Environment effect during exercise

How do hormones respond to heat in order to conserve electrolytes and fluid lost in sweat?

- ADH stimulates water reabsorption from the kidney tubules to form concentrated urine during heat stress - Aldosterone increases renal tubules' reabsorption of sodium and also acts on sweat glands to reduce sweat's osmolarity to further conserve electrolytes

Which mechanisms does the body use to attempt to maintain thermal neutrality?

- Alter heat transfer to the periphery - Regulate evaporative cooling (biggest one) - Vary the rate of heat production

What are the cardiovascular responses to immersion?

- Cardiovascular workload decreases (pressure on venous system, increased venous return, more blood comes to your heart) - Plasma volume increases - Hear rate decreases (even more in cold water) - the heart cannot contract and relax fully so you can't circulate the large amount of blood. - At a given exercise effort, heart rate is lower

What factors does sweat evaporation from the skin depend on?

- Surface exposed to the environment - Temperature and relative humidity of ambient air (relative humidity exerts the greatest impact on the effectiveness of evaporative heat loss) - Convective air currents around the body

What three integrated factors regulate body temperature during cold exposure?

- Vascular adjustments (vasoconstriction, "fine tuning") - Muscular activity (more contraction to produce more heat, shivering and increased voluntary activity) - Hormonal output (increase in heat producing hormone output like epinephrine, norepinephrine, thyroxine)

Which two competitive cardiovascular demands exist when exercising in hot weather?

1. Oxygen delivery to active muscles must increase to sustain exercise energy metabolism 2. Peripheral blood flow to the skin must increase to transport metabolic heat from exercise for dissipation at the body's surface - vasodilation

How much of an increase in core temp can a person tolerate?

9F (5C) Can tolerate 18F(10C) drop

How does altitude affect fluid loss?

A depressed thirst sensation at altitude negatively affects body fluid balance. The cool, dry air causes considerable body water to evaporate as air warms and moistens the respiratory passages. Respiratory fluid loss often leads to moderate dehydration and accompanying symptoms of dryness of the lips, mouth, and throat.

What's a Gamow Bag hypobaric chamber?

A portable chamber to treat altitude sickness by simulating lower altitudes. A person rests and sleeps in the small chamber; reducing the chamber's total air pressure simulates the barometric pressure of a given altitude. Reductions in barometric pressure bring about proportionate reductions in inspired air's PO2.

How does circulation change with an increase in altitude?

A reduction in circulatory efficiency in moderate and strenuous exercise offsets benefits of acclimatization. Reduced maximum exercise blood flow results form the combined effect of decrease max HR and max stroke volume.

What factors affect heat tolerance?

Acclimatization Exercise training Age Gender Excess body fat

Which reflex would you check with patients after being bedridden for a long time?

Achilles tendon. Just know that reflexes will be affected from long periods of being bedridden.

What are some longer-term adaptations to altitude?

Acid-base adjustment Hematologic changes: an increase in the blood's oxygen carrying capacity provides the most important long-term adaptation to altitude as is due to: - Initial decrease in plasma volume - Increase in erythrocytes and hemoglobin synthesis Cellular adaptations: - Increased capillary concentration in skeletal muscle, reducing distance for oxygen diffusion between blood and tissues - Formation of additional mitochondria and an increase in aerobic enzyme concentration - Expanded oxygen storage within specific muscle fibers via increased myoglobin, which facilitates intracellular oxygen delivery and utilization, particularly at low tissue PO2

What is nitrogen narcosis?

Also called rapture of the deep. Nitrogen acts like an anesthetic gas. Similar to alcohol intoxication. Depth and pressure increases worsen it.

What happens to exercise performance with an increase in altitude?

Altitude has no adverse effects on events <2 min bc mostly anaerobic. Small improvements in endurance at altitude during acclimatization probably relate to: - Increases in minute pulmonary ventilation - Increases in arterial oxygen saturation - A blunted lactate response in exercise (lower epinephrine; impact on glucose metabolism - not enough for glycolysis, which is where lactate comes from; suppressed CNS drive)

Why does high ambient humidity make it harder for sweat to evaporate?

Ambient air's vapor pressure approaches that of moist skin. Therefore, evaporation decreases even though large quantities of sweat bead on the skin and eventually roll off. This response represents a useless water loss that can lead to dehydration and overheating.

What are the consequences of dehydration?

Any degree of dehydration impairs physiologic function and thermoregulation. When plasma volume decreases as dehydration progresses, peripheral blood flow and sweating rate decrease to make thermoregulation more difficult. Premature fatigue occurs from reduced plasma volume that increases heart rate, perception of effort, and core temperature.

What happens to blood pressure during exercise in the heat?

Arterial BP remains stable during exercise in heat because visceral vasoconstriction increases total vascular resistance.

How does motor control change with bedrest?

Movements shift from lower to upper body, weight of limbs is eliminated, neck and hips become flexed.

How much does your submax VO2 change during diving?

Not too much change.

What is the limiting factor of exercise on land and is it the same underwater?

On land it would be cardiovascular/lactate. The biggest influence on performance underwater will be ventilation. That will be the limiting factor for VO2max due to smaller lung volumes and increased density of air. Not able to get enough oxygen to the muscles, you have a set amount of oxygen and can't increase it when demand increases.

What is oxygen toxicity?

PO2 values exceed 318 mmHg. There will be visual distortion, rapid and shallow breathing, and convulsions. Tissues are not able to remove O2 from hemoglobin. Hemoglobin is then not able to remove CO2. High PO2 causes vasoconstriction of cerebral vessels.

How much does an acclimatized person sweat during exercise and what does it average on a daily basis?

Peaks at 3 L·h-1 during intense exercise in the heat and averages nearly 12 L on a daily basis.

What happens in the case of high-altitude cerebral edema (HAPE)?

Possible fatal neurological syndrome that develops within hours or days in people with AMS. It results from cerebral vasodilation and elevation in capillary hydrostatic pressures, causing movement of fluid and protein from the vascular compartment across the blood-brain barrier. Requires immediate descent to lower altitude and supplemental oxygen administration.

What are early warning signs of cold injury?

Tingling and numbness in the fingers and toes or a burning sensation in the nose and ears.

What are some medical problems associated with exercise in a hyperbaric environment?

Barotrauma - tissue injury caused by changing pressure. Gas toxicity - CO, O2, CO2 Decompression sickness - N2 bubble formation during ascent

What causes the urge to breathe?

Build up of arterial CO2 (high PCO2) - detected by chemoreceptors.

How does being bedridden affect calcium levels?

Calcium is lost in urine, less calcium is absorbed, more lost in feces. Decrease in bone density - higher risk of fractures. Increase in calcitonin - higher levels of calcium in plasma.

How do cardiac output and stroke volume change during submax exercise?

Cardiac output remains similar (because you increase heart rate) but the stroke volume becomes smaller.

Which three physiologic mechanisms are involved in heat dissipation?

Circulation: the circulatory system serves as "workhorse" for thermal balance Evaporation: sweating begins several seconds after initiation of vigorous exercise Hormonal adjustments: heat stress initiates hormonal adjustments to conserve electrolytes and fluid lost in sweat

Which regulatory mechanism takes precedence during exercise in hot weather?

Circulatory regulation and maintenance of muscle blood flow will take precedence over temp regulation, often at the expense of a spiraling core temp and accompanying health risk. You would think that the brain would send blood to the skin since it's more detrimental to allow the temp to increase, but it prioritizes an active organ and sends it to the muscles.

What are some adaptations caused by bedrest?

Continued increase in HR Decrease in baroreceptor reflex function Heart volume decreases Increase in peripheral resistance Thicker blood Loss of RBC mass Increased venules and decreased arterioles

How does excess body fat affect heat tolerance?

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. Large, overfat persons possess a smaller body surface area-to-mass ratio for sweat evaporation compared with leaner, smaller persons. They may sweat more, but they will be sweating more inefficiently. They have less sweat glands bc of the ratio so they are working harder to try and get lots of evaporation to happen, but it doesn't work. Excess body fat also directly adds to energy expended in weight-bearing activities.

What factors affect sweat-loss dehydration?

Exercise intensity Exercise duration Environmental temperature Solar load Wind speed Relative humidity Clothing

How does training affect heat tolerance?

Exercise training alone increases sweating response sensitivity and capacity so sweating begins at a lower core temperature. - Produce more dilute sweat - Beneficial response related to increase in plasma volume that occurs early in endurance training - Aids in sweat gland function during heat stress and maintains adequate plasma volume to support skin and muscle blood flow demands of exercise - Trained person stores less heat early during exercise and reaches a thermal steady state sooner and at a lower core temperature than an untrained person

What is depth limit determined by?

Gases in lungs can reduce to no smaller than residual volume. Depth limit is determined by the TLV:RV ratio. Individuals with larger TLV:RV ratios can dive deeper than those with smaller ratios.

Do humans adapt better to chronic heat or cold exposure?

Heat

How does core temperature change during exercise?

Heat generated by active muscles can increase core temperature to fever levels that incapacitate a person if caused by external heat stress alone. Within limits, increased core temp with exercise doesn't reflect heat-dissipation failure. A modest core temp increase reflects favorable internal adjustments that create an optimal thermal environment for physiologic and metabolic function.

What happens in the case of high altitude retinal hemorrhage (HARH)?

Hemorrhage in the macula of the eye produces irreversible visual defects. Probably results from surges in blood pressure w/ exercise that cause blood vessels in the eye to dilate and rupture from increased cerebral blood flow. Immediate descent to a lower elevation with supplemental oxygen or use of a hyperbaric chamber is the mandatory treatment.

* What are some immediate acclimatization adjustments to altitude?

Hyperventilation triggered by increased respiratory drive - Happens because chemoreceptors in the aortic arch and branching of carotid arteries detect reductions in arterial PO2 - This increases ventilation, raising alveolar oxygen concentration - Increase in alveolar PO2 with hyperventilation facilitates oxygen loading in the lungs Increased blood flow (cardiac output) during rest and submaximal exercise

What is meant by "live high train low"?

If you live high, train high - you won't reach max potential bc you can't put your body into a high-demand situation in training. You want to return to a lower level to train so that you can provide your body with stimulus/higher intensity.

What are physiologic adjustments during heat acclimatization?

Improved cutaneous blood flow - transports metabolic heat from deep tissues to the body's shell Effective distribution of cardiac output - appropriate circulation to skin and muscles to meet demands of metabolism and thermoregulation; greater stability in blood pressure during exercise Lowered threshold for start of sweating - evaporative cooling begins early in exercise More effective distribution of sweat over skin surface - optimum use of effective surface for evaporative cooling Increased sweat output - maximizes evaporative cooling Lowered sweat's salt concentration - dilute sweat preserves electrolytes in extracellular fluid

What has the largest effect on stroke volume in a hyperbaric environment?

Increase in afterload (hyperbaric pressure)

What happens when exercising in the cold?

Increased body heat loss isn't accompanied by increased heat production and individuals regulate at a lower core temp in the cold. Repeated cold exposure of the hands and feet brings about blood flow increases through these areas during cold stress. Metabolic heat generated by muscular activity contributes to thermoregulation during cold stress. Individual differences in body fat content exert a considerable effect on physiologic function in a cold environment during rest and exercise. The body loses heat about 2-4x faster in cool water compared with air at the same temp.

What can intense sweating for several hours do?

Induce sweat-gland fatigue that impairs core temperature regulation.

What does loss of plasma volume during dehydration do?

Initiates increases in systemic vascular resistance Reduces skin blood flow

How does the hypothalamus regulate body temperature?

It contains the central coordinating center for temp regulation within a range of 37°C ± 1°C. Temperature-regulating mechanisms are activated by either of these two: 1. Thermal receptors in the skin provide peripheral input to the hypothalamic central control center 2. Temperature changes in blood that perfuses the hypothalamus directly stimulate the hypothalamic control center

What happens in the case of high-altitude pulmonary edema (HAPE)?

It involves fluid accumulation in the brain and lungs; requires immediate descent to lower altitude on a stretcher or flown to safety.

What happens in the case of acute mountain sickness (AMS)?

It is a relatively benign condition that becomes exacerbated by exercise in the first few hours of exposure; treatment usually involves rest and gradual acclimatization.

What is decompression sickness?

It results from ascending too rapidly. There will be aching in elbows, shoulders, and knees, can cause emboli in blood. Nitrogen bubbles become trapped in body. Treat by placing diver in recompression chamber. Can prevent by using chart showing time to ascend from various depths.

What are the benefits of adequate fluid replacement?

It sustains evaporative cooling of acclimatized humans. Properly scheduling fluid replacement maintains plasma volume so that circulation and sweating progress optimally. A well-hydrated athlete always functions at a higher physiologic and performance level than a dehydrated one. Athletes must rehydrate on a regular schedule because the thirst mechanism imprecisely gauges water needs. Thirst doesn't kick in until you're very dehydrated.

Why would you use thigh cuffs on bedridden patients?

Loss of venous pump, helps with circulation.

How does exercising in the heat affect vascular constriction and dilation in different parts of the body?

Maintaining adequate skin and muscle blood flow during heat stress occurs at the expense of other tissues that temporarily compromise their blood supply. Prolonged reduction of blood flow to visceral tissue can lead to liver and renal complications that are sometimes noted with exertional heat stress.

What are the four potential avenues for heat exchange when exercising?

Radiation: objects continually emit electromagnetic heat waves - Despite cold temp, a person can remain warm by absorbing sufficient radiant energy from direct sunlight, or reflected from snow, sand, or water - Body absorbs radiant heat energy when the temp of objects in the environment exceeds skin temp, making evaporative cooling the only avenue for heat loss Conduction: direct contact until the two molecules are equal in temperature - Dependent on temperature gradient Convection: movement (for example a breeze creating flow of new colder molecules) **Evaporation: provides the major physiologic defense against overheating - Water vaporization from the respiratory passages and skin surface continually transfers heat to the environment - Cooling occurs when sweat reaches the skin and fluid evaporates - Cooled skin then cools the blood shunted from interior to the surface

How does acclimatization affect heat tolerance?

Repeated exposure to hot environments, when combined with exercise, improves capacity for exercise with less discomfort during heat stress. Optimal acclimatization necessitates adequate hydration. Full heat acclimatization doesn't occur without exposure to environmental heat stress.

What happens to aerobic capacity with an increase in altitude?

Small declines in VO2max become noticeable at an altitude of 589 m and thereafter, arterial desaturation decreases VO2max by 7-9% per 1000-m altitude increase to 6300 m, where aerobic capacity declines at a more rapid, nonlinear rate.

What is the difference stroke volume and cardiac output?

Stroke volume is the amount of blood that your heart pumps out with one beat, cardiac output is how much blood your heart pumps per minute.

What happens with an increase in altitude?

The density of air decreases progressively, PO2 decreases. Reduced PO2 and accompanying arterial hypoxia precipitates the immediate physiologic adjustments to altitude and longer-term process of acclimatization.

What plays the most important role in maintaining thermal balance?

The hypothalamic regulatory center. Peripheral receptors in the skin primarily detect cold; the hypothalamus monitors body warmth by the temp of the blood that perfuses the area.

Describe the changes in a hyperbaric environment.

The pressure underwater is greater than at sea level (hyperbaric). As pressure increases, gas volume decreases. On the descent - external pressure increases and air already in the body compresses. On the ascend - air taken in at depth expands. If breath is held while ascending, lungs may overdistend leading to spontaneous pneumothorax (lungs collapse).

How does age affect heat tolerance?

There are little age-related effects for thermoregulatory capacity or acclimatization to heat stress. Older adults do not recover from dehydration as readily from reduced thirst drive. Prepubescent children show a lower sweating rate and higher core temperature during heat stress. Children take longer to acclimatize to heat. Children exposed to environmental heat stress should exercise at a reduced intensity and receive additional time to acclimatize than more mature competitors.

What happens to maximal cardiac output and aerobic capacity during exercise in the heat?

They decrease because the compensatory increase in heart rate doesn't offset the decrease in stroke volume.

Why don't people who live at a higher altitude perform better at sea level?

They have a lower VO2max. They also have a reduced stroke volume, max heart rate, and less muscle mass. Reduced muscle mass due to less stimuli at higher altitude because you can't reach a higher % of intensity, not enough load being put on your muscles to increase in size.

How does being bedridden affect fluid loss?

Total loss of fluid from the vascular and tissue spaces is about 1-2 liters.

*Why does stroke volume decrease at a higher altitude?

Viscosity is higher, so there is a decreased preload and increased afterload (resistance).

Would it be better to leave sweat on during exercise or wipe it off with a towel?

When sweat becomes a vapor, it requires energy that can be taken from the heat at the level of your skin. It would be more optimal to leave the sweat and let it evaporate because the sweat itself doesn't cool the skin; rather, cooling occurs when the sweat evaporates.

What response do muscles have to bedrest conditions?

Without resistive exercise (even just walking) for 2-3 months - Leg muscle cross-sectional area decreases ~30% - Leg strength decreases ~50% - Shift occurs from slow to fast fiber types (because you're doing quicker short duration movements rather than anything repetitive for long duration) - Back muscles become weak (not used for stabilization), soft tissues at risk of injury - Contraction and relaxation times are decreased, fatiguability is increased Can be prevented with exercises and pressure cuffs!!

How does gender affect heat tolerance?

Women and men equally tolerate physiologic and thermal stress of exercise when matched for fitness and acclimatization levels. Gender difference occur for the following 4 thermoregulatory mechanisms: - Sweating (women have more sweat glands, start sweating at higher temperature though so they produce less sweat compared to men) - Evaporative vs. circulatory cooling (women rely more on circulatory mechanisms and men rely more on evaporative cooling) - Body surface area-to-mass ratio (women have a larger surface area, cool faster; same goes for children compared with adults) - Menstruation (body is already at a higher temperature during menstruation, won't sweat until an even higher temp)