Energy systems practice questions.

A basketball player performs a maximal 25 s shuttle effort. Which route supplies the greatest proportion of the ATP used?

• The phosphagen system using stored phosphocreatine
• The aerobic oxidation of muscle glycogen in mitochondria
• Anaerobic glycolysis of muscle glycogen
• Beta oxidation of free fatty acids from adipose tissue

Answer: Anaerobic glycolysis of muscle glycogen

The phosphocreatine store is largely spent within about 10 s, so beyond that the fastest remaining route is the anaerobic breakdown of glycogen to lactate, which dominates until roughly 2 min. All three systems still contribute at every moment; only their shares change.

Which feature distinguishes the phosphagen system from anaerobic glycolysis in the muscle of a sprinter?

• It yields the larger total amount of ATP of the two
• It uses muscle glycogen as its main substrate
• It depends on the rate of oxygen delivery to the muscle
• It resynthesises ATP without forming lactate

Answer: It resynthesises ATP without forming lactate

Phosphocreatine donates its phosphate directly to ADP in a single reaction, so no lactate is formed and the system is described as alactic. It has the highest rate of ATP resynthesis but, because the phosphocreatine store is very small, the lowest total yield, so it does not yield more ATP than glycolysis.

Which statement about the three energy systems during a 1500 m race is correct?

• All three contribute throughout, with their shares changing
• The aerobic system only begins to supply ATP after about two minutes
• The phosphagen system switches off as soon as glycolysis begins
• Anaerobic glycolysis stops completely once a steady state is reached

Answer: All three contribute throughout, with their shares changing

The systems are not switches but overlapping contributors whose relative shares shift with the duration and intensity of the effort. Aerobic ATP production begins with the first stride; it simply takes two to three minutes to reach its full rate.

According to the Fick equation, which product determines the oxygen uptake of a rower during an incremental test?

• Heart rate multiplied by the arteriovenous oxygen difference
• Stroke volume multiplied by the rate of pulmonary ventilation
• Cardiac output multiplied by the arteriovenous oxygen difference
• Cardiac output multiplied by the respiratory exchange ratio

Answer: Cardiac output multiplied by the arteriovenous oxygen difference

The Fick equation states that oxygen uptake equals the volume of blood pumped each minute multiplied by the oxygen extracted from each unit of that blood. Heart rate alone is only one of the two factors of cardiac output, so it cannot determine uptake by itself.

After eight weeks of threshold training a cyclist reaches the same blood lactate concentration at a higher power output than before. What has happened to her lactate inflection point?

• It has fallen, because trained muscle produces more lactate at any given power output
• It is unchanged, because the inflection point is fixed by the fibre types she was born with
• It has moved to a higher power output, so she can hold a faster pace aerobically
• It has moved to a lower power output, because her maximal oxygen uptake has risen

Answer: It has moved to a higher power output, so she can hold a faster pace aerobically

The lactate inflection point is the intensity above which lactate accumulates faster than it is cleared, and training shifts it to the right through greater mitochondrial density, capillarisation and clearance. That shift raises sustainable race pace even when maximal oxygen uptake barely changes.

Two athletes finish sessions of the same total oxygen cost, one a steady 45-minute ride and one six maximal 40-second efforts. Which comparison of the excess post-exercise oxygen consumption is correct?

• It is the same after both sessions, because the total oxygen cost of the two is the same
• It is larger after the steady ride, because that session lasted very much longer
• It is negligible after both, because oxygen uptake returns to rest within about a minute
• It is larger after the interval session, whose intensity leaves more to be restored

Answer: It is larger after the interval session, whose intensity leaves more to be restored

Excess post-exercise oxygen consumption tracks how far intensity has disturbed the body: phosphocreatine stores, oxygen bound to myoglobin and haemoglobin, catecholamine concentrations and body temperature all have further to travel back after maximal efforts. Total work done matters far less than the intensity at which it was done.