Thursday, March 7, 2013

Cardiac stress test / VO2 Max test

Now that I no longer have a trainer, I also no longer have periodic VO2 Max tests although, for a completely different reason, I have been doing a number of cardiac stress tests which follow a similar protocol. I decided to pay a visit to my local Reebok Sports Club where, 5 years ago I did a series of medical and physiological tests to make sure I wasn't literally going to kill myself by training too hard. The results I got at the time were surprisingly good considering I had only stopped smoking and started exercising 4 months previously. I remember that they thought that the spirometer (which measures lung capacity) was broken because the reading it was giving was "too high".

There were several reasons for wanting to go back. Firstly, I wanted to take a snapshot of where I am now, after having recently achieved personal best times in 10K, Half Marathon and Marathon, so that I can use the results as a benchmark in the future. I was also curious to see how much I had improved in terms of thresholds, maximum heart rate and VO2 Max, etc., in the last 5 years. Although I have done a number of tests in the interim, very few of them were conducted up to my maximum because I typically had a competition looming for which it wasn't convenient to push myself too hard. The cardiac stress tests I had done recently also fell short of my maximum because they were based off the inaccurate formula of 220-age for maximum heart rate. What I was mostly interested in, though, was to see whether the abnormality that had been detected in my heart function (a CRBBB - a tongue-twisting Complete Right Branch Bundle Block) was something that I had developed in the last five years - perhaps as a direct result of my training - or something genetic. I'll also admit that I relish any excuse to go to the Reebok Sports Club - it is by far the swankiest gym I have ever been to and you never know if you are going to see someone famous...

According to the records, the CRBBB was not present in the tests I did 5 years ago. As last time, I was connected up to a cardiogram and made to wear a mask which measures the rate of oxygen - carbon dioxide gas exchange in my breathing. In other words, I did a cardiac stress test and a VO2 Max test at the same time. The O2 - CO2 exchange is a way of measuring what proportion of your energy you are deriving from metabolising carbohydrates or from fats. From this you can estimate where your aerobic and anaerobic thresholds are which are useful indicators for training purposes. The device is also able to measure the absolute volume of O2 that you are able to make use of or "burn" - this is the famous VO2 Max (once it has been divided by your weight). Unlike the other cardiac stress tests I had done recently, the protocol was to increase the speed while keeping the incline at 1%, until I could no longer keep pace.

When the doctor stopped the test, I felt as though I could have gone through at least one more increase and so I was still giving her the "thumbs up" - I felt sure that I couldn't be at maximum heart rate, especially as I hadn't been anywhere near that level for years. I was also convinced that the treadmill speed was much less than the 20 kph that I actually finished at. It turned out that both my O2 consumption and my heart rate had plateaued so continuing the test wasn't going to tell us anything we didn't already know. Compared with 5 years ago, my maximum heart rate had dropped a couple of pips to 190 bpm, my VO2 Max had increased from 68.02 ml/min/kg to 68.92 ml/min/kg and the speed at VO2 Max had increased from 18 kph to 20 kph. Some of my improvement in VO2 Max comes from a slight loss in weight but, relative to the general population, I should have expected a general decline in VO2 Max, rather than an increase. Actually, I just checked it - the difference is exactly due to my change in weight but the measurement of litres of O2 per minute was rounded to the nearest 0.1 (5.7 litres/min in both cases).

The CRBBB showed up on the cardiogram, of course, but the doctor said that it was very common amongst athletes and that I shouldn't worry about it other than doing regular checkups. From my own Googling, it looks like the Complete RBBB is still relatively uncommon in athletes (3%) while an Incomplete RBBB is much more common (9%); in both cases the incidence is higher than in the general population (in total about 1.5% of people between 40 and 65). I had thought that the word "block" meant that one of my arteries or veins was actually blocked but what it really refers to is a slightly faulty electrical system. When the heart beats, there is a concert of coordinated electrical impulses which cause it to pump blood around the body. The block refers to a delay (which, if it is greater than 120 ms, is considered to be a "complete block") in the electrical impulse to the right ventricle. According to the article I mentioned, this seems to be associated with a dilation of the right ventricle as a specific adaptation of the heart to exercise. The way I understand it which, of course is likely to be completely wrong, is that the right ventricle is not activated directly but more as a consequence of the prior sequence of contractions; a Left BBB is much more serious, however. The only thing to be careful about is that the defect is not due to some degenerative type of heart disease which might lead to more serious problems further down the line.

Disclaimer: If you have a similar condition then you should know better than to trust anything written on the internet rather than a qualified cardiologist!

No comments:

Post a Comment