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

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.