What is graded exercise testing?
Graded exercise testing (GXT) is the most widely used test to see the dynamic relationship between exercise and your body systems- heart, lung, muscles, and brain. This has been done for over 200 years. Early experiments had people exercise in normal and hypoxic conditions. They looked at the impact of blood pressure on heart efficiency. They then started to collect the expired air and did testing to determine oxygen and carbon dioxide and air volume amount.
Exercise was then added to the mix. That is how VO2 max, the upper limit or “ceiling” of maximal oxygen uptake was made.
What is VO2 max?
VO2 max is the highest attainable value of maximal oxygen intake. It is seen when you are exercising at maximal effort, and you go from aerobic (oxygen) exercise to anaerobic exercise.
What happens when you exercise?
Your body works together as a complex system. When you exercise,
- Blood vessels dilate to get more blood flow to the muscle to bring in oxygen and remove carbon dioxide.
- Heart rate and stroke volume (the amount of blood pushed out with each beat) increase to maintain blood pressure
- Brain receptors increase sympathetic drive. This helps the heart contract more and helps venous blood return to the heart.
Heart rate increases linearly during incremental to maximum exercise. The heart reaches a maximum rate- you need to have the heart relax to allow it to fill.
Why do we care? Fitness is related to mortality
This is not new. Heart disease and all cause mortality are linked to exercise tolerance, and poor fitness is an independent precursor to mortality. To just cite some studies,
- 32K men and women, ages 20-80, 265K living-years had 690 deaths. When analyzed, low cardiorespiratory fitness was a predictor for all cause mortality and future heart disease
- Meta analysis showed a 1MET increase in VO2 max had a 15% reduction in all cause mortality and cardiovascular disease.
- Low fitness (defined as <7.9 METS) had substantially higher risk for all cause mortality and cardiovascular disease.
How is graded exercise tolerance done during our VO2 max at Biohackr Health?
There are different protocols and machines used to test this. Some use treadmills, others bikes. How long the stages are, how much you increase it at each stage- incline? speed? how much?, and total test duration vary. Some increase speed and then incline. Some have a constant speed and only increase incline. Some increase speed and incline together. How quickly you increase varies. Some use 1 minute stages, others longer. The studies indicate you ideally want to hit VO2 max between 8-12 minutes.
When trying to decide what protocols to do at Biohackr Health, we looked at the studies (see below). We took into consideration also different levels of fitness and possible impairments from sport injuries. We want the test to be reliable and valid. Standardizing as many variables as we can helps improve accuracy.
- We offer three protocols, with different speeds and inclines.
- We want you to do the same protocol when retesting for better accuracy of your result.
We do know other external factors affect your result. Calorie restriction, bed rest, temperature, and illness can change your value.
- We like you to do this at the same time of day
- We like you to do this after an overnight fast with no caloric or caffeinated beverages before the test
- The temperature is controlled in our clinic.
- We do not recommend doing the test if you are sick or currently injured.
Between the treadmill and cycle, we like the treadmill as it works a greater muscle mass. This can produce up to 20% greater VO2 max values as you are using more muscle.
We measure multiple criteria during your test which help validate and analyze your results.
- Heart rate
- RER, the respiratory exchange ratio which looks at oxygen vs. carbon dioxide. When 1.0 or over, you are entering anaerobic respiration.
Hitting your max perceived greatest exertion (you feel like it is your max) does not always correlate with your “max,” particularly for people who are not as active/are more sedentary. That is why the gas testing is so valuable.
Schedule your VO2 max test
We offer the testing using professional, medical grade equipment in our Palo Alto office. (Soon to come to San Francisco). If you are on a weight loss journey, care about longevity and health, or want to see where you are in in your exercising, it is a great test. It will give you a barometer of your heart/lung/muscle health, which as stated above correlates with longevity.
I have done the test. I found the information fascinating, very informative (particularly when I go from burning fat to burning carbs at such a low heart rate!), and gave me a metric I can follow in my quest to age better. Healthy aging is important for heart, brain, diabetes, and more. I love flipping through the print out I received.
To book, click BOOK VO2. We will have our medical staff meet with you (virtual or in SF or PA clinic) to review the test and your history. Remember there is preparation ahead of your test (no eating, etc). To read that blog, click VO2 PREP.
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