In which Endurance 101 describes DIMR, which is a real thing

Endurance 101:  DIMR
When I first heard about DIMR, I laughed.  I was sure that it was a joke.

DIMR, which stands for Distance Induced Mental Retardation, is a condition readily observed in endurance riders in competition:

The further you ride, the dumber you get.

Unfortunately, it’s not a joke.  DIMR is real. 

DIMR is the result of a combination of three factors: 
·      Fatigue

·      Dehydration

·      Highway hypnosis, the mental state in which a person can respond appropriately to a host of external events in an appropriate manner with no recollection of consciously have done so. 

DIMR is inevitable, given the somewhat monotonous and rhythmic nature of the sport of endurance riding, which lulls the rider’s body and brain into a relaxed state which can easily lead to an advanced state of dumbness.  Marathon runners and Iditarod mushers report similar symptoms in late stages of their events, as do long-haul truck drivers:  their focus is on the road or trail ahead and the need to move down it.  At break points in the activity, these individuals (like endurance riders) struggle to concentrate on diverse stimuli, find it difficult to communicate with people who are standing still, and experience an inability to describe recent landmarks.

DIMR is temporary, and the effects can be greatly reduced by addressing the root causes of the condition.

If your horse has been properly conditioned for your event, you are probably also adequately fit for the exertion as well; however, if you need a reason to exercise more, the threat of DIMR might be a good motivator!  The more physically fit you are, the less fatigue you will experience from the event. 

Stress will also contribute to your fatigue level at a ride.  If you are worried about a lot of things, you will tire yourself unduly.  Try to problem-solve before ride day, so that you aren’t completely stressed-out during the event by trying to fix issues.

I also recommend that you start stocking-up on sleep a week before a long event, because even with the best of planning and organization, you will inevitably be short of sleep on ride day.  There is no substitute for sleep, and it’s a cheap and easy way to keep the stupids away from your brain.

Mental acuity begins to diminish in humans at 1% dehydration.  Unfortunately, most people begin to feel “thirsty” at 2% dehydration…and at 2% dehydration, you are already a little dumber!  Eeek. 

Head off dehydration by starting your day with a pint or two of water, not coffee, tea, or Mountain Dew!  Caffeine is a diuretic, and will act to rid your body of fluid.  Drink your morning cuppa if you must, but don’t count it as your pint or two of hydration.  If you find it difficult to drink a bunch of water in the morning (I do), eat salty food for lunch and dinner the day before a ride to encourage you to drink a bunch of fluid in advance of ride morning. 

Some people advocate drinking sports drinks during exercise, which ideally contain a nice balance of electrolytes; however, many commercially-available sports drinks also contain a bunch of sugar and gawd-knows-what-else.  If you know that you need electrolyte supplementation, do your homework and choose a beverage that will work for you and not make you sicker.  And do not try a new sports drink on the day of an event!  (voice of experience here).

If you do feel thirsty, you may need to drink up to a quart of fluid to replenish your loss and bring your body back to normal.  Do you suppose that’s easy to remember and accomplish when you are dehydrated and mentally fuzzy?  Nope.  It isn’t.   

The best way to fix dehydration is to prevent it.  Or, as a very wise endurance rider told me, “if you don’t need to pee desperately by the time you arrive at the vet check, you need to stay there and keep drinking water until you do desperately need to pee.”  (as I recall, she threatened me with duct tape to keep me in a check until I could prove that I was re-hydrated, but that may have been just a threat…or, maybe not…) 

Savvy endurance riders learn to monitor the color of their own urine as well as the color of their horse’s urine.  Just as with the horse: light color is good.  Dark color is bad.  If your urine is dark yellow, drink a pint of fluid now. 

In hot weather, that may mean that you need to drink a cup to a quart of water every hour—figure out where that water is going to be carried with you on the trail (on your saddle?  on your body?), and practice drinking it while you train to establish good habits in competition. 

Highway hypnosis
If you’ve ever driven from Seattle to Boise with no memory of the city of Spokane, you’ve experienced highway hypnosis.  Highway hypnosis happens when the monotony of repeated stimulus lulls your brain into a semi-hypnotic state.  The rhythm of a trotting horse is an excellent example of "repeated stimulus."  You’d think that the sound and the motion would keep you alert, but instead, it gradually numbs your brain, which is already a little numb from fatigue and dehydration, unless you have actively been combatting those issues!

How can you fight off highway hypnosis?  Keep your brain busy by chatting with your riding partners if you are riding in a group, or by singing to your horse if you aren’t.  When you run out of verses to your favorite songs, make up new verses…you have plenty of time out there on the trail to find the rhymes you need.  Consult your map periodically, and compare the landmarks you see around you with the landmarks on the map.  Compose haiku, text a message to your friends in camp if there’s any signal for your phone, or take photos! 

In other words, do whatever it takes to keep your brain alert. 

DIMR can last a few hours to a few days, depending on the severity of the condition.  If you allow yourself to get really dumb, it will take quite a while for your normal sharpness of wit to return.  If you intend to drive home the morning after the ride, do everybody on the road a favor, and prevent DIMR symptoms when you ride…or bring a designated non-DIMR driver!


  1. Note: If you've ever driven from Seattle to Boise, and you *remember* went the LONG way!

  2. Testing, testing, 1, 2, 3. Please tell me that my previous comment didn't get "eaten" :(

    WV: Fathee: Stupid, fathee computer - eating my long comment.


    VERY LONG COMMENT consolidated:

    Oranges. The scent of a freshly peeled orange wakes the brain up faster than anything. Try it on a long drive - take an orange, peel it. It works. It's also tasty. Maybe oranges at the stops to help combat DIMR?

  4. I have never heard of this. Like you, Aarene, my first thought was this is a joke, right?

  5. Drink mint tea or snuff tea tree oil. Works wonders for me on really long drives.
    That said, is there going to be a chapter for socially awkward personages (me) on how best to approach an endurance personage and ask them things like, "Can I follow you around like a puppy dog for awhile?" or "Niiiiiice horsie, me pet/walk/groom/get love all over?" Cause I fail at that, & I could really use some horse dirt under these nails. I did find a book from the 70's, The horseless rider,
    I keep it on the back of the toilet (yes, me time) & she makes just going up to a random person with a horse & offering to muck out their pasture in exchange for a ride is easy. I ask, really, what was she smokin'? So any tips would be appreciated :)

  6. Total real thing, especially before I figured out what food I would actually eat on ride day. Also, the first few nights after my first attempt at a 50, I fell asleep feeling like I was trotting, then jolting awake at a "spook."


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