“Week 4”: Explaining (probably) All Project Variables and Terminology
Eugene j -
Hey everyone! Next week, I hope to post twice because something very cool will happen in my internship on Friday unless something gets in the way. I want to keep what it is a secret for the next post. So look forward to it!
In this one, I’ll explain all the variables my project will consider and analyze. So, this will be technical and very comprehensive, and I will try my best to explain everything clearly.
Atmospheric Pressure: As altitude increases, atmospheric pressure is reduced exponentially. The oxygen concentration of the earth’s atmosphere is about 21% at all altitudes. The reason breathing gets more difficult at high altitudes is that the density of the atmosphere is reduced, so deeper breaths are needed to get the same amount of oxygen at shallower breaths at a lower elevation. The volume of air you breathe into your lungs contains fewer oxygen molecules in each breath.
Atmospheric pressure at sea level is 760 mmHg, and at Flagstaff’s elevation of 7,000 ft, it is 600 mmHg. Breathing in Flagstaff is the equivalent of breathing air with only 16.6% oxygen at sea level instead of 21%. The net result is 21% less oxygen than at sea level.
Acclimatization or Acclimation: The body adapts to the change in atmospheric pressure after a few weeks of living at high elevations. Many physiological changes occur, but the main related factors are the lungs increasing volume, you doing deeper breaths, more red blood cells being produced, and more vessels made throughout the muscles.
There is one significant uncertainty I am focusing on. The heart rate will initially increase, but there are differing opinions on whether an increased heart rate remains after acclimation. There is a lower mortality from cardiovascular diseases and problems for people living at high elevations. Still, it is uncertain whether this is because of some other part of acclimation or increased heart stress, causing improvements after long periods.
METs (Metabolic Equivalent): This unit measures the intensity of physical activity. This should roughly be the amount of oxygen the body consumes while sitting quietly. This is different for every person. 1 MET = 3.5 ml of O2/kg body weight/minute. There are other methods and equations to get a MET, but I am using this one because it is in relation to O2. MET is not directly connected to heart rate but to physical activity in the same way heart rate is.
While you sit in place, for every minute that passes, every kilogram of your body requires about 3.5 ml of O2 to survive. However, this assumes you are sitting around sea level. Sitting down at a high elevation would talk more than just 1 MET because there is less O2 in the same volume. Using the Ideal Gas Law, I approximated the number of METs that the body uses at Flagstaff’s elevation. You technically can skip this, but I want to show my work.
PV = nRT P=pressure in Atmospheres (atm), at sea level, pressure equals 1atm. V=volume in Liters n=moles of gas (mol), which is the unknown R=Ideal Gas Constant=0.0821 L*atm/mol*Kelvin T=temperature in Kelvin, room temperature is on average 295 K or 71.33°F.
1 * 3.5= n * 0.0821 * 295 —> n = 3.5 / (0.0821 * 295) —> n = 0.144512
Then convert to Flagstaff’s atmospheric pressure of 600 mmHg= 0.789474 atm, looking for volume
PV = nRT
0.789474 * V = 0.144512 * 0.0821 * 295 —> V = (0.144512 * 0.0821 * 295) / 0.789474 —> V = 4.433… ml of O2
4.433… / 3.5 = 1.266… METs
Physical activity at Flagstaff’s elevation is approximately 1.266… times harder/more intense than at sea level. This improved MET value is also more specifically why athletes would work out at Flagstaff compared to somewhere with a lower elevation. Exercise intensity is rated based on the MET value of the actions, with light exercises being less than 3 METs, moderate exercise being 3-5.9 METs, and vigorous exercise being 6 METs and above. So, walking at 4 mph is considered 5 METs and a moderate exercise, but at Flagstaff’s elevation, walking at 4 mph would be 6.33… METs and a vigorous exercise.
VO2 Max (Maximal Oxygen Consumption): This is closely connected to METs as it has the same units as METs (ml of O2/kg body weight/min). VO2 Max is the maximum rate at which the body can take in oxygen during physical activity. This depends on age, sex, and fitness. For example, someone with a VO2 Max of 35 would be capable of doing an activity with a MET value of 10 as long as they maximize their breathing. VO2 Max can be approximated with VO2 Max = 15 * (Max Heart Rate / Resting Heart Rate). Due to VO2 Max’s relation to heart rate and an inconsistency in calculation, I don’t believe that elevation affects VO2 Max in the same way as METs.
Following my previous METs calculation, the VO2 Max of 35 at sea level would be the equivalent to a VO2 Max of 27.63 at Flagstaff. However, other sources state that VO2 Max decreases 1-2% every 390 feet (120 meters) above 4900 feet (1500 meters), resulting in a VO2 Max from 33.12 to 30.91. I accept the other sources for VO2 Max’s change with elevation, but since there are no sources on METs changing with elevation, I will follow my ratio of 1.266… for Flagstaff.
Heart Rate (HR) is already widely understood.
Resting Heart Rate (RHR) is your HR when not doing any physical activity. RHR is not HR during sleep, as HR decreases even more.
Maximum Heart Rate (MHR) is the highest your HR can safely go. HR can go even higher, but at that point, there is not enough time for blood to flow fully into the heart, meaning the heart is no longer working correctly. MHR = 220 – Age.
Heart Rate Variability (HRV) is the variable time between heartbeats. HRV is controlled by the sympathetic nervous system, fight-or-flight, and the parasympathetic nervous system, rest and relax. A higher HRV is correlated to a well-functioning nervous system and shows. A healthy HRV is around 19 to 75 milliseconds, but athletes often have it even higher. A variable HR shows the body’s ability to adapt to changes and is most apparent at rest. HRV is measured from RHR because measuring the variable time with an elevated HR becomes difficult.
Heart Rate Recovery (HRR) is how much HR decreases from an elevated state during exercise one minute after stopping. The more HR decreases, the better the heart functions, reducing the risk of heart problems and diseases. A normal HRR is around 18 beats per minute.
Thank you for reading this extra-long post! I hope it isn’t too confusing.
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