Final answer:
The correct response is (a) VO₂ max. This represents the maximum volume of oxygen one can utilize during intense exercise, related to cardiovascular fitness. Age-predicted heart rate max guides the intensity of exercise, calculated as 220 minus the person's age.
Step-by-step explanation:
During a graded submaximal VO₂ test, clients should evaluate how hard they were able to exercise before reaching the barrier of age-predicted heart rate max. The correct answer is (a) VO₂ max.
VO₂ max is a measure of the maximum volume of oxygen that an individual can use during intense, maximal exercise. It is an indicator of an individual's cardiovascular fitness and aerobic endurance. The age-predicted maximum heart rate is a way to guide exercise intensity. This estimate can be obtained by subtracting the person's age from 220. For example, a 40-year-old individual would be expected to hit a maximum rate of approximately 180 bpm (beats per minute).
The concept of cardiac output (CO) is also pertinent when considering exercise intensity. CO is the volume of blood the heart pumps in a minute and it increases with exercise, as both heart rate (HR) and stroke volume (SV) increase. However, there is a point at which the HR continues to increase, but the SV starts to decrease, leading to a peak in the CO reached at submaximal levels of exercise before the onset of fatigue.