Thigh strengthening exercises are usually intended to target the quadriceps, as opposed to the hamstring or other muscles of the upper leg. Strengthening the thigh muscles will lead to a better ability to perform a huge number of activities, from sports that require jumping, climbing, and running to everyday activities like walking up stairs and lifting heavy things off the ground. Various thigh strengthening exercises include body weight strength training exercises, in which the weight of the body provides the resistance for the exercise, as with unweighted squats, and exercises that are performed with resistance from additional weights and machines, such as a leg extension machine.
Two of the most common thigh strengthening exercises that only require body weight for resistance are squats and lunges. To do a squat, stand with feet shoulder width or slightly farther apart, bend the knees and sink down in a sitting motion until the thighs are parallel or slightly above parallel to the floor, and then extend the legs to raise back up to a standing position. To do a lunge, stand upright and then take a big step forward with one leg, bending both knees so that each leg is bent, and then push back up into the standing position. Both squats and lunges can be done with added weight, usually by holding dumbbells or a barbell, but sometimes also with resistance bands or a weighted vest. A squat machine, found at most gyms, can be a useful way to add resistance to squats without needing to hold onto dumbbells or a barbell.
Leg extensions can also be performed without weights, by sitting in a chair and extending the knee so that the leg is straight out in front of the body. For most people, this will not provide enough resistance to build much strength, but for those recovering from an injury or who experience knee pain, as well as individuals who find more advanced exercises too difficult because of a lack of thigh strength, this can be a good starting point. Once strength improves a little bit, the addition of ankle weights can help the exerciser progress. Most gyms have a leg extension machine that works with the same motion as the unweighted version, but uses a padded bar with adjustable amounts of weight to provide anywhere from slight extra weight to a great deal of resistance, for advanced users.
Climbing the stairs every day instead of taking the elevator can be a great way to do thigh strengthening exercises outside of a normal workout. Even if there are too many flights of stairs to climb to avoid the elevator altogether, it is still beneficial to get off a floor or two early and climb the rest on foot. Walk up and down a few flights of stairs during break time at work, or even carefully take two steps at a time for an added challenge.