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Exercise Physiology Notes

Blood Flow Regulation

  • Strenuous exercise is a major stressor for the circulatory system.
  • Cardiac Output:
    • Increases 4-5x in non-athletes.
    • Increases 6-7x in well-trained athletes.
  • Skeletal Muscle Blood Flow (at rest):
    • Approximately 3-4 ml/min per 100 grams of muscle.
  • Blood Flow During Extreme Exercise (in athletes):
    • Increases 25- to 50-fold.
    • Can peak at 400 ml/min per 100 grams of skeletal muscle (endurance-trained).

Blood Flow During Muscle Contraction

  • Blood flow fluctuates with muscle contraction.
  • During Contraction:
    • Flow decreases due to blood vessel compression.
    • Can almost stop blood flow, leading to rapid weakening of contraction.
  • After Contraction:
    • Blood flow remains elevated for a few seconds.
    • Returns to normal within minutes.

Blood Flow in Muscle Capillaries

  • Exercise increases blood flow in muscle capillaries.
  • At Rest:
    • Capillaries have minimal blood flow.
  • During Exercise:
    • Capillaries fully open.
  • Increased capillary surface area helps diminished the distance for which oxygen and nutrients must diffuse through.
    • Two to threefold increase in capillary surface area

Oxygen's Role in Enhancing Blood Flow

  • Reduced oxygen levels in muscle enhance blood flow.
  • Mechanism:
    • Chemicals released locally act on arterioles.
    • Vasodilators: Nitric oxide, adenosine, prostaglandins.
    • Vasoconstrictors: Epinephrine and angiotensin II.
  • Oxygen Reduction:
    • Active muscles rapidly consume oxygen.
    • Decreased oxygen concentration leads to arteriolar vasodilation.

Sympathetic Stimulation and Arterial Pressure

  • Exercise increases arterial pressure via sympathetic stimulation.
  • Stimulatory Effects:
    1. Vasoconstriction in most tissues (except brain, active muscles, heart).
    2. Increased heart pumping activity.
    3. Increased mean systemic filling pressure (venous contraction).
  • Blood is rerouted to tissues with the greatest need.

Sex Differences in Athletes

  • Strength per Cross-Sectional Area:
    • No significant difference between sexes (3-4 \, \text{kg/cm}^2).
  • Total Muscle Performance Difference:
    • Dependent on total muscle percentage in the body.
  • Driving Force:
    • Sex steroids influence lean muscle mass development and maintenance.

Impact of Testosterone

  • Anabolic Effect:
    • Promotes protein deposition, especially in muscles.
  • Males with normal testosterone levels (even with minimal sports activity) have larger muscles than comparable females (approximately 40% increase)

Impact of Estrogen

  • Limited Impact Compared to Testosterone:
    • Causes increased fat deposition (breasts, hips, subcutaneous tissues).
  • Body Fat Percentage:
    • Young (16-19 yo) non-athletic females: ~34%.
    • Young (16-19 yo) non-athletic males: ~23%.
  • Increased body fat is detrimental to speed-demanding athletic performance.

Muscle Strength

  • Primarily determined by size.
  • Maximal Contractile Force:
    • 3-4 \, \text{kg/cm}^2 of cross-sectional area.
  • Example:
    • Weightlifter's quadriceps: 150 cm2 cross-sectional area.
    • Maximal contractile strength: 525 \, \text{kg}.
  • This force can lead to tendon rupture, cartilage displacement, compression fractures, and torn ligaments.

Holding Strength

  • Holding strength exceeds contractile strength by ~40%.
  • Greater force is required to stretch a contracted muscle than to shorten it.
  • Example:
    • 525 \, \text{kg} contractile strength becomes 735 \, \text{kg} during holding contractions.
  • Pushing muscles to this extreme can cause internal tearing.

Endurance

  • Dependent on nutritive support and glycogen stores.
  • Glycogen:
    • High-carb diets increase glycogen stores.
    • High-carb diets enhance endurance.

Muscle Metabolic Systems in Exercise

  • I. Phosphocreatine System:
    • Creatine + PO3 → ATP
  • II. Glycogen-Lactic Acid System:
    • Glycogen → Lactic acid
  • III. Aerobic System:
    • Glucose/Fatty acids/Amino acids → CO2 + H2O + Urea

Adenosine Triphosphate (ATP)

  • Direct energy source for muscle contraction.
  • High-Energy Phosphate Bonds:
    • Bonds store 7300 calories of energy per mole of ATP.
    • Releasing one phosphate releases 7300 calories, energizing muscle contraction.
  • ATP can supply energy for only about 3 seconds.

Phosphocreatine-Creatine System

  • Decomposes into creatine and phosphate ions.
    • Releases 10,300 calories per mole.
  • Muscles have 2-4x more phosphocreatine than ATP.
  • Phosphate transfer to ATP is nearly instantaneous.
  • Phosphagen Energy System:
    • Combined ATP and phosphocreatine.
    • Provides maximal power for 8-10 seconds.

Glycogen-Lactic Acid System

  • Glycogen is split into glucose for energy.
  • Glycolysis (Anaerobic):
    • Glucose → 2 Pyruvate molecules + 4 ATP molecules
  • Insufficient Oxygen:
    • Pyruvate converted to lactic acid, which diffuses into the blood.
  • ATP production without oxygen.

Glycogen-Lactic Acid System

  • ATP production rate: 2.5x faster than oxidative metabolism.
  • Useful for rapid energy during short contractions.
  • Half as fast as the phosphagen system.
  • Provides 1.3-1.6 minutes of maximal muscle activity (reduced power).

Aerobic System

  • Oxidation of foodstuffs in mitochondria.
  • Glucose, fatty acids, and amino acids combine with oxygen to release energy (AMP to ATP).

Energy System Usage in Activities

  • Phosphagen System:
    • 100-meter dash, jumping, weight lifting, diving.
  • Phosphagen and Glycogen-Lactic Acid Systems:
    • 200-meter dash, basketball, ice hockey dashes.
  • Glycogen-Lactic Acid System:
    • 400-meter dash, 1500-meter run, 1-mile run, 400-meter swim.
  • Glycogen-Lactic Acid and Aerobic Systems:
    • 800-meter dash, 200-meter swim, 1500-meter skating, boxing, 2000-meter rowing, football dashes, baseball triple.
  • Aerobic System:
    • 10,000-meter skating, cross-country skiing, 100-meter swim, tennis, soccer, marathon.

Recovery After Exercise

  • Stored oxygen is depleted in about a minute during heavy exercise.
  • Additional oxygen is required to replenish stores.
  • \approx 9 liters of oxygen needed for phosphagen and lactic acid system recovery.
  • Total oxygen debt: \approx 11.5 liters.

Recovery Example

  • Four minutes of heavy exercise.
  • Oxygen uptake increases 15-fold.
  • Post-exercise, oxygen intake remains elevated.
  • Repayment lasts over 40 minutes for lactic acid removal.
  • Alactacid oxygen debt (3.5 liters) in early stages.
  • Lactic acid oxygen debt (8 liters) in the latter portion.

Muscle Glycogen Recovery

  • Exhaustive depletion requires days to recover.
  • Recovery depends on diet: high carb, high fat, or high protein.
  • High-carb diet: 2-day recovery.
  • Other diets: up to 5-day recovery.
  • Athletes should consume a high-carb diet before events and avoid exhaustive events during the 48-hour recovery period.

Nutrients Used During Muscle Activity

  • Carbs, fats (fatty acids and acetoacetates), and amino acids.
  • Endurance events (4-5 hours) deplete glycogen stores, shifting to fatty acids for energy.
  • Liver releases glucose from glycogen during endurance events.

Athletic Training and Muscle Performance

  • Muscles under no load show minimal strength increase.
  • Muscles contracting at >50% maximal force develop strength rapidly.
  • Six nearly maximal contractions in 3 sets 3x/week are effective.
  • Untrained individuals can increase strength by 30% in 6-8 weeks with resistance training.

Muscle Hypertrophy

  • Determined by heredity and testosterone secretion.
  • Training can increase muscle size by 30-60%.
  • Primarily due to increased diameter of muscle fibers.
  • Very few split to form new fibers.

Hypertrophy vs Hyperplasia

  • Hypertrophy refers to the increase in muscle fiber size.
  • Hyperplasia refers to the increase in the number of muscle fibers.

Muscle Hypertrophy Changes

  • Increased number of myofibrils.
  • Up to 120% increase in mitochondrial enzymes.
  • 60-80% increase in phosphagen system.
  • Up to 50% increase in stored glycogen.
  • 75-100% increase in stored triacylglycerols.
  • Increased capacity of anaerobic and aerobic metabolic systems.
  • Maximal oxidation rate increases by as much as 45%.

Fast- and Slow-Twitch Muscle Fibers

  • Fast-Twitch:
    • Twice as large in diameter.
    • 2-3x more active enzymes for rapid energy release from phosphagen system.
    • Delivers extreme power for short durations.
  • Slow-Twitch:
    • Organized for endurance/aerobic energy.
    • More mitochondria and myoglobin.
    • More active aerobic enzymes.
    • More capillaries.
    • Delivers prolonged strength over extended periods.

Muscle Fiber Types

  • Sprinters have 80% fast-twitch muscle fibers.
  • Marathon runners have 80% slow-twitch muscle fibers.
  • Slow-twitch fibers are crucial for endurance, contracting slower and for longer durations, resisting fatigue, and using aerobic respiration with high myoglobin content.
  • Fast-twitch fibers are crucial for bursts of activity, contracting and relaxing rapidly with quick fatigue, using anaerobic respiration with low myoglobin content.

Ratio of Muscle Fiber types in Athletes

  • Marathoners: 18% Fast-Twitch, 82% Slow-Twitch
  • Swimmers: 26% Fast-Twitch, 74% Slow-Twitch
  • Average Male: 55% Fast-Twitch, 45% Slow-Twitch
  • Weightlifters: 55% Fast-Twitch, 45% Slow-Twitch
  • Sprinters: 63% Fast-Twitch, 37% Slow-Twitch
  • Jumpers: 63% Fast-Twitch, 37% Slow-Twitch

Respiration in Exercise

  • Normal oxygen consumption for a young male: 250 ml/min
  • Maximal oxygen consumption for a young male: 3600 ml/min
  • Athletically trained male: 4000 ml/min
  • Male marathon runner: 5100 ml/min
  • VO2 Max: Rate of oxygen usage under maximal aerobic metabolism.
  • Training can improve VO2 Max marginally (mostly genetic).

Cardiovascular System in Exercise

  • Delivers oxygen and nutrients to muscles.
  • Muscle blood flow increases dramatically (13-fold).
  • Flow decreases during contraction.
  • Blood flow can increase a maximum of about 25-fold during strenuous exercise.

Training's Effect on Heart Hypertrophy

  • Marathon runners have cardiac outputs ~40% greater than untrained.
  • Heart chambers enlarge ~40%, increasing heart mass.
  • Resting cardiac output is the same due to larger stroke volume at a reduced heart rate.
  • Heart-pumping effectiveness per beat is 40-50% greater than in untrained persons.

Stroke Volume and Heart Rate Comparison

Stroke Volume (ml)Heart Rate (beats/min)
Resting
Nonathlete7575
Marathoner10550
Maximum
Nonathlete110195
Marathoner162185

Body Heat in Exercise

  • All energy from metabolism converts to body heat.
  • Maximal efficiency of converting nutrient energy into muscle work is only ~25%.
  • Remaining energy converts to heat during intracellular chemical reactions.
  • Energy used for muscle work becomes heat due to:
    • Overcoming viscous resistance to muscle and joint movement.
    • Overcoming friction of blood flowing through blood vessels.

Heatstroke

  • Failure to dissipate heat generated during exercise.
  • Normal body temp rises from 98.6°F to 102°F or 103°F.
  • Hot/humid conditions can elevate body temperature to 106°F-108°F (destructive to cells).
  • Symptoms: Weakness, exhaustion, headache, dizziness, nausea, sweating, confusion, staggering gait, collapse, and unconsciousness.

Heatstroke Treatment

  • Failure to treat immediately leads to death.
  • Temperature-regulating mechanisms fail.
  • High temperatures double intracellular chemical reaction rates, creating more heat.
  • Treatment: Rapidly reduce body temperature.
    • Remove clothing, spray cool water, blow air with a fan, or use an ice bath.

Body Fluids in Exercise

  • 5-10 pounds of weight loss recorded in athletes during 1-hour endurance events (hot/humid environments).
  • Weight loss is due to sweat loss.
  • A 3% decrease in body weight diminishes performance.
  • A 5-10% decrease can lead to muscle cramps and nausea.
  • Replace fluids as they are lost.

Sodium Chloride and Potassium

  • Sweat contains sodium chloride; athletes take salt tablets in hot/humid conditions.
  • Overuse of salt tablets is harmful.
  • Acclimation (1-2 weeks) acclimatizes sweat glands, reducing water loss.
  • Aldosterone increases reabsorption of NaCl from sweat.
  • Potassium supplementation might be needed (aldosterone increases loss in urine and sweat).

Drugs and Athletes

  • Caffeine can increase athletic performance (7% improvement in marathon runners with ~2 cups of coffee).
  • Male sex hormones increase muscle strength but increase CVD risk, decrease HDL, increase LDL, and decrease testicular function.
  • Amphetamines and cocaine deteriorate performance and can cause death due to heart overstimulation.

Body Fitness Prolongs Life

  • Maintaining appropriate body fitness prolongs life.
  • Mortality between ages 50-70 is three times less in fit vs. non-fit individuals.
  • Body fitness and weight control reduce cardiovascular disease.
  • Maintenance of moderately lower blood pressure.
  • Reduced blood cholesterol and LDL while promoting HDL.
  • Fit individuals have more bodily reserves if they become sick.
  • Ability to increase cardiac output is up to 50% greater in fit elderly.

Body Fitness and Chronic Diseases

  • Reduces risk for chronic metabolic disorders like insulin resistance and T2DM.
  • Moderate exercise improves insulin sensitivity, reducing the need for insulin treatment in T2DM.
  • Improved fitness can reduce the risk for breast, prostate, and colon cancers.