Just like any you and I, your dog can gain unhealthy levels of weight and suffer from low energy levels due to being too inactive, especially in the winter. There are ways, however, to combat this with a few simple exercises and everyday physical activities for your dog. Some of these will even work great for older dogs who aren't used to frequent bouts of physical exercise. When it comes to trimming down your dog's waist line and getting it to become more active, the saying that you can't teach an old dog new tricks simply isn't true anymore. Even the slightest bit of exercise will provide some benefits to your dog.
One exercise to try an incorporate into the dog's daily routine is walking. While, it may not seem like much, walking is a great way to stay fit with your dog and it doesn't require much more than a leisurely stroll around the neighborhood. Try not to overdo the distance of the in the beginning. I recommend keeping the walks short and gradually increase the distance as it gets in better physical shape.
Another great exercise for your dog is walking up and down stairs. Walking the dog up and down the stairs a few times will make a notable a difference. Similar to walking, try to increase the reps on the stairs over time so it can get more benefits of the exercise over time.
My personal favorite dog exercise is a good game of fetch. My dog can play this for hours on end and never tired or bored. You'll need a few different toys and dog supplies for this one. The reason the different toys is so it can run further and longer after the different one, increasing its workout and activity level. For some of us who aren't really into high-levels of physical activity personally, a game of fetch is great because it doesn't require the same amount of physical output from us as walking does.
While this particular exercise may not apply to all dog owners, it is still a pretty fun activity. A swimming pool makes a great piece of exercise equipment for dogs. It is important to determine if your dog does or doesn't like the water. Some breeds do and others not so much. Try to see if swimming is something your dog would enjoy and have fun doing before planning out a whole list of swimming related exercises for it.
Regardless of what type of activity you choose, your dog will be better off for it. There are many great exercises out there which will benefit him or her. Just remember to have fun and be consistent with it so that you and your dog can enjoy many more years together.