Maximal Oxygen Consumption

Direct Measurement

Maximal Oxygen Consumption

• VO2max

• Greatest volume of oxygen that the body can consume per unit time

• Regarded as “gold standard” of aerobic fitness

Difference Between VO2max and VO2peak

• VO2peak is the highest level of oxygen consumption that can be achieved during a mode of exercise

• VO2max is the largest VO2peak 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

VO2peak = Delivery x Utilization

• Influenced by amount of O2 supplied to

muscles and ability of muscles to utilize available O2

• VO2 = Q x (a-vO2diff.)

– Called The Fick Equation– Q = Cardiac Output (L Blood/min)

– a-vO2 diff. = difference between arterial and venous oxygen content (L O2/L Blood)

• Delivery– cardiac output

1. blood volume 2. venous return3. 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 VO2max

• 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

VO2peak – 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 VO2max has been reached

Three Criteria for a Valid Peak Test

1) RER > 1.1

2) > 90% age-predicted max HR

3) Plateau in VO2 w/ increased intensity (not all subjects exhibit a plateau)

Change < 0.15 L O2/min (absolute VO2)

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 VO2max (ml/kg/min)Age

(years)Very High High Good Average Fair Low

Males            

20-29 >61 53-61 43-52 34-42 25-33 <25

30-39 >57 49-57 39-48 31-38 23-30 <23

40-49 >53 45-53 36-44 27-35 20-26 <20

50-59 >49 43-49 34-42 25-33 18-24 <18

60-69 >45 41-45 31-40 23-30 16-22 <16

Females            

20-29 >57 49-57 38-48 31-37 24-30 <24

30-39 >53 45-53 34-44 28-33 20-27 <20

40-49 >50 42-50 31-41 24-30 17-23 <17

50-59 >42 38-42 28-37 21-27 15-20 <15

60-69 >39 35-39 24-34 18-23 13-17 <13