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View Full Version : food for XC thought: mental effort increases physical fatigue, reduces HR variability



JER
Dec. 18, 2011, 01:29 AM
A recent study (http://www.ncbi.nlm.nih.gov/pubmed/22143842) -- on human subjects -- in the European Journal of Applied Physiology asked two groups of subjects to perform a series of fatiguing shoulder exercises. The control group did only the exercises, but the experimental group was also asked to perform mental arithmetic tasks along with the exercises.


Twelve participants, balanced by gender, performed intermittent static shoulder abductions to exhaustion at 15, 35, and 55% of individual maximal voluntary contraction (MVC), in the absence (control) and presence (concurrent) of a mental arithmetic task. Changes in muscular capacity were determined using endurance time, strength decline, electromyographic (EMG) fatigue indicators, muscle oxygenation, and heart rate measures. Muscular recovery was quantified through changes in strength and physiological responses. Mental workload was associated with shorter endurance times, specifically at 35% MVC, and greater strength decline. EMG and oxygenation measures showed similar changes during fatigue manifestation during concurrent conditions compared to the control, despite shorter endurance times. Moreover, decreased heart rate variability during concurrent demand conditions indicated increased mental stress. Although strength recovery was not influenced by mental workload, a slower heart rate recovery was observed after concurrent demand conditions. The findings from this study provide fundamental evidence that physical capacity (fatigability and recovery) is adversely affected by mental workload.

I don't think there's any reason to think the situation might be different for horses or any other mammal. The excellent Sweat Science blog (http://sweatscience.com/mental-effort-increases-physical-fatigue-reduces-hr-variability/) quotes from the body of the paper:


It has been shown that fatiguing contractions require high attentional demands due to changes in the excitability of motor cortex. As such, it could be argued that additional mental demand in the current study may have reduced available attentional resources needed to increase the drive to motor neurons to maintain the required force levels, resulting in early task failure (i.e., shorter endurance times).

On cross country, we're asking our horses to answer a series of often-difficult questions. We all know that XC can be very mentally fatiguing or even overwhelming for the horse but this study brings up the issues of physical fatigue and -- this is very important -- heart rate variability. A decrease in either (or both) of those things can spell disaster for a horse on XC.

It might make the difference in a horse not getting its legs up high enough. Or perhaps the loss of HR variability could contribute to a serious cardiac event, as it does in humans.

All very interesting, and also a reminder that physiological resources are not unlimited and so must be managed carefully.

:)

mugsgame
Dec. 18, 2011, 07:24 AM
Interesting - I am interested to know if you can increase performance in this area.

In my experience with newly backed horses they get mentally tired quicker than they get physically tired and as soon as that begins to happen you stop the session. As they get more used to the mental as well as physical exertion then you get longer sustained periods of concentration.

I also sometimes think you notice the same with horses who have been newly upgraded to a level but with time it seems to get easier so there must be capacity to develop mental and physical strength?

For me the top rider at mentally preparing horses on xc seems to be Andrew Nicholson. He has a wide range of horses in breeds but they all seem to come home from xc mentally very alert - is this fitness? the way he prepares them? or maybe the way he rides as he just looks to cruise round with hardly any pulls on the reins which means the horse is flowing and having to think less about gear changes, balance etc.

I would be interested to see this applied in the context of horse personality - is a sharper brained horse more able to sustain performance than a slightly more backwards thinking one?

JER
Dec. 18, 2011, 01:47 PM
Interesting - I am interested to know if you can increase performance in this area.

In my experience with newly backed horses they get mentally tired quicker than they get physically tired and as soon as that begins to happen you stop the session. As they get more used to the mental as well as physical exertion then you get longer sustained periods of concentration.

In humans, improvement happens via 'chunking (http://en.wikipedia.org/wiki/Chunking_%28psychology%29)'. This process works for physical as well as mental skills.

The question would be, how do we encourage 'chunking' in a horse?

I don't know how Andrew Nicholson prepares his horses for XC but his success might have something to do with how he presents informations/situations to them and then builds on it.

Conversely, watching an ill-fated run around a CCI****, as with the Oliver Townend's ride on Ashdale Cruise Master at Badminton 2011, what you see is a horse who repeatedly and increasingly fails to get his legs out of the way of the fence. He finally tipped up at the second part of the Quarry, but he almost lost it at the first element and before that, he very badly left a leg at the water. (Please note that I am using this as an example because the issues were very obvious.) Post-mortem, we know that ACM had a neurological problem, but given his repeated serious falls, the chicken-or-egg of this is up in the air.

Horses probably have varying abilities to chunk information and/or motor processes. I would think speed is a factor in this as well.

deltawave
Dec. 18, 2011, 04:21 PM
I think that's very interesting, but the whole business of heart rate variability spelling disaster for humans is a theory whose time has largely passed. It is sick or old hearts that generally lose the variability in the HR, and that is probably what predicts bad things like sudden death. Correlation, rather than causation.

Still, as an indicator of general autonomic fine tuning, it is still a fair marker.

However, it is something we can't possibly extrapolate to horses without an accurate means of precisely tracking their rhythm when they're out there on XC. :sigh:

wildlifer
Dec. 18, 2011, 05:32 PM
Why can't we track their rate variability? We have heart rate monitors that record everything and make really cool graphs (I'm dying to steal my endurance buddy's for a XC run someday). Are those not precise enough?

JER
Dec. 18, 2011, 05:54 PM
This was done on a treadmill.

Heart rate variability during exercise in the horse (http://www.ncbi.nlm.nih.gov/pubmed/9603047)

I suspect that asking the horses to do math problems would not affect the results.

This one looks more interesting:

Heart rate and heart rate variability during a novel object test and a handling test in young horses (http://www.horsonality.nl/Heartrate_HRV.pdf)

retreadeventer
Dec. 18, 2011, 07:13 PM
New Bolton has done a TON of heart rate studies in horses on the high speed treadmill.

I think if you train a horse well and thoroughly mental stuff is not that tough. My current horse can read a gymnastic like the back of his hoof. When he was younger, of course he had to learn to read them and I am sure it was more difficult on him mentally but now that he knows (from experience and repetition), I can't see it being just as mentally difficult as it used to be when he was learning. He just bangs right thru, no matter what pole/vertical/distance... he's done them all, and it's not a big deal to him.

Similarly upper level horses "read" the question on XC based on their experience and repetitions. I am sure some horses are "sharper" than others at learning and recognizing the gymnastic exercise presented by a XC question. The greener the horse, the more work the exercises, I am sure....but the sounder they are too and more physically capable.

Robby Johnson
Dec. 18, 2011, 08:21 PM
A recent study (http://www.ncbi.nlm.nih.gov/pubmed/22143842) -- on human subjects -- in the European Journal of Applied Physiology asked two groups of subjects to perform a series of fatiguing shoulder exercises. The control group did only the exercises, but the experimental group was also asked to perform mental arithmetic tasks along with the exercises.



I don't think there's any reason to think the situation might be different for horses or any other mammal. The excellent Sweat Science blog (http://sweatscience.com/mental-effort-increases-physical-fatigue-reduces-hr-variability/) quotes from the body of the paper:



On cross country, we're asking our horses to answer a series of often-difficult questions. We all know that XC can be very mentally fatiguing or even overwhelming for the horse but this study brings up the issues of physical fatigue and -- this is very important -- heart rate variability. A decrease in either (or both) of those things can spell disaster for a horse on XC.

It might make the difference in a horse not getting its legs up high enough. Or perhaps the loss of HR variability could contribute to a serious cardiac event, as it does in humans.

All very interesting, and also a reminder that physiological resources are not unlimited and so must be managed carefully.

:)

Interesting you make it about the horse; all I could think about was the rider! There is a lot to remember to make an XC trip successful.

deltawave
Dec. 19, 2011, 09:47 AM
Why can't we track their rate variability? We have heart rate monitors that record everything and make really cool graphs (I'm dying to steal my endurance buddy's for a XC run someday). Are those not precise enough?

We can track pulse rate pretty well, but to do really good heart rate variability requires a continuous EKG (not just pulse rate) signal and for the signal to not just be averaged every few seconds, which is how most "Polar" type of heart rate monitors work.

It is a matter of level of precision in the case of heart rate variability, and continuous EKG monitoring (the actual rhythm and QRS complexes) has proven to be very, very difficult in a moving horse outside of the hard-wired/treadmill environment.