Unusual heart rates and fitness

Question

About one month ago I started running every couple of days after being completely sedentary for ... well, essentially my entire life. I'm 23 years old, 5'11", 155 lbs, never done regular physical activity of any kind before that (except gym class, lifting a few weights every now and then, etc.)

I'm 100% healthy, but I have noticed that my heart rate seems to be a bit unusual. My resting heart rate is fairly low at 55 bpm, and when I run I can stay between 180 and 190 bpm for a fairly long time (at least 45 min). Today, after a 30 min run at 185 bpm, I tried sprinting for the first time (for like 5 sec), and my heart rate went up to 210 bpm. Somewhere between 195 and 205 must've been where my body crossed the lactate threshold. I then slowed down and went another 15 minutes at 190 bpm, all without any uncomfortable physical symptoms (like nausea, dizziness, or something).

Please assume my heart rate monitor is correct, if only for the sake of argument, since I've tested several and they all give identical results. Also, my heart rate doesn't seem to fluctuate abnormally, so irregular heart beats or PVCs are probably not the reason.

Having said all that, I'm definitely not some sort of super athlete: The speed at which I'm running with this heart rate is not high at all (about 10 km/h at 190 bpm) and my performance overall is not great.

My question is what this means in terms of my physical fitness, if it means anything. I'm not asking a medical question here, my heart is completely fine, which has been confirmed by doctors.

Does it mean that (a) I'm unusually fit, (b) I'm unusually unfit or (c) it doesn't mean anything and only performance counts? If it's (c), and it doesn't mean anything, I'd still be curious why my heart rate might be so unusual. I know that noone here can give me a definitive answer without further details, but maybe someone wants to venture a guess.

Answer 1

I had the same situation. There is nothing strange about it, but it suggests that you're relatively unfit. Here is why.

At any given intensity your body requires certain cardiac output (liters of blood/minute) to fill muscles with oxygenated blood and sugars. Cardiac output depends on two values: heart rate and heart stroke volume -- amount of blood shoot by left ventricle in one stroke. These two variables have complex dependency, because at high heart rates stroke volume decreases (left ventricle doesn't have time to relax and fill itself properly). This makes the process less efficient: heart requires more energy (consumed in strokes) to pump less blood. In trained athlete heart rate decreases (difference can be as much as 30 beats/min in sub-maximal activity (1)) and stroke volume increases in rest (50-70 ml/beat in untrained individuals, 70-90 ml/beat in trained individuals and 90-110 ml/beat in world-class endurance athletes (2)) and during exercise. This makes the process much more efficient, allowing for reduced heart rate and less energy consumption. Compared to untrained individual, in trained subjects net cardiac output remains relatively unchanged in sub-maximal exercise (it may actually even go down due to other effects, like increased efficiency of oxygenation), and significantly increases during maximal exercise.

Now, I want to emphasize, that sustained high intensity workout for long periods of time are not good for heart, even for well trained athlete (3). It can cause direct damage to heart, inflammation, fibrosis of heart muscle (all of this mainly in the right ventricle) and overgrowth of left ventricle muscle, leading to increased risk of heart attack. Please do not assume that absence of acute symptoms after training is a sign of healthy workout. More is not always better when it comes to exercise.

One final point. You're claiming to have "the lactate threshold" at 195-205, but you're making a large mistake. Even in well-trained individuals aerobic threshold is well below that value. You can make a thread-mill test in a sports lab to determine yours. It is probably below 150 beats/sec. As suggested by NIH, it is best to exercise 90% of time in aerobic zone, and only 10% beyond it (in fact, even sprinters train this way; one shall not overload heart).

1) Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics

2) McArdle WD, Katch FI and Katch VL. (2000) Essentials of Exercise Physiology: 2nd Edition Philadelphia, PA: Lippincott Williams & Wilkins

3) http://eurheartj.oxfordjournals.org/content/early/2011/12/05/eurheartj.ehr397.abstract

Answer 2

No worries

Having a resting heart rate around 55 bpm is not unusual. Frequently experiencing a heart rate over 200 bpm is not unusual. And neither are really an indication of overall fitness. And neither at this point should cause alarm. If there IS anything unusual about the numbers you provided is the range between your resting heart rate and the higher end of your heart rate.

In my experience, if you have lower resting heart rate, your max heart rate will typically also be lower than normal. In contrast, if you have higher max heart rate than "normal", you'll also have a higher than normal resting heart rate. This observation, is strictly based on my experience and not on research.

My resting heart can be as low as ~34 bpm, but my max heart rate is around 180 with a lactic threshold around ~160 depending on the exercise.

I would recommend not comparing your heart rate to others as it can drive you quite nuts and really make you question things like effort, overall fitness, health, etc. I would also recommend using your own heart rate to determine training zones as well as measuring performance and improvement over time.