How does aerobic capacity change as an individual ages, assuming no change in activity level?

As individuals age, aerobic capacity generally declines due to a variety of physiological factors, including changes in cardiovascular and muscular systems, as well as alterations in metabolism. This decline is often observed even when activity levels remain consistent. The linear decrease reflects the predictable trajectory of aerobic fitness through the aging process.

Muscle mass typically diminishes with age, leading to reduced strength and endurance, which in turn affects one's ability to perform aerobic activities. Additionally, factors such as a decrease in maximal heart rate and overall cardiovascular efficiency contribute to this decline.

While some may argue that aerobic capacity could remain stable or even fluctuate based on different life stages or specific training regimens, the most common trend observed in the general population is a gradual and linear decrease with age, assuming no change in activity levels. This is why the answer indicating a linear decrease in aerobic capacity as individuals age is correct.