Low-intensity race training does not induce left ventricular hypertrophy in 2-year-old Standardbred trotters

Abstract

The objective of the study was to evaluate the effect of low-intensity training on cardiac dimensions in young trotters compared with an untrained control group by use of echocardiography. Seventy-five 2-year-old Standardbred trotters undergoing low-intensity race training 3 to 4 days per week for 6 months were studied. Nine untrained age-matched Standardbred trotters served as controls. All horses were examined by echocardiography twice with an interval of 6 months. Left ventricular (LV) morphology and systolic function were studied with 2-dimensional guided M-mode echocardiography. An estimation of body weight was based on measurement of the chest girth circumference. A significant increase in LV internal diameter in diastole (LVIDd) (P = .005), LV muscle mass (LV mass) (P < .001), and mean wall thickness (MWT) (P < .001) during the 6-month study period for both the trained and untrained groups was observed. No significant differences in LVIDd, LV mass, MWT, and relative wall thickness (RWT) were observed between the 2 groups. Body weight was significantly correlated to the size of the cardiac measures LVIDd, LV mass, and MWT (P < .001). After the 6-month training period, the colts had larger LVIDd (P = .004) and LV mass (P = .002) than the fillies. The results indicate that the cardiac morphologic changes observed were mainly a result of normal physiologic growth. The amount of training over the 6-month period did not alter the different measures significantly from those of control group. When evaluating cardiac adaptive responses to training in young horses, serial echocardiographic measurements have to be performed. It is crucial to be aware of the considerable growth of the heart due to normal physiologic growth. In addition, it seems that an intense workload is required to achieve a training-induced increase in LV mass.