1. Integration of Cardiovascular and Respiratory Function  Oxygen consumption is the amount of O 2 taken up and consumed by the body for metabolic processes  It is equal to the amount of oxygen inspired minus the amount of oxygen expired  VO 2 is proportional to workload  VO 2 (L/min) = [V I (L/min) x %O 2 inspired] - [V E (L/min) x %O 2 expired] Oxygen Consumption (VO 2 )

2.  Theoretically, VO 2 is a function of both O 2 delivery to and O 2 uptake by the working muscle and other tissue  Another way to describe O 2 uptake is a-vO 2 diff, which represents the average amount of O 2 in the arteries minus the average amount of O 2 in the vena cava  Described mathematically by the Fick Equation  VO 2 (L/min) = (SV x HR) x [a-vO 2 diff (mlO 2 / 100 ml of blood)]

3. Oxygen Consumption (VO 2 )  Therefore, the maximal rate of oxygen consumption (VO 2 max) would theoretically occur at maximum SV, HR, and a-vO 2 diff  VO 2 max is more properly defined as the maximal amount of O 2 that can be taken in and used for the metabolic production of ATP during exercise  To determine VO 2 max in the lab, VO 2 is measured using a metabolic cart and computer system, while the participant performs incremental exercise to exhaustion

4. Oxygen Consumption (VO 2 )  Such exercise can be performed using either a cycle ergometer or a treadmill  VO 2 max is used as a measure of aerobic fitness, and is indicative of aerobic exercise performance  VCO 2 is calculated by measuring the difference between the amount of CO 2 expired and inspired  The amount of CO 2 produced and O 2 consumed varies depending on the type of fuel being used by the working muscle

5. Oxygen Consumption (VO 2 )  When fat is being oxidized and used to produce ATP, more O 2 is consumed as compared to the amount of CO 2 produced  When carbohydrate is the major fuel used to produce ATP, not as much O 2 is consumed relative to the amount of CO 2 produced  When only carbohydrate is being used, the ratio of VCO 2 to VO 2 is equal to 1  RER is close to 0.7 when the main fuel being used is fat  Therefore, RER allows a way to estimate relative contribution of the different fuels used in skeletal muscle during exercise

6. Limiting Factors for VO 2 max  The respiratory system could potentially limit VO 2 max through (a) inadequate ventilation and (b) oxygen diffusion limitations  The cardiovascular system could limit VO 2 max because of (a) inadequate blood flow and/or cardiac output, or (b) inadequate oxygen- carrying capacity (hemoglobin concentration)  Within the working muscle, a lack of mitochondria and the metabolic systems involved with the use of O 2 could also potentially limit VO 2 max

7. Limiting Factors for VO 2 max  Exercise physiologists are supporting the notion that it is the cardiovascular system that limits VO 2 max in healthy people  It appears that the cardiovascular system is unable to meet the demands of the working muscle and deliver an adequate amount of O 2  The limitation to VO 2 max within the cardiovascular system appears to be related to cardiac output (Q)

8. VO2max for Various Sports

9. The Rest to Exercise Transition  During incremental exercise, pulmonary ventilation initially increases at a rate proportional to the increase in workload  Eventually, a point is reached where ventilation increases much more rapidly than workload  This point is called the VENTILATORY THRESHOLD, and it normally occurs at about 65-85% of VO 2 max, depending on the individual’s level of fitness  Increase in ventilation thought to occur because of an increase in LACTIC ACID ACCUMULATION in the blood

10. The Rest to Exercise Transition  The energy demands of the exercise can no longer be met by only the aerobic metabolic systems  Hence, the anaerobic system are also used to meet the increasing energy requirements of the exercise  Eventually, a point is reached where blood lactate concentrations rise exponentially, resulting in very high concentrations  This point is referred to as the LACTATE THRESHOLD

11. Lactate Threshold

12. The Rest to Exercise Transition  When blood lactate levels begin to accumulate rapidly, this is referred to as the ONSET OF BLOOD LACTATE ACCUMULATION (OBLA)  With proper aerobic training, the OBLA curve can be shifted to the right such that OBLA occurs later and during higher levels of intense exercise