Can unloading body weight affect VO2 max results during performance testing?

[trannh]

Hello,

I am new to the physical therapy field and I have a huge interesting in performance testing, especially VO2 testing. I am currently working on a project involving such testing. I was wondering if anyone knows the effects of unloading during VO2 max testing. For example, if a user begins to hold on to the treadmill handrails during the testing, they are unloading their body weight making them able to keep going longer. Does anyone know the effects or possible effects such unloading has on the VO2 results for such a test? Is there any relationship between the two? Thank you very much for any help or recommendations.

 

[SW VandeCarr]

Hello,

I am new to the physical therapy field and I have a huge interesting in performance testing, especially VO2 testing. I am currently working on a project involving such testing. I was wondering if anyone knows the effects of unloading during VO2 max testing. For example, if a user begins to hold on to the treadmill handrails during the testing, they are unloading their body weight making them able to keep going longer. Does anyone know the effects or possible effects such unloading has on the VO2 results for such a test? Is there any relationship between the two? Thank you very much for any help or recommendations.

If by unloading, one sill maintains the same level of effort, as measured by VO2 Max, one stands to gain better performance in some other measure. So if "unloading" allows one to run faster by not having to support one's full weight on the their legs, the aim is to do so while maintaining VO2 Max. I'm not sure if this helps in improving VO2 Max.

However, you could be talking about "unloading" in another way. This study of healthy non-smoking moderately trained men indicates that high effort interval training is superior to long distance running in improving VO2 max.

http://www.ncbi.nlm.nih.gov/pubmed/17414804

 

[trannh]

Thank you for your response. By unloading, I mean the user makes themselves lighter, reducing the effort needed to keep going. In VO2 testing, the user must keep going until they cannot go anymore. However, if the user makes themselves lighter and reduces how much energy is needed to keep going, that will skew the VO2 data, mostly likely showing that they are more fit than they really are. I was just wondering if anyone knows any kind of relationship between the two. So for example, if the patient reduces their body weight by 20% by holding on to the treadmill handrails, how much does that affect the VO2 measurements or what kind of effects would you expect to see? Thank you

 

[SW VandeCarr]

Thank you for your response. By unloading, I mean the user makes themselves lighter, reducing the effort needed to keep going. In VO2 testing, the user must keep going until they cannot go anymore. However, if the user makes themselves lighter and reduces how much energy is needed to keep going, that will skew the VO2 data, mostly likely showing that they are more fit than they really are. I was just wondering if anyone knows any kind of relationship between the two. So for example, if the patient reduces their body weight by 20% by holding on to the treadmill handrails, how much does that affect the VO2 measurements or what kind of effects would you expect to see? Thank you

Yes, I understand that the subject is effectively making themselves lighter. I don't understand why you think you would be overestimating fitness if the subject performs the same amount of work when using the handle bars as when not using them. The work that is done by supporting body weight is shifted to running when the subject uses the handle bars. VO2 Max is a function of work per unit time. If you decrease effective mass you can you maintain the same level of work by increasing velocity.

Perhaps I don't understand your question. I'll let someone else respond.

 

[trannh]

So what you're saying is that by unloading body weight using the handle bars would not reduce VO2 max because work would stay the same? So if the user is making themselves lighter, they could keep work the same by running faster. I think I understand the point you're trying to make. Thank you for clarifying. Another question that comes to mind is what if the user is unable to keep the same level of work by increasing velocity? For example, the user is a patient with a potential cardiovascular condition. When the patient begins to tire and starts to hold on, there should be a decrease in body weight but would there also be a decrease in work load? If so, would that difference in work load affect VO2 measurements?

 

[SW VandeCarr]

So what you're saying is that by unloading body weight using the handle bars would not reduce VO2 max because work would stay the same? So if the user is making themselves lighter, they could keep work the same by running faster. I think I understand the point you're trying to make. Thank you for clarifying. Another question that comes to mind is what if the user is unable to keep the same level of work by increasing velocity? For example, the user is a patient with a potential cardiovascular condition. When the patient begins to tire and starts to hold on, there should be a decrease in body weight but would there also be a decrease in work load? If so, would that difference in work load affect VO2 measurements?

All I'm talking about is maintaining work level at VO2max by "unloading" weight. Using the formula from physics, the relevant work here is done when a mass goes from 0 to some velocity according to the forumula $KE = mv^2/2$. If you decrease effective mass 2O% you only need to increase velocity by about 12% to maintain the same level of work because of the squared term. Obviously, if the subject has health issues, that's a different problem altogether. The reason it's easier for the subjects is because they are recruiting more muscle mass (using the arms), but the total work effort need not change.

EDIT: Strictly speaking, since the subject is running in place (he/she has no momentum), one could say no work is being done but we calculate it as if the subject is in motion.