Labrador Retrievers are often categorised in one of two ways: English Labs or American Labs. The differences are principally behavioural, though there are differences in appearance as well. Behaviorally, English Labs tend to be more easily trainable, and are often considered better for non-professional owners to keep as pets or hunting companions. American Labs tend to be more energetic and, having been bred to compete in field trials, are better suited for professional owners with more experience and time to devote to training. In terms of appearance, English Labs tend to more prominently exhibit the 'blocky' heads for which Labrador Retrievers are known, whereas American Labs tend to be leaner and longer-legged.
A vigorous dog may or may not be high-energy, but everything he does, he does with vigor: he strains on the leash (until you train him not to), tries to plow through obstacles, and even eats and drinks with great big gulps. These dynamos need lots of training to learn good manners, and may not be the best fit for a home with young kids or someone who's elderly or frail. A low-vigor dog, on the other hand, has a more subdued approach to life.