Utility of Including Verification Stage When VO2max Testing in Hypoxia
Faculty Advisor Name
Nicholas Luden, Ph.D.
Department
Department of Kinesiology
Description
VO2max is the gold standard measurement of cardiorespiratory fitness and can be used to predict a range of functional outcomes such as endurance performance and risk for all-cause mortality. VO2max was first introduced in 1923 and was originally defined utilizing a VO2 plateau, meaning that there is no further increase in VO2 despite increasing work rate. The likelihood of VO2 plateau occurrence has been shown to be as low as 17% and as high as 100%. The criticisms of this primary criteria led to the development of secondary criteria. Secondary criteria include specific critical values of respiratory exchange ratio, blood lactate, and age-predicted max heart rate. The specific values are dependent on the investigation and have been criticized due to lack of validity and sensitivity to test duration, exercise modality, and inter-subject variability. Due to the importance of obtaining accurate VO2max values and the limitations of primary and secondary criteria, a subsequent verification stage has been proposed to help confirm VO2max attainment. A verification stage is typically performed after a short rest period and consists of one or more stages performed at or near maximal workload until volitional fatigue. Ofter, there is no significant difference between VO2 values achieved during the graded exercise test (GXT) and the verification phase, which provides support that VO2max was likely achieved in the initial GXT. It is known that VO2max is negatively influenced with increasing altitudes above sea level. Research has reported delayed VO2 kinetics in hypoxia which may lead to premature fatigue prior to VO2max achievement. Due to this premature fatigue, it cannot be certain that the VO2 peak at the time of exhaustion reflects a true VO2max, thus demonstrating the need for a verification stage to confirm VO2max. However, virtually nothing is known about the importance of including a verification stage in hypoxia. Therefore, the purpose of this study is to evaluate the impact that normobaric hypoxic and normoxic conditions have on determining VO2max with a verification stage as well as clarify the need for a verification stage in each condition. We predict that the verification stage VO2max will exceed the VO2max reached in an incremental GXT in normobaric hypoxic conditions but not normoxic. It is also predicted that traditional primary and secondary criteria for achievement of VO2max will exhibit poor sensitivity and specificity in normobaric hypoxia and normoxia. Twenty subjects will complete two exercise trials, consisting of a GXT and verification test on an electronically braked cycle ergometer. One trial in normoxia and one trial in hypoxia, separated by at least 48 hours. Normoxia is at 404 meters above sea level and normobaric hypoxia is simulating 2500 meters above sea level by breathing through a large reservoir that is continuously fed by two large generators. Subjects are blinded to the testing condition and the order of testing is randomized and counterbalanced. Dependent measurements will be analyzed using a series of repeated-measures ANOVAs and will use an alpha level of 0.05 to establish statistical significance.
Utility of Including Verification Stage When VO2max Testing in Hypoxia
VO2max is the gold standard measurement of cardiorespiratory fitness and can be used to predict a range of functional outcomes such as endurance performance and risk for all-cause mortality. VO2max was first introduced in 1923 and was originally defined utilizing a VO2 plateau, meaning that there is no further increase in VO2 despite increasing work rate. The likelihood of VO2 plateau occurrence has been shown to be as low as 17% and as high as 100%. The criticisms of this primary criteria led to the development of secondary criteria. Secondary criteria include specific critical values of respiratory exchange ratio, blood lactate, and age-predicted max heart rate. The specific values are dependent on the investigation and have been criticized due to lack of validity and sensitivity to test duration, exercise modality, and inter-subject variability. Due to the importance of obtaining accurate VO2max values and the limitations of primary and secondary criteria, a subsequent verification stage has been proposed to help confirm VO2max attainment. A verification stage is typically performed after a short rest period and consists of one or more stages performed at or near maximal workload until volitional fatigue. Ofter, there is no significant difference between VO2 values achieved during the graded exercise test (GXT) and the verification phase, which provides support that VO2max was likely achieved in the initial GXT. It is known that VO2max is negatively influenced with increasing altitudes above sea level. Research has reported delayed VO2 kinetics in hypoxia which may lead to premature fatigue prior to VO2max achievement. Due to this premature fatigue, it cannot be certain that the VO2 peak at the time of exhaustion reflects a true VO2max, thus demonstrating the need for a verification stage to confirm VO2max. However, virtually nothing is known about the importance of including a verification stage in hypoxia. Therefore, the purpose of this study is to evaluate the impact that normobaric hypoxic and normoxic conditions have on determining VO2max with a verification stage as well as clarify the need for a verification stage in each condition. We predict that the verification stage VO2max will exceed the VO2max reached in an incremental GXT in normobaric hypoxic conditions but not normoxic. It is also predicted that traditional primary and secondary criteria for achievement of VO2max will exhibit poor sensitivity and specificity in normobaric hypoxia and normoxia. Twenty subjects will complete two exercise trials, consisting of a GXT and verification test on an electronically braked cycle ergometer. One trial in normoxia and one trial in hypoxia, separated by at least 48 hours. Normoxia is at 404 meters above sea level and normobaric hypoxia is simulating 2500 meters above sea level by breathing through a large reservoir that is continuously fed by two large generators. Subjects are blinded to the testing condition and the order of testing is randomized and counterbalanced. Dependent measurements will be analyzed using a series of repeated-measures ANOVAs and will use an alpha level of 0.05 to establish statistical significance.
