The aims of this study were to evaluate effects of a 6 week resistance training on electrocardiographic (ECG) and blood parameters of police dogs. Our hypothesis was that this training protocol improves fitness, contributing to the welfare of these animals. Nine dogs, 18.56±0.53 months old, were evaluated before (M1) and six weeks after (M2) a training protocol using treadmill. Their training program was performed 2 times/week, and included 20 min of treadmill activity on a speed compatible with 60-80% of HRmax on weeks 1 and 2, same exercise of weeks 1 and 2 with a 5% grade added between 7.5 and 12.5 min in weeks 3 and 4, and, finally, same exercise of weeks 3 and 4 with three short bursts of strenuous exercise, 60 min after the end of treadmill activity. On both moments, animals were examined before (T0) and after (T1) an incremental effort test, and at 30 (T2) and 120 min (T3) of recovery, measuring heart rate, respiratory rate and body temperature. Blood samples were taken to determine erythrogram, aspartate aminotransferase, creatine kinase, triglycerides, lactate and glucose. Electrocardiographic variables were analysed at T0 and T1. All variables were analysed by one-way ANOVA and Tukey tests, with P≤0.05. After training, there was an increase on the length of work on treadmill of 41.5% for the German Shepherd (P=0.0139) and 21.4% for the Belgian Malinois (P=0.0085) along with a increase of maximal speed of 34.0% for the German Shepherd (P=0.0084) and 15.9% for the Belgian Malinois (P=0.0241). It was observed in physiological, blood and ECG parameters differences between M1 and M2 (P<0.05). Other findings included a lower rest QTc value at T0 after training (P=0.0194). The chosen training led to a better fitness of the police dogs as all of them worked more intensively with a low cardiovascular requirement in M2. In conclusion, current exercise protocol in a treadmill improved dogs fitness, when we analysed ECG, physiological and blood parameters, making possible that animals may be used in more extended and multiple missions, contributing welfare of these animals.