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Research article - Peer-reviewed, 2022

Reduced high-intensity training distance in growing horses had no effect on IGF-1 concentrations, but training onset interrupted time-dependent IGF-1 decline

Johansson, Lisa; Ringmark, Sara; Skiöldebrand, Eva; Bergquist, J.; Jansson, Anna


This study investigated plasma insulin like growth factor (IGF)-1 concentrations in 16 young Standardbred horses introduced to systematic high-intensity training at two different levels of intensity. Growth and locomotion asymmetry and correlations between these and plasma IGF-1 concentrations were also examined. From September as 1-year olds to March as 2-year olds (Period 1), all horses were subjected to the same submaximal training program. In March (start of Period 2), the horses were divided into two groups (n=8) and one group was introduced to regular high-intensity training. The other group was introduced to a program where the high-intensity exercise distances were reduced by 30%. These two training programs were maintained for the remaining 21 months of the study (Periods 2, 3, and 4). There was no effect of training group on plasma IGF-1 concentrations. A continuous decline in IGF-1 levels was observed throughout the study (P<0.0001), with one notable interruption in Period 2 when the IGF-1 concentration remained at the level seen at the start of Period 1. Growth rate of body length was equally high in Periods 1 and 2 (P>0.05). Front and hind limb asymmetry was elevated in Period 2 compared with Period 1. There were positive correlations between IGF-1 concentrations and changes in body condition score, and a negative correlation between IGF-1 concentration and weight. These results indicate that introduction to high-intensity training induces IGF-1 release in horses, but that a 30% difference in the distances used in high-intensity training does not affect IGF-1 levels. The temporary interruption in decline in IGF-1 release with the onset of high-intensity training may influence growth pattern and locomotion asymmetry, but further studies are needed to assess causality.


locomotion symmetry; growth; body length; exercise

Published in

Comparative Exercise Physiology
2022, volume: 18, number: 3, pages: 201-209

Authors' information

Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry (AFB)
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management
Bergquist, J.
Uppsala University
Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry (AFB)

UKÄ Subject classification

Medical Bioscience

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