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

Figures

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  Figure 1. Workflow of the endurance training program (EPT). The beagle dogs were subjected to an incremental exercise test (IET-1) and their lactate threshold (LT) was determined. Treadmill slope was set to 7.5%, with 0.5 m/s speed increments, every 5 min. Blood samples were collected at the following timepoints: before the IETs and between each incremental step (A). Next, dogs from group T underwent an eight-week aerobic conditioning training on the treadmill (B) with the intensity set to 70–80% of the velocity corresponding to the lactate threshold (VLT). Then, the IET was repeated for group T (IET-2). Group C did not undergo tests or training (negative control). D = day; W = week; HR = heart rate.

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  Figure 2. Changes in cardiac morphology of dogs submitted to eight weeks of training. (A) LVDd: left ventricular internal diameter at the end of diastole; (B) LVDd/Ao: left ventricular internal diameter at the end of diastole to aorta ratio; (C) LA/Ao: left atrium-to-aorta ratio. Bars are standard errors. *: Difference from week zero (W0); (p < 0.05).

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  Figure 3. Volumetric changes in the heart in dogs submitted to 8-week endurance training program. (A) LVVd: left ventricular volume in diastole; (B) LVVs: left ventricular volume in systole; (C) SV: systolic volume; (D) EF: ejection fraction in milliliter (mL) and percentage (%). *: Difference from week zero (W0); (p < 0.05).

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  Figure 4. Changes in the diastolic function of dogs submitted to 8 weeks of physical training. E: the velocity of early ventricular filling velocity (A); IVRT: isovolumetric relaxation time (B); A: the velocity of late ventricular filling velocity (C); E/IVRT: the ratio of early ventricular filling velocity to isovolumetric relaxation time (D); E/A: the ratio of early-to-late left ventricular filling velocities (E); E/E’: ratio of the mitral flow E wave and mitral annulus E’ wave velocities (F). *: Difference compared to week zero (W0); #: Difference between groups (p < 0.05).

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  Figure 5. Changes in myocardial deformation (A) Strain and (B) strain rate of the left ventricle in dogs after 8 weeks of physical training. *: Difference from week zero (W0); (p < 0.05).

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  Figure 6. Principal component analysis (PCA) of the dogs undergoing an eight-week endurance training program. In plot (A), each dot represents one dog in the respective training week (W0 and W8), and echocardiographic variables are analyzed. Plot (B) shows scatterplots corresponding to groups (C-W0, control in week 0, purple; C-W8, control in week 8, blue; T-W0, trained in week 0, light green; T-W8, trained in week 8, dark green) and similar condition profiles cluster together. A clear separation between control and trained dogs is observed. In (C), the barplot reveals the echocardiographic variables’ contribution on dimensions 1 and 3. The reference red dashed line shown on the barplot corresponds to the expected value if the contribution were uniform. The variables with a contribution above the reference line could be considered the most important on the selected dimensions.

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  Figure 7. Heatmap of echocardiographic variable scores of dogs submitted to eight weeks of the endurance training program. The color gradient represents score magnitude; the blacker, the more massive the echocardiographic response.