I started doing spinning and have hence been exposed to a lot of talk about maximum heart rate (MHR), not being able to pass 94% of MHR and that being above 90% being very hard. The first half of the spinning training last Wednesday was disturbed by my heart rate monitor not being able to receive the heart beats and hence stuck at 76% and suddenly jumping up to 91% (of a too low MHR) and staying there. After changing the strap and sensor I got more reliable measurements in the second half. My heart rate is shown below (averaged over 30 seconds to smooth out measurement errors). What I don’t understand is how the hardness of the training relates to my heart rate. I can relatively comfortable have a heart rate of 90-91% of my MHR but when trying to increase the intensity my heart rate stays the same or even drops a little. The last 4 minutes were hard but my heart rate is only 2% above the comfortable zone, while my breathing rate hit it’s maximum. Any comments?