heart rate changes

poynedexter

i've been noticing a trend in my heart rate response during turbo training in the last couple of months. i'v been doing sessions which can last up to 2 hours, and while doing high Z2 into sweet spot intensity my heart rate will gradually rise, stabilize for a period then gradually start to fall by up to 10 bpm while the power and cadence remains constant. the perceived effort also falls slightly. it tends to happen at around the same point in most sessions, between 70- 90 mins. again typically is when my garmin reads about 700 kcals in.

my question is why does this happen? is it that my system is tiring and its slowing my heart rate trying to reign me in? is it related to muscle/ liver glycogen levels dropping? if so then why does the heart rate dip.

i'm interested to know why this happens. i do tend to eat well generally, and track my cals and macros. any ideas?

birdie23

How much are you drinking while on the turbo? Can happen because of dehydration.

There's lots of other potential reasons but that and overheating are pretty common I believe.

poynedexter

usually just less than 2 bottles per hour and the turbo is well ventlated with a fan too. i stepped off for a toilet break after an hour today with a heart rate at about 143 and had to up the power by 10 ish watts to get it near 140 beats for the 2nd hour. (plus i'm running a stages and the tacx power so i 'm sure the effort was not lower).

i honestly think its fuel related. maybe blood sugar etc changing.

sloppyschleckonds

Why are you even bothered if you are training with power.

poynedexter

its not a matter of being bothered, its about understanding whats behind it or the reason for it. i've dropped abut 14lb in weight in the last few months, and have been looking/ studing a few metrics along the way. this aspect of my training hasn't gone unnoticed.

birdie23

poynedexter wrote:

its not a matter of being bothered, its about understanding whats behind it or the reason for it. i've dropped abut 14lb in weight in the last few months, and have been looking/ studing a few metrics along the way. this aspect of my training hasn't gone unnoticed.

Heart rate is very fluid. If you do three big days in a row you should notice that your heart rate is suppressed on the third day. Saying that, you would expect it to drift upwards, if anything, during one session.

diy

It could be the point of glycogen depletion. But that doesn't explain how the power stays the same, unless you subconsciously pedal more efficiently.

poynedexter

not sure if this link will work. it shows 2 60 turbo efforts separated by a pee stop. and remember there are 2 PM's showing me a watts increase to keep the effort going?

173 watts 139 av beats 152 max beats 90 rpm
182 watts 137 av beats 144 max beats 89 rpm

diy

SO the first session includes the warm up? Did you die of boredom after that?

poynedexter

no, the warm up was the first 10 mins, then 2 x 60 mins. boredom no, its my z 2 turbo spin. i'm enjoying the break from the crap weather, and theres enough higher zone work being done to appreciate z2.

neeb

I've noticed very vaguely similar patterns when warming up - HR is initially slightly higher for the same power output.

This is just my theory and should be taken with a mountain of salt, but I wonder if it reflects an increase in heart stroke volume as the heart muscle warms up. Cardiac output is stroke volume x HR, so if your ventricles fill more and contract more efficiently they will pump more blood and the HR required to maintain the same output will fall slightly. Intuitively it makes sense that when you you've been exercising for a short while the heart muscle loosens up a bit and perhaps stroke volume increases slightly.

Would love to have the thoughts of someone who knew what they were talkng about on this hypothesis..

diy

Google "the brody effect" changes to surface size, blood volume etc effect ECG as blood is a good conductor and it can be measured.

Yanis Nayu

I notice that I become more efficient when warmed up, particularly on long rides first think in the morning. I often have negative aerobic decoupling on long steady rides. It could be that, although turbo training seems to make my hr inexorably creep upwards.