I'm on a beta blocker. I've been taking a 25mg dose of Metoprolol Succinate every day since my doctor read me the riot act for being obese. That was about 2 1/2 years and 85 pounds ago.
You can read a long and exceedingly boring Wikipedia article about the medication here , but essentially Metoprolol is a beta blocker I take to treat high blood pressure. And by taking a beta blocker, I am not able to get my heart rate above a certain BPM.
As you can imagine, having my heart rate artificially limited sucks. Based on the the very common Fox and Haskell method, my maximum heart rate should be 180 BPM. The best I can usually do is 155.
Actually, all things considered, I get off OK. If I had become obsessed with sprinting, I'd be in trouble. But with endurance sports, I can stay in the aerobic zone (70-80% MHR) and perform well enough to go home happy every day. Technically, I can get into the lower part of my anaerobic zone (80-90% MHR). But from a practical standpoint, that ends up being sort of useless. Since I can only hit the bottom anaerobic threshold and thus have no real way to effectively train in this zone (at least that I know of), my body has developed little capacity to deal with lactic acid build-up.
Today was a good example of my limits. I went out with OC Velo for a 40 mile ride. About 20 miles in there was a nasty little hill with a grade of 4-9% over 2 miles. If you look at the graphs below, you can see both the climb profile and how my HR essentially table tops at 155 BPM. Clearly this is not an ideal situation for climbing.
Though the average speed for the entire ride was 18.5 MPH, mile 20 and 21 where 9.8 and 9.4 MPH respectively. A climb is going to be slower, but it's still relative - I was dropped within 100 yards of the start. Within half a mile my legs where on fire and I was contemplating leaving my bike on the side of the road and hitch-hiking home.
You can see my heart rate spike again, but only briefly, just after mile 35. At this point we where on the flats and our speed was between 23 and 28 MPH between miles 35 and 39.
I'm not exactly sure what this means. I hope it means that overall, my engine is strong, pretty well tuned and it will only hit it's limit on more extreme terrain. That seems to be the case, anyway.
The good news is that there is a chance that I might be done with the medication. I've got 23 doses left and no refills. So when I see the doctor later this month, who knows? Maybe it's time to wean myself off of it. I'm in a whole different place health wise and hopefully that has helped.