Aerobic

Introduction to Aerobic Exercise

• Historical Context in Curriculum: There used to be a specific "aerobic comp" (competency assessment), but it has since been integrated as a component of other competencies, focusing primarily on the warm-up and cool-down phases of exercise.
• Clinical Importance: Despite the lack of a standalone assessment, aerobic exercise is considered a critical component of physical therapy. It is essential to properly warm up patients before initiating therapeutic exercise (Ther-Ex), strength training, or flexibility protocols.

Definitions and Core Concepts of Fitness

• Fitness: Defined as the ability to perform physical work. This is not restricted to "gym fitness"; it is relative to the individual. For someone in an L&I (Labor and Industries) clinic, fitness involves the ability to perform their specific active job routine.
• Maximum Oxygen Consumption ($VO_2$ max):
  • Represents the body's ability to efficiently consume and use oxygen during physical activity or at rest.
  • Testing Procedure: Conducted on a bike or treadmill. Intensity and speed/incline are increased progressively. The subject wears a face mask with a tube connected to specialized machines to measure oxygen consumption.
  • Commercial Accuracy: Devices like Apple Watches can estimate $VO_2$ max. Studies suggest they are accurate within a range of $5$ to $10$ units, which is sufficient for healthy individuals but may be a significant discrepancy for sedentary populations.
• Myocardial Oxygen Consumption: Specifically refers to the amount of oxygen the heart muscle (myocardium) uses, as opposed to the skeletal muscles.
• Aerobic Exercise Conditioning (Training): The process of improving energy utilization through specific cardiovascular exercises. This relies on the physiological principles of intensity, duration, and frequency.
• Adaptation: Increased efficiency of the cardiovascular system. These changes typically manifest after $10$ to $12$ weeks of consistent training intensity.
• Endurance:
  • General Endurance: The ability to work for prolonged periods and resist pain.
  • Muscular Endurance: The ability of isolated muscle groups to resist fatigue (e.g., lower extremity endurance from being on one's feet often).
  • Cardiovascular Endurance: The ability of the entire body to perform large, dynamic exercises for long periods.

Physiological Mechanisms and Energy Systems

• Anaerobic Glycolytic System: Provides short bursts of energy for activities lasting up to $30$ to $60$ seconds (e.g., sprinting off a block). This system does not require oxygen.
• Aerobic System: Kicks in after the initial anaerobic burst, utilizing glycogen and fats to fuel endurance-based activities.
• Concept of Specificity:
  • Improvements are specific to the type of training performed. Running improves running; swimming improves swimming.
  • Cross Training: Used to give specific muscles a break while still recruiting similar fibers and maintaining aerobic capacity.
• Upper Body vs. Lower Body Demand: Using the Upper Body Ergometer (UBE) creates a higher cardiovascular output and oxygen demand on the heart than walking, despite the muscles being smaller.
• Deconditioning:
  • The decrease in muscle strength and cardiovascular efficiency occurs rapidly in sedentary individuals (within $1$ to $3$ days).
  • The Hospital Rule of Thumb: One day spent in a hospital bed results in approximately one week of deconditioning, meaning it takes a week to recover back to the patient's baseline for every single day of bed rest.

Muscle Fiber Classifications

• Type 1 (Slow-Twitch): High oxidative capacity, low anaerobic capacity. These are red fibers due to high vascularity and capillary density. They are utilized for endurance activities like marathons.
• Type 2 (Fast-Twitch): Generally anaerobic with lower capillary density, appearing white or pink.
  • Type 2a: Intermediate fast-twitch fibers. These can be recruited for both anaerobic and aerobic activities.
  • Type 2x: The specific fast-twitch fiber found in humans. (Note: Older textbooks and small mammal studies refer to "Type 2b," but humans do not possess 2b fibers; we have 2x).

Measurement of Energy Expenditure (METs)

• Kilocalories (Calories): A standard measurement of energy burned.
• Metabolic Equivalents (METs): The amount of oxygen consumed per kilogram of body weight ($mL/kg/min$).
  • Baseline (1 MET): Sitting at rest, breathing, not talking or writing.
  • Light Activity: $1$ to $2.9$ METs.
  • Moderate Activity: $3$ to $5.9$ METs (e.g., mowing the lawn/pushing a mower or bricklaying).
  • Vigorous Activity: $6$ to $8.8$ METs.
• MET Charts: Comprehensive lists (found in the "Big Red Book") correlate activities like shoveling snow or running to specific MET values based on a standard $150$-pound male.
• RPE (Rate of Perceived Exertion): A subjective "rainbow color chart" where patients report how hard they feel they are working. This is different from the calculable MET scale.

Physiological Responses to Aerobic Exercise

• Cardiovascular Response:
  • Increase in Heart Rate (HR).
  • Decrease in vagal stimuli: Blood is redirected away from internal organs (vagus nerve distribution) toward working muscles.
  • Increase in cardiac myofiber force development.
  • Increase in Cardiac Output and Systolic Blood Pressure.
• Respiratory Response:
  • Increased gas exchange (respiration) at the alveoli.
  • Increased respiratory frequency (above the normal $12$ to $18$ breaths per minute).
  • Increased ventilation (movement of air).
  • Blood Shunting: Blood is shunted away from the digestive system during exercise. When exercise stops, blood returns to the intestines/stomach, which is why athletes often need to use the bathroom immediately after a race.

Fitness Testing and Clinical Assessments

• Field Tests:
  • Time Test: Measuring the time taken to run $1.5$ miles.
  • Distance Test: Measuring the distance covered in $12$ minutes.
  • Walking Tests: Used for less active or older adults, such as the $1$-mile walk test or the $2$-minute and $6$-minute walk tests.
  • Clinical Utility: $2$ and $6$-minute walk tests are used to determine if patients can wean off supplemental oxygen before discharge.
• Multistage Tests:
  • Bruce Protocol: A treadmill-based test involving $4$ to $6$ stages, each lasting $3$ to $6$ minutes. Speed and incline increase each stage.
  • Modified Bruce: Used for those with higher pathology risks.
  • Termination Criteria: The test stops if the patient hits $85\%$ of their max heart rate, exceeds $115$ beats per minute (in certain protocols), or expresses inability to continue.
• Stress Test: Used by cardiologists to diagnose heart conditions or clear patients for work; requires EKG/ECG monitoring.

Exercise Prescription (FITT-VP)

• Frequency:
  • General recommendation: $150$ minutes per week.
  • Optimal: $3$ to $5$ days per week.
  • Minimum for change: Exercise performed only