Wk 1 - Control of internal environment and cardiopulmonary exercise testing Flashcards
What is homeostasis?
-Homeostasis -> A fundamental principle of body function. All variables of physiological mechanisms must operate within a narrow range of values. There needs to be a balance between different variables. This means that homeostasis of one variable is not independent of other variables.
-Homeostasis -> One of the core concepts critical to understanding physiology. Claude Bernard 1857.
-Homeostasis -> Maintenance of a constant and ‘normal’ internal environment
Steady state (exercise) and homeostasis
-Steady state (exercise) -> Physiological variable is unchanging, but not necessarily ‘normal’. Balance between demands placed on body and body’s response to those demands. Examples: heart rate, body temperature and arterial blood pressure.
What are the biological control systems of the body?
- Intracellular control systems -> Protein breakdown and synthesis, energy production, maintenance of stored nutrients
- Organ systems -> Pulmonary and circulatory systems, replenish oxygen and remove carbon dioxide.
+A single bout of exercise can cause a lot of stress on multiple organ systems in the body
What are the biological control system components?
+Biological control systems are a series of interconnected components that maintain a physical or chemical parameter at a near constant value. Components:
* Sensor or receptor – detects changes in variable
* Control centre – assesses input and initiates response
* Effector – changes internal environment back to normal
What are the negative, positive and gain feedbacks within physiological feedback systems?
-Negative feedback -> Response reverses the initial disturbance in homeostasis. Most control systems work via negative feedback. Example: respiratory systems control of CO2 concentration in extracellular fluid.
-Positive feedback -> Biological response increases the original stimulus. Example is childbirth.
-Gain (or sensitivity of the response) -> Degree to which a control system maintains homeostasis. Pulmonary and cardiovascular systems have large gains (thus more capable of maintaining homeostasis)
What are 4 examples of homeostatic controls?
- Regulation of body temperature - Thermal receptors send message to brain. Response by skin blood vessels and sweat glands regulates temperature.
- Regulation of blood glucose - Requires the hormone insulin. Diabetes – failure of blood glucose control system
- Regulation of cellular homeostasis – Stress proteins (heat shock proteins). Repairs damages proteins to restore homeostasis in response to changes in temperature, pH and free radicals.
-Exercise is a major test for homeostatic control. Exercise disrupts homeostasis by changes in pH, PO2, PCO2 and temperature in cells. Inability to maintain steady state = fatigue and cessation of exercise.
What is adaptation and acclimation?
-Adaptation -> Change in structure and function of cell or organ system. Results in improved ability to maintain homeostasis but occurs much more slowly e.g. across generations. Many adaptive changes occur within cells and are linked to genetic changes.
-Acclimation -> Adaptation to environmental stresses e.g. heat or hypoxic stress. Results in improved function of existing homeostatic system. Change in phenotype that is reversible and occurs very rapidly (sometimes in a few minutes).
What is hormesis?
-Hormesis -> Process in which a low-to-moderate dose of a potentially harmful stress (for example, chemical agent or environmental stress) results in a beneficial adaptive response on the cell or organ system. Exercise-induced hormesis defines much of what we know about exercise-induced adaptation in the body.
Draw and describe the diagram for exercise-induced hormesis:
-Exercise-induced hormesis control -> Changes in structure and function of cells or organ systems. Improved ability to maintain homeostasis.
Describe the 5 mechanisms by which cellular adaptation occurs:
-Cell signalling pathways promote cellular adaptation
-Cell signalling -> Communication between cells using chemical messages (CM). Coordinates cellular activities. Important for maintaining homeostasis. Five different cell signalling pathways exist in cells:
1. Intracrine signalling – CM inside cell triggers response
2. Juxtracrine signalling – CM passes between 2 connected cells
3. Autocrine signalling – CM acts on that same cell
4. Paracrine signalling – CMs act on nearby cells
5. Endocrine signalling – CMs (that is hormones) released into blood. (Affects cells with specific receptor to the hormone).
What does fitness testing do?
-Testing allows coaches and sports scientists to analyse the progress an athlete is making with objective, quantitative measures, and extract information on the effectiveness of programming, recovery modalities and readiness to return to play following injury
-Aerobic capacity i.e. VO2 Max, is a vital component and determining factor for performance in sports/ events lasting longer than ~3 mins predominantly reliant on aerobic energy production
Draw the testing loop
Describe cardiorespiratory fitness (VO2 max testing)
-Cardiorespiratory fitness refers to the interactions between the heart (cardiac) and the lungs (respiratory) that maximise performance and recovery
* The ability of an individual to perform a strenuous task for a prolonged period (where large muscle groups are used) defines an individual’s cardiorespiratory endurance
* The maximal rate of oxygen consumed defines an individual’s cardiorespiratory power, and is known as VO2 max/ peak
What are the 3 types of cardiorespiratory fitness tests:
- The first type compares an individual’s performance to population norms e.g. beep test, step test
- The second is a submaximal prediction test (e.g. treadmill walking), often performed in older, clinical populations
- The third directly measures cardiorespiratory fitness based on an individual’s maximal oxygen consumption (absolute VO2 max) at or near to exhaustion
-The higher the VO2 max, the greater ability an individual has to sustain aerobic work at a higher intensity for a longer time
What defines and determines VO2 max?
-VO2 Max -> ‘Physiological ceiling’ for delivery of O2 to muscles. Affected by genetics and modified by training.
-Oxygen uptake increases linearly until maximum oxygen uptake (VO2 Max) is reaches. No further increase in VO2 with work rate.
How do you verify that VO2 max has been reached?
-Gold standard for verification of VO2 max is a plateau in O2 consumption despite an increase in work rate
-Most participants do not achieve a plateau in O2 consumption during an exercise test
-If a plateau in O2 consumption is not achieved, what secondary criteria can confirm VO2 max has been achieved? Criteria include:
1. Reaching age-predicted max HR
2. Achieving a blood lactate concentration of 8 mmol/L or higher
3. Attaining a respiratory exchange ratio (RER= VCO2/VO2) of 1.15 or higher
4. Verification test – individual performs another exercise test after a period of recovery at a higher intensity than the last stage of the incremental test to see if they can reach a higher VO2 max
Describe VO2 max in endurance athletes:
-Elite endurance athletes typically have values of 60+ for females and 70+ for males
-Positive correlation between VO2 mac and endurance performance but this becomes weaker in well-trained athletes
-VO2 max isn’t that trainable in elite endurance athletes who may have already maximised adaptations
-Performance often improves independent of VO2 max at an elite level: running economy, lactate threshold and anaerobic capacity
Describe velocity at VO2 max
-The speed at which VO2 max is elicited – how fast are you running when you reach your VO2 max?
-Stronger predictor of endurance running performance than VO2 max alone, particularly for middle-distance events which are run ~95-120% VO2 max
-A combined measure of VO2 max and running economy – the oxygen cost of running at a given speed (ml/ kg/km)
What is fractional utilisation (% of VO2 max)?
-Whilst having a large V02 max is important, the ability to sustain a high percentage of that VO2 max (fractional utilisation) without fatiguing is equally important
-This is largely determined by the lactate threshold – the maximum intensity at which lactate production and clearance are in equilibrium and above which, lactate accumulates, and exercise becomes unsustainable.
-Therefore, the lactate threshold is also a strong predictor of performance for longer distance events (~15 min+)
What is anaerobic capacity?
-The ability to produce, tolerate and sustain maximal/ supramaximal work rates through anaerobic energy production
-Capacity to go beyond VOW max is dictated by anaerobic capacity (100% for every additional workload > VO2 max)
