VO2 peak occurs when:

VO2 peak is the highest rate of oxygen consumption measured during incremental exercise testing, typically indicating an individual's aerobic capacity. It is essential for accurately assessing cardiovascular and muscular fitness.

The correct choice emphasizes that VO2 peak can be claimed before a plateau in VO2 is reached, making it possible to record maximum oxygen consumption without having achieved the absolute maximum effort associated with VO2 max. Additionally, it recognizes the importance of the respiratory exchange ratio (RER)—a ratio of carbon dioxide production to oxygen consumption—in confirming that the individual has reached high-effort exercise levels. An RER greater than 1.15 typically suggests a shift to anaerobic metabolism, aligning with maximal effort indicators.

Therefore, if the exercise test is stopped prior to the plateau in VO2 while also observing an RER greater than 1.15, it signifies that the test participant has reached a peak effort indicative of high metabolic demands, reaffirming that substantial energy is being expended.

This comprehensive view ensures that the resulting VO2 peak adequately reflects the exercise intensity and physiological responses, supporting effective assessment and programming in a clinical exercise physiology context.