Conditioning Program Prescribed from the External Training Load Corresponding to the Lactate Threshold Improved Cardiac Function in Healthy Dogs

SIMPLE SUMMARY: Regular exercise is a stressful stimulus that elicits physiological responses in systolic and diastolic functions in human athletes, the so-called “athlete’s heart”. The present study reports findings obtained from echocardiography to measure the ventricular dimensions at rest in beagle dogs undergoing an endurance training program carried out on a treadmill with the intensity set at 70–80% of the velocity corresponding to the lactate threshold. Echocardiography was performed with routine measurements of the left ventricular systolic and diastolic function by the two-dimensional and Doppler techniques. After the training, the principal component analysis of echocardiographic variables was conducted to evaluate dimensional changes in left ventricular function. Principal components analysis was able to capture the qualitative echocardiographic changes produced by the endurance training. Eight weeks of the lactate-guided endurance training program could lead to concomitant left ventricular dilation without hypertrophy of the ventricular walls, emphasizing the left ventricular systolic and diastolic functions. These results suggest that submaximal aerobic training may induce physiological cardiac remodeling, improve the left ventricular functions, promote health, and minimize any injuries produced during heart disease, although its effectiveness for the latter effect must be confirmed in future studies. ABSTRACT: This research focuses on the adjustments in systolic and diastolic functions that are not fully understood in dogs submitted to athletic training. Beagle dogs carried out an endurance training program (ETP) prescribed from the external training load, corresponding to 70–80% of the lactate threshold (VLT) velocity. Eighteen dogs were randomly assigned to two groups: control (C, n = 8), active dogs that did not perform any forced exercise, and trained (T, n = 10), submitted to the ETP during eight weeks. All dogs were evaluated before and after the ETP period using two-dimensional echocardiography, M-mode, Doppler, and two-dimensional speckle tracking. A principal component analysis (PCA) of the echocardiographic variables was performed. The ETP improved the left ventricular internal dimension at the end of diastole (LVDd), the left ventricular internal dimension at the end of diastole to aorta ratio (LVDd: Ao), and the strain rate indices. PCA was able to capture the dimensionality and qualitative echocardiography changes produced by the ETP. These findings indicated that the training prescribed based on the lactate threshold improved the diastolic and systolic functions. This response may be applied to improve myocardial function, promote health, and mitigate any injuries produced during heart failure.