Whether you've experienced a tennis injury or you just spend a lot of time typing on a computer, you may find that repetitive motions can cause some muscles to get stronger while others weaken. Among those that may tend to be ignored are the extensor muscles of the hand, called the Extensor Digitorum, which originates near the elbow and helps to open the fingers and bend the wrists. Strengthening this area is fairly simple by using an "extensor" exercise tool for the hand, though you can also do a basic exercise with no equipment at all.
Make a tight fist with your hand and squeeze your fingers in toward your palms tightly. Hold the position for five seconds.
Open your fingers as wide as you possibly can, and hold that open position for five seconds. Repeat this opening and closing sequence three or four times.
Place your fingers inside your extensor tool. These tools come in various configurations, but typically the thumb hole is at an opposing side from the finger holes. Fit your fingers into the holes and tighten any straps the tool might have snugly around the wrist. If you have the choice between extensor tools or resistance settings, start with the lightest amount of resistance.
Close your fingers and thumb together, with each digit extended out straight and pointed away from you. Then open all the digits as wide as you can go and hold for five seconds. The added resistance of the tool will make opening your fingers more challenging than you were likely to experience with the basic opening and closing technique you started off with. Open and close your fingers with them pointed away from you three or four times, holding the position for five seconds each time.
Point your fingers up toward the ceiling, recruiting the muscles of your hands in a different way than the position pointed away from you. Open your fingers and hold the position for five seconds, and then close your fingers. Repeat the motion three or four times.
Do these exercises every other day to help strengthen the extensor digitorum muscle. If you have a tool with varying resistance, move up to heavier resistance after a few weeks of use.