Sports Physiology: Limits and Gender Differences

• Sports physiology explores the limits of bodily mechanisms under extreme stress.
• Exceeding these limits can lead to lethal consequences.
• Metabolism during a marathon race can increase to 2000% above normal, compared to a 100% increase during high fever.
• Quantitative data in sports physiology is primarily based on young male athletes due to more complete measurements being available.
• Basic physiological principles apply to female athletes, but quantitative differences exist due to body size, composition, and testosterone levels.
• Women generally have two-thirds to three-quarters of the muscle strength, pulmonary ventilation, and cardiac output values of men due to muscle mass.
• Strength per square centimeter of cross-sectional area is almost equal between male and female muscle.
• Differences in total muscle performance are due to the greater muscle percentage in the male body, influenced by endocrine factors.
• The top female marathon runner has a running speed about 11% less than the top male performer.
• Women sometimes hold records faster than men in events like the two-way swim across the English Channel, where extra fat provides advantages.
• Testosterone increases protein deposition, leading to about 40% larger muscles in males.
• Estrogen increases fat deposition in females in areas such as breasts, hips, and subcutaneous tissue.
• Nonathletic young females have about 34% body fat, while nonathletic young males have about 23%.
• Obesity prevalence has increased in developed countries, with about 37% of the adult population in the United States being obese.
• Increased body fat negatively impacts athletic performance in speed-dependent events or those relying on muscle strength to body weight ratio.

Muscles in Exercise

• Success in athletic events depends on muscle strength when needed, power in work performance, and the duration of activity.
• Muscle strength is mainly determined by its size, with a maximal contractile force between 3 and 4 kg/cm².
• Muscle enlargement through training leads to increased muscle strength.
• Example: A world-class male weightlifter with a quadriceps muscle of 150 square centimeters can have a maximal contractile strength of 525 kilograms (1155 pounds).
• High forces from the patellar tendon can cause ruptures or avulsion from the tibia.
• Similar forces on joints can lead to displaced cartilages, compression fractures, and torn ligaments.
• Holding strength is 40% greater than contractile strength, requiring more force to stretch out a contracted muscle.
• Holding contractions increase the force on the patellar tendon to 735 kilograms (1617 pounds), compounding problems for tendons, joints, and ligaments.
• Forceful stretching of a maximally contracted muscle is a reliable way to induce muscle soreness.
• Mechanical work is the amount of force applied by the muscle multiplied by the distance over which the force is applied.
• Muscle power is the total amount of work a muscle performs per unit time, determined by contraction strength, distance, and contraction frequency.
• Power is measured in kilogram meters (kg-m) per minute.
• Highly trained athletes can achieve the following maximal power levels with all muscles working together:
  • First 8 to 10 seconds: 7000 kg-m/min
  • Next 1 minute: 4000 kg-m/min
  • Next 30 minutes: 1700 kg-m/min
• Extreme power surges are possible for short periods like a 100-meter dash, while endurance events involve lower power output.
• Efficiency for translating muscle power into athletic performance varies with activity speed, with faster activities being less efficient.
• The velocity of a 100-meter dash is about 1.75 times that of a 30-minute race, despite the 4-fold power difference.
• Endurance depends on nutritive support, particularly the amount of glycogen stored in muscles before exercise.
• High-carbohydrate diets enhance endurance.
• Endurance times for marathon-speed running vary with diet:
  • High-carbohydrate diet: 240 minutes
  • Mixed diet: 120 minutes
  • High-fat diet: 85 minutes
• Glycogen storage in muscles varies with diet:
  • High-carbohydrate diet: 40 g/kg muscle
  • Mixed diet: 20 g/kg muscle
  • High-fat diet: 6 g/kg muscle

Muscle Metabolic Systems in Exercise

• Muscles use the phosphocreatine-creatine, glycogen-lactic acid, and aerobic systems.
• Adenosine triphosphate (ATP) is the energy source for muscle contraction.
• High-energy phosphate bonds in ATP store 7300 calories of energy per mole.
• Removal of phosphate radicals from ATP releases energy for muscle contraction, converting ATP to ADP and then to AMP.
• Muscle ATP sustains maximal muscle power for only about 3 seconds.
• Continuous ATP formation is essential.
• Phosphocreatine can decompose into creatine and phosphate ion, releasing energy.
• Phosphocreatine's high-energy phosphate bond has more energy than ATP's: 10,300 calories per mole versus 7300.
• Phosphocreatine rapidly reconstitutes ATP.
• Muscle cells contain two to four times more phosphocreatine than ATP.
• The combined ATP and phosphocreatine form the phosphagen energy system.
• The phosphagen system provides maximal muscle power for 8 to 10 seconds.
• Stored glycogen in muscle splits into glucose for energy; this glycolysis occurs without oxygen.
• Each glucose molecule splits into two pyruvic acid molecules, forming four ATP molecules.
• Pyruvic acid converts to lactic acid when there is insufficient oxygen.
• The glycogen-lactic acid system forms ATP molecules about 2.5 times as rapidly as mitochondrial oxidation.
• The glycogen-lactic acid system provides 1.3 to 1.6 minutes of maximal muscle activity in addition to the phosphagen system.
• During the aerobic system, glucose, fatty acids, and amino acids combine with oxygen in the mitochondria to release energy.
• Maximal power generation rates vary among the energy systems:
  • Phosphagen system: 4 moles of ATP/min
  • Glycogen-lactic acid system: 2.5 moles of ATP/min
  • Aerobic system: 1 mole of ATP/min

Energy Systems Used in Various Sports

• Phosphagen system: Almost Entirely:
  • 100-meter dash, jumping, weight lifting, diving, football dashes, baseball triple
• Phosphagen and Glycogen-Lactic Acid Systems:
  • 200-meter dash, basketball, ice hockey dashes
• Glycogen-lactic acid system, mainly:
  • 400-meter dash, 100-meter swim, tennis, soccer
• Glycogen-Lactic Acid and Aerobic Systems:
  • 800-meter dash, 200-meter swim, 1500-meter skating, boxing, 2000-meter rowing, 1500-meter run, 1-mile run, 400-meter swim Aerobic System:
  • 10,000-meter skating, cross-country skiing, marathon run (26.2 miles, 42.2 kilometers), jogging
• Endurance of systems:
  • Phosphagen system: 8-10 seconds
  • Glycogen-lactic acid system: 1.3-1.6 minutes
  • Aerobic system: Unlimited time (as long as nutrients last)
• The phosphagen system supports power surges, the aerobic system sustains prolonged activity, and the glycogen-lactic acid system provides extra power during intermediate races.

Recovery of Muscle Metabolic Systems After Exercise

• Energy from phosphocreatine reconstitutes ATP, and energy from the glycogen-lactic acid system can be used to reconstitute phosphocreatine and ATP.
• Energy from oxidative metabolism reconstitutes all systems, including ATP, phosphocreatine, and glycogen-lactic acid.
• Reconstitution of the lactic acid system means removing excess lactic acid, achieved via conversion back to pyruvic acid (oxidative metabolism) and reconversion into glucose (mainly in the liver).
• Even during early stages of heavy exercise, a portion of aerobic energy capability is depleted via oxygen debt and glycogen depletion.
• Oxygen Debt:
  • Stored oxygen in the body is used for aerobic metabolism. The body contains about 2 liters of stored oxygen that can be used for aerobic metabolism: (1) 0.5 liter in the air of the lungs, (2) 0.25 liter dissolved in the body fluids, (3) 1 liter combined with the hemoglobin of the blood, and (4) 0.3 liter stored in the muscle fibers
  • After exercise, stored oxygen must be replenished, and about 9 more liters of oxygen must be consumed to reconstitute the phosphagen and the lactic acid system.
  • Total extra oxygen needed is about 11.5 liters, called the oxygen debt.
  • During heavy exercise, oxygen uptake increases more than 15-fold.
  • Oxygen uptake remains above normal after exercise to allow more oxygen to return to the phosphagen system.
  • Early portion of oxygen debt (alactacid) is about 3.5 liters, and the latter portion (lactic acid) is about 8 liters. Recovery of Muscle Glycogen:
  • Muscle glycogen depletion can take days to recover from.
  • Recovery is significantly influenced by diet: high-carbohydrate diets allow full recovery in about 2 days.
  • High-fat or high-protein diets lead to minimal recovery, even after 5 days.
  • Athletes should consume a high-carbohydrate diet and avoid exhaustive exercise 48 hours before an event.

Nutrients Used During Muscle Activity

• Muscles use carbohydrates, fats (fatty acids and acetoacetic acid), and proteins (amino acids) for energy.
• Glycogen stores deplete in endurance events lasting longer than 4-5 hours; muscle then depends on fats.
• Carbohydrate use is higher in the early stages of exercise, but fat use increases over time.
• Liver glycogen releases glucose into the blood, serving as an energy source: Glucose solutions during athletic events can provide 30-40% of required energy.
• Muscle glycogen and blood glucose are preferred for intense activity.
• Fat supplies more than 50% of the energy after the first 3-4 hours of a long-term endurance event.

Effect of Athletic Training on Muscles and Muscle Performance

• Maximal Resistance Training Increases Muscle Strength:
  • Muscles increase little in strength without load.
  • Muscles contracting at more than 50% maximal force rapidly develop strength, even with few daily contractions.
  • Six maximal muscle contractions in three sets three days a week yield optimal strength gains without chronic muscle fatigue.
  • Untrained individuals can experience a 30% strength increase in the first 6 to 8 weeks, followed by a plateau.
  • Muscle hypertrophy accompanies strength gains.
  • Muscle training can increase muscle strength by more than 100% in the elderly.
• Muscle Hypertrophy:
  • Size of muscle growth is determined by genetics and testosterone secretion, in men it can cause considerable muscle growth
  • Muscles can hypertrophy with training (30-60%), mainly due to increased fiber diameter.
  • Changes include increased myofibrils, up to a 120% increase in mitochondrial enzymes, a 60-80% increase in phosphagen components, a 50% increase in stored glycogen, and a 75-100% increase in stored triglyceride.
  • Capabilities of both anaerobic and aerobic metabolic systems are increased, the maximum oxidation rate increases by 45%.

Fast-Twitch and Slow-Twitch Muscle Fibers

• Muscles have varying percentages of fiber types.
  • Gastrocnemius muscle = more fast-twitch (forceful contraction)
  • Soleus muscle = more slow-twitch (prolonged activity)
• Fast-twitch fibers = twice the diameter, quick energy for short bursts.
• Slow-twitch fibers = endurance and aerobic energy, more mitochondria and myoglobin.
• Capillaries are more common near slow-twitch fibers.
• Fast-twitch fibers = provide power for seconds to minutes.
• Slow-twitch fibers = provide endurance for minutes to hours.
• Genetics play a role in fiber type ratio, some appear born to be marathoners, while others, sprinters.
• Approximate percentages in quadriceps muscles of different types of athletes:
  • Marathoners: 18% Fast-Twitch and 82% Slow-Twitch
  • Swimmers: 26% Fast-Twitch and 74% Slow-Twitch
  • Average male: 55% Fast-Twitch and 45% Slow-Twitch
  • Weight lifters: 55% Fast-Twitch and 45% Slow-Twitch
  • Sprinters: 63% Fast-Twitch and 37% Slow-Twitch
  • Jumpers: 63% Fast-Twitch and 37% Slow-Twitch

Respiration in Exercise:

• Critical for optimal performance in endurance athletics
• Oxygen Consumption and Pulmonary Ventilation in Exercise:
  • Normal oxygen consumption for a young man at rest 250 ml/min -Under maximal, consumption increases to: -Untrained average male:3600 ml/min -Athletically trained average male: 4000 ml/min -Male marathon runner: 5100 ml/min
• Total pulmonary ventilation (L/min) can reach up to 120, severe exercise
• Limits of Pulmonary Ventilation: -Pulmonary ventilation at maximal exercise: 100-110 L/min -Maximal breathing capacity 150-170 L/min -Maximal breathing capacity is is about 50% greater than the actual pulmonary ventilation during maximal exercise.
• Effect of Training on VO2max -The rate of oxygen usage (in L/min) under maximal aerobic metabolism is Vo2max -Training on VO2max showed to increased only 10%
• Oxygen-Diffusing Capacity of Athletes -Oxygen-diffusing capacity is a measure of which oxygen can diffuse from the pulmonary alveoli into the blood. ml/min measured diffusing capacities: -Nonathlete at rest : 23 -Nonathlete during maximal exercise :48 -Speed skater during maximal exercise: 64 -Swimmer during maximal exercise: 71 -Oarsman during maximal exercise: 80 -Athletes who require greater amounts of oxygen per minute have higher diffusing capacities

Blood Gases During Exercise

• Oxygen pressure of the arterial blood and carbon dioxide pressure of venous blood remain normal due to the respiratory system's ability to provide adequate aeration.
• Neurogenic mechanisms stimulate respiration during exercise.
• Effect of Smoking on Pulmonary Ventilation in Exercise: -Nicotine constricts terminal bronchioles of the lungs, increasing the resistance of airflow. -Irritating effects of smoke fluid secretion into the bronchial tree, as well as some swelling of the epithelial linings.
• Cardivascular Function in Exercise -Muscle Blood Flow -A key requirement of cardiovascular function in exercise is to deliver the required oxygen and other nutrients to the exercising muscles. -The muscle blood flow increases drastically during exercise. -The actual contractile process itself temporarily the decrease muscle blood flow Restsing vs During: -Resting blood flow: 3.6 -Blood flow during maximal exercise: 90 Thus, muscle blood flow can increase a maximum of about 25-fold during the most strenuous exercise
• Work Output, Oxygen Consumption, and Cardiac Output During Exercise: -All related because muscle output increases oxygen consumption (oxygen consumption dilates the muscles increase venous return increasinig cardiac)

Types of Cardiac output

• Cardiac output in a young man at rest: 5.5 L/min
• Maximal cardiac output during exercise in a young untrained man: 23 L/min
• Maximal cardiac output during exercise in an average male marathoner: 30

Effect of Training on Heart Hypertrophy and on Cardiac Output

• Results because of the fact that the heart chambers of marathoners enlarge about 40%
• The marathon heart mass also increases 40% or more Type comparison of Cardiac function -Resting: -Norathlete: Stroke Volume (ml) 75 & Heart Rate (beats/min): 75 -Marathoner: Stroke Volume (ml) 105 & Heart Rate (beats/min): 50
• Role of Stroke Volume and Heart Rate in Increasing Cardiac Output: -During sustained strenuous exercise, the increase in heart rate by far accounts for a greater proportion of the increase in cardiac output
• Relation of Cardiovascular Performance to Vo2max -During maximal exercise, both the heart rate and stroke volume are increased to about 95% of their maximal levels.
  • Because the cardiac output is equal to stoke volume times heart rate, the cardiac output is about 90% of the maximum that the person can achieve.

Body Heat in Exercise

• Almost all the energy released by the body's metabolism of nutrients is eventually converted into body heat.
• During endurance athletics the body temperature often rises from its normal level of 98.6°F to 102°F or 103°F (37°C to 40 °C).
• Heatstroke: -At this level, the elevated temperature becomes destructive to tissue cells, especially the brain cells. -Symptoms: extreme weakness, exhaustion, headache, dizziness, nausea, profuse sweating, confusion, staggering gait, collapse, and unconsciousness.
• Treatment of heatstroke: remove all clothing, maintain a spray of cool water on all surfaces of the body or continually sponge the body, and blow air over the body with a fan.
• Body Fluids and Salt in Exercise -Weight reduction loss by 3% can diminsh a persons preformance significantly
• Excess fluic consumption can be driven by thrift but algo be due to conditioned behavior tha is based on recommedstions to dirnk the fluid.
• Experience with the military electrolyte problem- a loss of potassium, some suppliemental fluic contiain amount of potassium olong with soduim, usually in thr form of fruit juices

Drugs and Athletes

• Caffine increased improvemement in the experiment a perfomred marthoan by 7%
• Use of male sex hormones (androgens) cause of cause cardivascular risks, as they cause Hypertension, and stroke
• Body Fitness Prolongs Life:
  • Multiple studis have shown that people mainatin appropraite body fitness, using judicious regularmins exercise have has addtinal benefits.
• Body fitness and weight control greatly reduce cardiovas-cular disease The athletically fit person that more bodily reserves to call on when he or she does become sick.