Energy Systems
Which energy system produces ATP the fastest but has the lowest total capacity?
Phosphagen system – provides immediate ATP for high-intensity, short-duration activity.
Why is “lactic acid buildup” considered a myth?
Lactic acid doesn’t exist in the body; it’s lactate (lactic acid minus H⁺). Lactate can be reused as fuel.
How does endurance training affect VO₂max and red blood cell volume?
Increases VO₂max by 10–30% and expands RBC volume, improving oxygen delivery.
Define an acute response to exercise.
A rapid, short-term physiological change occurring during or immediately after a single bout.
What is overreaching and how does it differ from overtraining?
→ Overreaching = short-term performance decline reversible with rest; overtraining = chronic maladaptation and prolonged decline.
What term describes the total of all catabolic and anabolic reactions in the body?
Metabolism
At rest, about what percentage of ATP is derived from fats versus carbohydrates?
~70% from fats and ~30% from carbohydrates.
What is the difference between lactate threshold (LT) and onset of blood lactate accumulation (OBLA)?
LT = when lactate is produced faster than it can be cleared; OBLA = sharp increase in lactate production/slope
What does VO₂ measure, and what are its typical units?
Volume of oxygen used per minute; measured in mL·kg⁻¹·min⁻¹.
Define an adaptation to exercise.
A chronic, long-term change resulting from repeated training that persists over time.
Name the two subtypes of overtraining and what causes each.
Parasympathetic (excessive volume, endurance); Sympathetic (high-intensity overload, anaerobic/resistance).
During short, high-intensity exercise, which two high-energy molecules supply immediate ATP?
Stored ATP and creatine phosphate (CP)
What energy system is the primary source of ATP for high-intensity activity up to ~2 minutes?
Glycolytic system – breaks down carbohydrates to produce ATP.
Define glycolysis and list its two possible fates for pyruvate.
Breakdown of glucose or glycogen to form ATP; pyruvate → lactate (fast glycolysis) or enters mitochondria (slow glycolysis).
What is VO₂max and what systems of the body contribute to it?
Maximum rate of oxygen use; depends on lungs, heart, blood, and muscles.
Give one acute and one chronic cardiovascular change from training.
Acute: increased HR, SV, and Q. Chronic: increased SV, lower resting HR, increased capillary density.
What is a key indicator that overtraining has occurred?
Decreased performance despite continued or increased training load.
Which chronic muscular adaptation to resistance training is more pronounced in Type II fibers than Type I fibers?
Hypertrophy (increase in myofibrils and structural proteins)
Explain why all three energy systems are active at any given time, even if one predominates.
All systems work together to replenish ATP; intensity and duration determine which contributes most.
What training adaptation allows LT and OBLA to occur at higher percentages of VO₂max?
Aerobic training increases lactate clearance and oxidative efficiency, shifting thresholds to the right.
What does the Respiratory Exchange Ratio (RER) indicate, and how does it change from rest to exercise?
RER shows fuel use; ~0.75–0.85 at rest (fat), 0.85–1.0+ during exercise (carb use increases).
Why does plasma volume decrease and hematocrit increase acutely during cardio exercise?
Fluid shifts out of blood and sweat loss reduce plasma volume, making blood more concentrated (↑ hematocrit).
What happens to VO₂max and cardiac output within two weeks of detraining?
Both decrease; aerobic enzyme activity and endurance decline.
What two main changes occur in skeletal muscle with long-term aerobic training that improve endurance performance?
Increased mitochondrial density/size and increased capillary density
Describe what causes the shift from fat to carbohydrate utilization as exercise intensity increases.
Higher intensity requires faster ATP production; carbs oxidize faster than fats, so reliance shifts to carbs.
Describe how lactate can be cleared and reused after exercise.
Through the Cori Cycle — lactate is transported to the liver and converted back to glucose.
Explain the terms oxygen deficit and oxygen debt (EPOC).
Deficit = at exercise onset, O₂ supply lags demand. Debt (EPOC) = elevated O₂ uptake post-exercise to restore baseline.
Describe how stroke volume and heart rate change with chronic aerobic training and what that means for cardiac efficiency.
Stroke volume increases, resting HR decreases → higher cardiac output with less effort (greater efficiency).
List three physiological changes that occur after four weeks of detraining.
Reduced muscle respiratory ability, decreased glycogen levels, increased lactate production.
Explain why cellular changes to absolute levels of enzymes and substrates may result in no change to relative levels of anaerobic metabolism after resistance training.
Both anaerobic and aerobic enzyme capacities increase proportionally, so at a given workload the relative energy contribution from each system stays about the same.