[RC] rider weight studies, part 1 - Susan E. Garlinghouse, DVM
Tried to send this in one big post, but got it slung back at
me, so I’ll try again in smaller pieces.
I haven’t been on RC lately, but thought I’d
de-lurk and add a few comments to the current thread concerning my Tevis
studies. Although, it sounds like everyone already has a pretty good
handle on what the results concluded.
Ed, you commented:
>This type of statistical result, that is one that
does not make sense intuitively, >raises caution flags to me. It causes me
to wonder if it is a correlation of an >accidental nature and not a cause
and effect.
I was
initially surprised at the results as well, but as Truman will attest, you let
your data tell you what your results are, you don’t plan your results and
make the data fit your preplanned ideas. Over several years of data
collection, I eventually ended up with over 1200 data points that all supported
the original conclusion---the higher the total mass is over a combined weight
of 1200 lbs, the more likely you are to pull due to a lameness issue.
Note that there is not a clear cut defining line---ie, it’s not like a
horse and rider team weighing 1250 lbs will magically attain 100% completion
rates simply by dropping 100 lbs. It’s just that the upward trend
starts to markedly shift upward right around 1200 lbs. But the statistics
were solid, and were checked pretty darn closely by a number of physiologists
and statisticians in the field a lot smarter than I am before it was approved
for publication in the peer-reviewed journal(s).
>I can
see how heavier horses possibly could be at a disadvantage, but I don't see why
>the carrying of a lower percentage of body weight than a lighter horse
would put them >into a further disadvantage.
Maybe
I’m misunderstanding you, but I don’t think that conclusion was
drawn. The conclusion that is drawn in the study is that all other things
being equal (as far as those parameters which could be quantitatively
measured), a horse and rider team carrying heavier total weight is at a
disadvantage over a horse/rider team carrying less weight, REGARDLESS of how
the weight is divided between horse and rider (within reason). Example, a
1200 lb horse carrying a 200 lb rider, carrying less than 17% of his body
weight, is still at a biomechanical disadvantage over a 900 horse carrying the
same rider, even though the smaller horse is carrying over 22% of his body
weight.
This
assumes that both horses are at a similar body condition score, which
presumably provides adequate body fat and intramuscular glycogen stores for the
job at hand. The disadvantage shifts if the 1200 lb horse is in good body
condition, but the 900 lb horse is excessively thin and underweight---that is,
a horse that in good condition should probably weigh several hundred pounds
more than he does. In that case, even though total mass is less than the
1200 lb horse, the thin horse is at higher risk of metabolic failure (and this
seems to be a stronger influence than the total mass biomechanical influence),
and ALSO at higher risk of lameness secondary to metabolic failure (ie, tying
up, cramping, etc).
