Welcome Players! From Olympic competitions to Tour-De-France scandals, utilizing methods to train at altitude for performance dates thousands of years. Why are athletes so concerned with training at elevation? What benefits does it bring? Are there risks involved? In this article we look at the physiological response the human body has at altitude, how it affects physical performance, and what you can do to take advantage of the pro’s while limiting the con’s.
Contents:
The Warm-Up
Physiological Effects of Altitude
Altitude Illness & Acclimatization
Effects of Altitude on Performance
Competing at Altitude
Final Thoughts
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The Warm-Up
How High are you?
Er. Maybe I should clarify…
At what elevation are you currently situated?
Something that very few, if any, athletes consider about their competition is the effect of altitude.
For the most part because much of the sporting world occurs at relatively normal (sea-level) altitude.
Of course there are the cities above:
Mile High Denver (1,609m | 5,280 feet)
Salt Lake City Utah (1,319 m | 4,327 feet)
Flagstaff Arizona (2,134 m | 7,000 feet)
We see this topic rise to the front of main stream media every decade or so when the Olympics is hosted in a high-altitude city, like the 1968 Summer Games in Mexico City (2,240 meters | 7,350 ft) where the USA T&F team enlisted the help of trusted breathwork and altitude-training experts to gain an edge on the rest of their international competition.
And if you compete in a mountain sport: Skiing/Snowboarding, Hiking, Climbing, etc. you are likely familiar with the effects of altitude.
But what about the rest of us? The football players, soccer stars, basketball prima-donnas (yes you basketball players are very dramatic), baseball sluggers...
Does altitude matter for you?
The short answer is, probably not.
But you’re not here for the short answer.
We’re going to explore what happens to human physiology when you are at higher elevation, how it can affect your performance, and find out if we can mitigate the negative effects of performing at altitude while optimizing the beneficial effects of training at altitude.
Let’s get climbing.
Physiological Effects of Altitude
I’m going to assume you have some working knowledge of physiology.
To put it simply, the largest effects of altitude are seen in how our body metabolizes calories for energy and how that energy is delivered to our cells.
Altitude changes the “set-point” for at what intensity our body uses a specific energy system, as well as changes the amount of oxygen (and nutrients) available to our muscles at any given time.
We’re going to look at specifically how the red blood cell’s role in transporting oxygen is VITAL to the performance of any endurance variable, how altitude changes that oxygen (and carbon dioxide) transportation, and then how changes in those two things lead to to a shift in energy system use further complicating endurance performance.
Role of RBC (Red Blood Cell) in Transporting Oxygen
Again, in a simple overview:
We inhale. Air travels into our lungs where the oxygen is diffused into the blood via capillaries in the lungs.
But oxygen doesn’t just hop into the ol’ blood train and hang on. It needs a partner. A chauffeur, if you will.
And this job is assigned to the very trustworthy, and reliable, hemoglobin.
Hemoglobin is a protein within the red blood cell that has one big job: transport important gasses to and from the cells of tissues.
Now most people only think of hemoglobin as an oxygen-chauffeur, but that is only half of the job. When hemoglobin picks up oxygen in the lungs and takes it to the muscle, it doesn’t return empty handed.
When it arrives at the muscle cell, it delivers oxygen (O2) and picks up carbon dioxide (CO2). This is important!
It then brings CO2 back to the lungs so it can deliver it, we exhale that CO2, and then the process repeats.
So how does hemoglobin know when to pick up O2 and when to pick up CO2?
By something called, aptly, the oxygen-hemoglobin dissociation curve:
The curve visually depicts the relationship between the amount of oxygen bound to hemoglobin and the partial pressure of oxygen in the blood.
The higher the partial pressure of oxygen in the blood, the greater the affinity (attraction) that hemoglobin will have to pick up that oxygen and carry it within the RBC.
If the partial pressure of oxygen is low, there will be a lower affinity for hemoglobin to oxygen.
This only explains hemoglobins relationship with O2.
For it’s relationship with CO2, we look to what’s called the Bohr effect:
The Bohr effect describes hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and/or decreased blood pH. This lower affinity, in turn, enhances the unloading of oxygen into tissues to meet the oxygen demand of the tissue.1
When there are higher partial pressures of CO2 (and/or decreased blood pH [because higher CO2 concentrations lower pH anyway]), the greater the disassociation of oxygen and higher affinity hemoglobin has to pick-up CO2 for it’s ferry-ride back to the lungs.
Ok, now that the technicals are out there, let me simplify it:
Hemoglobin has affinity for both oxygen and carbon dioxide. Which it has a greater affinity for is dependent upon the concentration of both O2 & CO2 currently in the blood (partial pressure), and the pH level of the blood.
When concentrations of O2 in the blood are high, CO2 is low, hemoglobin will have an affinity for O2.
When concentrations of O2 in the blood are low, CO2 is high, hemoglobin will have a higher affinity for CO2.
And now the coolest part about the Bohr effect (for nerds like me), is that not only does the affinity for each molecule change in relation to the partial pressures & concentrations, but it actually helps kick off attachment of one molecule in favor of the other!
For example: We breathe in. Big concentration of O2 is diffused into the blood. Partial pressure of O2 is high. Hemoglobin swoops in and attaches O2 in the RBC. Then the RBC travels down to the tissue of the muscle. When it gets there it finds that the partial pressure of CO2 is high (byproduct of cellular metabolism is CO2). This high partial pressure of CO2 along with the low concentration of O2 works to help increase the rate of detachment of O2 off the ferry (hemoglobin) quickly so that CO2 can get on (also quickly) and get taken back to the lungs so it can be expired.
This is a magical system! Truly ingenious.
It allows for both O2 and CO2 to get to their respective destinations quickly AND efficiently.
For O2, the goal is to get from the lungs into the muscle as quickly as possible. Both the high affinity for O2 from hemoglobin in high-partial pressures allows it to bind to its transporter fast, but the Bohr effect of being released quickly in presence of higher CO2 concentrations means that O2 will get dropped off and deposited into the muscle for continuous metabolism very fast!
On the flip side, when O2 get’s dropped off at the muscle, there is a building pressure of CO2 that the muscle needs to get rid of, FAST. CO2 causes decreased pH and will inhibit performance of the muscle if it sticks around too long, we need to get this CO2 back to the lungs for exhalation ASAP. Here comes a RBC loaded with oxygen-bound hemoglobin. As soon as it gets the muscle, the oxygen disassociates rapidly as CO2 binds, allowing that RBC to make a quick turnaround back to the lungs while maximizing the efficiency of Oxygen deliver.
Pretty cool right?!?
Altitude Effects on Oxygen
Ok, now that we have a working understanding of Oxygen/Carbon Dioxide transport via hemoglobin, we can talk about the main affect altitude has on human physiology.
It’s actually quite simple really.
There’s less oxygen available!
Ok - everyone strap in. We’re going to go on a little ride as an Oxygen molecule.
At sea level, the percentage of oxygen that makes up the air we breathe is ~20.9%, I’m going to round up to 21% for simplicity.
In addition to the 21% of oxygen in air, there is the barometric pressure. As the famous Evangelista Torricelli once wrote, “We live submerged at the bottom of an ocean of the element air!”
With an atmospheric pressure of ~100 kPa, the 21% of oxygen in the air is packed closely together. More pressure = denser molecules = more oxygen delivered in each breath of air we take.
Ok. Now we start traveling up. As altitude increases the barometric pressure decreases. The % of oxygen in the air (atmosphere) is still 21% - but - because there is less pressure from the weight of the atmosphere at higher altitude, there is less concentration of oxygen molecules per volume measurement of air!
Instead of those oxygen molecules being packed closer together within the air, they are now spread apart. This means with every breath we take we are getting lessoxygen into our lungs from the same amount of air.
The relationship between atmospheric pressure at specific altitudes and it’s resultant effect on the partial pressure of oxygen that we inspire is the culprit as to almost all of the physiological affects that happen at altitude.
Now - note that the column for “Oxygen Levels” is not the TRUE content of oxygen (we know it’s always 21%), it’s the EFFECTIVE oxygen concentration when factoring in the drop in atmospheric pressure at altitude.
This makes all the difference!!
See what happens when traveling to Aspen, Colorado, at an elevation of ~2438m / 8000ft, the effective oxygen concentration is 25% LESS than sea level.
With 1/4 less oxygen available per breath of air, you can imagine the impact that would have on not only resting physiology but certainly exercise performance.
But you don’t have to just imagine… let’s see exactly what those affects are!
Physiological Compensation for Reduced Availability of Oxygen
Acute effects
The first thing the body does to make up for this lack of oxygen compared to sea level is speed up breathing.
Hyperventilation (hyper = fast, ventilation = breathing), will allow for a greater inhalation of liters of oxygen per minute, making up for some loss in oxygen efficiency.
To maintain this increased ventilatory rate, your heart rate will also increase. The quicker heart rate is necessary to continue the rate of absorption of oxygen into the blood. Faster breathing means faster heart rate means more blood (and oxygen) delivered to the cells of the tissue. All of this is necessary just to try and maintain similar levels of oxygen saturation at altitude.
The effects on heart rate and respiration rate are the most important to know, but there are more acute changes…
There are increases in blood pressure, urination, and negative impacts to sleep (both reduced quantity and quality).
But these are all acute effects. When you’ve been exposed to altitude, or stay at altitude, for a prolonged period of time the body is able to generate much better adaptations even in the short term.
Chronic Effects
While all the acute affects happen in as little as a few hours, chronic exposure to altitude brings along a whole new set of adaptations (or compensations, depending on how you look at it).
We’ll start by looking at what happens to our acute changes over chronic exposure:
Alveolar minute ventilation (respiratory rate) progressively increases over the first 8–10 days at altitude and then plateaus
Over the following 10 days at altitude (after acute exposure), heart rate tends to decrease [48,49], while elevated systemic blood pressure persists [47]. 2
Ok, now for the cool stuff.
The first is that the body produces more erythropoietin (EPO) [eh·ri·thruh·poy·tin].
What is EPO? EPO is a magical hormone that stimulates red blood cell production!
That’s right, more EPO = more red blood cells. You may already be concluding based on the importance of red blood cells & hemoglobin that the more RBC’s we have the better…
Not only does EPO increase, producing more RBC’s, but… hemoglobin concentrations also increase!
Whether the increase in hemoglobin is attributed to loss in blood plasma concentrations, rise in EPO, or rise in RBC’s, is unclear to me at this time. But, the rise in hemoglobin has been found to be both an adaptation to altitude in expeditions (climbs), and those who live at altitude (like Tibetans).3
Below is a good visual representation of the acute and chronic effects of altitude exposure in humans:
(note that the small graph is displaying effect size (+/-) over time)
The physiological consequences of being at high-altitude are:
hyperventilation
increased pulmonary artery pressure
increased cardiac output via increased heart rate
decreased blood plasma volume
increased eryhropoiesis
increased hemoglobin and hemoglobin concentration
Altitude Illnesses & Acclimatization
Ok. So we know now both the acute and chronic effects being at altitude has on human physiology.
And while a comprehensive guide to mitigate these effects, or endure them with the least possible inhibition on performance, is outside the scope of this article, I would be remiss not to at least touch on the dangerous (and potentially fatal) affects of rapid ascension into high- or ultra-high altitude environments without proper acclimatization.
First up in altitude sickness is Acute Mountain Sickness (AMS).
“AMS is the most common form of altitude illness. AMS is ashort-lived (2-7 days) illness similar to an alcoholic "hangover." AMS symptoms include headache, nausea, fatigue, and lightheadedness. AMS develops within the first 6-24hrs of altitude exposure, and its incidence and severity increases in direct proportion to ascent rate and altitude (Table 1).”4
Then there’s advance-stage AMS, whichcan become High Altitude Cerebral Edema (HACE)
“HACE is a potentially fatal, although not common illness (usually less than 2% of persons ascending above 3,660m). HACE is an exacerbation of unresolved, severe AMS and most often occurs in people who have AMS symptoms and continue to ascend. If left untreated, HACE can progress to coma and death in 12 hrs or less. Prevention of HACE is the same as for AMS.” 5
Next is High Altitude Pulmonary Edema (HAPE):
“HAPE is a potentially fatal, although not common illness (usually less than 10% of persons ascending above 3,660 m). Individuals making repeated ascents and descents above 3,660m may have an increased susceptibility to HAPE. Prevention of HAPE is similar to that of AMS. However, in lieu of acetazolamide, persons with prior history of HAPE may take a vasodilator such as nifedipine (20 mg sustained release every 8 hrs). Recent research suggests that sildenafil and inhaled beta agonists, such as salmeterol, may also provide prophylaxis for HAPE.” 6
Altitude sickness is a very dangerous game to play, and any adverse effects of elevation should be taken extremely seriously.
The linked resources to the Army’s Guide on Altitude Acclimatization along with other credentialed and recognized resources for prolonged exposure to altitude is of utmost importance to understand before attempting to perform at significant altitude.
Effects of Altitude on Performance
So what does all the physiological changes at altitude mean for performance?
Reduced oxygen capacity means a marked reduction in VO2 max.
One last quote from the Army’s Research on Altitude Acclimatization:
“During ascent to altitude, the progressive decline in the oxygen partial pressure causes a decline in maximal aerobic exercise performance. However, sub-maximal physical activities require the same amount of oxygen uptake at altitude as needed at sea level. Thus, expressed in relative terms, the oxygen uptake required for a submaximal physical activity now represents a greater proportion of the reduced maximal oxygen uptake. Thus, submaximal physical perfomnance is also impaired at altitude (Figure 1: Road March example). Furthermore, at a given altitude, the magnitude of the performance decrement will not be constant, but will vary in proportion to the duration of the activity. For example, high intensity exercise tasks lasting 2-5 min, 20-30 min, and >1 hr at sea level will average about 5%, 12%, and 30% longer, respectively, at an altitude of 3,000 m. These estimates were derived from highly trained athletes or research subjects who had been living and training at altitude for greater than 10 days.
So, the lower your VO2 max the harder sub-maximal exercise will be because the greater percentage of VO2 max you are using (this is called aerobic efficiency).
You can imagine how this has significant impacts on aerobic performance both from a capacity and intensity point of view.
Alright - with all the fun stuff out of the way, how do you maximize the positive adaptations of being at altitude??
And let’s be clear, there are positive adaptations for being at altitude. If we took the list of adaptations again:
hyperventilation
increased pulmonary artery pressure
increased cardiac output via increased heart rate
decreased blood plasma volume
increased eryhropoiesis
increased hemoglobin and hemoglobin concentration
And removed the adaptations that can carry over from exposure at altitude but would not be seen at sea level:
hyperventilation
increased pulmonary artery pressure
increased cardiac output via increased heart rate
decreased blood plasma volume
increased erythropoiesis
increased hemoglobin and hemoglobin concentration
And we remember that at sea level we have a denser concentration of O2 molecules available in each respiration… (do you see it yet??)
Ok I’ll just spell it out…
Chronic adaptations of prolonged altitude exposure results in increased hemoglobin concentrations and increased red blood cell concentrations, which when returning to sea-level atmosphere temporarily increases the oxygen-carrying capacity of the blood and allows for more oxygen to be delivered to the cells of the tissue in the same unit of volume of air over time.
English please…
Better oxygen utilization!!
The result of chronic exposure at altitude means that your body adapts to have a greater efficiency of oxygen use, from it’s binding to hemoglobin, to transport via RBC’s to the cells, to then that cell utilizing oxygen to produce ATP which then creates movement.
This is like a super power! The more oxygen available to your cells the longer and harder you can perform.
So while being at altitude produces a marked reduction in performance, if you spend enough time at altitude to allow the chronic adaptations to take place (>15-20 days), you will return to sea-level with a more efficient aerobic energy system.
Now, this might sound awfully familiar to any endurance sport fans out there, especially those who enjoy Cycling and… the Tour de France…
Doping
Yup. That’s right. The super-power-like benefits of being at altitude were the same benefits Lance Armstrong artificially created by injecting… EPO! (along with some other stuff too)7
Doping is nothing new, but endurance athletes use every means at their disposable (legal or not) to maximize their aerobic efficiency and gain an edge on the competition.
Morals aside, understanding the effects and adaptations of altitude it is quite clear how artificially injecting EPO into an endurance-training athlete improves the oxygen-carrying efficiency of hemoglobin, as well as the increases the concentration of RBC’s (which carry oxygen-bound-hemoglobin), will have enormous positive affects on endurance performance at both sea-level and altitude.
This leads to better oxygen efficiency, better aerobic efficiency, and a higher VO2 max, all critical metrics for endurance performance.
Competing at Altitude
But for those that want to stay ethically clear, or those without the means, there are other (legal) means to reap the benefits of altitude adaptation without breaking any rules.
Utilizing training at altitude is nothing new, as athletes and competitors have been doing it for thousands of years. Cyclists were doing it before doping with EPO became popular, but as far as I can tell proper training at altitude consumes an incredible amount of resources.
There’s the logistical and financial costs of being at altitude, living there, getting your equipment there, getting appropriate gear, etc. Then there’s the effort, of leaving your home / base of training. And then finally there’s the time and efficiency lost due to training at altitude, even though being at altitude can produce chronic benefits.
One reason doping became a panacea for endurance performance is because you could now get all the benefits of being at altitude (chronic adaptations via EPO injection), with none of the performance penalties (performance decrease due to decreased aerobic efficiency at altitude while training).
There’s a double-edge sword when it comes to utilizing altitude at a training modality:
You train at altitude inducing the positive adaptations on aerobic efficiency
- BUT -
You have diminished aerobic capacity while training at altitude, potentially inhibiting the effectiveness and quality of your training
So you either train inefficiently at altitude to chase these chronic positive adaptations, or you train at sea-level to maximize your training effectiveness and hope the negative effects of altitude (if you’re competing at altitude) don’t blunt your performance as much as your competitor.
Fortunately sport science has taken this topic very seriously and there is a plethora of research that have all come to one common consensus:
Live High Train Low
Bob Marley might have a different definition to this saying, but in Sports-Science it’s the proven method of optimizing chronic altitude adaptations without suffering negative performance consequences.
As the name implies, the most efficient way to incorporate altitude training is by living at altitude (AKA spending a significant portion of the day there - we’ll get into actual hours next), and training at low- or sea level-altitude.
Traditionally this meant being at a location where it was relatively easy to travel between altitudes as well as have the requisite resources to carry out training.
It doesn’t help a cyclist to be at the right altitude in the Himalayas if they can’t get down to sea level to train.
Likewise, no athlete is going to want to spend their days on a desolate mountainside where the only activities to do at basecamp are throw rocks and kick stones.
In comes modern science - where biohackers and nerds unite to pioneer hypoxic oxygen chambers and nitrogen-diluted apartments.
It’s important that I make this distinction now, between natural altitude acclimatization and artificial, because the dosage of exposure is individual to each.
Let’s start with the good ol’ fashioned way.
Live-High, Train-Low at Natural Altitude
Remember, the goal of living at altitude is to induce chronic physiological adaptations that result in increased EPO concentrations, leading to a greater oxygen capacity, and thus improve endurance performance when returning to sea level.
For natural exposure, the longer you’re at altitude the better. Simply put, the only time you should not be at altitude is when you’re going low to train.
A study that used hypoxic exposure of ~22 h/d for 4 weeks at a natural altitude of 2500m resulted in significant increases in erythrocyte volume (8%), treadmill VO2max (4%), and 5000-m-run performance (1.3%) at sea level.8
The systematic review also showed that hypoxic exposure ≤ 2 weeks in duration will probably not increase erythrocyte volume; rather, a minimum of 3 to 4 weeks appears necessary for accelerated erythropoiesis to occur.
It found that while the more time spent at altitude the better, that was not the case for at what elevation to be at. The higher the better is certainly not true.
Although there is relatively limited data on the subject, the data suggests that the optimal beneficial range of altitude is 2000-2500m for most athletes, while keeping in mind that there is considerable individual variability in the altitude-acclimatization response.
Live-High, Train-Low at Artificial Altitude
The script changes a little bit when incorporating hypobaric chambers or nitrogen-diffused rooms, creating a low-oxygen environment.
Studies have found that athletes can be exposed to higher altitudes (2500-3000m) for less time (12-16h/day) and receive performance enhancing affects. Although these effects are not as great as those seen with natural altitude acclimatization, the benefit here is that the athletes will not see any performance-limiting effects of training that are caused from altitude exposure.
It is common for athletes using the live high, train low natural model to experience loss of power, speed, or experience sluggishness due to the acute physiological changes that being at altitude elicits. While it’s great for chronic adaptations, it makes acute work effort more difficult.
Thus there’s a balance that needs to occur between altitude exposure for chronic adaptation and limited altitude exposure for maximizing training efficiency.
To this end the artificial hypoxic environments are becoming more and more popular.
Below is a comparison of red blood cell mass change comparing natural and artificial elevations. While it’s clear the natural model is superior with respect to RBC and hematological adaptations, there is much more research that needs to be done to evaluate affects on performance of the individual between the models.
U.S. Olympic Team Application
A very pointed example included in the research review (cited a second time here, I encourage those interested to read the full paper), is in the preparation the US Olympic Speed Skating team took by integrating the live high train low model leading up to the 2002 Salt Lake City Winter Olympics.9
“Three years before the Salt Lake City Olympics, the speed skaters began living in the Deer Valley/Park City area of the western US state of Utah (~2500 m) to enhance erythrocyte volume and acclimatize at an elevation markedly higher than the altitude of their competition venue (Utah Olympic Oval ~1425 m). The athletes continue to use Deer Valley/Park City as their base of operation and use different LH+TL methods depending on the specific phase of the competitive season.
During the base phase of the season (~4 months), the speed skaters focus almost exclusively on moderate-intensity, high-volume, dry-land training at 2000 to 2500m. There is minimal emphasis on high-intensity training during this phase, so essentially the athletes adhere to the traditional LH+TH model at this time. There are also some sea-level training blocks during the base phase, but the training intensity remains moderate.
During the precompetition phase of the season (~3 months), the speed skaters use a LH+TL regimen in which they continue moderate-intensity, dry-land training at 2000 to 2500 m. They complement this with high-intensity off- ice interval training using in-line skates on an oversized treadmill while breathing supplemental oxygen, which allows them to temporarily and conveniently train at “sea level.” They also spend significant time on ice during the precompetition phase, with emphasis on technical refinement, as well as continued advancement of their conditioning.
During the competition phase of the season (~5 months), the emphasis is on high-intensity, race-pace training, and the speed skaters use the Utah Olympic Oval (1425 m) to train low. In addition, they use supplemental oxygen (portable backpack unit) in conjunction with select high-intensity on-ice training sessions at the Utah Olympic Oval during the competition phase.
Approximately 4 weeks before a major competition such as the World Championships, the speed skaters abandon use of supplemental oxygen.
The US long-track speed skaters enjoyed unprecedented success in the 2002 Salt Lake City Winter Olympics, with 6 athletes winning 8 medals, including 3 gold medals and 2 world records.”
This is a great birds-eye view of how the live high train low model can be utilized to enhance performance intelligently.
Note a few things:
the amount of time allotted to encourage altitude adaptation: moving to a moderate-altitude environment 3years before the competition date! Much different than research protocols who only look at weeks-months at a time
The use of periodized programming in altitude application: utilizing general preparatory and aerobic volume phases at altitude to encourage the most beneficial aerobic adaptations within altitude, while transitioning to sea level for selective medium and all high-intensity efforts hoping to maximize the muscular adaptations of training
The selected use of non-natural altitude implementations: the use of supplemental oxygen to either increase oxygen allowing for high-intensity training at high natural altitude, or the use of nitrogen-dilution/lower supplemental oxygen at sea level to simulate altitude
The effect logistics plays on the selection of the associated tools and resources
Final Thoughts
Understanding the effects of altitude are vital for any sports or competitions that take place in altitude.
For most sports though, this information is of little use.
The time and effort required to properly utilize altitude for beneficial effects on performance is reserved for elite competitors in the highest level of endurance competitions.
With that said, what kind of performance improvements are expected when incorporating an altitude-training model?
Performance improvements were seen to be <2%.
Of course, this quantitative result comes from short-term research studies, and while I’m sure improvements from all-in methodology’s like the Olympic team’s use would be much greater, we will never be able to know for sure. Without a control and long-term testing, it’s impossible to quantify the improvement.
And thus we reach the intersection of Art & Science, where the science of altitude-training tells us that it can only be used to improve so much, yet there are renowned artists (athletes) who have proven that just because you can’t see (or measure) the results, doesn’t mean they’re not there.
Whether you decide to use altitude training as a potent performance enhancer, or simply try not to suffocate when you go on the once-a-year snowboard trip, do so safely and with the right information.
And most importantly, enjoy the heights!
Learned something new about performance at Altitude? Share the highness with a friend.
Disclaimer: This is not medical advice. The content is purely educational in nature and should be filtered through ones own lens of common sense and applicability.
