Hi Vignesh, Labrador is such an active animal in this planet that even an hour of brisk walking seems just not enough for this breed. Also, humans are not as active as dogs. If you walk a dog for an hour, you yourself need to burn a lot of calories.
Walking is more structured way of exercising these animals. If you want your dog to get exercise enough to keep him tired all day then you have to make him run. If you have a big roof you can make him run on there. Or, if you have a park then you can take him at the time when there are no-one there. You just have to buy a cosco ball and throw it for your dog to run and chase it. Running is the best form of exercising for dog and 15 minutes of running will be equal to 45 minutes of your walking with the dog. Also, you yourself will preserve your own energy.
Labradors in general tend to get bored with walking on leash and as puppies they love to run and retrieve things. As they grow older, even if they run 20-25 minutes on per day basis that's all they need and you don't necessarily have to take them for long walks as running will meet all their exercising requirment.
Also, the more he runs the more he gets tired making him less destructive at home. More exercise will mean increase their appetite which will promote their over-all growth.