Week 6 Flashcards
(24 cards)
Range of internal body temp? Facts?
Humans are homeotherms - maintains a constant internal body temperature, regardless of changes in the external environment.
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
What is core temperature?
Core temperature is the internal temperature of the body, especially that of the hypothalamus, which serves as the body’s thermoregulatory center. It reflects the temperature of vital organs and remains relatively constant despite environmental changes.
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 (there are variations or differences in temperature in different areas.)
Normal range is 32-35
Cool = <30
Warm = 30-35
Hot = >35
Thermal gradient with core, heat travels from high to low
Temperature regulation?
Homeostasis of body temperature relies on:
Thermoreceptors (temperature sensors):
- Peripheral (skin) and central (brain).
Effectors (regulate response):
- Adrenal medulla – ↑ metabolic heat via catecholamines.
- Sweat glands – promote evaporative cooling.
- Skin arterioles – control blood flow to the skin (heat loss/retention).
- Skeletal muscles – generate heat via shivering.
Physiological control of thermoregulation?
Temperature changes are detected by thermoreceptors:
Peripheral (skin) and central (hypothalamus) sensors send afferent signals to the brain
The brain sends efferent signals to restore normal temperature via:
Heat Conservation & Production:
- Shivering thermogenesis: involuntary muscle contractions generate heat
- Voluntary muscular activity: physical movement raises metabolic heat
- Non-shivering thermogenesis: hormones increase metabolic rate
- Vasoconstriction reduces heat loss by constricting blood vessels
Heat Loss:
- Vasodilation: blood vessels widen to increase skin blood flow and heat loss
- Sweating: sweat glands release fluid; evaporation cools the body
Effectors involved:
- Blood vessels, sweat glands, skeletal muscles (shivering), and behavioral responses (e.g., seeking shade or warmth)
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 impairs heat dissipation.
Risk of Dehydration:
- Decreases sweat rate and plasma volume.
- Reduces cardiac output, maximal oxygen uptake, muscle strength, and work capacity.
Performance effects of heat? Causes?
Performance Impairment:
- Prolonged high-intensity exercise is significantly impaired in hot conditions.
- Heat stress → ↑ Heart rate, ↑ core & skin temperature, ↓ power output.
Causes of Impairment:
Competing blood flow demands between:
- Thermoregulation (skin)
- Working muscles
- Central nervous system (CNS)
Heat alters skeletal muscle function and metabolism.
Performance Reduction:
- Endurance performance drops by 4–17% in the heat (self-paced trials).
Heat-Related Warning signs? Health Impacts? Treatment?
Warning Signs:
- Thirst, profuse sweating, fatigue, headache, nausea
- Chills/goosebumps, dizziness, cessation of sweating
Moderate Symptoms (“Middle Ground”):
- Muscle cramps, pale/cool skin, weakness
- Strong rapid pulse, hot/dry skin, confusion
Heat Illness Spectrum:
- Heat cramps → Heat exhaustion → Heat stroke (life-threatening)
Treatment:
- Quickest cooling method: Cold water immersion
- Also remove from heat, hydrate, rest in shaded/cool area
How can heat stress be mitigated before and during exercise?
Before Exercise:
- Heat acclimation & aerobic training:
- Improves skin blood flow & cardiac output distribution
- Lowers sweating threshold, increases sweat rate, reduces sweat salt concentration
- Lowers core and skin temperatures, saving cardiac output for muscles
Immediately before:
- Pre-cooling (ice vests, cold drinks) lowers core temperature
- Optimize hydration to maintain plasma volume
During Exercise:
- Hydration: Regular fluid intake to replace losses
- Clothing: Light, moisture-wicking fabrics to promote evaporation
- Cooling: Use ice packs, misting sprays for external cooling
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? Exercise?
Peripheral vasoconstriction: Reduces skin blood flow to conserve core heat
Shivering thermogenesis: Involuntary muscle activity increases heat production
Non-shivering thermogenesis: Hormonal response (e.g. catecholamines) raises metabolic heat
During exercise in cold:
- Body faces dual demands — generating movement and maintaining temperature → increased metabolic cost
Specifc Physiological responses to exercise in cold?
Increased submaximal VO₂: due to greater heat loss
Increased ventilation: from elevated sympathetic stimulation
Higher lactate levels: reflecting increased carbohydrate metabolism
Increased central blood volume: caused by peripheral vasoconstriction
Decreased skin blood flow: vasoconstriction limits heat loss
Reduced lipid mobilization: less blood flow to fat cells
Lower heart rate during submax exercise: linked to increased central blood volume
Leptin release from adipose tissue: stimulates sympathetic activity
Decreased exercise capacity in water: due to greater heat loss
Summary:
- Submaximal exercise has a higher metabolic cost (shivering)
- Maximal exercise performance impaired by reduced oxygen delivery
Physiological Adaptations of Cold Acclimatisation? How fast? Why it matters?
Begins within ~1 week of exposure
- ↓ Skin temperature threshold for shivering → body tolerates lower temps before triggering a response
- ↑ Non-shivering thermogenesis → more heat produced without movement (e.g. brown fat activation)
- Improved peripheral blood flow → maintains warmer hands & feet in the cold
- ↓ Shivering + better sleep quality in cold environments
Why it matters:
These adaptations help maintain core temperature, reduce discomfort, and improve cold tolerance, especially during repeated or prolonged exposure (e.g. outdoor training or cold-weather operations).
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.
Example 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 (↑ pressure = ↓ volume)
High Altitude Effects:
- Same % of O₂, CO₂, and N₂ in the air
- But lower atmospheric pressure → lower partial pressures of gases (especially O₂)
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?
Reduced PO₂ at altitude disrupts oxygen delivery, triggering rapid physiological changes:
Respiratory Adjustments:
- Hyperventilation (via chemoreceptors) ↑ alveolar O₂
- ↓ CO₂ → respiratory alkalosis
- Diuresis increases HCO₃⁻ excretion to correct pH
Cardiovascular Adjustments:
- ↑ Resting Heart Rate & Cardiac Output to maintain O₂ delivery
Environmental Stressors:
- Cold, dry air → dehydration risk
- Increased UV exposure → sunburn, snow blindness
Impact of Altitude on Exercise Performance?
VO₂max Decreases with Altitude
- Reduced oxygen availability limits aerobic capacity
- Minimal impact on efforts lasting less than 2 minutes (anaerobic activities)
Submaximal Exercise
- Increased ventilation at the same workload to compensate for reduced oxygen per breath
- Elevated sympathetic nervous activity increases heart rate and cardiac output
Maximal Exercise
- Maximal heart rate decreases due to increased parasympathetic (vagal) activation
- May reduce cardiac strain and have a cardioprotective effect
Lactate Paradox
- Lower lactate production at maximal effort despite reduced oxygen availability
Beneficial effects of acclimatisation? (Vascular, Metabolic, Cellular Changes)
Vascular Changes:
- Increased capillarization (partly from reduced muscle mass) → better O₂ delivery
Cellular/Muscular Adaptations:
- ↑ Myoglobin content
- ↑ Aerobic enzymes (e.g. citrate synthase)
- No significant change in mitochondrial density
Metabolic Changes:
- Improved lactate clearance and oxidation in muscles
- Widened a-vO₂ difference → enhanced oxygen extraction
Beneficial effects of acclimatisation? (Ventilatory, CV and blood changes)
Ventilatory Adaptations:
- Sustained hyperventilation
- Kidneys excrete bicarbonate → restores blood pH
- ↑ Minute ventilation after ~4 days
Cardiovascular Adaptations:
- ↓ Cardiac output (CO) at rest/submax
- ↑ O₂ extraction reduces central strain
Blood Changes:
- Polycythemia: ↑ EPO → more RBCs → ↑ O₂ carrying capacity (e.g. Peruvians: 260 mL O₂/L blood)
- ↓ Plasma volume → ↑ hematocrit & [hemoglobin]
- ↑ 2,3-DPG → rightward shift of O₂ dissociation curve (Bohr effect) → better O₂ unloading
VO₂max Enhancement via RBC Manipulation:
- Blood letting (800 mL) reduces VO₂max
- Reinfusion 1 month later restores RBCs → VO₂max increases
Summary of high altitude training - Benefits, Detriments and Strategy?
Benefits:
- Enhanced O₂-carrying capacity: ↑ RBC mass, hemoglobin, hematocrit
- Cellular adaptations: ↑ capillary density & oxidative enzyme activity
- Circulatory efficiency: Improved O₂ delivery and utilization
Detriments:
- ↑ Blood viscosity → reduced flow from higher hematocrit
- Cardiovascular strain: ↑ HR & BP due to sympathetic drive
- Detraining effect: ↓ training intensity from low O₂; possible muscle loss
- ↑ Ventilatory demand: May cause respiratory fatigue
Strategy:
- Live high, train low
—22 h/day at 2–2.5k m
or
—Simulated 2.5–3k m for 12–16 h/day - Intermittent hypoxia: 3 h/day, 5×/week at 4–5k m (simulated)
