Exercise and the Environment Notes

Exercise and the Environment

Introduction to Exercise and the Environment

• The lecture series will cover exercise in various environmental conditions.
• Topics include:
  • Exercise in the heat.
  • Exercise in the cold.
• Guest lecturer: Dr. Andrew Keetch.

Exercise in the Heat

Heat Regulation as a Limiting Factor

• Heat regulation is a significant complicating factor in exercise performance, particularly in extreme environments.
• Exercising on hot, humid days can substantially decrease performance.

Body Temperature Regulation

• The body's internal temperature is strictly regulated by the hypothalamus, located at the base of the brain.
• The hypothalamus receives input from receptors in the skin and major glands.
• The hypothalamus regulates temperature by transferring heat to the periphery through:
  • Evaporation from the skin (sweat).
  • Radiation.
  • Conduction.
  • Convection.

Heat Gain and Loss

• The body gains heat from muscles working; however, muscles are inefficient: only ~25% of ATP goes into work while the rest is lost as heat.
• Offloading heat is crucial in hot environments.
• Two major factors influence the body's ability to regulate temperature:
  • Humidity.
  • Temperature.

The Role of Humidity

• Evaporation accounts for around 80% of heat loss.
• Humidity affects evaporation:
  • Decreased humidity = higher evaporation.
  • Increased humidity = lower evaporation.
• High humidity combined with high temperature significantly impairs the body's ability to offload heat.
• With high air temperature (greater than skin temperature), convection does not work, making the body dependent on evaporation.

Impact on Performance

• Endurance performance, and even strength and power events (e.g., ball sports like football), will be impaired.

Normal Body Temperature

• Normal core temperature is around 37 degrees Celsius, typically ranging from 36.1 to 37.2 degrees Celsius.
• Temperatures above 38 degrees Celsius indicate a fever.
• Temperatures above 40 degrees Celsius severely impair physiological function.

Thermoregulation

• Thermoregulation is primarily controlled by the preoptic anterior hypothalamus.
• The hypothalamus receives input from thermoreceptors in the skin, brain, spinal cord, and major organs (kidney, liver, etc.).

Response to Heat Stress

• Increased blood temperature is sensed by the hypothalamus, activating the sympathetic nervous system (SNS).
• Responses include:
  • Vasodilation in the skin for heat loss.
  • Activation of sweat glands for evaporation.
  • These processes aim to decrease body temperature.

Response to Cold Stress

• Decreased blood or skin temperature influences the hypothalamus but with less SNS activation.
• Responses include:
  • Vasoconstriction in the skin to reduce heat loss.
  • Activation of skeletal muscles, causing shivering to generate heat.

Exercise and Metabolic Heat Load

• Exercise results in a large metabolic heat load, disturbing body temperature regulation.
• The cardiovascular system is primarily affected.

Cardiovascular Drift

• Increased SNS activity leads to increased cardiac output via an increase in heart rate.
• Vasodilation occurs in the periphery (skin) for convection heat loss, and vasoconstriction occurs in non-essential tissues.
• Over time (minutes to hours), blood volume decreases due to sweating, reducing plasma volume and blood volume.
• Less blood returning to the heart decreases stroke volume; heart rate increases to compensate and maintain cardiac output.
• The cardiovascular system becomes overloaded and must prioritize blood flow to either exercising muscles or the skin.
• At a critical temperature (around 40 degrees Celsius), the body prioritizes heat loss over exercise, shutting down exercise to offload heat.

Prioritization of Heat Loss

• The cardiovascular system cannot provide sufficient blood to both working muscles and the skin simultaneously.
• Elite athletes in hot, long endurance events may experience a significant drop in performance as the body prioritizes heat loss.

Data on Power Output and Temperature

• A study compared power output during a 30-minute cycling time trial at 32 degrees Celsius (hot) versus 23 degrees Celsius.
• Elite road cyclists showed a significant drop in power output in hot conditions, demonstrating the body's prioritization of heat loss.

Glycogen Utilization and Lactate Accumulation

• The body relies more on glycogen utilization in hot conditions, leading to more lactate accumulation from anaerobic glycolysis.
• Data from exercising at 70% VO2 peak showed increased glycogen utilization and lactate accumulation at 40 degrees Celsius compared to 20 degrees Celsius.

Cardiac Physiology Changes

• Exercising at 43 degrees Celsius significantly affects cardiac physiology compared to 26 degrees Celsius.
• Rectal temperature increases more at higher temperatures.
• Stroke volume decreases significantly at 43 degrees Celsius.
• Heart rate increases to compensate for the drop in stroke volume.
• VO2 max decreases substantially in hot conditions.

Electrolyte Loss and Hormonal Regulation

• Sweating in the heat leads to the loss of key minerals, especially sodium chloride and potassium.
• Training can improve control of body fluid balance via the release of aldosterone and antidiuretic hormone (ADH).
• Aldosterone retains sodium at the kidneys, while ADH retains water.
• The hypothalamus activates the pituitary gland and adrenal cortex, influencing the HBA axis and fluid balance.
• Training can improve the body's ability to retain sodium and chloride, but not potassium, calcium, or magnesium.

Risk Factors

• Six key risk factors for exercising in the heat:
  • Internal heat production.
  • Air temperature.
  • Humidity levels.
  • Air velocity.
  • Radiant heat.
  • Clothing.

Stages of Heat Illness

• Three stages of heat illness:
  • Heat cramps (mild): cramping, fatigue, thirst, and sweating.
  • Heat exhaustion (moderate): headache, chills, rapid pulse, and nausea.
  • Heat stroke (severe): loss of consciousness or confusion.
• Treatment involves stopping exercise, whole-body cooling (ice baths, cold towels), and immediate medical attention.

Guidelines for Practicing and Competing in the Heat

• Avoid events during the hottest times of the day.
• Avoid wet bulb temperatures above 28 degrees Celsius.
• Ensure fluids are available and intake matches fluid losses (1 liter sweat loss = 1 kg weight loss).
• Be aware of signs of heat illness and have procedures for stopping events and removing affected athletes.

Chronic Exposure to Exercising in the Heat

• Acclimation: short-term (first couple of weeks).
• Acclimatization: long-term (months to years).
• A key physiological adaptation is an increase in plasma volume, leading to a higher stroke volume, lower heart rate during submaximal exercise, and higher VO2 max.
• Bodies retain water more efficiently and sweating becomes more dilute, with less sodium, optimizing evaporation heat loss.

Physiological Changes with Acclimation

• Data shows that acclimated individuals have a lower rectal temperature and lower heart rate during prolonged exercise.

Heat Acclimation Meta-Analysis

• A 2016 meta-analysis of 96 articles found that heat acclimation can take as little as 7 days for positive adaptations and at least 14 days for changes in sweat response.
• Heat acclimation has a moderate to large beneficial effect on lowering core body temperature, maintaining cardiovascular stability, and improving heat loss pathways.
• Other benefits include reduced oxygen consumption, improved glycogen sparing, increased power output at lactate threshold, reduced lactate concentrations, and improved perceived exertion and thermal sensation.

Recommendations for Heat Acclimation

• Spend as much time as possible exposed to high temperatures, starting at least 14 days prior to an event.
• High-intensity exercise is preferable, and being active is better than being sedentary.
• Track heart rate during exercise as a practical monitoring method.

Cooling Strategies for Athletes

• A study at the Australian Open Tennis examined cooling methods during simulated match play at 45 degrees Celsius.
• Ice application (wet towel filled with crushed ice) was the most effective at lowering skin and limiting rectal temperature rise.
• A fan plus cold wet sponge was also reasonably effective, but a dry fan had minimal effect.

Recommendations for Cooling Athletes

• Use ice towels (ice-filled damp towel around the neck, cold damp towels on the head and thighs) or dampen the thighs, neck, and arms and sit in front of a fan.
• Drinking cold water or sitting in front of a fan without skin wetting is not optimal.

Sex Differences

• Women have the same capacity for exercising in the heat as men at the same relative intensity but have lower sweat rates.
• Women have more active sweat glands but less sweat production per gland, which is advantageous in humid climates but disadvantageous in hot, dry climates.

Conclusion

• Exercising in heat or cold elicits different physiological responses. Acclimation can improve performance, but there are health risks. Staying informed helps athletes stay safe.

Exercise in the Cold

Introduction to Exercising in the Cold

• The main focus is on retaining heat and limiting the drop in core and skin temperature.
• Cold water is more dangerous than cold air due to its higher thermal conductivity, 26 times greater than air.
• Heat loss is four times faster in cold water, resulting in a core temperature drop of about 2 degrees Celsius per hour around 15 degrees Celsius.
• Limited time in cold water is crucial.

Hypothermia

• Hypothermia can occur even at temperatures around 10 degrees Celsius in cold water.
• Moving water leads to faster heat loss; exercising in water can help retain heat.

Body's Response to Cold

• Hypothalamus leads to:
  • More metabolism.
  • More vasoconstriction.
  • Muscle shivering.
• All help to limit temperature loss.
• Responses to cold depend on circumstances.

Types of Cold Acclimation

• Cold Habituation: Repeated exposures without significant heat loss result in less shivering and vasoconstriction, leading to a drop in core temperature over time (e.g., skiing with warm clothing).
• Metabolic Acclimation: Repeated exposures with heat loss enhance metabolism and muscle shivering, increasing heat production (e.g., swimming in cold water).
• Insulative Acclimation: Enhanced vasoconstriction to insulate the body and retain heat when increased metabolism cannot prevent heat loss.

Factors Affecting Heat Loss

• Body composition:
  • More subcutaneous fat helps retain heat via insulation.
  • Lower body surface area to mass ratio reduces heat loss.
• Females have more subcutaneous fat, which is an advantage.
• Children have a higher BSA to mass ratio, putting them at a disadvantage.
• Core temperature is linearly affected by ambient temperature.
• Below 18 degrees Celsius, non-shivering thermogenesis and shivering increase to produce heat.

Impact on Exercise Performance

• Muscle function significantly decreases.
  • Less contractile force and less recruitment of muscle fibers.
  • Lower velocity of contraction and power output.
• Power and strength sports are negatively affected.
• Superficial muscles are more affected than deeper muscles.
• As temperature drops and fatigue increases, metabolic heat production decreases, exacerbating the cold's effects.
• Glycogen depletion during sustained endurance exercise in the cold increases the risk of hypothermia. Carbohydrate intake is important.

Glycogen Depletion and Fat Oxidation

• Glycogen depletion occurs because there is less fat oxidation.
• Catecholamine release during exercise normally leads to free fatty acid oxidation, but in the cold, vasoconstriction reduces subcutaneous fat mobilization.
• Instead, glycogen supplies are used more, leading to quicker depletion and hypoglycemia.
• Hypoglycemia leads to decreased muscle function, less high-intensity exercise, and less shivering, resulting in reduced heat production and increased risk of hypothermia.

Wind Chill

• Wind chill combines air temperature and wind speed to reflect the perceived temperature.
• High wind speeds significantly increase convection heat loss, increasing the risk of tissue freezing.

Stages of Hypothermia

• Hypothermia (low heat) occurs when core temperature drops below 35 degrees Celsius.
• Mild hypothermia: Core temperature between 34.5-35 degrees results in compromised hypothalamic function, affecting thermoregulation.
  • Treatment: Remove from the cold, provide dry clothing, blankets, and warm beverages.
  • Core temperatures are even worse below: 29.5:
• Core temperature below 29.5 degrees Celsius results in complete loss of thermoregulation.
  • Treatment: metabolism slows down, handle the person gently to avoid stimulating a heart arrhythmia.

Cardiorespiratory Effects of Cold

• Low core temperature slows heart rate via direct innervation of the SA node.
• Cold air does not damage lungs but slows ventilation (frequency and tidal volume).

Health Risks

• Frostbite: Peripheral tissue freezes due to vasoconstriction, lack of oxygen, and nutrients, leading to tissue death.
  • Treatment: Gradually rewarm only when there is no risk of re-freezing.
• Exercise-Induced Asthma: Excessive drying of airways affects about half of winter sport athletes.
  • Treatment: Beta-agonists and steroid inhalers.

Conclusion

• Understanding how the cold affects the body is crucial for maintaining safety and performance while exercising in cold conditions.

Exercise and Altitude

Introduction

• Main issue: low pressure, not air composition.
  • Air composition remains fairly consistant.
• Barometric pressure decreases with altitude.
  • Sea level ~ 760 mm Hg
  • 8000m ~ 250 mm Hg
• Affects partial pressure of oxygen.

Definitions

• Hypobaria : Low pressure.
• Hypoxia : Low oxygen in pulmonary circulation.
• Hypoxemia : Low oxygen in the muscle tissues.

Altitude Levels

• Sea Level : No change.
• Altitude ( > 1500m ) : Negative effecs start happening. Performance decreases.
• Moderate Alt. ( 2000m - 3000m ) : Significant decrease in performance. Can be restored w/ acclimation ( living in Alt. for awhile ). Start suffering from Acute Altitude sickness.
• High Alt. ( > 5000m ) : Severe hypoxic effects from lower barometric pressure.

Altitude and Air Temperature

• At altitude, it gets colder: air temperature decreases by 1 degree Celsius per 150 meters of climbing.
• Less Humidity : There is less water.

Solar Radiation

• There is more radiation because UV rays travel faster and better through the atmosphere.
• water normally absorbs sun radiation, so less water means less absorbed raditaion.
• snow even amplifies radiation.

Physiological Response

Ventilation and Pulmonary Diffusion

• When you move to altitude, you get an increased ventilaton right away ( breath more rapidly ).
• This stimulates baroreceptors and chemoreceptors which = increase in pulmonary ventilation.
• Pulmonary Diffusion : Not a limited factor.
• Alvealar P.O.2 still equivalent o what's up in the capillaries.
• Low Alveolar P.O.2 overall -> Change in oxyhemoglobin dissociation curve ( more saturation of oxygen in hemoglobin will help limit the offloading of C.O.2 from pulmonary ventilation ).

Problems

• Decrease in oxygen exchange @ skeletal msucle because there is less P.O.2 gradient.
  • Sea level : 60mm Hg
  • Altitude : 33mm Hg - 23mm Hg
• High Pressure gradient pulls oxygen into tissues, but at Alt, there's a small gradient between the two so the muscle needs more oxygen and obviously effects exercise performance.

Blood Volume

• Hours to days after arriving, see a drop in Blood Plasma. Losing water form urinating and breathing, so hematocrit will go up so blood will be lot's thicker. Results in increased blood pressure.
• Weeks/Months - Kidneys start producing erythropoietin = more red blood cells = Blood volume back where it was = Blood Oxygen higher = More oxygen to working muscles.

Effects On Performance

• Endurance performance affected immediately. Stroke volume decreases, hear rate will increase. After weeks of settling down, muscles extract more oxygen, Q - Cardiac Output, decreases again and heart rate also decreases again.
• At Max performance, Q decreases , because stroke volume and hear rate decline. O2 delivery at Maximal workload severely affected due to hypoxia = Vo2 max goes way down. Linear drop in VO2 max.
• 6km above sea level and VO2 max roughly halves.

Other Physiological Changes

• Metabolic Rate speeds up + More reliance on Glucose / Anaerobic Rate = Increased Lactate.
• Lose fluids faster from skin / Urine, therefore need 3 to 5 Liters fluids / day.
• Iron intake must increased to support increased hematocrit. Body fat goes down.

Acute vs Chronic Changes

• Changes from Acute do not effect sprining b/c they're anaerobic so they're negligibly effected. Thinner hair = Thowing Sports are better ( Javelin/Discus ) because there is less resistance ( world record Bob Beamon ).
• Chronic - Weeks/Months - Oxygen being consumed and endurance increases -> positive adaptations.
• Takes 3 weeks living/training in the area.

Physiological Variables

• Rest H.R rises. Minute Ventilation is higher. Haemoglobin concentration rises also.
• Maximal Exercise - Stroke volume drops , therefore Cardiac Output takes dive b/c drop in Stroke Volume = Vo2max declines right away. H.R increase to balance/compensate is a surprising non-factor.

Acclimation

• Main Adaptation : Enhanced erythropoeitin leading to red blood cell production and oxygen. Higher the altitude = this becomes higher.
• Ratio of cardiac output is normally ~6:1 , acute and chronic hypoxia = drop by factors of ten to one. Exercise drops performance. Acute needs more blood to output same 02 levels.

Conclusion

• Positive adaptations occur in athlete, good results from acclimating. The more RBC'S = Vo2/ Lactate threshold/ Endurance is better.
• Train = bad to altitude and leads to altitude sickness, etc. Compete = bad to b/c any adverse effects kicked in ->compete ASAP after arriving is more preferable , maybe on the day or the day before.
• Best of both : Live in Altitude but train on low is better/ High Altitude / Training Low b/c athletes can train at sea levels and there's still great physical. Oxygen chambers allow athletes o live at High and Train Low easily.

Experiments

• Athletes asigned to either 1700+ - 2800 level , different sleeping alt but same training altitude lead to about
  2000m / 2500 is when best improvement occur, due to elite athlete committing significant commitment .

Athletes Specific Program

• Swimming - 120 weeks , leads to about 30% of there trining time at altitude, so big time commitment pays off the medals.
• Training modification can change intensity ( below Lactate ) and frequency + intensity to keep acclamation stable, and iron to female.

Monitoring and Preventing

• Pusle- ox to tract oxygen, mood questionnaires , urine amount to assess what lost, checking + preventing alitudes sickenss ( common , day2-3 ), headaches, nausea, etc , medications to prevent. If it get worse leads to sever. Lower you training volume leads to much much higher athlete sickness