Which of the following is an example of a direct measurement of maximum heart rate?

A maximal effort test, such as a VO2max test, is the correct answer as it provides a direct measurement of maximum heart rate. During this type of test, an individual exercises at increasing levels of intensity until exhaustion, allowing for the estimation of maximum heart rate through physiological responses to exertion. This approach yields accurate and specific data, reflecting the true maximum heart rate attained by the individual under maximum exertion conditions.

In contrast, other options involve indirect methods or do not provide a clear measure of maximum heart rate. For instance, a step test typically assesses cardiovascular fitness and places the body under effort, but it does not directly measure the maximum heart rate achieved. Pulse palpation requires the observer to measure the heart rate at a given moment, often while the subject is at rest or during moderate activity, which may not reveal the maximum heart rate. A walking test similarly assesses lower levels of cardiovascular performance and does not push an individual to their maximum capacity, making it unsuitable for determining maximum heart rate.