@ECSSTV (Mixed Physiology & Metabolism session)
is entirely good Lu imagine this you are a professional exercise scientist and a coach one day one of your athletes comes to you saying I will not travel to a high altitude I he that this can boost my performance as it can increase my fat oxidation which will definitely delay my fatigue as a professional exercise scientist you’ll basically believe in the experiment so you decide to take this at into the lab and test his V2 Max twice one time at the at which the oxygen percentage is reduced and the other time in the normoxia at which the oxygen percentage is 21% and based on his V2 Max at each condition you select two tests that are similar in relative intensity so you can start analyzing and comparing the results between boths and guess what you find that this guy actually got an increase in the fight oxidation despite of the reduction in the oxygen percentage so you start wondering if this is the case with everyone so you simply start reporting more people and then you notice something that is very weird some people are reporting an increase in the fat oxidation Rel to the energy expenditure and some are reporting at decrease actually this story represents the UNC consistency of the current literature about the effect of hypoxia on substrate utilization and that’s why our study aim to investigate the effect of hypoxia on maximum fat oxidation during cycling my name is y I’m from Hamed khif University let’s start by a very simple question why did we decide to study maximum fat oxidation specifically simply because it’s literally important to everyone because we consider it as a metabolic Health indicator and indeed there are many factors that can affect the maximum F oxidation assessment during exercise such as cardiorespiratory Fitness um diet equipment that you are using and many many other factors however the factor that can affect the maximum F oxidation the most is the intensity and that’s conditions like hypoxia can affect the maximum fat oxidation because the hypoxia itself can affect the intensity there are two main Concepts that I would like to introduce for you before going deeper in this presentation first of all we assess carbohydrates and fats during exercise using equations and those equations are depending mainly on the O2 and the CO2 and that’s why having a steady state of the V2 and the PC2 during the exercise is really important for an accurate measurement especially that it has been found that the BO2 can be faster than the vco2 so how can we get this stud simply by a step test what do you mean by a step test step test means that the exercise intensity is increasing but every few minutes and this is a real example of the step test that we have used in our study so basically the intensity was increasing every 4 to 8 minutes and we selected 8 minutes for the higher intensities because physiologically when that intensity gets harder the require um require auration to achieve this steady state the second concept that I would like to introduce for you is the idea of normalizing the intensi let’s say that you are exercising at 100 WS at the hypox this 100 Watts at the hypoxia is going to feel harder compared to exercising at 100 watts in the normoxia even though it’s the same exact absolute intensity however if you normalize the intensity you should actually feel the same conditions because you should have similar metabolic stress or similar metabolic disturbance but the question is how should we do this normalization should we do it based on maximum responses like B2 Max I’m going to answer this question but after introducing the exercise intensity domain model which is a simple model that divides the exercise into main three domains the moderate domain which Ends by the gas exchange the heavy domain which Ends by the RCB or the respiratory compensation point and the last domain is the Extreme RC domain which Ends by the end of the exercise now let’s get back to the question how should we do this normalization should we do it based on maximum responses the short answer is definitely no I’ll tell you why let’s say that we have two guys they are exercising at 60% of their V Minds at that case we are risking that one person might be exercising within the heav domain the other might be exercising within the M domain however if we normaly the intensity based on the exercise prescription model or bed on the officials those two guys should feel the same at the same relative int so what do we know about the topic so far as I have mentioned in the introduction UNC consistent results and do you know what is common between most studies using theats as a way to normalize the intensities and unfortunately some of those studies do not consider that the participants require longer regation at the heavy domain to achieve that uh city states and that’s why our study aim to investigate the effect of hyrox oxidation using the the exercise intensity prescription model as a way to normalize the intensity and of course we selected longer duration for the intensities that put the participants within the Heine and we hypothesize that we are going to have a reduction uh in the F oxidation at the hypoxia because it’s oxidation and we are basically reducing the oxygen and assembly so we basically recruited participants who were healthy an altitude the P three months and each of them visited the lab for four visits uh in two of those visits they had the V marks test at each condition and based on the V Max test we identified the thresholds at each condition and based on those thresholds we selected the intensity for the step test the step test a to have three stages that place the participants within the motor domain and three other stages that place the participants within the heavy domain and as I have mentioned we selected longer duration over here to make sure that hopefully the participants in this slide you can see the B2 on the Y AIS on the left side and the power output on the X AIS and actually the black dots represent the normoxia while the white dots represent the hypoxia and as you can see the metabolic rate of the V2 was almost similar across all of the stages between both of the conditions and if you notice that the white dot is slightly shifted towards the left side compared to the black do because we reduced the absolute intensity just to normalize the intensity however despite of this normalization or reducing the absolute power output as you can see here the V2 as a percent of the gas exchange and RCB was actually similar across all of the stages the conclusion of this slide is that we were able to successfully select intensities that were well match in both conditions and despite of the similar metabolic between both of the conditions the participants got a 25% of reduction in their maximum P oxidation at the hypoxia compar to the normoxia and that point was supported by an increase the blood lactate reduction in the energy expenditure while there was no significant differences in terms of the carbohydrates between both conditions and this might be explained by the fact that the carbohydrates is actually less dependent on oxygen compared to to the fats and I would like to mention that there is a study that reported that there is an increase in the f but post exercise so it is possible that this increase post exercise is a compensatory mechanism for the reduction that can happen during the exercise one of the most interesting findings in our study that we noticed that the maximum idation was happening a different percentage of the V2 Max and actually this can make you question whether normalizing using the V2 Max can be considered as an accurate way to normalize the intensity in such a studies or no and was happening at the same percent uh in terms of the V2 as a percent of the gas exchange thresold and the RC lastly I would like to mention that there was no significant relationship between the gas exchange and the maximum oxidation and this could be explained by the fact that the gas exchange is mainly depending on vat mechanisms while the maximum oxidation is mainly depending on um metabolic mechanisms so in other words the underlying mechanism between both of them might be a bit different on the other hand participants who had a higher po2 Max regardless of the condition they had a higher maximum PA oxidation which is not really surprising we all know endurance trining can lead to many physiological and hormonal adaptations that can incase maximum P oxidation so what are the practical implications of our study well based on our findings we think that maybe using the exercise intensity prescription model can lead to more homogeneous results even in terms of the substrate utilization and that’s why maybe future researchers can use uh the exercise prescription model as a way to normalize the intensities and investigate the effect of chronic hypoxia on maximum F oxidation I would like to to end my presentation by a critical question actually in our study we noticed a 16% in the VX add the hypoxia compared to the normoxia do you think if uh if we had an athlete who stopped with training for a while this athlete if if he or she got a reduction by 16% in his or her bomax is he’s going to have or she’s going to have an also a decrease by 25% in the maximum P idation I personally don’t know the answer thanks everyone thank you Dr Nathan and Dr ju my supervisors and thanks to my colleague da thanks everyone thank you H for an excellent and very enthusiastic talk um are there any questions from the public present here I have question you diet days before or do you have any fasting condition or something like that that’s a very good question yes actually all the participants they had 12 to 8 hours of fasting that 12 was for for those people who came at the morning and uh the eight were for those people who came at night and actually the the same night was repeated before each step test just to get consistent results thanks for your question any other questions oh really late in the afternoon no questions means that you have uh you did a great presentation but I maybe have one more question did you because in the beginning of your presentation you spoke about oxygenation like local responses measurements did you include that in these in this experiment or or not yes actually we we assessed U the oxygenation and de oxygenation of the Blood using the MIRS however uh we didn’t have the time to work on the analysis of this yet okay I think it will be interesting as well to compare like some general with some local responses and then maybe uh another question uh like do do you already have an idea like just a hypothesis about the underlying mechanisms uh of the impact of the hypoxia on this different substrate utilization Yes actually um there are studies that shows that there is a direct effect of the hypoxia on the on the endal function so maybe um if it can increase the diameter this can uh make it up for the oxygen which can affect the subate utilization honestly the is a bit complicated and unfortunately there are no much studies that investigated that but hopefully we can answer this question with more clear answer in the future thank you yeah well thank you very much for an excellent speech
2 Comments
الف مبروك يايمنى
Nice ❤❤