Bradycardia, like everything else, is an individual value. The "norms" we use are based on statistical analysis and can be way off for specific individuals. Bradycardia is a symptom of an enlarged heart. The function of the heart is to pump blood and maintain pressure at a given state. The latter is the real thing you worry about not the heart rate unless it is too low to provide enough pressure. Pressure is controlled by several factors including heart rate, heart volume per beat (and efficiency of the heart in the actual pumping), arterial dilation, and capillary resistance.
Back in my youth I trained hard to run marathons and approached it in a scientific way. I adapted my running and emphasized increasing my VO2 max which is a measurement of aerobic to anaerobic function. I wanted to raise my threshold for anaerobic running so embarked on years of fartlek sprints designed to raise the threshold. I have an inherent and genetic issue that makes it hard for me to increase my speed. My fast-twitch to slow-twitch muscle fiber ratio is heavily biased towards slow-twitch. This means I can run long and relatively slow and it was very hard to increase speed hence why I was approaching the anaerobic threshold. You can't change your muscle fiber ratio as that is genetic. Anyway, what I ended up achieving is an enormous heart but I did raise my anaerobic threshold (and coincidentally my heart rate recovery time is almost super-human). My heart grew to a very large size and can cope with high stresses. his came in very handy for me as I added biathlon skiing to my mix in my late 30's and the heart rate recovery is key to shooting well after skiing hard. It also helps in combat where you run hard (carrying a heavy load) and have to shoot quickly and accurately. The same for rescue operations under fire where you spring to a victim under fire and then have to perform emergency field medical procedures which are impossible if your heart is beating too fast. So, there are some practical advantages to this kind of training other than marathon performance.
My resting heart rate is in the mid-40's (and I am 70 now). My problem is if I have surgery it drops into the 30's and they freak out, alarms going off and panic ensues so I have to always stress that I have this condition which is normal before I have a medical procedure. I am physically fine. I still work out a lot and in particular do fartlek type training swimming. This maintains my anaerobic threshold which is around 130 bpm now in my old age. I have no cartilage in my knees now (parachuting problems unrelated to running but associated with my military career) so I no longer run but I hike, swim, and mountain bike a lot. I am in great health and have almost no medical problems at all. I did develop exercise-induced arrhythmia somewhere along the line which occurs when my heart rate goes above roughly 130 bpm. However, I know about it and I have a procedure of holding my breath for 3 heartbeats and it normalizes after a weird very hard skipped beat. I have demonstrated this to the cardiologists while doing a stress test who were amazed at it. That said I do try and keep my heart rate under 130 bpm which isn't hard to do except when hiking/climbing hard in the mountains at high elevations. Pacing is the key. I also do sauna 3 times a week and it can get up in that range which is an indirect measurement of core temperature. The heart rate increases as core temperature also increases. When my internal core temperature reaches 41 degrees my heart rate is roughly at 130 bpm. So, I use my heart rate to decide when it is time to leave the sauna. Heat stress is another thing you can train into and is beneficial by also raising non-specific innate immune responses (heat shock proteins) which is a benefit of doing saunas. This also has implications for performance under stress like fire fighting or operations in high-temperature environments.
The bottom line is if you have a reason for the bradycardia, like years of running, then it is of no consequence UNLESS you are having issues with blood pressure. Low blood pressure is far more healthy than high blood pressure and if syncope is a problem then it can be accommodated. I experience it myself frequently when standing up too fast. So, don't do that. It is kind of that simple. I don't bother with medical exams and physicals unless I have a reason to suspect something is wrong. But I am in this business so know what I am doing. Athletes always have medical issues that are not "normal" and require medical specialists familiar with this kind of physique. My local GP is the same age as me and he still runs marathons so we understand each other completely (he is in fact a cardiologist but works as a government GP and maintains a private practice for cardiology). I have to add here in our small town on Lake Balaton Hungary we have the National Cardiological Institute and hence our small town of 10,000 people has a plethora of cardiologists (more than 100). The Institute Director is a friend and my wife's cardiologist is the Chief of emergency medicine and intensive care and sees her in his private clinic. It is fun as we all debate the finer points of cardiology, physical training, and things like statins. I am a PITA to some of them but we all are more or less agreed on things.