The concept of the "cardio triangle" is discussed in the context of cardiorespiratory fitness and the goal of maximizing the area of a triangle, which has a base and a peak. This concept is explored in the following excerpts:

1. At 00:44:38 to 00:44:54, it is mentioned that if someone is committed to developing their cardiorespiratory fitness, they should remember that the goal is to maximize the area of a triangle. The triangle has a base and a peak, and the aim is to optimize both aspects.

2. This idea is part of a broader discussion on VO2 max and its importance in cardiorespiratory fitness. For instance, VO2 max is described as a significant metric, although not necessarily the single best one, due to its extensive study and available data (00:17:10 to 00:17:19).

3. To improve VO2 max, different exercises and methods are recommended, such as using a hill for intervals (00:50:37 to 00:50:54) or performing specific time intervals on various machines like treadmills and rowing machines (00:53:49 to 00:53:55).

By focusing on these points, the concept of the cardio triangle emphasizes the balance and optimization of different elements of cardiorespiratory fitness, particularly through targeted exercises and understanding key metrics like VO2 max.