EP - Introduction to Exercise Flashcards
Describe the ATP energy system:
Adenosine Triphosphate (ATP): The primary energy carrier in cells, providing immediate energy for muscle contractions.
Structure: ATP consists of adenine, ribose, and three phosphate groups; energy is released when the terminal phosphate bond is broken (ATP → ADP + Pi + energy).
ATP Resynthesis: ATP is continuously regenerated through three main energy systems—aerobic, anaerobic, and ATP-PC.
Storage & Usage: Limited stores in muscle (~2-3 seconds of maximal effort), requiring rapid replenishment.
Describe the aerobic system:
If the demand for energy is sufficiently slow, enough O2 can be delivered to the muscles so that ATP can be replenished without lactate build up
Used during steady state exercise
Always a lag, energy must be supplied initially by the PCr/ATP andanaerobic systems
Oxygen deficit, paid off by the oxygen debt, provided by anaerobic metabolism
Pathways used:
- Glycolysis
- Krebs cycle
- Electron transport chain
End Products: ATP, CO₂, and H₂O; no lactic acid accumulation
Efficiency: Produces ~36-38 ATP per glucose but is slow; dominant in endurance activities
Describe the anaerobic system:
Anaerobic glycolysis (partially + quickly) creates ATP to transfer energy at approx 45% of the rate of PCr/ATP system
Glycogen broken down to lactate but produces metabolic poison - lactic acid
Oxygen-independent: Provides ATP rapidly but inefficiently for short-duration, high-intensity activities
Inefficient: produces less ATP per molecule of glucose than aerobic metabolism
Critical during explosive efforts like sprints, jumps, and weightlifting
Describe slow twitch muscle fibres:
Slow Oxidative, type I
Slow calcium handling, low ATPase, so slow speed of contraction
High mitochondrial density and capillary supply for oxygen transport
High myoglobin content (stores oxygen, giving red colour)
Primarily use the aerobic system, making them fatigue-resistant
Low force output but highly efficient for endurance activities (e.g., long-distance running, cycling)
Describe the 2 fast twitch fibres:
Type IIa - Fast Oxidative-Glycolytic Fibres:
- intermediate fibres; can function aerobically and anaerobically
- more resistant to fatigue than Type IIx but generate moderate power
- used in mid-duration activities
- high speed of contraction, good fatigue resistance
Type IIx - Fast Glycolytic Fibres:
- rely on anaerobic metabolism
- greatest anaerobic potential, fastest contraction speed but lowest fatigue resistance
- very quick ATP turnover in absence of oxygen
- used in explosive movements
Describe the different types of contraction:
Isotonic contraction
- muscle length changes during contraction
- Eccentric: muscle lengthens while resisting a force
- Concentric: muscle shortens while generating force
Isometric - muscle generates force without changing length or increasing the angle between 2 joints
Describe the lactic acid threshold:
Point at which blood lactate accumulation in working muscles > lactate oxidation by non working muscles (reproducible level of 3 mmol/litre)
Depends on heart and lungs ability to supply oxygenated blood to the tissues, therefore related to fitness and overall aerobic ability
While VO2 max may arguably be genetically determined, LAT can be trained
LAT can therefore be used as an index of relative fitness
Measured as blood lactate concentration
Training adaptations:
- aerobic training increases mitochondrial efficiency, delaying lactate accumulation
- interval training improves lactate buffering and clearance capacity
Describe the basal metabolic rate:
Energy required to maintain vital functions at complete rest.
Measured under strict conditions:
After 12 hours fasting
After a full night’s sleep
In a thermoneutral environment
While lying at complete physical and mental rest
It reflects the energy used by the body to maintain homeostasis — e.g., breathing, circulation, cellular metabolism, and thermoregulation
Increased by muscle mass, body surface area, hormones (like thyroxine), and growth states
Describe the resting metabolic rate:
RMR is the energy expended at rest, but less strictly controlled than BMR
It includes energy used for vital functions plus a small amount for minimal movement or recent digestion
RMR is easier to measure in practice and slightly higher than BMR
Measured after a short rest (around 30 mins), usually without overnight fasting
RMR is often used to estimate daily energy needs and calorie expenditure in fitness and nutrition planning
Describe different measurement techniques of energy demand:
Direct calorimetry - measures heat production in a chamber to estimate energy expenditure
Indirect calorimetry:
- Measures oxygen consumption (VO₂) and carbon dioxide production (VCO₂) to estimate energy expenditure
- VO₂ max tests determine an individual’s maximal oxygen uptake (aerobic capacity)
Respiratory Exchange Ratio:
- Ratio of CO₂ produced to O₂ consumed.
- 0.7 = Fat oxidation, 1.0 = Carbohydrate oxidation, >1.0 = Anaerobic metabolism
Describe the MET:
= Metabolic Equivalent of Task
Standardised unit of average resting oxygen consumption
1 MET = Energy expenditure at rest (~3.5 mL O₂/kg/min)
Light activity (<3 METs, e.g., walking).
Moderate activity (3-6 METs, e.g., jogging).
Vigorous activity (>6 METs, e.g., sprinting)
Describe the major pathways used in the anaerobic system:
Two Major Pathways:
ATP-PC (Phosphocreatine) System:
- Uses stored phosphocreatine (PC) in muscles to rapidly regenerate ATP
- Lasts ~10-12 seconds (e.g., sprinting, weightlifting).
No by-products, but quickly depleted
Anaerobic Glycolysis (Lactic Acid System):
- Converts glucose into pyruvate without oxygen, producing lactic acid as a by-product
- Generates 2 ATP per glucose, sustaining activity for ~30-90 seconds
- Causes muscle fatigue due to lactate and H⁺ accumulation (reducing pH)
Describe the Frank-Starling law in skeletal muscle:
Optimal sarcomere length (~2.0–2.2 µm in skeletal muscle) allows maximal overlap of actin and myosin → maximal force generation
If sarcomeres are too short (overlap too great) or too long (too little overlap), force production decreases
In skeletal muscle, optimal length is fixed and force is recruited by motor unit activation
In cardiac muscle, length is adjusted by venous return, and contraction strength changes intrinsically with filling
