UMass Amherst KIN 470 - Lab 3 Handout_Vo2Max_adjusted (4 pages)

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Lab 3 Handout_Vo2Max_adjusted



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Lab 3 Handout_Vo2Max_adjusted

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School:
University of Massachusetts Amherst
Course:
Kin 470 - Exercise Physiology
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LABORATORY 3 MAXIMUM OXYGEN CONSUMPTION IMPORTANT TERMS 1 2 3 4 5 6 7 Cardiac Output Oxygen Delivery Oxygen Utilization AVDO2 Maximal aerobic power VO2 max Incremental exercise test Ventilatory Breakpoint IMPORTANT CONCEPTS 1 2 3 Max VO2 HR max SV max AVDO2 max Fick Equation Relationship of VO2 work and heart rate Measurement of VO2max a Incremental test b Prediction test INTRODUCTION In the early 1920 s Hill and Lupton reported that each individual has a maximum level of oxygen uptake The energy required for work to be done above this maximum level is provided by anaerobic metabolism In the 1950 s Astrand and Taylor developed standard experimental techniques for measuring the maximum oxygen consumption denoted as VO2 max The procedure they developed depends on the progressive relationship between VO2 and work rate At a certain point further increases in the work rate do not produce any further increases in VO2 VO2 max is generally considered to be the best single physiological indicator of an individual s ability to sustain dynamic muscular activity and is a measure of aerobic power Measurement of VO 2 max involves a progressive incremental test performed on an exercise device such as a treadmill or cycle ergometer The test can either involve work being performed continuously or with rest periods interspersed between exercise bouts discontinuous test The two factors that determine VO2 max are the capacity for oxygen delivery and oxygen utilization Maximum oxygen delivery is a direct function of the oxygen carrying capacity hemoglobin saturation and cardiac output Q which is the amount of blood pumped by the heart per minute Cardiac output is dependent on stroke volume the amount of blood pumped per heartbeat SV and heart rate HR Q SV HR Oxygen utilization depends on the cellular capabilities of the muscle for aerobic metabolism These include aerobic enzyme activity number and size of the mitochondria muscle perfusion and capillary density The difference in oxygen content between arterial and venous blood AVDO 2 reflects the magnitude of oxygen utilization by the muscle The total oxygen consumption is therefore a product of Q and AVDO2 VO2 Q AVDO2 Rearranged this gives VO2 HR SV AVDO2 1 During exercise changes in HR SV and AVDO2 account for the changes in oxygen consumption In most individuals stroke volume reaches maximum levels at approximately 40 of VO2 max Heart rate and AVDO2 increase throughout the range of exercise intensity and are responsible for VO 2 increases throughout incremental exercise There is much debate over what is the limiting factor for VO2 max Some researchers report that skeletal muscles are able to use oxygen at a higher rate than what can be met by the cardiovascular and respiratory systems The current predominant opinion is that the cardiac output is the primary limitation of whole body oxygen consumption There is a fairly broad range of values for VO2 max depending on such factors as exercise mode training status age and gender Since the whole body uses oxygen it follows that a larger individual has a greater absolute VO2 max l min than a smaller person both at rest and during exercise For comparative purposes VO2 max is usually expressed relative to body mass ml kg min or relative to lean body mass ml kg LBM min LBM body mass fat mass When expressed relative to body weight typical VO 2 max values for college age men and women are approximately 48 and 40 ml kg min respectively Other typical values are represented in Table 1 Table 1 Typical VO2 max values ml kg min Population Males Females College Student 48 40 Elite distance runner 83 65 Sedentary middle aged adults 35 30 Post myocardial infarction patients 22 18 Severe pulmonary disease patients 13 13 MEASURING MAXIMAL AEROBIC CAPACITY Routine testing of VO2 max has traditionally been performed on a treadmill or cycle ergometer Unless specific exercise training has occurred on a particular apparatus the highest values are found with a treadmill running protocol This is due primarily to the larger amount of muscle mass working against gravity Moreover local muscle fatigue on a cycle or rowing ergometer may force exercise cessation before a participant reaches maximum levels DIRECT MEASUREMENT INCREMENTAL EXERCISE TESTS The VO2 max test is a graded or incremental test of increasing workload It may be performed continuously or discontinuously with 5 10 minute rest periods between workloads The length of each workload is about 2 3 minutes to allow steady state to occur at least for the lower workloads The participant exercises to the point at which he she can no longer continue Psychological factors motivation may influence an individual s effort to achieve a maximum level The following objective physiological criteria are used to assess whether a true max has been attained 1 2 3 4 A plateauing or decrease in VO2 despite further increases in workload This is the best predictor for attaining a true VO2 max An RER 1 1 Exercise HR is within 15 bpm of age predicted max HR 220 Age Blood lactate concentration 70 80 mg 100ml The test is generally accepted as a maximum value if two of the first three criteria are met If a maximum is not achieved the value is referred to as peak VO2 During incremental exercise to maximum increased CO2 and resulting lower pH in the blood acts as a strong ventilatory stimulus causing ventilation rate to rise disproportional to the oxygen uptake response This ventilatory response results in a deviation from linearity when plotted against workload or VO2 The point of delineation is the ventilatory breakpoint VBP This transition typically correlates with increased lactate in the blood and is sometimes used to predict the lactate threshold Late onset of the ventilatory threshold is a good indication of endurance performance and can be used to ensure a test is at least near maximal TESTS TO PREDICT MAXIMAL AEROBIC CAPACITY Often it is impossible to directly determine VO2 max because of equipment limitations or time constraints when testing large numbers of people Also there may be medical or legal problems administering exhaustive test to older sedentary individuals or those individuals in high risk categories for coronary disease Monetary considerations must also be considered and submaximal tests have been devised to predict VO2 max using a measure of physical activity current height and weight and the HR response to submaximal workloads and or time to complete a given distance i e 1


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