Week 6 Flashcards
Range of internal body temp? Facts?
Humans are homeotherms
Normal range is 36-38, more precisely 36.5-37.5
More reactive to cold, effects are seen at 35 and below but can more normal when hotter, up to 40 which can occur from illness or exercise
Extreme range is 22/6-44 where thermoregulation is impaired and extreme effects occur
Core temp definition?
Temp of the hypothalamus, the thermoregulation centre of the body
Core temp assessments
Oesophageal - thermostat through nose and throat near entry point of RA
Rectal - Usually in addition to above, 15cm rectally, comfort issues and slow due to muscle mass heat and slow changing
Stomach (Telemetry pill) - Swallow and sit and takes temp, also slow collecting temp data and can be interfered with exercise etc but can be used to track such as during exercise, wireless but expensive
Oral - commonly done at home but reliability issues
Tympanic - depends on type, infrared are good but not during exercise due to blood near face.
Skin temp?
Heterogeneous
Normal range is 32-35
Cool = <30
Warm = 30-35
Hot = >35
Thermal gradient with core, heat travels from high to low
Temp regulation?
Homeostatic maintenance of body temp require operation of temp sensors (peripheral and central thermoreceptros) and regulated effectors (adrenal medulla, sweat glands, skin arterioles and skeletal muscles)
Physiological control of thermoregulation?
Body temp increases/decreases sends afferent signal to brain which sends efferent signal to increase or decrease to normal range in response via mechanisms
Heat Conservation and Production:
- Shivering Thermogenesis: Involuntary muscle contractions generate heat. - Voluntary Muscular Activity: Physical movement increases metabolic heat. - Non-shivering Thermogenesis: Hormonal stimulation increases metabolic rate. Blood vessels constrict
Heat Loss:
- Blood Flow to Skin: Vasodilation increases heat loss; vasoconstriction reduces it.
- Sweating: sweat glands release fluid, Evaporation of sweat cools the body.
Homeostatic Regulation:
- Thermoreceptors:
- Peripheral (Skin) and Central (Hypothalamus)detect temperature changes.
Effectors:
- Blood Vessels,Sweat Glands,Skeletal Muscles(shivering),Behavioral Responses.
Heat exchange and energy balance ?
S=M±Cv±Cd±R–E
- S= Heat Storage
- M= Metabolic Heat Production
- Cv= Convective Heat Exchange
- Cd= Conductive Heat Exchange
- R= Radiant Heat Exchange
- EE= Evaporative Heat Loss
Exchange = loss or gain
(Kcal/min or watts)
Energy Balance in Exercise:
- ~75% of energy from metabolism is lost as heat during exercise.
Biophysical properties heat exchange is effected by?
Surrounding temperature, humidity, air motion, radiation, and clothing.
Hot and humid is most challenging as we can’t lose as much heat to environment as
Exercise performing in the heat?
Increased Demand on Heat Loss Mechanisms:
- Higher skin blood flow and sweating.
- Reduced core-to-skin temperature gradient.
- Dehydration:
- Decreases sweat rate and plasma volume.
- Reduces cardiac output, maximal oxygen uptake, muscle strength, and work capacity.
Performance effects of heat?
- Prolonged high-intensity exerciseis notably impaired in hot conditions.
- Power Output, Heart Rate, Core and Skin
Temperature:- Higher temperatures increase heart rate and core temperature, reducing power output.
Causes of Impairment:
- Competing demands for blood flow betweenthermoregulation,working muscles, and theCNS.
- Heat-related changesin skeletal muscle function and metabolism.
Performance Reduction:
- Self-paced endurance exercise trials show4-17% reductionin the heat.
Heat-Related Health Impacts? Treatment?
Warning signs: Thirst, profuse sweating, fatigue, headache and nausea, chills or goosebumps, cessation of sweating, faintness or dizziness
Middle ground: Muscle cramps, pale and cool skin, weakness, strong and rapid pulse, hot and dry skin, confusion
Heat illness: Heat cramps, heat exhaustion, heat stroke
Quickest way to lower body temp is cold water immersion
Mitigating Heat Stress?
- Before Exercise:
- Heat Acclimation and Aerobic Training:
- Improves cutaneous blood flow and cardiac output distribution.
- Lowers threshold for sweating, increases sweat output, and lowers salt concentration in sweat.
- Reduces skin and core temperatures, conserving more cardiac output for active muscles.
- Heat Acclimation and Aerobic Training:
- Immediately Before:
- Pre-cooling(e.g., ice vests, cold drinks) to reduce core temperature.
- OptimizingHydration Statusto maintain plasma volume.
- During Exercise:
- Hydration: Regular intake to offset fluid loss.
- Clothing: Light, moisture-wicking to enhance evaporation.
- Cooling Strategies: External cooling with ice packs or misting.
Cold stress?
Hypothermia
Core temp below 35 degrees
- 2°C drop → Maximal shivering.
- 4°C drop → Ataxia and apathy.
- 6°C drop → Unconsciousness.
- Further drop → Ventricular fibrillation, reduced brain blood flow, asystole, death.
Heat loss exceeds heat production, mechanisms include - conduction, convection, radiation and evaporation
Important to protect
Physiological Responses in Cold?
- Peripheral Vasoconstrictionto conserve core heat.
- Shivering and Non-Shivering Thermogenesis:
- Shivering increases muscle activity to produce heat.
- Non-shivering thermogenesis increases metabolic heat production through hormonal responses.
However increasing demands as body is exercising and trying to maintain temp.
Physiological responses to exercise in cold?
Increased Submax Vo2 - greater heat loss
Increased Ventilation during subax exercise - increased sympathetic stimulation
Increased lactate conc - increase carb metabolism
Increased central blood volume - peripheral vasoconstriction
Decreased exercise capacity in water - Greater heat loss
Decreased skin blood flow — peripheral vasoconstriction
Decreased lipid mobilisation - reduced blood flow to adipocytes
Decrease HR during submax exercise - Increased central blood volume
Release of Leptin from adipose tissue - Increased Symp stimulation
In summary:
- Submaximal Exercise: Higher metabolic cost due to shivering.
- Maximal Exercise: Reduced oxygen delivery to muscles, impairing performance.
Cold Acclimatization/Acclimation?
- Physiological Adaptations:
- Lower skin temperature threshold for shivering.
- Increased Non-Shivering Thermogenesisto maintain core temperature.
- Improved Peripheral Blood Flow:
- Maintains higher hand and foot temperatures.
- Enhanced Cold Tolerance:
- Reduced shivering, improved sleep quality in cold conditions.
- Adaptation Timeline: Begins within one week of exposure.
Effect of Altitude on Performance?
- Short-Term Anaerobic Performance:
- Lower air resistance at high altitude enhances speed in short sprints and jumps.
- Example: Bob Beamon’s long jump world record in 1968 (Mexico City).
- Long-Term Aerobic Performance:
- Decreased partial pressure of oxygen (PO2) impairs oxygen delivery to muscles.
- Result: Reduced aerobic performance in endurance events.
Performance Comparisons of Altitude at different competitions ?
- 1964 Tokyo Olympics (Sea Level)vs.1968 \
Mexico City Olympics (High Altitude)
- Sprint Events: Improved or unchanged due to lower air resistance.
- Endurance Events: Decline in performance due to reduced oxygen availability.
Barometric Pressure and Altitude?
- Boyle’s Law:
- Gas volume is inversely proportional to pressure.
- High Altitude Effects:
- Same percentages of O2, CO2, and N2 in the air but lower partial pressures.
- Key Terms:
- Hypoxia: Low PO2 (at altitude).
- Normoxia: Normal PO2 (at sea level).
- Hyperoxia: High PO2.
- Hypoxaemia: Low levels of oxygen in the blood.
Short-Term Physiological Responses to Altitude?
Oxygen Transport Cascade:
- Reduced PO2 disrupts oxygen transport, triggering physiological adjustments.
Immediate Responses:
- Ventilation Changes:
- Hyperventilationdue to chemoreceptor activation.
- Increases alveolar O2 but lowers CO2, leading to respiratory alkalosis.
- Diuresis: Increased bicarbonate (HCO3-) excretion to balance pH.
- Hyperventilationdue to chemoreceptor activation.
- Cardiovascular Changes:
- Increased Resting Heart Rate and Cardiac Output:
- Compensates for reduced arterial oxygen content.
- Other Environmental Stressors:
- Cold, dry air (reduced humidity) causing dehydration.
- Increased UV exposure leading to risks like sunstroke and snow blindness
- Increased Resting Heart Rate and Cardiac Output:
Impact on Exercise Performance?
VO2max:
- VO2max decreasesas altitude increases.
- Reduced oxygen availability limits aerobic capacity.
- No significant impacton events lasting less than 2 minutes (anaerobic).
Sub-Maximal Exercise:
- Increased Ventilationfor the same workload:
- Compensates for fewer O2 molecules per liter of air.
- Cardiovascular Response:
- Increased Sympathetic Nervous Activity (SNA):
- Raises heart rate and cardiac output for sub-maximal workloads.
- Increased Sympathetic Nervous Activity (SNA):
- Maximal Exercise: Cardiac strain reduced
- Maximal Heart Rate Decrease:
- Caused by increased parasympathetic (vagal) activation.
- May have acardioprotective effect.
- Lactate Paradox:
- Lower lactate production at maximal effort despite reduced oxygen availability.
- Maximal Heart Rate Decrease:
Beneficial effects of acclimatisation? (Vascular and Cellular Changes)
Vascular and Cellular Changes
- Increased Capillarization:
- Partly due to muscle mass reduction.
- Muscular Adaptations:
- Increased myoglobin and aerobic enzymes (e.g., citrate synthase).
- No significant changein mitochondrial density.
- Metabolic Changes:
- Enhanced lactate consumption and oxidation by active muscles.
- Widened a-vO2 Differenceafter acclimatization.
Beneficial effects of acclimatisation? (Ventilatory, CV and blood changes)
- Ventilatory Adaptations:
- Hyperventilation continues, but bicarbonate excretion by kidneys normalizes blood pH.
- Improved Minute Ventilationafter 4 days.
- Cardiovascular Adaptations:
- Decreased Cardiac Output (CO):
- Increased O2 extraction reduces reliance on central delivery (lower cardiac strain).
- Decreased Cardiac Output (CO):
- Blood Changes:
- Polycythemia:
- Increased erythropoietin (EPO) raises red blood cell (RBC) count.
- Enhances O2 carrying capacity (e.g., Peruvians at altitude: 260 mL/L).
- Decreased Plasma Volume:
- Increases hematocrit and hemoglobin concentration.
- 2,3-DPG Increase in RBCs:
- Shifts the O2 dissociation curve to the right (Bohr effect), improving O2 delivery to tissues.
- Polycythemia:
- Effect of subtracting and adding RBC’s
- Effect of blood letting (800 mL) and subsequent reinfusion one month later of same red blood cells on VO2max
Summary of high altitude training?
Benefits: - Enhanced Oxygen Carrying Capacity:
- Increased RBC mass, hemoglobin, and hematocrit.
- Cellular Changes:
- Improved capillary density and oxidative enzyme activity.
- Circulatory Adjustments:
- More efficient oxygen delivery and utilization.
Detriments: - Increased Blood Viscosity:
- Due to higher hematocrit, which can impede blood flow.
- Cardiovascular Strain:
- Elevated heart rate and blood pressure due to increased sympathetic nervous activity.
- Detraining Effect:
- Reduced training intensity due to lower oxygen availability.
- Possiblemuscle mass lossfrom catabolism and reduced activity.
- Increased Ventilatory Response:
- Higher breathing rates can lead to respiratory fatigue.
Solution: Live high, train low to drive EPO response.
>22h day between 2-2.5k m required, or stimulated 2.5-3k m for 12-16 h a day
Intermittent hyperbaric hypoxia - 3h day 5 days a week at 4-5k m.
