My VO2max test - what, why, how, HRM related info
Posted on 2013-01-10 by heybales
Finally going to report on my VO2max test July '12, and provide some insight either for deciding if useful to you, or what can be gotten from it. Read as far down as you desire, details get better, or worse. Bottom section on HRM's might be interesting, though math is involved.
What it is.
So this is the treadmill or cycle ergometer test with electrodes for your heart and face mask for your breathing.
The results of the test vary by what they will tell you and push you to. Most will give you info on your baseline resting sitting level stats, the HR bpm point you cross lactate/anaerobic threshold (LT/AT, producing more lactic acid than clearing out causing "the burn"), the HR bpm point you reached VO2max and what it was, and if pushed your HRmax, then usually your voluntary lung ventilation capacity and what was reached during the workout.
They measure the expired gases, and of course the air is calibrated for what is in it going in. By seeing how much O2 and CO2 came back out, you can tell how much fat or carbs were burned by the oxygen used, therefore how many calories in that process.
Why it might be useful to do.
You are doing endurance training for anything that lasts longer than 90 min at a strong intensity, and want to improve performance. Specifically knowing your LT/AT level allows training to improve that point before too much lactate acid is going to shut you down. It also allows seeing from your VO2max HR what level your aerobic zone should be for endurance and to improve that. Both AT and VO2max can be improved quickly if coming from no cardio exercise, but after that initial improvement, gains can be hard to come by and require details to do it right.
For Garmin HRM's too, calorie burn info specific to you can be used on it.
How it is done and tips to good test.
When you find a place that does it, confirm you'll receive at minimum the following stats - AT HR, VO2max & HR, MaxHR.
At best ask if they can provide the following raw data in 20 sec or better increments - time, HR, VO2, VCO2.
Find out if they do a baseline reading sitting for 5 min, and what it would take to increase that to 10 min to really get calm and resting. That would give you an included RMR test if you can receive above raw data for it too.
Find out if you get choice of treadmill or cycle ergometer, and what is the ramping protocol. My first test was total walking, no running allowed, just getting up to 22% incline at 3.7 mph at end, with changes to speed and incline every 10 seconds. Second test allowed running so 22% at 4.9 mph, still changes every 10 seconds. Those are high or fast ramping protocols, trying to get to HRmax before you just plain get tired. There are some low or slow ramping ones, warmup walk, and then straight to walking fast or jogging, and every 3 min speed and incline go up constantly. Jumps are major, and you get to same point of failure. Hard to get useful HR data out of this method because of the jumps in effort.
Same alternate methods used on the bike.
The reason for finding out is so you can practice that type of workout to improve body's ability to handle it. My first test, I'd done no walking at 22% incline, and my achilles cramped up before I reached HRmax, even though legs had no problem yet. I later did my own slow ramping running test and found my HRmax on my own. They may limit the pedaling on cycle to 80 rpm, and you are used to 95 rpm, so better get used to it for more valid test.
Do NOT workout for 2 days before. My first test I worked out night before, second test triathlon 3 days before. Both prevented me from reaching HRmax, but the other figures were valid so it didn't matter that much to me. Also wearing headgear and wires may prevent reaching max.
Do NOT eat before the test, so schedule it in the morning. Metabolising food will skew the VO2/VCO2 stats invalidating the test.
And confirm you'd like the full test results and raw data mailed to you.
So my first test in Feb '11 - 203 lbs with clothes. This was 7 months after my triple ankle break, with 4 months of using it again and doing spin bike cardio during the first 3 months in a boot, so kept some fitness.
Max voluntary ventilation 140 L/min, peak during exercise 93 L/min (so lungs were not limiting factor, had spare air)
Anaerobic Threshold @ 171.
VO2max @ 178.
HRmax @ 178.
VO2max 44.3 mL/kg/min (adjusted for true tested HRmax of 194) 48.2
My second test in Jul '12 - 180 lbs with clothes. This was 3 days after Long course triathlon, so I knew too tired to reach HRmax, but it was the other stats I was after.
Max ventilation 180 L/min, peak during exercise 106 L/min.
AT @ 177.
VO2max @ 180.
HRmax @ 180.
VO2max 52.2 mL/kg/min (adjusted for true tested HRmax of 194) 57.0.
So lung function improved 29% voluntary forced breathing test, and 14% during exercise. So lungs are not limiting factor to getting enough oxygen.
AT improved 4%. Considering it was already 88% of HRmax, there wasn't much room for improvement, but got up to 91% HRmax now. Avg is 80-85% of HRmax.
HRmax didn't change in reality though I couldn't hit it in the test, but that usually doesn't change anyway except for dropping lower if unfit and getting older.
VO2max improved 18%, but that is not adjusted for weight. If I maintained and only dropped weight, the old VO2max of 48.2 mL/kg/min would become 54.4 at recent testing weight, so really only improved 5%.
Calorie burn info. (math)
So calories burned is totally related to the amount of oxygen used, so the data that can hopefully be obtained from the test can share some interesting results.
So the amount of O2 and CO2 in the air is already known, and machine calibrated to that. What you expire is measured and once subtracted from what was available, becomes the stats inhaled VO2 and exhaled VC02 (Volume in L / min). More CO2 than what is normally in the air indicates along with how much O2 came back out, shows how much O2 was used to metabolize carbs and fat.
So here is my own sample data near the top of my aerobic range, 89% of AT (177).
HR 157 - VO2 3.054 L/min - VC02 2.791 L/min.
If you divide VCO2 / VO2 you get Respiratory Exchange Ratio (RER), so 0.914. (0.707 is 100% fat burn, 1.0 is 100% carb burn)
The amount of calories burned per L of O2 is 3.8151 + 1.2318 * RER, so 4.941 Cal/L O2 in this case.
Since I used 3.054 L/min of O2, that means 4.941 * 3.054 = 15.09 cal/min.
Also from that RER, it is known what % of carbs was burned - RER^2 * -87.0843 + RER * 489.7265 - 302.6869 = 72% carbs.
Leaving 28% fat calories burned.
So this is how I measure my calorie burns for my workouts and report them (except lifting). The HRM is merely telling me my avgHR for the session.
Now, interesting point in that math - did you see age, gender, or weight as a factor at all? No, it's not. As long as that fitness level is maintained, no matter my weight, if I hit 157 HR, I burn 15.09 cal/min.
So where does weight come into play? If I wore a 10 lb vest, my pace would have to slow down to stay at 157 HR, right?
That's where weight comes into play. If I tried to maintain the same pace with more weight, my HR would of course be higher, and O2 usage would be higher, and calories and % carbs burned would be higher. If older, then probably harder to maintain pace too at same HR.
Now, it's almost a straight line if you graphed it, from lowest HR below light exercise, to highest HR at AT/LT point, the increase in VO2 and VCO2, and therefore basically calories/min burned.
HRM calorie burn principles. (worse math)
So what is a HRM trying to do to get to same cal/min burned?
First, for those HRM's with no VO2max stat, they are calculating your BMI from height and weight. There is research giving formula's for estimated VO2max based on BMI with slight improvements if age and gendor is factored in. If HRM doesn't get those stats, they are using other research formula to estimate VO2max.
So now with an estimated or calculated or manually entered VO2max figure of say 57 mL/kg/min at HRmax, the HRM is calculating that HRmax or allowing manual input at 220-age, so it would get 176 in my case if not corrected.
But the straight line for calorie burn is only to AT HR. So that is assumed to be about 80-85% of HRmax, though a HRM may adjust that based on other derived info.
So 80% HRmax is 141 in this example, calculated AT threshold.
Other experimental data shows a relation between 63-92% of HRmax corresponds to VO2max between 40-85%. %VO2max = (%MHR-37.182) / 0.6463
So 141 being 80% of HRmax, would equal 66% of VO2max.
66% of VO2max 57 is 37.6.
Now you can get to VO2 L/min by dividing out weight, say 65 kg the HRM knows about.
So 37.6 * 65 / 1000 = 2.444 L/min VO2, and the RER at the upper end is 1.
So the HRM now has a calculated line upper HR of 141 and that is 2.444 L/min of VO2 and RER of 1. That means 5.047 cal/L O2, which is 2.444 L/min, or 12.33 cal/min. So HR 141 = 12.33 cal/min.
So now the calculated line lower HR is called the FlexHR point, and on avg is about 90, though knowing gender tightens that up better.
So HR 90 is 51% HRmax, which is calculated to be 21.4% VO2max, or 12.2 mL/kg/min.
So again get the weight out, 12.2 * 65 / 1000 = 0.793 L/min VO2, and the RER at the lower end is estimated to be 0.75. That means 4.739 cal/L O2, with 0.793 L/min VO2, means 3.76 cal/min. So HR 90 = 3.76 cal/min.
Now you just get a slope equation on that line, HR 90 & 3.76 cal/min, with HR 141 & 2.33 cal/min. y=mx+b
calories = (HR - 67.6242) / 5.9510
Test - HR 141 = 12.33 cal/min
Compare to actual - HR 157 = 15.02 cal/min. My actual VO2 test measured one was 15.09. Different weight and HRmax values though.
So, that was with HRmax being way off in the HRM (real 194, calculated 176), but using real VO2max stat, and the weight being different between the two also. Would have been pretty off if VO2max had been estimated at normal 45.
So that is what a HRM is trying to do. You'll notice a bunch of assumptions in there that can really start throwing things off.
VO2max calculated from BMI, assuming bad BMI, bad fitness level.HRmax calculated.AT point assumed to be 80-85%, or whatever they use.FlexHR point assumed to be around 90, or whatever they use.Conversion from %HRmax to %VO2max assumed to be the same.
So that's why HRM's can be so far off on calorie burn estimates if you start becoming fit, and go by the defaults.