Which of the following is considered a sign of volitional exhaustion when assessing VO2 max?

Volitional exhaustion during a VO2 max assessment indicates that a subject has reached their maximum capacity and can no longer continue the exercise test due to fatigue. A key sign of this exhaustion is when a subject requests to stop the test. This request typically occurs when the individual feels they can no longer maintain the required intensity or effort, reflecting both physical and psychological limits.

In the context of VO2 max testing, volitional exhaustion is a crucial endpoint since it represents the maximum effort an individual can exert. This is distinctive from other options; for instance, muscle cramping may occur during intense exercise but does not necessarily indicate voluntary cessation of effort. Similarly, a subject requesting to continue suggests they still possess the capacity to perform, while a drop in heart rate might be indicative of fatigue but does not directly imply volitional exhaustion on its own. Thus, the significance of a subject's request to stop serves as a clear marker for reaching maximum exertion during the evaluation.