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Written by Mark Andrews. Published online 28.06.10
 © Copyright Equine Science Update  2010
Benefit of exercise on insulin sensitivity
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Unless dietary restriction below maintenance energy requirements is also employed, moderate exercise on its own is not enough to counter insulin resistance in obese or overweight horses, according to research published in the American Journal of Veterinary Research.
Dr Rebecca Carter and colleagues at Virginia Tech examined the effects of exercise training alone on overweight or obese, insulin-resistant horses. Feed intake was limited during the study to 100% of maintenance energy requirements.

Twelve Arabian or part-bred Arabian geldings took part in the study. All had body condition score ≥7 (where 1 is emaciated and 9 obese.)

Eight horses were exercised. They followed a low intensity exercise program for 4 weeks followed by higher intensity exercise for a further 4 weeks. Finally they had two weeks without exercise (detraining). A control group of four horses received no structured exercise.

Low intensity
exercise regime:  

On a horse exerciser, 4 times a week:
10 minutes walking (at 1.1m/s)
+ 30 mins trotting (2.5m/s)

Higher intensity exercise regime

On a horse exerciser, 2 times a week:
10 minutes walking (1.1m/s)
+ 30 mins trotting (3m/s)

and

On a treadmill, 2 times a week:
10 mins walking (1.3m/s)
+ 10mins trotting (3.7m/s on a 3° incline)
(target heart rate 130 bpm)
+20 mins cantering (6.3m/s on a 3° incline)  
(target heart rate 160 bpm)
The researchers found that the horses’ body weight had fallen by 2% following the low intensity exercise and by a similar amount after the 4 weeks of higher intensity exercise. Compared with pre-exercise values, the estimated fat mass fell by 21% after the light exercise and by 34% after higher intensity exercise.

However, about half of the body weight lost during the exercise stages was put back on again within the two weeks of detraining with no exercise.

Despite the weight loss, the researchers found no improvement in insulin sensitivity, when measured two days after their last exercise session. This indicates that although there may be improvements in insulin sensitivity during exercise or up to 24 hours after an exercise session (as has been shown in previous research), there may be no prolonged training effect of exercise on insulin sensitivity in overweight/obese horses.

They measured a number of variables including glucose, triglyceride, insulin, leptin, and nonesterified fatty acids (NEFAs). Frequently sampled IV glucose tolerance tests were also performed. The researchers found no significant difference between the exercised and control groups throughout the study.

They conclude that a more pronounced reduction in adiposity, or a higher volume, frequency or intensity of exercise training may be needed to enhance insulin sensitivity in overweight or obese, insulin-resistant horses.

Dr Carter adds "even though our study did not show long-term training effects of exercise, there still are probably improvements in insulin sensitivity during and shortly after an exercise session. Therefore, ROUTINE exercise (every day) may be beneficial for improving insulin sensitivity."

For more details see:

Effects of exercise training on adiposity, insulin sensitivity, and plasma hormone and lipid concentrations in overweight or obese, insulin-resistant horses.
Carter RA, McCutcheon LJ, Valle E, Meilahn EN, Geor RJ.
Am J Vet Res. 2010 Mar;71(3):314-21.
Images courtesy Dr Rebecca Carter