36 yr old female here, been exercising since I was 18, sports, skating, aerobic classes, etc. Currently a weight lifter (since 2000) and inline speed skater. Something really weird happened when I was stationary cycling at my gym...
I cycle as part of my inline speed skating training. Anyway, I did a 5 minute warm-up then went into my work time, I pedaled on resistance 7 at 100 rpms steadily which equated to my working at 82% of my MHR. Of course my legs started hurting as usual since this session was only my 5th session as I just added this activity into my training program. Well, my HR was nice and steady at 82% of my MHR until I got 17 min into my session and then all of a sudden out of nowhere, my HR jumped up to 90% of my MHR, verified by both my coded Polar Heart Rate monitor and the monitor on the bike itself. My HR then REMAINED ELEVATED, at 90% of my MHR for the remainder of my workout, 13 minutes. Now in addition to the jump itself being weird, my legs also actually felt BETTER after a couple minutes at 90% of my MHR, I actually didn't feel like I was working quite as hard. I mean don't get me wrong, it was still hard, but it seemed more tolerable to me. So yeah, there I was at 90% of my MHR for the remaining 13 min of my workout. I completed the 13 min then cooled down for 5 minutes.
So I want to know, WHY? Why did my HR just suddenly jump up after 17 min and STAY up? And secondly, why did my legs actually feel BETTER once that occurred? This really has me very intrigued and baffled, can anyone offer any explanation?