Dynamic exercise training in foxhounds. I. Oxygen consumption and hemodynamic responses

Ten foxhounds were studied during maximal and submaximal exercise on a motor-driven treadmill before and after 8-12 wk of training. Training consisted of working at 80% of maximal heart rate 1 h/day, 5 days/wk. Maximal O₂ consumption (V̇O₂(max)) increased 28% from 113.7 ± 5.5 to 146.1 ± 5.4 ml O₂ x min^-1 x kg^-1, pre-to posttraining. This increase in V̇O₂(max) was due primarily to a 27% increase in maximal cardiac output, since maximal arteriovenous O₂ difference increased only 4% above pretraining values. Mean arterial pressure during maximal exercise did not change from pre- to posttraining,with the result that calculated systemic vascular resistance (SVR) decreased 20%. There were no training-induced changes in O₂ consumption, cardiac output, arteriovenous O₂ difference, mean arterial pressure, or SVR at any level of submaximal exercise. However, if post- and pretraining values are compared, heart rate was lower and stroke volume was greater at any level of submaximal exercise. Venous lactate concentrations during a given level of submaximal exercise were significantly lower during posttraining compared with pretraining, but venous lactate concentrations during maximal exercise did not change as a result of exercise training. These results indicate that a program of endurance training will produce a significant increase in V̇O₂(max) in the foxhound. This increase in V̇O₂(max) is similar to that reported previously for humans and rats but is derived primarily from central (stroke volume) changes rather than a combination of central and peripheral (O₂ extraction) changes.