General Principles and Exercise Science
Energy systems
The ATP–PCr (phosphagen) system dominates maximal efforts up to about 10 seconds; anaerobic glycolysis contributes from roughly 10 seconds to 2 minutes; oxidative phosphorylation underpins everything longer and supplies almost all energy at rest and in steady state. In team sports all three overlap, so a question asking for "the predominant system" wants the dominant contributor, not the only one.
Determinants of endurance performance
VO₂max, lactate threshold (the highest intensity at which blood lactate remains steady - typically 50–70% of VO₂max untrained and 70–85% trained) and movement economy. In trained athletes lactate threshold predicts endurance performance better than VO₂max. Lactate is a fuel and gluconeogenic precursor, not the cause of the acidosis; the H⁺ comes largely from ATP hydrolysis.
Training principles
Overload, specificity, reversibility, individuality and periodisation. Prescription uses the FITT-VP framework. 1 MET = 3.5 mL·kg⁻¹·min⁻¹; moderate intensity is 3–6 METs, vigorous above 6.
Integrative physiology
Cardiac output rises from ~5 to 20–25 L/min (higher in elite endurance athletes); stroke volume plateaus at 40–60% of VO₂max while heart rate keeps rising; the arteriovenous oxygen difference widens. Systolic pressure rises while diastolic stays flat or falls slightly.
Traps: HRmax = 220 − age has a standard deviation of 10–12 bpm and cannot be applied to an individual; eccentric muscle actions produce more force at lower metabolic cost but cause damage and DOMS; children have lower glycolytic capacity and poorer thermoregulation, yet supervised resistance training is safe and effective.
Rule of thumb: use the standard metabolic equations to convert a treadmill or cycle workload to VO₂, and remember running costs roughly 1 kcal·kg⁻¹·km⁻¹.