Heart rate does not increase with intense workout

I am a 54 year old women with high blood pressure (managed), overweight, and recently had multi level fusion/Disc L1 - S1. Over the last 3 months I have been working out with weights and riding exercise bike, gradually increasing the time and weight loads. My concern is that during a 40 min bike workout with a mid range of 91rpm 12.5 k workout that I cannot increase my heart rate beyond 89. I try to push the rpm and still no response. This is not true in all workouts as 1 in 4 workouts my heart rate during cardio workout of bike will be 137 - 155. I'm not sure if this is cause for concern. My normal routine is 5- 7 min of bike, 40 min weight/ball (core)and then finish with 40min on bike. In the beginning I thought the readings on the bike were not functioning properly and changed bikes but it didn't make a difference.
What am I doing wrong?

[anxiousmomtobe?]

Are you working with a trainer?  Mine recommends 30 minutes cardio, 10 minutes stretching than 20 minutes with weights.  The weight training will increase with my fitness level.

[calex]

Initially that was my routine. I have private session with Pilates instructor weekly so try and incorporate some core with my weight training.
My concern still remains my heart rate during cardio workout. This morning my rate was 130 - 151, but 2 days ago I couldn't get the rate to rise higher than 89 during a 40 min session on the bike.

[anxiousmomtobe?]

Have you seen a doctor, maybe you need a stress test.

[mmfd]

You mentioned that your hypertension was managed.  That usually means that you are taking some medication for it.  Many of them can affect your heart rate, esp. its response to exercise.  Are you on a beta blocker for your bp?  It is reasonable and common to have your heart rate not go above 89 on a beta blocker.   Depending on the time of day you take your med and when you exercise, your heart rate will vary.  If you aren't on any meds then I have no clue, but it is much better for your heart rate to not go up really high with exercise, than to have it go too high and take too long to recover!

[billyz]

I have the same problem and I am in shape, not overweight and not on any medication... one day I can go out for a ride and my heart rate instantly rises, those rides I feel strong & go very fast, but then there are other times where my heart just wont go up and those days I feel weak... this is a total mystery to me and it has been going on for many years! Is it heart, blood, sugar? This is very depressing, because it should be pretty much the same for each ride! Anyone have this & got it corrected?

[Dr Arora]

Hi, according to your age a heart rate of 140 to 150 you the target heart rate during exercise and you are achieving that target during most of the exercises. There is nothing to worry if you are not able to achieve this target on a bike. There could be several reasons for this, one is you might not be doing this exercise with the same intensity as with others. Second is,there might be some faulty reading on the bike as regard to the heart rate. it's not a major concern. regards.