## 4 Discussion
Likewise, [PERSON] and [PERSON] [20] proposed that horses preferentially choose a velocity that requires the least energy expenditure, which might entail using a specified stride length and/or stride frequency [21]. Thus, one of the effects of retraining to become a saddle horse on the gait may be that horses have a more excellent capacity to adjust their stride length, resulting in reduced energy expenditure and avoiding unnecessary fatigue. However, further investigations are needed to confirm this interpretation. [PERSON] et al. [13] discovered that stride length was not changed after five months of treadmill training statistically. On a treadmill, the stride lengths were not affected by training because the speed is fixed so that the horses may employ their ideal stride length/frequency inside each speed step [12]. Furthermore, exercises on a horizontal treadmill require less energy than exercises on the ground [22]. The differences between the outcomes from the previous study are possibly due to the different training environments because [PERSON] et al. trained on a treadmill. In contrast, the horses used in the current study were trained on the ground and were mounted. [PERSON] et al. [14] reported the effects of training a Standardized for three years to be a racehorse. The results of three years of training increased stride length, stride duration, and swing phase. Contrary to the previous study, a retired racehorse was retrained to become a saddle horse in this study. Although the effect of retraining was not statistically significant in the stride lengths, all stride lengths were reduced in both Walk and Canter. [PERSON] [21] showed that the relationship between stride length and velocity was linear, and velocity can be estimated by multiplying stride length by frequency. Since the retrained horses did not have to run at the maximum speed as in a race, this reduction of the stride lengths is considered the effect of retraining as racehorses are converted to saddle horses. In particular, the results show that the right side of the stride length decreased to a greater extent. Considering that only one side of the body (right side) had a greater effect, the cause can be the horse's asymmetry. It has been reported that the left femur was significantly enlarged in Australian Thoroughbreds [23]. The cause was from running clockwise repeatedly. The difference in pressure repeatedly applied to the left leg of Australian Thoroughbreds when turning a curved corner caused the asymmetry between the left and right hind limbs [23]. On the contrary, the right legs greatly affected Korean Thoroughbreds racing counterclockwise. As a result, the stride lengths of the right fore/hind feet were changed more than those of the left side through the saddle horse conversion training. These changes mean that the retraining positively affected the imbalance of the horse's body. In lameness examinations, lunging that rotates in only one direction is used. This rotation in only one direction induces artificial lameness and examines the movement to compensate for the lameness [24]. Considering that lunging causes lameness, in the case of a racehorse that runs only in one direction for a long period, the imbalance in the left and right of the body becomes chronic. It naturally affects the movement, resulting in compensatory movements (front-back/left-right movements of the head and the body increase). Previous studies [24; 25; 26] have shown that lameness in horses is related to compensatory head and body movements. The current study showed that the left-right (x-axis) movements of the center of mass and the center of the head decreased after the saddle horse conversion training. These results can be considered as more balanced and as less movement to compensate for the head and body imbalance, meaning straightness has improved. In addition, the head-neck angle was smaller than before training in all events of Walk and in five events of Canter.