I would greatly appreciate any thoughts, advice, or pointers to other sources on the following topic:
Is oxygen intake, relative to the rate of respiration, at aerobic/anerobic thresholds ever (or often) a limiting factor in overall cardiovascular fitness?
What I am interested in figuring out is if my rate of respiration (when I am exercising hard - HR at 170 bpm) due to weak breathing muscles (or bad breathing technique) might be a factor (maybe a significant factor) in my ability to deliver oxygen to my muscles and keep me down in an aerobic zone. At this heart rate (for sustained exercise of about 10 minutes) my respiration rate is only about 25-28 breaths per minute - this seems low to me. Thoughts?
By way of background, I do not have any know breathing problems, I am 44 years old, had been sedentary until about 6 months ago (3 months of primal pb for fitness and 3 months of CrossFit).
Do you feel like you're not getting enough oxygen? Our respiration rate is tied to our oxygen demand and the amount of CO2 we have to blow off. Respiration also has a perfusion quotient, as in how much blood is available in the capillaries around the alvioli as well as the health of those capillaries. It's known as the ventolation/perfusion ratio (V/Q ratio).
People can have problems with the repiratory portion of this ratio such as asthma, bronchitis, emphysema and other types of COPD which cause the lungs to become stiff and unable to inflate as much as they need. This would cause the RR is increase in order to get enough oxygen. These people are also known as CO2 retainers since they tend to not blow off enough.
There can also be issues with the perfusion to the lungs. This happens with atherosclerosis and also with the neurovascular damage that occurs in diabetes which reduces blood flow to the small alviolar capillaries. People with these problems also tend to have a faster RR.
So, this little physiology lesson () is a short way of telling you that a slower RR is unlikely to indicate a problem. Our bodies have many mechanisms to ensure that they remain adequately perfused, increased RR, fatigue, peripheral cyanosis (blue lips and finger tips) as blood is shunted to the organs and eventually lack of consciousness (the brain's way of putting your head at the same level as your heart and getting enough blood ).
If you are able to exercise as you wish, without undue fatigue, light-headedness or signs of cyanosis then I imagine that your body is getting all the oxygen you need. Slower, deeper respirations are far more effective at delivering oxygen as larger areas of the lungs are inflated and therefore more capillaries are exposed to oxygen.
In general I do feel like I get enough oxygen; however at near peak levels of exercise if feels like my limiting factor is breathlessness vs. dealing with lactic acid.
Let me give you a specific example: Yesterday I did a 2000m row in 8 1/2 minutes. During the last 2-3 minutes of the row, I was at 177 beats per minute (HR) vs. a measured max heart rate of 196 bpm - This is 90% of max. And yet I had an RR of only 28. Why wouldn't my body kick up my respiration a bit in order to drive more oxygen and lower my HR???? Or is it more likely that I don't have the capillary network to use more oxygen and getting more oxygen to the lungs isn't the problem?
For what it's worth, my heart rate monitor reported that my peak ventilation rate was 81 l/min (not sure how this was calculated).
The Respiratory System is a significant limiter for many athletes.
I would suggest that reducing your respiration rate (versus increasing) would lead to a drop in your HR. First, increasing RR requires an increase blood flow to the lungs, etc. vs. the other muscles in your body that are propelling you. Second, it has been my experience that as RR increases, most people decrease their respiratory volume (shallower/smaller breaths) - essentially meaning they get the same volume of O2 into their system in spite of their additional work (more breaths = more work).
One "test" you could try is picking a steady pace (say at 55 to 65% of max HR) and once you have a steady HR focus on your breathing with slower big (yoga/belly breaths - not high up in your chest) and see if your HR drops; this is easiest to test in a controlled environment. Here is an example:
Pedaling at a cadence of 85rpm at a speed of 14mph with a HR of, say, 135 BPM; make sure your HR is steady for a couple of minutes (+/- 2 BPM). Maintain the speed and cadence then focus on reducing the respiration rate with belly breathing, yoga breathing or other style/technique. Does your HR drop? A reduction in HR indicates that your change in breathing has allowed for "free" speed.
Human beings, by changing the inner attitudes of their minds, can change the outer aspects of their lives.
William JamesUS Pragmatist philosopher & psychologist (1842 – 1910)