PHGY 213 Exercise Physiology Post-Lab Tutorial Notes

Distinctions Between Sex and Gender

• Biological Sex:

  • Defined biogically through physical characteristics.
  • Chromosomes: Females typically possess $XX$ chromosomes, while males typically possess $XY$ chromosomes.
  • Reproductive Organs: Includes internal and external genitalia specific to male and female reproductive roles.
  • Hormones: Characterized by different hormonal balances, such as higher levels of testosterone in males and estrogen and progesterone in females.

• Gender:

  • Defined culturally through societal norms and expectations.
  • Roles and Responsibilities:
    • Females often occupy roles related to caring and service jobs.
    • Males are often associated with roles in construction and defense.
  • Attributes:
    • Stereotypical female attributes include being fragile or emotional.
    • Stereotypical male attributes include being risk-taking or aggressive.
  • Entitlements and Socioeconomic Factors:
    • Gender impacts workforce participation, with males traditionally seeing higher rates and greater financial autonomy.
    • Females may face financial dependence, inferior healthcare access, and different societal entitlements.

Determinants of $VO_2 \text{ max}$

• Total Body Hemoglobin ($tHb\text{-mass}$):

  • $VO_2 \text{ max}$ is directly related to the total amount of hemoglobin in the body.
  • The formula used to describe this relationship is: ${VO_2 \text{ max}} = \beta \times tHb\text{-mass}$.
  • $\beta$ represents a scaling factor, which is approximately $3.2-3.4\,mL\,O_2$ per gram of hemoglobin mass in humans.

• Maximum Cardiac Output ($Q$) and Oxygen Extraction:

  • Based on the Fick Equation: ${VO_2 \text{ max}} = Q \times (a-vO_2 \text{ difference})$.
  • $Q$ (Cardiac Output) is calculated as: $Q = \text{Stroke Volume} \times \text{Heart Rate}$.
  • $(a-vO_2 \text{ difference})$ represents the arterial-venous oxygen difference, reflecting the amount of oxygen extracted by the tissues.

Sex Differences in $VO_2 \text{ max}$

• Hemoglobin Levels and Oxygen Diffusion:

  • Females generally exhibit lower capillary hemoglobin concentrations compared to males.
  • This distribution difference results in reduced oxygen diffusion to working muscles, contributing to lower observed $VO_2 \text{ max}$ values in females.

• Cardiac Output and Training Response:

  • Females often demonstrate a blunted cardiovascular response to endurance training compared to males.
  • After one year of endurance training, males typically show a more significant increase in left ventricular mass and maximal oxygen uptake.
  • Limited maximum cardiac output in females reduces the total delivery of oxygen to the muscles.

• Body Composition and Fat Percentage:

  • There is a negative correlation between body fat percentage and $VO_2 \text{ max}$.
  • An increase in fat percentage leads to an increase in total body mass without a corresponding increase in oxygen-consuming (lean) tissue.
  • This relative decrease in metabolically active tissue results in a lower $VO_2 \text{ max}$.

• Respiratory Anatomy:

  • Females typically have smaller lung volumes and narrower airways compared to males.
  • Females have a reduced ventilatory capacity and lower maximal expiratory flow rates.
  • During exercise, the maximal flow-volume loop limits can be reached more quickly in females, restricting total ventilatory capacity and contributing to lower $VO_2 \text{ max}$.

Post-Exercise Physiological Recovery

• Heart Rate ($HR$):

  • $HR$ remains elevated immediately after exercise to continue perfusing the muscles with oxygen and to facilitate the clearing of metabolic waste products.

• Blood Pressure ($BP$):

  • $BP$ remains elevated post-exercise due to sustained increases in cardiac output ($CO$), often referred to as addressing the oxygen debt.

• Ventilation ($VE$):

  • Increased ventilation persists after exercise because the rise in $CO_2$ levels during physical activity continues to trigger respiratory drives until homeostatic levels are restored.

Calculations for Mechanical Efficiency

• Calculation of Mechanical Work ($MW$):

  • Standard formula: $MW = m \times g \times h$
  • Expanded formula: $MW = \text{mass (kg)} \times \text{acceleration } (9.81\,m/s^2) \times \text{vertical distance (m)}$
  • Vertical distance formula for stepping exercise: $\text{Vertical distance} = 0.406\,m \times \frac{\text{cadence}}{\text{SEQUENCE}} \times \text{time of exercise}$
  • Example calculation: $MW = 84\,kg \times 9.81\,m/s^2 \times [(\frac{132 \text{ cadence}}{6} \times 3\,\text{min}) \times 0.406\,m]$

• Calculation of Energy Cost ($EC$):

  • Convert kilocalories to Joules: $EC = \text{kcal} \times 4200\,J/\text{kcal}$
  • Example: $EC = 50.53\,\text{kcal} \times 4200\,J/\text{kcal} = 212,226\,J$

• Calculation of Efficiency Percentage:

  • Formula: $\text{Efficiency (\%)} = \frac{\text{Mechanical Work}}{\text{Energy Cost}} \times 100$
  • Example calculation: $\text{Efficiency (\%)} = \frac{33,119.856\,J}{212,226\,J} = 0.1561 \times 100 = 15.61\%$

Experimental Data and Extrapolation

• When extrapolating experimental data from a heart rate graph, it is essential to identify the appropriate heart rate range.
• Heart rate values should be used accurately on standard growth or performance curves to estimate $VO_2$ levels effectively.