physiological mechanisms involved in

1. the transfer of heat to the periphery 2. the loss of heat from the body 3. the regulation of overall core body temperature

Maintenance of BP:

1. visceral vasoconstriction increases total vascular resistance 2. intest exercise with accompanying dehydration

in aquatic environments conduction...

1. water absorbs several thousand times more heat than air 2. water conducts heat away from the warmer body parts 3. lose more heat in water

Shivering during exercise:

1. will occur during strenuous activity if the core temp remains low 2. when shivering stops the metabolic rate of the individuals falls, shivering may not be able to prevent a decline in core temperature 3. muscle fatigue will not depress the shivering response

sweat rate can increase to ____ L/hour

2.0 L/hour

during exercise metabolism can increase ___ to ___ times above resting

20 to 25 x (1C ever 5 to 7 min)

with extreme heat ______ % of CO passes through the skin

25-30%

average cutaneous blood flow rate is about __________ mL/min in a thermoneutral environment

250 mL/min

acclimatized individuals can lose water at a rate of approximately ___ L per hour through sweating

3 L

shivering along increases whole body metabolism by __ to __ fold

3 to 5

how many kcal of heat are lost per liter of water vaporized?

580 kcals

higher heart rates at ____ submit levels of exercise in heat

ALL (this does not offset decreased SV)

temperature regulation is _______ in order to _____ BP and muscle blood

compromised, maintain

Radiation

consists of electromagnetic heat waves

Hypothalamus

contains specialized neurons that coordinate and control temperature regulation of the body

CO: Maximal Exercise

decreased SV, proportional to fluid deficit and reduced blood volume

overall Cardiac Output...

decreases

as SV ____, HR _____

decreases, increases

Conduction

direct heat transfer required molecular contact (through solid, liquid, or gas)

what is the best defense against overheating?

evaporative cooling

shivering

exercise metabolism; can produce an oxygen consumption of approx. 1200 mL/min

what increased the risk of heat illness

exercising in a dehydrated state

T/F Trained and Untrained athletes have different core temps at any given %Vo2

false they are the same

aldosterone

from kidney, increase in Na reabsorption (increase in fluid, by decrease in urine output)

Posterior hypothalamus responsible for

heat conservation

anterior hypothalamus responsible for

heat loss

Evaporation:

heat loss via water vaporizing from the respiratory passages and skin surface

how does conduction work

heat moves through deep tissues to the cooler skin surface

what does increased metabolic rate increase?

heat production

sweat remains ______ to other body fluids

hypotonic

when will core temperature rise

if the heat gain exceeds heat loss (seen during prolonged and intensive exercise)

hypovolemia from sweating _____ plasma osmolality

increases

CLO unit

index of thermal resistance

what does the CLO unit indicate

insulating capacity of any layer of air trapped between skin and clothing

shivering

involuntary muscle contractions

how is extra heat production in trained individuals lost?

larger sweat output

Football uniforms

limit heat exchange

what creates a zone of insulation?

little air movement or convection, this minimizes further conductive heat loss

Core temp during exercise: aerobically fit individuals perform _____ & _______ higher levels of hyperthermia

longer, tolerate

convection

loss of heat due to movement of air or water adjacent to the skin

As sweating increases, both water (plasma) and electrolytes are _______

lost --- blood becomes hypertonic

Ideal clothing in the heat:

most clothing is more effective in allowing evaporative heat loss (cottons and linens absorb moisture)

does radiation require molecular contact

no

loss of body water impairs exercise events that take longer than ____ minute

one minute

what does thermoregulations primarily protect against?

overheating

effects of clothing on thermoregulation

reduces radiant heat in warm environments and helps prevent conductive and convective heat loss in the cold

what is the most important factor when determining how well evaporative cooling functions?

relative humidity

sweating starts within several _______ of the start of vigorous exercise (evaporation)

seconds

Ideal clothing in the cold:

several layers of light clothing lined with various materials often provide the best benefits 1. blocks air movement 2. allows water vapor from sweating to escape 3. saturation of a garment affects heat exchange

Cardiac Output: Submaximal Exercise

similar CO in hot and cold

what does the decrease in plasma and electrolytes cause?

specific hormones are released

Thermoregulation in cold stress: vascular adjustments

stimulation of the cutaneous cold receptors (vascular adjustments, muscular activity, and normal output)

what is conduction influenced by

temperature gradient and thermal qualities of the surface

Heat transfer: temperature gradient can flow from:

the body to the environment in extreme cold, increase heat production and minimize heat loss to prevent a decline in core temp

what happens to the effectiveness of conduction, convection, radiation, and evaporation when ambient air exceeds body temperature

the effectiveness is reduced

what was the CLO unit developed by?

the military

how is excessive body fat beneficial in cold environments

the receptors are on the medial part of the body, excess body weight would create a larger barrier with the periphery

what initiates coordinated response?

the temperature of the blood heightens activity and stimulated the hypothalamus

Thermal Balance

the temperature of the body's inner tissues is dependent on the factors that add/subtract body heat

why what the CLO unit developed?

to develop standards for the insulate properties of clothing and to meet environmental challenges

T/F: almost any level of dehydration can compromise performance and the ability to maintain thermal balance

true

vasopressin (ADH)

water moves back to blood (from hypothalamus)

does a fit individual generate more total heat?

yes

what can the average cutaneous blood flow rate fall to in environments that are extremely cold

zero

what is the main physiological system maintaining thermal balance?

circulatory system

Cardiac Output

CO = SV x HR

what are compromised in hot environments?

CV function and exercise capacity

increased heat production occurs because of what two "calorigenic" adrenal medulla hormones?

Epinephrine, Norepinephrine

Thermodynamics: Max Ex: L O2- Min -1, and Max EX kcal-min-1

Max Ex: O2: 4 L, 20 Kcal

Thermodynamics: Resting O2-Min -1, and resting kcal-min-1

Resting O2: 0.25 L, Kcal: 1.3

prolonged cold exposure results in the increased release of what hormone?

Thyroxine

T/F: physiological means that regulate heat loss are the same regardless of internal or external means

True

sweat is what type of solution

a hypotonic saline solution

what does the hypothalamus act as

a thermostat

what forms the basis of the wind chill temperature index?

air flowing over the body produces a cooling effect

what accelerates heat loss?

air passing ex. riding a bike

hormonal adjustments are stimulated by:

aldosterone and vasopressin (ADH)

Other hormones that play rolls in the increased heat production?

aldosterone and vasopressin (antidiuretic)

Exertional Heat Stress: greater dependence on ____ metabolism compared to cooler conditions

anaerobic

what are changes in blood temperature detected by?

anterior hypothalamus

at what temperature does physiological symptoms become impaired?

between 38 and 40 C

in radiation the ________ is usually warmer than the _____

body, environment

relative workload determines what

change in core temperature with exercise 50% Vo2 max = 37.3 C 775% Vo2 max = 38.5 C