VT1 is called the First Ventilatory Threshold. It is a marker of intensity that can be heard in a person’s breathing at a point where lactate begins to accumulate in the blood. As the intensity of the exercise begins to increase, VT1 can be identified at the point where the breathing rate begins to increase. A person who is at VT1 can no longer talk comfortably while exercising. VT2 is called the Second Ventilatory Threshold. It is a higher marker of intensity that can also be heard in the person’s breathing. At VT2, the lactate has quickly accumulated in the blood and the person needs to breath heavily and can no longer speak at this intensity. At this point, the exercise duration will also decrease due to the intensity level. This marker can also be called the anaerobic threshold or lactate threshold. VO2 max is the maximal consumption of oxygen. It is the maximum capacity of the body to transport and use oxygen during exercise and reflects a person’s physical fitness. Measuring VO2 max is a laboratory procedure that requires equipment to measure the amount of oxygen consumed and the amount of carbon dioxide expelled. This test will take an individual to the absolute maximum exercise intensity that he or she can achieve; maximum heart rate can also be measured at this point. A deconditioned individual has a lower VO2max than someone who is conditioned. As an individual becomes more conditioned, his or her VO2 max will increase. Here is a simple way to picture these markers of exercise intensity: REST ---------VT1 (breathing begins to increase) --------------VT2 (out of breath, high intensity) ------------------VO2max (exercise needs to conclude due to exhaustion) A sedentary person will reach VT1, VT2 and VO2max at a much lower intensity of exercise than a more physically active person. For example, an extremely deconditioned person may reach his or her VT1 just while walking. Conversely, a more conditioned person will reach these markers at a higher intensity of exercise. For example, he or she may reach VT1 at a running speed of 6 miles per hour.