Physical fitness is an important aspect of golf today. I stress it with the juniors who come to my camps all the time.
In putting, lower-body stability and a strong core is especially important. Here's a great way at home to improve strength, stability and improve your putting.
You don't even need a putter.
What you do need is a stability ball or exercise ball. Start by sitting on the ball and spreading your feet wide. Extend your arms slightly in front of your body and make a short putting stroke. As you do this, you'll feel your core working as you try to stay balanced on the ball.
Once you master this, move your feet together. The smaller base on the ground puts even more stress on your core. Continue making the same putting stroke.
For the more advanced players, lift one foot off the ground. With just one foot on the ground, you'll really have to work hard to stay stable.
This improves your putting because it trains you to keep your core muscles tight. When your core is tight you're more likely to make a consistent putting stroke.