Final answer:
With aging and lower exercise intensity and volume, there is a decrease in maximal heart rate and maximal O₂ difference in healthy adults, while the impact on maximal stroke volume might be less pronounced.
Step-by-step explanation:
The question is asking what happens to certain cardiovascular parameters such as maximal heart rate, maximal stroke volume, and maximal O₂ difference as a result of aging in healthy adults combined with lower intensity and volume of exercise. As people age, their hearts undergo various changes, impacting their cardiac capacity during physical activities. Typically, aging is associated with a decrease in the maximal heart rate primarily because there is a reduction in the heart's ability to beat as rapidly during activity or stress in comparison to when one was younger. Stroke volume, which refers to the amount of blood pumped by the left ventricle of the heart in one contraction, may however be less affected especially in those who maintain regular, albeit less intense, exercise. The maximal O₂ difference, which indicates the body's ability to extract and utilize oxygen from the blood, is also expected to decrease, as aging affects the efficiency of various physiological systems involved in oxygen delivery and utilization.
Therefore, the correct answer is:
d. Decrease in maximal O₂ difference.