Maximal Oxygen Consumption Direct Measurement

Maximal Oxygen Consumption VO 2 max Greatest volume of oxygen that the body can consume per unit time Regarded as “gold standard” of aerobic fitness

Difference Between VO 2 max and VO 2 peak VO 2 peak is the highest level of oxygen consumption that can be achieved during a mode of exercise VO 2 max is the largest VO 2 peak for an individual –The mode of exercise during which VO2max occurs can vary, but is typically running or stair stepping –For individuals trained at a specific mode of exercise, it usually matches the mode of the training

VO 2 peak = Delivery x Utilization Influenced by amount of O 2 supplied to muscles and ability of muscles to utilize available O 2 VO2 = Q x (a-vO 2 diff.) –Called The Fick Equation –Q = Cardiac Output (L Blood/min) –a-vO 2 diff. = difference between arterial and venous oxygen content (L O2/L Blood)

Delivery –cardiac output 1. blood volume 2. venous return 3. resistance to blood flow –muscle capillary density Utilization –amount of lean mass –#/size of mitochondria –#/activity of oxidative enzymes –muscle fiber type Factors Involved In Delivery and Utilization

Influences on VO 2 max Largely genetically determined Training can improve it 5-20%, depending on initial fitness level Males score ~ 15–30% higher than females –Differences between gender due to: Muscle mass Hemoglobin concentration –However, many women can score higher than average men

VO 2 peak – Direct Measurement Can be measured either in absolute terms (liters per minute, L/min) or in relative terms (milliliters per kilogram of body weight per minute, ml/kg/min) Direct measurement during a maximum, graded exercise test provides most accurate assessment Increases in workload by increasing speed/grade of treadmill or resistance on bike until subject cannot continue

Measurement Issues Involves a large supramaximal anaerobic component How do we know when the VO 2 max has been reached

Three Criteria for a Valid Peak Test 1)RER > 1.1 2) > 90% age-predicted max HR 3) Plateau in VO 2 w/ increased intensity (not all subjects exhibit a plateau) Change < 0.15 L O 2 /min (absolute VO 2 )

Why RER? As exercise intensity increases, RER increases due to the greater increase in VCO2 relative to VO2 a. changes in substrate utilized b. non-metabolic CO2 (the product of anaerobic metabolism) RER allows us to see when the anaerobic contribution begins

Norm Values for VO 2 max (ml/kg/min) Age (years) Very HighHigh GoodAverageFairLow Males 20-29> < > < > < > < > <16 Females 20-29> < > < > < > < > <13