Influences of Physical Training on the Heart of Dogs

To investigate the effects of physical training on cardiac dimensions and function, eight dogs were exercised for 12 weeks by treadmill running 1 hour/ day, 5 days/week. Five dogs were confined in cages as controls for an 8-week period. Heart rates were monitored by telemetry during rest and exercise. Maximum QRS spatial magnitudes were calculated from records of McFee lead electrocardiograms. Left ventricular end-diastolic dimensions were determined radiographically by the bead and clip technique. No statistically significant changes occurred during the control period. Training produced statistically significant decreases in heart rate at rest (72 beats/min to 49 beats/min, P < 0.005) and at a standard work load of 6.1 mph on a level treadmill (205 beats/ min to 158 beats/min, P < 0.005) and statistically significant increases in work load (5.4 mph to 9.1 mph, P < 0.005) at a standard heart rate of 194 beats/min. Improvements were rapid during the first 4 weeks of training but gradual during the remaining 8 weeks. Training caused small but statistically significant increases in left ventricular end-diastolic wall thickness (8.7 mm to 9.3 mm, P < 0.0025), estimated left ventricular mass (83.6 g to 91.2 g, P < 0.01), and maximum (McFee) QRS spatial magnitude (4.0 mv to 4.8 mv, P < 0.05).