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Friday, June 28, 2013

Heat and heat conditioning

Please someone explain to me why I can write posts for this blog day after day after day for a paltry $5/month (that’s what I make on Google ads), but I can’t even think of a good subject, let along actually START my Ride and Tie Vet Student scholarship worth $1,000. 


In the comments yesterday Crysta (author of the blog Go Diego Go) brought up heat conditioning, which was a tangental point to the discussion of multidays versus doing the mileage in one chunk and the effect of hot afternoons versus rest. 

As it’s no less than 105 degrees here until we get a break of temps in the 90’s for fourth of July, I think now is an excellent time to talk about heat and heat conditioning. 

The heat of the afternoon, even with appropriate heat conditioning, takes the toll on a horse and rider (which is why I think a one day 100 in the summer may be easier physiologically than the same mileage over 36 hours - see previous post on the subject). 

The cumulative heat load that builds up over a hot afternoon has to be dissipated whether or not the horse and rider is conditioned for the heat or not.  The heat conditioned team can do so “better” and has less of a risk of ending up in distress......but energy and physiological resources still have to be “spent” to keep the body cool. 

There is a neutral operating temperature range for all species where no extra energy has to be spent to maintain body temperature (shivering, sweating etc.). The animal’s metabolic rate within this temperature zone is steady and the same as the resting metabolic rate - ie no extra energy expended.  Above and below this temperature range the metabolic rate rises as various physiological mechanisms “kick in” to either cool or warm the animal.  I think it’s natural to think about the calories or energy expended to keep ourselves warm when we fall below the thermal neutral zone (TNZ), however metabolic rate and energy expended increases when we go above the TNZ too! 

***It is important to keep in mind that this “neutral zone” is in a NON-exercising animal.  

A naked human TNZ is 28-30 degrees C, while a clothed one 22-25 degrees C.  One resource I have states the TNZ for humans as 33-35 degrees C (but whether this with clothing or in the birthday suit I'm not sure?).

For those of you (like me) that are a bit C-->F challenged:
22*C = 71.6*F
25*C = 77*F
28*C = 82.4*F
30*C = 86*F
33*C = 91.4*F
35*C = 95*F

For the sake of this discussion I’m going to assume that we are all wearing clothing and let’s call the human TNZ where we can maintain body temperature without expending energy as 80*F. 

The equine TNZ is much lower than humans. Depending on the time of year (thus coat) and body condition, most of my sources peg the equine TNZ as 30-50*F for a horse in temperate climates. 

In both the human and the horse the TNZ drops when you add exercising.......The physiologic structures that are propelling the horse down the trail and the rider up and down in the saddle, such as muscles, are generating heat.  The environment has to be that much colder to compensate for the increase in body heat, OR some sort of physiologic mechanism needs to kick in to actively disperse that extra heat. 

Depending on the coolness of the ride, the rider *might* be in their TNZ (if the ride is 60*F, that might be the right temperature for an exercising endurance rider to stay within the thermal neutral zone).

However, it can safely be assumed that when doing endurance rides, the horse is absolutely expending energy to stay cool and maintain a normal core temperature.  If you consider that at least for those of us in California’s central valley, we are regularly doing summer rides where the temps are in the mid 90’s or higher in the afternoon - that is a LOT of energy expended by the horse to cooling mechanisms during the ride.

No wonder I feel beat and the horse looks tired after a hot ride!

Some of the mechanisms a horse employs as they compete in temperatures above their thermal neutral zone are:

-blood vessel dilation

-increased respiration - accounts for about 25% of heat dissipation in the horse

-increased heart rate

-increased blood flow to skin (which transports heat from body core to the skin, which it unloads into the environment - a process greatly accelerated by animals with a sweating mechanism), and sweating (as an interesting side note.......Did you know that camels sweat?  And that marsupials and rodents don’t sweat but moisten their bodies by salivating and licking themselves?????????) In a concept that comes up over and over in biology, as the body size of an animal increases, the relative amount of surface area decreases.........which makes horses relatively inefficient at dissipating large amounts of heat through the skin....which is also the single most important way for a horse to dissipate heat!!!!!  Evaporation through sweating accounts for about 65% of heat dissipation in the horse.

- As FYI points since these aren’t strictly a physiologic changes, but they are all ways to dissipate heat....wind is your friend  :)  Have a hot horse that you have sponged and scooped?  But the air is just sitting there and not helping you out and now you have a rather wet, coolish horse but want to get cooler?  Generate some wind!  And put your horse in the shade.  And let him drink water. And periodic short walks to help muscles pull heat out of deeper tissues. 

All of these mechanisms “cost” something in physiological currency.  You don’t get anything free in this world..........In summary: If you are at an endurance ride, your horse is spending energy to keep cool. The hotter the ride or the time of day, the bigger that energy expenditure is.  This is a biological fact that has nothing to do with how much “heat conditioning” you have.  This is the cost of staying alive and moving forward in the heat.

So, if hot weather is going to cost my horse energy no matter what, what IS the point of heat conditioning? 

Heat conditioning allows you (and your horse) to actually function and perform in hot conditions instead of dying In some cases heat conditioning will reduce the physiologic “cost” of the cooling mechanisms, and in other cases it will just make them more available/effective/active.

How can you heat condition or function in the heat better?

General conditioning - just having muscles that are more fit will impact “heat conditioning”.  Fit muscles generate less heat to achieve the perform the same level of “work”.  Less heat generated is less heat that needs to be dissipated. Conditioning also expands capillary beds which improves the flow of blood to the skin and muscles which will make the horse more efficient at dumping the heat outside the body to the environment.

Live somewhere hot.  This sounds contrite, but it’s true.  I’ve grown up my entire life in an area where triple digits for weeks on end is not abnormal.  I’ve never had air conditioning, worked outside, and don’t notice hot temps unless it’s a really high humidity (50+) or it’s over 115*F or so.

Wear long sleeves and sweat shirts all the time.  Especially if you are working inside with an airconditioner.

Drive with the windows up and no air conditioning.  (If Tess is with me I have to make an exception - in that case I’m in a heavy jacket while I drive).

Don’t get sunburnt - I find that how much heat I can handle for how long takes a dramatic downward turn if I allow myself to get sunburnt.

Walk in the shade, run in the sun.  This actually works.  Try it!

Exercise in the middle of the day.  I do all my runs and rides at noon until the weather starts to hit triple digits.  Since I’ve started doing this, I haven’t had any problems with the heat.

My horse wears a fly blanket.  I don’t think that it makes her any hotter than without it (she’s not any more sweaty under it).  But if it does?  *shrug* I consider that a fringe benefit.

Exercise in clothes that make you sweat - live in the bay area and running in the afternoon only gives you a high of 75*F?  Where a sweat shirt and pants. 

Run high intensity intervals- this is how even in cooler weather I raise my core temp and practice living with sweat dripping down my armpits and having my respiration up really high.

Don’t clip for training.....and then +/- clip for competition if necessary

Lose weight

Get younger: From a article in the Equine Veterinary Journal Supplement: “Ageing compromises the ability to handle the combined demand of exercise and thermoregulation in part due to decreased absolute pre-exercise PV.”  Or in plain english, as you age your plasma volume (PV) decreases and the decrease in PV is to blame for why old horses reached a core temperature of 40*C faster during exercise and had a greater HR when they reached this temperature.

How long will it take to “heat condition”? says that most horses will need at least 3 weeks in a warmer climate to allow their bodies to adapt.

As this post is taking WAY more time than it should (HOURS!!!!) I’m not going to try and find any more sources on this.  Three weeks feels about right.  Two-three weeks is about how long it takes me acclimate to really hot weather and be active in it.  2-3 weeks is about how long it takes for a physiologic system to do some major shifting in metabolic pathways, gene upregulation etc.  2-3 weeks is how long it takes for vegetables not to taste bitter to me after I cut out all refined sugar in my diet.  2-3 weeks seems to be the magic number for a body to adapt, so that sounds entirely reasonable to me.........

Although, after reviewing this post, maybe this wasn’t a complete waste of my time?  Maybe I could rework this subject as my Ride n Tie Scholarship submission? 

References: here is a partial list of my references - I originally had them within the post, but it started to get a bit messy.



  1. Does manually whacking stinging nettle in this pea soup of humidity count? Or do I have to continue whacking for three weeks.

  2. Hahahahaha! Yes that would just take you 3 weeks to "fully adapt" to the maximal capacity. But it will help as long as you don't over do it. Over doing it screws everythign whether it's muscle repair, a stress fracture in your bone, or heat exhaustion. I got heat exhaustion once, years ago. it took 2-3 YEARS of being careful before I could handle the heat as well as before....and I hear stories of endurance horses overridden in the heat that are NEVER THE SAME AGAIN, and one specific story where a successful endurance horse never competed again after getting too hot at a ride, surviving, but obviously not competely.

  3. I use a cotton sheet on Bo, so it is easy to launder and it does a good job getting him used to sweating and recovering when worked for 20 to 30 to 40 minutes (building up) at a trot. I figure at this point, Bo is already fit for Tevis and only needs to acclimate more to the heat so that he sweats more efficiently and recovers better. He doesn't need any conditioning, and we don't need to tire him out or risk an injury, so he won't get much work in the way of having a rider on his back.

  4. This is one of my blog posts on the topic, with links to more research on heat acclimation:

  5. Karen, don't you live in NV where its hotter than even where I live??????

    Stupid it a cotton horse sheet or a bed sheet? And do you saddle up over the sheet?

    Totally agree with you regarding conditioning between now and tevis! Not needed, not wanted, and overall a really bad idea. I'm planning on a couple of hacks but that's it.

  6. I'm sitting outside reading right now, easily 95 in the shade, feels good to me! A quick ride this morning was just to play in the lake, the heat isn't bad but the humidity is tough! You wanted some heat conditioning, I think the next week you'll get some and more!

  7. We have had some summers where I am that have never even hit triple digits, and more often than not when we do get that hot it is only for a handful of days. Most of the time it is maybe 80's to low 90's, though we often get afternoon thunder clouds/showers so that ups the humidity. On the sheet - it's a cotton horse sheet. I free longe in a big field, it only takes a time or two for the horse to get the hang of it and what we are doing. Warm up, do a working trot for increasing periods of time (starting with maybe 10 minutes), then a cool down period. One year I did this and measured HR and body temp before and after and was amazed at the improvement over just a couple of weeks. I suppose another option would be to heat train the by wrapping them in bubble suits between now and Tevis? (lol) They'd probably get a rash or something tho....:D

  8. I live near a Civil War battlefield in Virginia, where July and August are usually pretty miserable with heat and humidity. Anyway, a couple of years ago, there were Civil War re-enactors on horseback when the heat index was 120-128 degrees for several days in a row. As far as I know, no horses (or people) died during that stretch of really awful weather. After reading your post, I guess the reason the horses were OK is because they were acclimated and maybe not doing really hard, prolonged work? But what about during the actual Civil War? So many battles took place in southern states, where summer temps/humidity had to be really awful. Do you think the horses were just used to it? Or do you think that it was metabolically challenging or that the cavalry took special conditioning measures with their horses?

  9. In the CW days the horses got to the battlefield by marching there, so in a way they heat conditioned themselves over the days and weeks that were spent getting from location to location. We didn't trailer or fly them at high speeds from a moderate climate to something with the high temps and humidity of Virgina in a matter of hours or days.

    The book "War Horse" by Dimarco has a good section that describes some of the cavalry's movement of horses and it reminds me a lot of endurance riding. Here is a blog post I wrote about the book, including an excerpt that stated that the goal of the cavalry was to cover 25 miles in less than 6 hours

    I know that a heat index of above 150 is when we get really concerned at endurance rides, at least the ones I've been too, and 120-128 is actually something that I've seen in CA on a semi regular basis - even during reenactments. With that sort of heat index the people that have the most issues and tend to have to go lay down are those from the bay area where the weather is more mild. Those of us from the central valley tend to not have the same issues. Running around the battlefield in the middle of the day in a full wool uniform is certainly a unique type of heat training!!!!!!!

    So I think in answer to your question, I think the horses were conditioned to it, especially considering how the cavalry moved from place to place, and I think that people were more used to it as well. And I think that there probably WERE heat related deaths among horses and people in the 1860's, but in modern reenacting, especially if you are going back east, there is a HUGE awareness of the heat and the ramifications of higher heat indexes and precautions are taken.

  10. Just.curious.....did you know I was a reenacting when you asked the question?

  11. I forgot one of my tips for heat conditioning.....sleep under a blanket at night. I kept my down comforter on the bed even though its summer and I sleep mostly under it (sometimes allow my feet and legs to poke out). I think this has really helped. Not as good as active conditioning, but supports my other efforts I think.

  12. Thanks for the info on the CW stuff and the link to your blog post! I had no idea that you were reenacting, though. Just a coincidence:) One other question, though. I thought there was a difference between heat index, which is the perceived temperature based on temperature and humidity, while the temperature PLUS humidity is considered a different value and is the one to be most concerned about when conditioning. I was reading on Wikipedia at this link: that a heat index over 105 degrees F is considered the danger zone while I think I've read (maybe in The Horse) that when the temperature plus humidity is over 130, caution should be used and when it is over 150, that's sort of the danger zone. But, I'm still really new to all of this stuff, so do you have any clarification for a new girl?

  13. The only one I'm familiar with is.the heat plus humidity and 150 is what I've been told......I'll do a bit of research and report back :-)

  14. Thanks for your help! Here's a link I found for how to calculate the heat index: It looks more complicated than the average person would want, but easy enough to use with a spreadsheet like Excel. Or you could just use the online calculator and plug in temp and humidity. Anyway, I also discovered something interesting when I checked the projected temp and humidity for today in my area. At 7 am, the temperature was 66 degrees F and humidity was 97%, which equals 163, which would be into the danger zone category (although the heat index is only 67 degrees using the above formula). Yet, through the day, the temperatures are rising and the humidity is getting lower, so by 4 pm, the temperature will be 87 with humidity of 48% (135) and not really worth getting excited about. But, the humidity will start going up in the evening and be in the 90s most of the night. So, regarding your thoughts on whether one 100 mile ride is more difficult than two 50s, I'm wondering if there is more than just the heat of the day to consider. I know you were thinking that two 50s would put a horse through two hot afternoons, but what if it is common for the humidity to go down during the day and up at night? Then, those two hot afternoons may not be as bad as riding through evening and night with much higher humidity levels.

  15. I live in an area which usually has very low humidity in the day or night, and there's usually a bug temperature change between day and night(90 or 100 degree night with night temps in the 60 or lower 70s) so I don't think I get the same elative numbers as you are back east. but I would have to so some experimenting. But at least in my area I don't think the heat and humidity is ever worse in the night than the afternoon. This would definitely be region dependent, something I hadn't considered.

    The second thing I'm unsure about is exactly how the tnz is impacted by the comined heat and humidity calculations. All my research was based on temps only. are all 150 days the same in respect to tnz no matter whether that number is mostly made up if temps, humidity, or an even split? I don't know and I haven't seen anything on this. I think the only safe thing that everything ahead with is that in both scenarios the horse is above tnz and thus expending energy to dissipate heat. The answer to the answer of two afternoons versus one afternoon and a night might depend on the answer of how tnz related to the heat numbers and what happens at night in a partucular region. Or we could be off base and thus has nothing to do it the

    1. Just checked the stats in my area and its 92 with 40 percent humidity. Which is why I'm MISERABLE. Its NEVER that humid. 20s or lower is much more normal with high nineties or true digits.

  16. I nominated your blog for an award. Lots of good information on your site.

  17. Thanks nuzzling muzzles!!!!!!

    Gail out if.curisity I've been checking temps and humidity here throughout the day. This morning was 92 and 40 percent. At 1p 101 and 30. At 6p 102 and 15. we are scheduled for 106 and higher through fourth of July with lows in mid seventies. We probably won't see humidity above 10 percent again! If I was back where you are I would probably have to completely relearn how to manage an endurance horse in the heat.

  18. Wow! I think 106 degrees is bad no matter what the humidity is:) Still, we do have days with temps over 100 AND humidity that can actually hover in the 90% range, making life miserable for everyone. We will sometimes have a short, severe thunderstorm on those days, but in my experience, the rain only makes things more humid and steamy. And I think you're probably right that the temperature as compared to the humidity must have some impact on how easy/difficult a ride is. Just the two values added together can't be the whole story. I'm definitely going to pay more attention as I ride this summer and see if I notice any differences.

  19. My most striking heat-and-horse experience to date was getting handed a draft cross to cool off after he'd had a hard run XC on an exceptionally (for our area) hot and muggy day. I sponged and scraped and sponged and scraped for what felt like forever and just felt completely helpless; he wasn't in distress but he was just _not cooling down._ It finally started to rain and I practically danced for joy -- it seemed like the only way I was ever going to get enough water on that horse. I was already convinced that I wanted to ride light horses forever, but _man,_ if I hadn't been, that would have done it.

    I assume people sometimes send horses from other/cooler regions to Tevis and presumably other desert they tend to prep at home as best they can or send the horse out early to heat-condition in place?

  20. Also the idea of driving around hot weather with the windows rolled up makes me want to die.



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