Temperature Regulation

Temperature Regulation During Exercise

• Normal body temperature is 37°C
• A larger difference between skin temperature and core temperature facilitates heat loss.
• It is more challenging to lose heat in a hot environment.

Heat Stress

• Cutaneous vasodilation increases blood flow to the skin, which increases heat loss through radiation.
• Sweating increases heat loss through evaporation.

Cold Stress

• Shivering increases muscle activity, resulting in increased heat production.
• Cutaneous vasoconstriction reduces blood flow to the skin, decreasing heat loss through radiation.
• The release of catecholamine and thyroxin increases metabolic rate, which increases heat production.

Mechanisms of Heat Production

• Voluntary heat production through exercise accounts for 70-80% of energy produced and subsequently lost as heat.
• Involuntary heat production includes shivering and nonshivering thermogenesis, which is due to hormones.
• Involuntary mechanisms account for 60% of total energy and heat production.

Heat Gain During Exercise

• Heat gain during exercise primarily occurs through muscular activity.
• Sun and air temperature contribute radiation, humidity, and temperature.

Heat Loss During Exercise

• Radiation involves the transfer of heat from one surface to another.
• Conduction is not as important during exercise, due to muscle contraction.
• Convection includes heat loss through wind, fans, and air movement during running; it also includes muscle blood flow convection
• Evaporation occurs via sweat loss.

Factors Affecting Evaporation

• Air temperature and relative humidity affect evaporation.
• Convective currents (wind) influence evaporation.
• The amount of exposed skin impacts evaporation.

Environment and Heat Loss

• Heat is easily lost through radiation and evaporation indoors.
• Heat loss is more difficult via radiation and evaporation outdoors, potentially increasing the risk of hyperthermia.

Relationship Between Exercise Intensity and Core Temperature

• Increased intensity is associated with increased muscle mass usage, heat production, core temperature, and the risk of hyperthermia.
• Core temperature increases as exercise intensity increases.

Mechanism of Heat Loss During Exercise

• Radiation contributes the most to heat loss during rest.
• Evaporation becomes more important during exercise.

Ambient Temperature's Effect on Heat Loss

• Less heat is lost through radiation and transferred through evaporation as temperature increases.
• Hot air temperature reduces the skin-air temperature gradient, causing heat loss via radiation and increased heat loss via evaporation.
• Cold air temperature increases the skin-air temperature gradient, increasing heat loss via radiation and decreasing heat loss via evaporation.

Exercise Performance in a Hot, Humid Environment

• Central nervous system dysfunction, also known as central fatigue happens due to an increased core temperature.
• Cardiovascular dysfunction includes an increased sweat rate, decreased plasma volume, venous return, end-systolic volume (ESV), stroke volume (SV), and cardiac output (Q); this results in decreased muscle and skin blood flow, leading to decreased mean arterial pressure (MAP).
• Accelerated muscle fatigue involves increased MG use, LA, and H+ production leading to impaired exercise performance.

Reducing Risk of Heat Injury

• Risk of heat injury can be reduced by being aware of environmental factors.

Effect of Clothing on Core Temperature

• Clothing impacts how much heat can be lost, and type of clothing affects core temperature

Effect of Acclimation on Heat Tolerance

• The body adapts to heat exposure, which decreases core temperature

Lower Core Temperature

• Lower core temperature comes from increased plasma volume, sweat rate, and heat loss

Altitude and Air Pollution

• Lower atmospheric PO2 has implications for VO2 max and performance.
• Lower barometric pressure, not lower %O2 in air, is the key factor.
• Lower partial pressure of oxygen (PO2) in the arterial blood impacts O2 levels in arterial blood.
• Lower air temperature increases risks related to cold stress and injury (hypothermia, frostbite).

Hypoxia and Hypoxemia at Altitude

• Hypoxia refers to lower air PO2
• Hypoxemia refers to lower arterial PO2
• Low PO2 in air leads to low HbO2 saturation, low PO2 arterial, and low O2 content decreasing O2 delivery, known as a-vO2 difference.

The Effect of Altitude on VO2max

• At sea level during maximal exercise: VO2max = 20 L/min x (200 ml O2/L blood – 50 ml O2/L blood) = 3000 ml/min
• At an altitude of 4000 m during maximal exercise: VO2max = 20 L/min x (150 ml O2/L blood – 50 ml O2/L blood) = 2000 ml/min

Changes in VO2 Max with Increasing Altitude

• VO2 max decreases by about 6% per 1,000 m of elevation.
• Extreme altitude have a greater effect on VO2 max than moderate altitude

The Impact of Altitude on VO2 Max

• Reduced alveolar a O2 decreases atmospheric PO2 which affects VO2 max

Equation Indicating the Relationship on Altitude

• VO2 max= HRmax x SVmax (same) x aO2-vO2max (↓ arterial O2 content, ↓ 02 extraction by Muscle and venous O2 content)

Altitude and Performance: Short Events

• Performance in short events improves at a higher altitude, because anaerobic events do not need as much oxygen
• Lower air density means there is less air resistance

Altitude and Performance: Long Events

• Lower VO2 max will result in poorer aerobic performance.
• Living and training at an altitude may improve endurance performance

Heart Rate (HR) Response to Submaximal Exercise

• Heart rate is higher at the same intensity (VO2) to compensate for lower a-vO2 at altitude.

Ventilation Response to Submaximal Exercise

• Lower atmospheric PO2 at altitude means there is less O2 per liter of air.
• At the same VO2 intensity, ventilation (VE) is higher to compensate for lower O2 per liter of air.

Adaptation to Altitude

• Exposure to altitude increases RBC production.
• Reduced PO2 in arterial blood = increased EPO, increased RBCs, increased HbO2, and increased PO2 in arterial blood.

Altitude Training

• Training at a higher altitude is useful for endurance competitions.
• Combining benefits of altitude exposure with sea level training is ideal

Live High, Train Low Method

• With the live high, train low method EPO and VO2 max is achieved
• Exercise intensity is elevated, due to training at low altitude,
• Decrease in arterial levels increase EPO and Hemoglobin levels

Carbon Monoxide Effects on VO2 max

• CO raises HbCO, reduces HbO2, and decreases arterial O2 reducing VO2 max

Factors regarding Adaptations to Training

• Overload: Stressing the body past a 'normal' capacity
• Specificity: Adaptations will generally be specific to exercise.

Endurance Training and VO2 Max

• Typical training leads to a 15-20% improvement.
• High-intensity training leads to a 30-50% improvement.
• Prolonged training leads to a 40-50% improvement.
• Athletes with low-conditioned VO2 max can undergo up to 50% improvement.
• Athletes who are highly trained can only get a 2-3% improvement.
• Genetics account for 50% of VO2 max.

Muscle and Cardiac Adaptation

• Why does training increase VO2 max
• Heart gets biggern and stronger, improving oxygen and extracting capabilities

Adaptations of Increasing VO2 max

• Initial rise due to cardiac adaptations
• Occurs later due to muscle adaptations
• Higher Q Max, not HR Max
• Occurs early in training, A-VO2 max occurs later

Factors effecting Cardiac Output

• Cardiac output stays the same but stroke volume increases
• Increase in the SNS and the Frank Starling mechanism increases stroke volume
• Increase in MAP slightly reduces stroke volume
• increase In venous return and EDV increase stroke volume

Increase in SV Maximally

• The heart undergoes major adaptations to strength, resulting in increased SV
• At max: Increase SV max and VO2 max

Submaximal Exercise

• Maintaining the same oxygen uptake and Q
• Increased blood plasma and return increases stroke volume
• Increased contractility to ^SV
• Decreased TPR = decreased MAP, stroke volume

Factors that effect A-VO2 max

• Muscular adaptations improve O2 capacity
• Mitochondria, myoglobin, and capillaries help
• Increase in capillaries delivers more O2 to muscles
• Increases in mitochondrial and Mb improve O2 into the muscle

Muscle Shift

• Caps and mb consistent with a shift from llx to lla fibers

The Effects on Oxygen during Endurance training

• Muscles can use smaller amounts of O2 earlier during exercise
• Aerobic ATP production increases and anaerobic production decreases
• Anaerobic is reduced, glycolytic and atp proudction is lowered, less lactate
• Anaerobic reduces, atp-pc depletion occurs but pc is increased

Effects on substrate utilization

• Muscle adaptation increases, blood flow slows and uptake in oxygen increases
• FFA use rises and there is more use of CHO
• Mitochondria enzyme increase for beta-oxidation leading to less Cho use and more FFA use

Lactate and H+ production

• There has to be balance on the enzyme and H type increases

Linking adaptaions

• Muscle change due to higher CA2 and change in free radicals
• Leads to more mitochondria

Changes Following Detraining

• Muscular and cardiac adaptations detrain quickly when training is stopped
• Cardiac happens first while HR stays the same

Anaerobic Training Adaptations

• Anaerobic adaptations improve high performing exercises
• Buffer capacity is increased and PH is maintained
• Lactate production is reduced, with force production maintained

Production Of Force

• Force production stimulates muscle receptors
• Muscle protein helps with hypertrophy

Nutrition for Performances

• CHO levels at 45-65%
• Proteins and fats at lesser percentages