Impact of heat on heart rate and effort.

RebornRider

Well-known member
May 31, 2019
619
624
NorCal USA
It was very hot today, up to 106F (41C) according to my Garmin. It was educational to see that my heart rate was a solid 20 beats/min higher today than back when it was in the low 70s (21-22C). The first 10 miles of the charts below are the exact same route.

I needed trail mode (middle of 3 assistance modes) in several places today where I usually use eco mode. Whenever I see a post about "My XYZ motor is losing power", I always wonder if the rider is losing power, maybe because of heat.

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irie

E*POWAH Elite World Champion
Subscriber
May 2, 2022
2,220
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Chichester, W.Sussex, UK
Remaining hydrated is absolutely critical ...

"Dehydration occurs when you lose more fluid through sweating, illness, fever or urination than you consume in food and water. Dehydration can negatively affect your organs and bodily functions, including your heart and cardiovascular system. When you are dehydrated your blood volume, or the amount of blood circulating through your body, decreases. To compensate, your heart beats faster, increasing your heart rate and your blood pressure. Also, when you are dehydrated, your blood retains more sodium, thickening your blood and making it harder for your blood to circulate through your body. Keeping your body hydrated helps your heart pump blood more easily and allows oxygen to reach your muscles, which helps the muscles work efficiently."

 
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RickBullotta

E*POWAH Elite World Champion
Jun 5, 2019
1,824
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USA
Overhydration is a risk as well - I've seen it in endurance events in hot weather. Also, humidity makes a HUGE difference in your body's effectiveness at cooling via perspiration. If it's very hot AND very humid, consider shortening your effort or keeping the effort lower. Also, in extreme heat I almost always "pre-perspire" and soak my head and clothing in water before starting the ride. Lastly, maintaining an electrolyte balance is important in these conditions - but again, you can have "too much of a good thing" if using supplements.
 

Stihldog

Handheld Power Tool
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Jun 10, 2020
3,170
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Coquitlam, BC
Forgot to fill my water bottle once. On a very hot day, at high altitude, I found a creek. Used my shirt as a filter to fill up the “tank”. It wasn’t one of those bio-chemical-Lycra shirts either, that Roadies use …it was a plain old cotton t-shirt.

There’s so many risks when using creek water …gotta do what you gotta do though. Did this several times during work also. I was lucky.

I think it’s more dangerous to be dehydrated. Weird things start to happen.
 
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Stihldog

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Jun 10, 2020
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Coquitlam, BC
High bpm heart rate. It’s been told to me (my wife ) that the recovery rate is very important. I’ve hit a 190 bpm a few times during an uphill climb while trying to break a KOM or at least setting a personal best.

Within minutes my rate returned to 120bpm…and eventually 110bpm. I try to reach 170bpm a few times during a ride but 120-140 seems to be my norm.

Now going downhill at a high rate of speed is just a mind-f**k for me. There’s other things to worry about.
 

steve_sordy

Wedding Crasher
Nov 5, 2018
8,674
8,946
Lincolnshire, UK
I read somewhere that your max heart rate unless under close medical supervision is 220-your age. In 2005, I was riding up a long steep hill and it was blisteringly hot. I was sweating like a pig and I don't remember being dehydrated. I happened to have a heart rate monitor on my chest with a readout on the bars. I was watching it climb and wanted to see what happened when it got to my "maximum". :unsure:

I was 54 in 2005, so max heart rate nominally should have been 166. As my rate rose above 155, I wasn't feeling too good; my breathing seemed OK and my legs ached a bit, but not enough to make me stop. By the time I got to 164, I felt really bad. It was as though my heart was about to burst from my chest and I had developed a pounding headache. I felt so bad that I stopped within sight of the top of the hill; I no longer wanted to see what would happen after 164, I felt as though the only "after" I would see would be the afterlife! :eek: .

It didn't take long to recover; it could have been psychological of course. But I have never since been tempted to get even close to my "maximum" (now 147 bpm).
 

RebornRider

Well-known member
May 31, 2019
619
624
NorCal USA
Being the hyper-literal engineer that I am, I've always wondered about max heart rate. Mine is at least 180, because that is the highest I've seen since I started wearing a chest strap monitor on every ride. At the 180 bpm point in my climb yesterday I was working pretty hard, but nothing felt like I was in dangerous territory, It just felt like a good workout. The heat exhaustion effects didn't kick in until about mile 10, and I was in really bad shape by about mile 17.

According to the 220 rule, I should stay below 150, but I exceed that on my regular rides even in mild temps. It never feels particularly taxing.
 

arTNC

Member
Feb 1, 2024
226
262
Texas
Being the hyper-literal engineer that I am, I've always wondered about max heart rate. Mine is at least 180, because that is the highest I've seen since I started wearing a chest strap monitor on every ride. At the 180 bpm point in my climb yesterday I was working pretty hard, but nothing felt like I was in dangerous territory, It just felt like a good workout. The heat exhaustion effects didn't kick in until about mile 10, and I was in really bad shape by about mile 17.

According to the 220 rule, I should stay below 150, but I exceed that on my regular rides even in mild temps. It never feels particularly taxing.
Yeah, I think that 220 rule is a general "safe" level in a kind of average way. So much can depend on other factors like the individual's health and fitness too. My "safe" level would be 148, and I can often blow by that with no issue during or after crossing that threshold. I'm not claiming that people should poo-poo such general warnings, but knowing your personal health and fitness and how your body corresponds with such guidelines can play a factor.

Oh, edit to add: on the heat?...you bet that has a big impact on heart rate and many other factors. Here in Texas I ride mid-morning usually, and when I quit I try to make sure the ride is over before it goes over 90F. Even with age aside, I think doing much riding as the temps near or exceed 100F can be unhealthy to some degree even if it feels OK.
 

steve_sordy

Wedding Crasher
Nov 5, 2018
8,674
8,946
Lincolnshire, UK
@RebornRiderm

I'm sure that the "220-your age" guideline cannot possibly be true for everybody. I wondered about whether fitness made a difference, but if you are unfit, you just get to your maximum a lot quicker. When I first bought my heart rate monitor, it came with advice on "zones", ie what range to be in the fitness zone, the fat burning zone, and the Olympic zone and so forth. I found most of them to be boring, so I just went as fast as I could all the time. When I got knackered, I slowed down for a while until I recovered. At that time of my life and where I lived, I didn't know anybody who rode a bike, so I had nobody to compare myself with.

I too never had problems with rates in the mid 140's, lower was a bit boring. But I assumed it was that high because I wasn't fit! But I had no idea how fit I was (which is why I bought the monitor). I just went at it until it felt like I was working hard.

If you are fit, but have a naturally slow (or fast) heart rate, does that make a difference to how quickly you get up to the maximum? I don't know but I assume it will do. When I was watching one of the Moon landings, one of the astronauts was bounding about on the surface, no doubt ecstatic at the experience of being six times stronger for his weight than usual. I remember the data across the bottom of the screen showing his heart rate peaking at 200 bpm. The guy would have been about 40 at the time (it takes time to be the best of the best) and would have been at the peak of his mental and physical fitness. But Mission Control were very alarmed and told him to stop.

When my son-in-law was in his 30's he was a very keen competitive triathlete. In his 40th year, he represented England in the event. So, I would assume that he was very fit indeed (he certainly looked it!). His resting rate was 50 bpm. But he suffered occasionally from atrial fibrillation, which is when the heart rate speeds up and stays there. I've just checked with him now and he got over 180bpm. That rate was viewed as life threatening by his consultant, probably because he could not reduce the rate by himself, he needed electric shocks of the "CLEAR! ZZZZZZZ! type of intervention. :eek:
 

RebornRider

Well-known member
May 31, 2019
619
624
NorCal USA
FWIW, I was a long distance "fun runner" from ages 30 to 65. Not competitive, but because I really enjoyed running and its benefits. (Oh, those endorphins!) I averaged 6-ish miles during the lunch hour 3 or 4 times per week. Towards the end of this period, I ramped up for and ran a marathon. I suspect that 35 years of regular aerobic exercise probably strengthened my heart.

My based-on-absolutely-nothing rule of thumb is that I should be safe up to about 90% of my actual maximum heart rate, which works out to be 162. In early spring, when I'm out of shape, I have to back off my perceived effort to stay under 160. When I reach a reasonable state of fitness, I have to work really hard to reach 160 when riding the flat section between the park and my house.
 

Litespeed

New Member
Dec 23, 2023
17
13
Vista California
It was very hot today, up to 106F (41C) according to my Garmin. It was educational to see that my heart rate was a solid 20 beats/min higher today than back when it was in the low 70s (21-22C). The first 10 miles of the charts below are the exact same route.

I needed trail mode (middle of 3 assistance modes) in several places today where I usually use eco mode. Whenever I see a post about "My XYZ motor is losing power", I always wonder if the rider is losing power, maybe because of heat.

View attachment 143174

View attachment 143175
Trust me on this. The older you get, the more it becomes a thing. I try to start early, hydrate and keep electrolytes in my hydration pack. Also good to hydrate a day or 2 before riding. Even on an ebike the heat can get to ya. Not as bad as on the "struggle bike" but excessive heat can I am told affect the motor.
 

RickBullotta

E*POWAH Elite World Champion
Jun 5, 2019
1,824
1,556
USA
Here's a good article that quantifies the increased cardiac effort required to maintain cooling in hot conditions.

 

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