ACSM-EP Anatomy & Physiology — Questions and Answers
Question 1: A client at rest has a heart rate of 75 bpm and a stroke volume of 70 mL per beat. What is the resting cardiac output?
- 3.5 L/min
- 5.25 L/min (Correct answer)
- 7.5 L/min
- 9.3 L/min
Correct answer: 5.25 L/min
Cardiac output = HR x SV = 75 x 70 mL = 5,250 mL/min, or about 5.25 L/min.
Cardiac output (Q) equals heart rate times stroke volume. Here 75 beats/min x 70 mL/beat = 5,250 mL/min = 5.25 L/min, which is typical for a resting adult (about 4-8 L/min). Choosing 7.5 L/min results from using a stroke volume of 100 mL, and 3.5 L/min from an arithmetic or unit error. During maximal exercise Q can rise to 20-25 L/min or more in healthy adults.
Question 2: During maximal exercise a client has a heart rate of 180 bpm, a stroke volume of 100 mL, and an arteriovenous oxygen difference of 15 mL O2 per 100 mL blood. Using the Fick equation, what is the approximate VO2?
- 1.2 L/min
- 3.6 L/min
- 2.7 L/min (Correct answer)
- 27 L/min
Correct answer: 2.7 L/min
Q = 180 x 0.100 L = 18 L/min; VO2 = Q x a-vO2 diff = 18 x 0.150 L/L = 2.7 L/min.
The Fick equation states VO2 = Q x (a-vO2 difference). Cardiac output is 180 x 100 mL = 18,000 mL/min = 18 L/min. The a-vO2 difference of 15 mL/100 mL equals 150 mL per liter (0.150 L/L), so VO2 = 18 x 0.150 = 2.7 L/min. The 27 L/min option is a decimal-place error, and 3.6 or 1.2 L/min come from misreading the units. Both Q and the a-vO2 difference rise during exercise and together determine VO2max.
Question 3: What is the primary physiological reason a highly trained endurance athlete has a higher VO2max than a sedentary peer of the same age?
- A much higher maximal heart rate
- A greater maximal stroke volume and cardiac output (Correct answer)
- A lower arteriovenous oxygen difference
- A lower maximal ventilation
Correct answer: A greater maximal stroke volume and cardiac output
Maximal heart rate is similar between the two, so the higher VO2max is mainly due to a larger maximal stroke volume and cardiac output.
VO2max = maximal cardiac output x maximal a-vO2 difference. Endurance training does not meaningfully raise maximal heart rate (it is mostly age-determined, and may even fall slightly), so the central adaptation is a larger left ventricular volume, blood volume, and stroke volume. Peripheral adaptations (capillary density, mitochondria) increase oxygen extraction, so a-vO2 difference is higher, not lower. This is why the central limit to VO2max in healthy people is considered to be oxygen delivery.
Question 4: According to the size principle of motor unit recruitment, which motor units are recruited first as force demands increase?
- Large, fast-twitch units with high thresholds
- Smaller, slow-twitch units with low thresholds (Correct answer)
- Fast glycolytic units only
- All motor units simultaneously
Correct answer: Smaller, slow-twitch units with low thresholds
The size principle states that small, low-threshold slow-twitch motor units are recruited first, with larger fast-twitch units added as force demands rise.
Henneman's size principle says motor units are recruited in order of size, from small Type I units with low thresholds to larger Type IIa and then IIx units. This allows fine control at low force and the efficient use of fatigue-resistant fibers first. During light aerobic activity mainly Type I fibers are used; Type II fibers are recruited during high-intensity or heavy resistance efforts. Recruiting all units simultaneously does not occur in normal voluntary movement.
Question 5: Which energy system is the predominant source of ATP during the first 10 seconds of a maximal-effort sprint?
- Aerobic oxidation of fat
- Aerobic oxidation of carbohydrate
- Phosphagen (ATP-PC) system (Correct answer)
- Anaerobic glycolysis
Correct answer: Phosphagen (ATP-PC) system
The phosphagen (ATP-PC) system supplies most ATP for maximal efforts lasting up to about 10 seconds.
The ATP-PC system provides immediate energy by breaking down stored phosphocreatine and is dominant for maximal efforts of roughly 0-10 seconds. Anaerobic glycolysis becomes the main contributor from about 10-30 seconds and up to 2 minutes, while the oxidative system dominates efforts longer than about 2-3 minutes. Aerobic fat oxidation is the slowest to supply ATP and supports low-intensity prolonged work. Recognizing which system dominates by duration is a core exercise physiology concept.
Question 6: During 45 minutes of moderate-intensity steady-state exercise, which hormonal response is expected?
- Increased insulin and decreased epinephrine
- Decreased insulin and increased glucagon and catecholamines (Correct answer)
- Increased insulin and increased glucagon
- No change in any glucoregulatory hormones
Correct answer: Decreased insulin and increased glucagon and catecholamines
Insulin falls while glucagon, epinephrine and norepinephrine rise to mobilize glucose and fatty acids.
During prolonged exercise insulin secretion falls, while glucagon, epinephrine, norepinephrine, cortisol and growth hormone rise to increase hepatic glucose output and lipolysis. Muscle contraction also increases glucose uptake independent of insulin, which is why exercise lowers blood glucose in people with diabetes. Rising insulin with falling catecholamines would be the opposite of the fuel-mobilizing pattern needed. This is why insulin-treated clients may need dose or carbohydrate adjustments around exercise.
Question 7: In the sliding filament mechanism, which event directly allows myosin heads to bind to actin and form cross-bridges?
- ATP binding to the myosin head
- Calcium binding to troponin, which moves tropomyosin off the active sites (Correct answer)
- Hydrolysis of creatine phosphate in the sarcoplasm
- Sodium release from the T-tubules
Correct answer: Calcium binding to troponin, which moves tropomyosin off the active sites
Calcium released from the sarcoplasmic reticulum binds troponin, shifting tropomyosin and exposing actin binding sites.
When a motor neuron action potential reaches the muscle fiber, calcium is released from the sarcoplasmic reticulum and binds troponin. This moves tropomyosin away from the myosin binding sites on actin so cross-bridges can form. ATP binding to myosin actually causes detachment from actin, and ATP hydrolysis re-cocks the head for the next power stroke. Without ATP, cross-bridges stay attached, which explains rigor mortis.
Question 8: Which blood pressure response is expected during a graded dynamic exercise test in a healthy adult?
- Systolic and diastolic both rise linearly
- Systolic rises progressively while diastolic stays the same or decreases slightly (Correct answer)
- Systolic decreases while diastolic rises
- Both systolic and diastolic fall
Correct answer: Systolic rises progressively while diastolic stays the same or decreases slightly
During dynamic exercise systolic BP rises with workload while diastolic BP stays about the same or falls slightly.
Systolic BP typically rises about 10 mmHg per MET during graded dynamic exercise because of increased cardiac output. Diastolic BP remains within about 10 mmHg of resting or declines slightly due to vasodilation in active muscle. A fall in systolic BP of more than 10 mmHg with increasing workload, or a diastolic rise above 110 mmHg, is a reason to stop a test per ACSM. Resting SBP above 200 mmHg or a failure to rise are abnormal findings.
Question 9: During a graded exercise test, the point at which minute ventilation begins to rise disproportionately faster than oxygen uptake is called the:
- Ventilatory threshold (Correct answer)
- Maximal oxygen uptake
- Respiratory exchange plateau
- Anatomical dead space point
Correct answer: Ventilatory threshold
The ventilatory threshold marks the nonlinear rise in VE relative to VO2 as buffering of lactate adds CO2.
The first ventilatory threshold (VT1) is the point where VE increases out of proportion to VO2, reflecting increased CO2 production from bicarbonate buffering of lactic acid. It corresponds roughly to the upper limit of moderate intensity and is the basis of the talk test. VO2max is the highest uptake attained, not a threshold in the VE-VO2 relationship. Anatomical dead space is the volume of conducting airways that does not take part in gas exchange.
