Chapter 1 textbook notes

Mass Balance Principle

Homeostasis is achieved by balancing inflows and outflows of a mass within a body compartment; at steady state, inflow equals outflow.

Flow Principle

Flow of a substance equals the energy gradient times the conductance: Flow = (High energy − Low energy) × Conductance.

Inflow

Mass entering a compartment.

Outflow

Mass leaving a compartment.

Energy Gradient

Driving difference in energy content across a barrier that causes flow, such as a concentration gradient.

Conductance

Ease with which flow occurs for a given gradient; higher conductance means greater flow; inverse is resistance.

Resistance

Opposition to flow; the greater the resistance, the smaller the flow for a given gradient.

Feed-forward Control

Anticipatory regulation that minimizes disturbance to homeostasis (e.g., early ventilation increase at exercise onset).

Feed-back Control

Regulation based on current values detected by sensors to return toward a set point.

Set Point

Target value that a controlled parameter is regulated around.

Sensor

Detector of the current value of a regulated parameter.

Controller

Regulatory center (often the brain) that compares current value to the set point and activates effectors.

Elastic Recoil

Tissues’ tendency to return to their original size after expansion, e.g., lungs during breathing.

Homeostasis

Maintenance of a relatively stable internal environment despite external changes.

Interstitial Space

Fluid-filled space between cells.

Intracellular Space

Fluid inside cells; site of many cellular processes, including ATP use.

ATP

Adenosine triphosphate; the energy currency of the cell.

VO2 Max

Highest rate of oxygen uptake during maximal exercise; a measure of aerobic capacity (units typically ml·kg−1·min−1 or L·min−1).

VO2 Peak

Highest VO2 reached during an incremental test; may not equal true VO2 max.

Anaerobic Threshold

Intensity at which metabolism shifts from primarily aerobic to anaerobic; definitions vary and are debated.

Normal Distribution

Bell-shaped distribution where most values cluster around the mean; ~95% of values lie within ±2 SD.

Skewed Distribution

Asymmetric distribution where most values cluster away from the center; mean and median differ.

Descriptive Statistics

Statistics that describe data (e.g., mean, median, mode; variance; SD; SEM).

Mean

Average value; measure of central tendency.

Median

Middle value in an ordered data set.

Mode

Most frequently occurring value in a data set.

Variance

Average squared deviation from the mean; a measure of dispersion.

Standard Deviation

Spread of data around the mean; square root of the variance.

Standard Error of the Mean

Estimate of how far the sample mean is likely to be from the population mean; reflects precision.

Inferential Statistics

Methods to infer population-level conclusions from sample data (e.g., tests of significance, p-values).

Paired t-test

Statistical test comparing means of two related samples to determine if they differ.

p-value

Probability that observed differences could occur by chance under the null hypothesis; common threshold is 0.05 for significance.

Correlation Coefficient (r)

Measure of linear relationship between two variables; ranges from −1 to 1; r² indicates explained variance.

External Validity

Extent to which study results generalize beyond the study sample.

Reliability

Reproducibility of a measurement across repeated trials.

Validity

Accuracy of a measurement: whether it measures what it is intended to measure; also relates to generalizability (external validity).

Units and Notation (dot notation)

In exercise physiology, the dot denotes rate (e.g., V̇O2; ml·min−1); units like ml·kg−1·min−1 are used for relative measures.

V̇O2 (Rate of Oxygen Uptake)

Volume of oxygen consumed per unit time; typically expressed as L·min−1 or mL·min−1.

V̇O2 Max vs Absolute/Relative

Absolute VO2 max is in L·min−1; relative VO2 max is in mL·kg−1·min−1 (accounts for body mass).

Hemoglobin-Oxygen Binding (Hb-O2) Sigmoidal Curve

Oxygen saturation of hemoglobin increases in an S-shaped (sigmoidal) fashion with increasing PO2.

Partial Pressure (PO2, PCO2)

PO2 is the driving force for O2 diffusion; PCO2 is the driving force for CO2 diffusion in blood.

Sigmoidal Relationship

S-shaped relationship where small changes in the independent variable produce large changes in the dependent variable in the mid-range.

Exponential Relationship

Change that is proportional to the current value; characterized by a time-constant (τ) and half-time.

Half-time

Time required for a quantity to reach half of its initial value in an exponential process.

Time-Constant (τ)

Time to reach about 63.2% of the total change; used to describe VO2 kinetics and other exponential processes.

Steady-State (SS)

A constant level of a variable after an initial transient during exercise or other stimulus.

Curve-Fitting and Least Squares

Statistical method to fit a chosen curve (linear, exponential, sigmoidal) to data by minimizing the sum of squared deviations (least squares).

Line of Best Fit/Linear Regression

Best straight-line approximation to data: y = mx + b; m is slope, b is intercept.

External vs Internal Validity

External validity concerns generalizability; internal validity concerns study design and causality within the sample.

Measurement Calibration

Process of ensuring measurement tools provide accurate, consistent values.

Gatorade Sport Science Institute (GSSI)

Organization providing sports science resources and research related to hydration and performance.

Canadian Society for Exercise Physiology (CSEP)

Canadian professional organization offering certifications and guidelines in exercise physiology.

Ergogenic Aids

Substances or methods claimed to enhance physical performance (e.g., caffeine, steroids, training).