Your inner-thigh muscles are responsible for adducting your upper legs, or drawing them closer together. When people talk of groin strains, they're referring to damage to the fibers in these muscles. You have two major inner-thigh muscles, the adductor longus and the adductor brevis. Exercising these muscles means adducting them against some form of resistance, and there are plenty of options for doing this.
Anatomy of the Inner Thigh
The inner thigh is controlled by three main, paired muscles -- the adductor longus, the adductor brevis and the adductor magnus. The adductor longus originates at the middle of the pubic bone and inserts about two-thirds of the way down the femur, or thigh bone. The adductor brevis originates in approximately the same spot as the adductor longus but inserts much higher on the femur and thus rotates the thigh as much as it adducts it. The adductor magnus originates on the pubic bone and inserts, fan-like, all along the medial aspect of the femur.
Adductor-muscle strength is often notably lacking even in athletic people. A good, beginner-level, groin-strengthening exercise is the adductor squeeze, also called crook lying. Lie on your back with a ball or bunched-up towel between your knees, which should be flexed at about 90 degrees. Slowly squeeze the object with your groin muscles, holding maximal pressure for about five seconds. Repeat 10 times. You can do the same thing with your legs fully extended. Repeat these exercises three times daily for optimal results.
Intermediate and Advanced Exercises
Once beginner groin exercises become easy, move to intermediate exercises. You can use an elastic resistance band attached to your ankle and a wall positioned lateral to your working leg. Bring your leg inward against the resistance of the band about 30 degrees until your legs are touching. Use a chair for balance with your opposite arm. You can also do lunges. Place your hands on your hips and lower your rear knee to the ground while your opposite leg flexes. Then, return to a standing position. Perform three sets of 10 of each exercise a day.
Before working your adductor muscles, as with any part of your body, a good warm-up is in order to help prevent injury and allow you to do maximal work with these muscles. For example, you can do leg swings. Stand with your feet about shoulder-width apart, bend your knees and point them out at about 45 degrees. Lunge slightly to one side so as to extend the adductors of your opposite leg. Return to a vertical position and repeat on the opposite side. Repeat the entire sequence three times.