Gas Exchange Test Result – Confusion

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  • #22429

    I had a gas exchange test done at Real Rehab a few days ago. I suspected aerobic deficiency syndrome when I started the 24-week plan, which prompted me to get tested to better inform my training. The tech had me warmed up on the treadmill for 10 min, then increased the grade 2% every 4 min for 30 minutes.

    My confusion/questions from the test are as follow:

    (1) My crossover point occurs at 168 HR (see attached chart). The tech mentioned that my AeT is more in the range of 163-173 HR and anaerobic threshold 177-185 HR. For the past month I have been training mostly at 130 HR determined from the DIY treadmill test. Is it possible that my crossover point is not close to my AeT? I don’t think I can nose breath at 163 HR.

    (2) During the 4-min cool-down phase after bringing my HR to close to AnT, my RER remains close to 1 (see attached table). The tech pointed out the slow recovery back to aerobic state and suggested that I add interval training 1x per week to rectify this (e.g. go 1 min as hard as possible and then slow down for 5 min or so for 45 min). Does this sound like HIIT, which is something I should avoid?

    (3) The tech brought up an interesting point about training in a fasted state – the body might think that it’s in a starvation state and will try to conserve the fat reserve instead of utilize it. How can I be sure this isn’t happening when training fasted? Maybe it’s the intensity I’m training at?

    Thanks in advance! Will appreciate any insight anyone has!

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    alisonG on #22447

    I think Scott might have more insight than I do- but here’s my two cents. I’ve spent some time playing around with these concepts and training and noticed a few things- I was lucky enough to test myself on the same lab equipment that Real Rehab has a few times.

    a.) This might vary from person to person, but I find that from measuring myself and from seeing a few other people’s results- my aerobic system takes a little longer than 10 minutes to fully “boot up” and I had the most accurate results after a good long 20-25 min warm up at really easy intensities. The fact that your fat burning goes up after a few minutes at the lower end of your HR range makes me wonder if your warmup was too short.

    b.) I was able to push my fat burning ability all the way to max HR effort without getting a crossover point mostly due to playing with my diet (I did this out of curiosity). But I was pretty slow because my training volume was on the lower end at that point- so the lab results didn’t correlate well to what my treadmill testing results were (using a HR monitor and looking for the 5% HR drift w pace)- which did line up nicely with the nose breathing results.

    c.) Unless the tech took into account your current training goals and training history, I wouldn’t pay too much attention to the suggestion to add 1 min intervals- that seems kind of random unless there’s a really good rationale.

    d.) As for your body going into “starvation mode”, I’m not aware of anything that supports that training in a fasted mode will cause that. Maybe if you were living all the time in a fasted mode it would… but you are just fine going for a hour jog in the morning before breakfast. 🙂

    jeanna on #22448

    Thanks for the insights @alisongillespie!

    a.) The tech originally wanted the warm up to be 5 min but I was able to request 10 min. Should have pre-warm up myself at home per the Lab Guidelines article. But then in Real Rehab’s instruction email, they say no physical activity the day of the test…. At least the test was done in a fasted state (the instruction is to fast for 12 hours prior).

    b.) Interested in knowing how you modify your diet. The resting test suggested that I am burning more carb than fat at rest (65% CHO, 35% fat). The tech said it has to do with my diet and suggested shifting my macronutrient intake according to the Hand model with 1:1 ratio of carbohydrates (mainly veggie and fruits) and protein. The tech also mentioned not to worry too much about fat intake as it will come as part of the protein intake?

    c.) The tech is aware that I’m training for mountaineering. The point brought up was that after encountering steep uphill sections of a climb my body is slower to recover (i.e. switch back from anaerobic to aerobic state). But ideally for most part of a climb I am not even supposed to go up to Zone 4/5 so I shouldn’t have to worry about the switch back later?

    d.) Good point here. The tech mentioned this can happen to people on a diet whereby they lose weight at the beginning and then plateau because their body has entered into a “starvation mode”. Since I’m not dieting I don’t have to worry about this I supposed.

    alisonG on #22455

    1.) Re: warmup- yeah, following Scott’s instructions are key here. I think he had a PDF to bring to appointments explaining what a warmup consists of – because there’s a lot of variations in protocol among many testing locations.

    2.) I got that result by playing with diet in that I wanted to see what my response was to a higher fat diet- and I should also say that I didn’t actually keep that going as I got into my training. I worked with an actual RD for my “real” diet that was sustainable and worked well – and this is where individual results vary. But I still had a fairly significant input from fat and not nearly so carb-heavy as the 1:1 idea. I mean, you could eat cans of tuna fish and eat fruit/veggies and you definitely aren’t going to get much fat with that- so I do think paying some attention to all three macros is good. As my training progressed, I did end up getting a crossover point at a fairly high HR and I was also better able to do higher intensity things- so it all depends what you are aiming for!

    3.) Exactly. If you are training for mountaineering, there really aren’t times where you are pushing the anaerobic zones and if you are, it better be because an angry marmot is chasing you across the snowfield or something 🙂 So think back to your goals, your primary limitations (aerobic base, strength, etc) where you are in your training cycle and then ask if adding 1 min intervals every week makes sense given that. For some people it might and for some people not. I think you are asking the right questions.

    4.) Yeah- I mean, you did the test in a fasted state and clearly can burn fat.

    Anonymous on #22469


    I concur with everything Alison has already stated.


    jeanna on #22473

    Hi Alison! Thanks for providing more insights and I have got a few last questions I hope…

    1) It seems very likely that my gas exchange test results are inaccurate due to insufficient warm up. Is there anything I can do with the test results? Can I somehow still use the MEP of 168 HR to inform my training? Maybe redo the treadmill test with a starting heart rate higher than 130 (maybe 140 or 145)? Or instead of trying to nail down my AeT, should I just train by feel (i.e. train at an intensity where I can nose breath and also hold a conversation)?

    2) Wondering why you didn’t keep the higher fat diet after you started training? Is it not providing enough energy for the training?

    3) Rather than angry marmots :P, I am more concerned about keeping up with the group I’m climbing with. To stay within Zone 1/2, I don’t think I can maintain a minimum of 1000 ft/hr on non-technical parts of the climb. I guess I should wait until I have built an adequate aerobic base before going on climbs…

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