Real VO2Max--Measure Your Athletic Potential
Introduction: Real VO2Max--Measure Your Athletic Potential
VO2Max is an interesting concept that proposes that there is a natural limited ability to extract Oxygen nutrient out of the air and consume it. It is like the IQ of sports activities--some algorithm that tells you how gifted you are in doing a variety of athletic contests. It was worked on at the beginning of the last century and relied on bags of exhaled air that were carefully measured with arcane gas analysis that have only gotten more complex. The machine needed to measure this is expensive enough that just taking the test costs about $150. It requires a room with strange machines, assistants, masks and treadmills. Or you can just get an Apple watch that "does some math" and puts out a number that's based on a variety of well regarded tests --"name of a random doctor who correlated the expensive test with some easily measured thing like heart rate while walking". They always tell you that <PERSON> has a very high one and Sled dogs in Alaska have one that twice as high as Lances. It gets lower as you age, females lower than males and seems to have some basis in physiology--it is the amount in cc's of oxygen gas used in one minute per kg of tissue.
To measure this you actually have to carefully measure the amount of gas going in and out of your body, the level of CO2 and Oxygen in this gas, its humidity and temperature and use a confounding number of formulas to get to this number. (Or just make it up based on shoe size...) This Instructable will enable you to build a 3D printable portable device to do this with reasonable accuracy that costs about $150 and can be used for testing in a variety of sports. It can be Bluetooth/Wifi connected and provide a wealth of information during use. The breathing components can be easily separated from the expensive sensors to limit worries of virus transmission. It could be cheaply offered at health clubs or to individual users to evaluate training progress.
Step 1: Gather Your Materials
The only thing that is expensive in this build are the very fine sensors that are necessary to do the analysis. The heart of the design is based on the https://www.instructables.com/3D-Printed-Spiromete...
spirometer design that measures the volume flow through a tube using this sensor:
1. SDP816-125PA Pressure Sensor, CMOSens®, 125 Pa, Analogue, Differential $30 Newark, Digikey
2. TTGO T-Display ESP32 CP2104 WiFi bluetooth Module 1.14 Inch LCD Development Board $8 Bangood
3. 279
Gravity: I2C Oxygen Sensor $55. DFRobot
4. SCD30 Gas Detection Sensor, Carbon Dioxide, 40000 ppm, 3 % $55
5. Lipobattery 600 Mah $3
6. Switch $1
7. Connector cables $2
8. Dead Snorkel $1
9. Silicone Film High Temp Thin Rubber Sheet Gasket Super Clear Flexible 12x19.7 x1/32 inch
These sensors have been carefully tested for use in this device...there are cheaper but wildly dysfunctional alternatives. I have used different oxygen sensors in the past that required separate ADC and booster boards but found this new one from DFRobot has built in I2C and works very well. (I get no money from no-one)
Step 2: 3D Print It
The design is based on previous valved snorkel designs: https://www.instructables.com/3D-Printed-Snorkel/...that utilize one-way valves to prevent the collection of dead air in the snorkel tube. In this case we build a breather apparatus that sucks air in one way and exhausts it through a flexible tube borrowed from a snorkel that connects it to the gas-measuring device. In this way we only measure the exhaled quantity of gas and the level of CO2 and O2 in the exhaled portion. Without the one way valve we would get admixing of the incoming and outgoing flow. The design for the one way valves and their assembly can be found in the above Intstructable. The valve material is soft silicon sheet that is easily cut out with a 3D printed guide.
The Venturi tower is the same design as in the spirometer with extra enclosures for the O2 sensor and the CO2 sensor with built-in covers that make them air-tight and do not interfere with gas laminar flow. The only modification to the computer housing that contains the differential pressure sensor is to enlarge it slightly to accommodate the extra room need for the two I2c connector cables.
Step 3: Wire It
The wiring for this device is very simple. 832