When given the choice between deep, rhythmic, more diaphragmatic breathing, or short rapid almost hyperventilatory breaths, it is almost instinctive to think that the aforementioned strategy is more advantageous than the latter. Certainly, one would assume that the quest for oxygen will be much more fruitful when your respiratory rate is more controlled, substantial, and relaxed. However, as of late, we have noticed an alarming trend in many of the clients that we have tested; and this trend becomes even more alarming when it is justified by misinformation….
At rest, respiratory rates (RR) are between 8 and 12 breaths per minute (bpm). However, during exercise, it is common to see RR at or slightly above 70 bpm in highly trained athletes. While it is safe to assume that the demand for oxygen increases with exercise intensity, as evidenced by VO2max testing, it is not so clear why RR are so varied among the endurance population. What is clear is that athletes with higher VO2maxs (>55ml/kg/min) almost always exhibit maximal RRs at or above 60 bpm. One could assume that athletes with higher VO2maxs require faster RRs simply to continue the flow of oxygen that is so critical to aerobic exercise. However, that is not the case. What is of greater importance and is often overlooked is the amount of CO2 produced as a resultant byproduct of BOTH aerobic and anaerobic respiration- which commonly operate in tandem when energy demand is high. Unfortunately, most athletes and coaches are so concerned with increasing the adaptive mechanisms that assist in oxygen delivery and consumption; they pay precious little attention to the overwhelming buildup of CO2 within the body. Examine the following equation:
H+ (acid) + HCO3- –> H2CO3 –> H2O + CO2 (gas)
Notice that the symbol “H+” denotes the presence of acid within the blood. HCO3- represents the bicarbonate buffers that exist within the blood to stabilize blood pH. During rest, these two molecules exist in a delicate balance that holds the blood’s pH at 7.1. For those of you who remember your 9th grade chemistry, you’ll remember that a pH of 7.0 is neutral, a pH of 1.0 is extremely acidic (such as stomach acid), and a pH of 14 is incredibly alkaline (such as lime). Therefore, the blood’s pH remains very close to neutral, mostly to protect the delicate tissues of the brain from any acidic damage. Now, during high intensity exercise (above the anaerobic threshold), lactic acid produced in the muscle cell is immediately escorted away from pH-sensitive contracting muscle tissue and ushered right into the blood. This process is analogous to you tossing your accumulating garbage over the fence into your neighbor’s yard. However, the blood carries within it bicarbonate buffers (HCO3) that function to eliminate this biochemical waste before it accumulates. Notice the above equation where acid (H+) bonds to the buffer (HCO3-) to form a neutral molecule (H2CO3), which is harmless within the body. This molecule then travels back to the heart via venous return and is then sent to the lungs where it is converted to CO2 (gas) and water vapor. When you exhale, the newly created CO2 from acid buffering is expelled into the atmosphere via your expired breath therefore preserving blood’s neutral pH.
Even when exercise intensities increase and blood acid levels become elevated, this process can serve to safeguard the brain and internal organs from the acidic onslaught brought about by muscle tissue continually dumping acid into the blood- but only under one condition: You must continue exhaling CO2 at a rate that is proportional to lactic acid buildup.
In chemistry, many reactions, like the one above, can in actuality, run in reverse if the products (CO2 + H2O) become so abundant that they outnumber the reactants (H+ + HCO3-) Meaning, if CO2 isn’t expelled at the same rate that H+ is produced, the reaction will begin flowing in reverse thus producing acid rather than eradicating it. This is MAJOR biochemical event inside the body. At this point, RRs, CO2 expiration, and perceived effort increase exponentially as the brain begins to panic in response to the steadily decreasing pH of the blood. Because the brain is in direct contact with both the blood and the contracting muscle tissue, any change in pH due to the blood’s inability to properly dispose of CO2 will increase the level of acid to which the brain is exposed. This has profound consequences that can result in death IF the pH of the blood drops to 6.9 or below. Now, luckily humans are equipped with certain shut-off mechanisms that prevent such a circumstance from ever happening. However horses and dogs are not as lucky. If you’ve ever heard of a hound so motivated after it’s quarry that it “ran itself into the ground”, believe it. It’s true. The accumulation of lactic acid due to extreme sustained exercise intensities created a condition known as “metabolic acidosis”, which can be fatal. Fortunately for us, the brain, when threatened with a massive exposure to blood-acid, has an innate understanding that if neural drive to the muscle is reduced, muscle contraction occurs on a more sporadic basis and less forceful basis thus stemming the flow of acid into the already overwhelmed blood. This “central fatigue hypothesis” prevents any damage to the brain, internal organs, or muscle. However, it does not help you, as an athlete, as your performance now comes to a very punctuated end.
Now, back to the original argument, CO2 expiration. Most untrained athletes, at max, only take around 45 bpm, which is only 2/3 that of elite endurance athletes. Because of this reduced CO2 output, the ability of the acid-buffering reaction to keep running forward and continuing its important role is highly compromised. If more CO2 was expelled via quick, rapid, forceful exhalations, more H+ could be removed from the circulated blood supply before the brain senses a drop in blood-pH thus initiating central fatigue.
This is in a direct contradiction to current paradigm that deep breathing will aid in oxygen transfer and will prolong an aerobic status in the working muscles. While more diaphragmatic breaths do have an effect, its basis is much more psychological than physiological. Recent research has shown that when breathing rates are below 30-32 bpm, the athlete’s perceived exertion is actually lower than when breathing rates are above 35 bpm even when exercise intensities are the same. Thus most athletes find it more comfortable to voluntarily depress RRs even at high intensities where CO2 expiration will act as the primary determining factor in an athlete’s anaerobic tolerance- not VO2max. This can be likened to putting a governor at 90mph on a sports car whose top speed is rated over 200. Due to the electrical inhibition coming from the governor, the car will never fully realize its ability to operate close to its estimated maximum. This is the exact mechanism by which your brain systematically limits muscles from contracting and further contributing to the already overwhelming level of acid in the blood.
Lactic acid clearance is the limiting factor for athletes operating near VO2max and serves as the metabolic governor to protect the vital tissues of the body. It is critical not to limit respiration rates when the energy demand is high simply due to the overwhelming effects of central fatigue. It is vital to your performance as an athlete to practice frequent forceful exhalations when you train at or near ~85-90% VO2max. This will assist your body in removing the acidic by-products of anaerobic respiration, stabilize blood-pH, and will allow your brain to continue providing neural input to your working muscles. These effects will allow you to increase your anaerobic tolerance, cardiovascular output, and afford you a faster recovery from sustained high-intensity endurance exercise.
- Most athletes take only 45 (bpm = breaths per minute) at 80% VO2max and above
- Elite athletes have been shown to take 65 bpm at or near VO2max
- Lower respiratory rates (RR) can severly limit your ability to remove CO2 from your blood and DO NOT increase oxygenation of blood as could be expected
- CO2 is directly linked to the level of acid in your blood
- Failure to remove CO2 via exhalation will result in an inability to remove lactic acid in the blood
- The brain is very sensitive to changes in blood pH
- As acid builds up in blood due to a low RR at very high intensities, the brain reduces the level of stimulation to the muscles = “Central Fatigue”
- As the brain reduces central drive to the muscles, your perceived exertion increase exponentially
- This is done to prevent the muscles from continually producing more and more lactic acid which could damage the sensitive tissues in the brain and internal organs
- Once you stop, your blood pH begins to return to normal and you can eventually continue the exercise
- To keep this from happening, make sure you practice rapid, forceful exhalations when exercising at high intensities