Strengthening your quadriceps and hamstrings can help you develop resilience against fatigue and reduce your risk of injuries in sports and recreational activities. In addition to flexing and extending the knee, your quadriceps produce force to accelerate while your hamstrings function like brakes to decelerate your body when you run or walk. Strong quadriceps also absorb shock better when your foot strikes the ground. Since most sports and activities require you to move in a standing position, it is better to train both muscle groups in such a position rather than sitting on a machine.
Lower-Body Circuit Training
Warm up your body by jogging and skipping rope for five minutes. Perform dynamic flexibility exercises to prepare your body and mind for the upcoming workout. Do leg swings, walking butt kicks, torso twists and arm swings, for example.
Stand with your feet about shoulder-distance apart and hold a medicine ball -- about six to 12 pounds -- near your chest with both hands. Your feet should be pointing forward. Inhale as you squat down as low as you can so that your buttocks move below the level of your knee. Keep your back straight and your heels on the floor. Do not hunch your shoulders. Exhale as you stand straight up. Perform 10 to 12 reps.
Stand and face a plyometric box or a similar sturdy platform with your feet together. The platform should be about as tall as your knees or slightly higher. Put your left foot on top of the box and exhale as you step your body on top of the box like you're climbing a staircase. Bring your right knee toward your ribs as you balance on one leg for one second. Use your arms to help you balance if necessary. Inhale as you step down from the box to the starting position. Perform 10 reps per leg. Maintain a steady rhythm as you step up and down.
Stand with your feet together and step back about two feet behind you with your right foot. Your right buttock should automatically tighten as you extend your right hip. Inhale as you lunge down by bending your legs together until your right knee almost touches the floor. Keep your back straight and do not hunch your shoulders or lean forward excessively. Exhale as you push into the floor with your left foot to bring your right foot back to the starting position. Perform 10 reps per leg.
Rest for one minute and repeat the circuit two to three more times. Vary the lunges and step-ups by moving your body in different directions, such as out to the side, or by adding a torso rotation.
Strength and Power Superset
Stand and face the plyometric box and put your right foot on top of it. Bend your left leg and swing your arms slightly behind you to initiate the jump. Exhale as you jump straight up while swinging your arms over your head. Extend your spine slightly and switch the position of your legs while you're in midair. Land gently on the box with your left foot and your right foot on the floor. Land on the ball of your feet and toes, not on your heels. Repeat the movement as fast as you can for 16 to 20 reps. Rest for 10 to 15 seconds before continuing with the next exercise.
Stand with your feet together and step forward with your right foot about two feet in front of you with your hands positioned near your chest like you're going to catch a basketball. Inhale as you lunge down by bending both legs until your left knee almost touches the floor behind you. Keep your back straight, and do not hunch your shoulders. Exhale as you step back to the standing position. Perform 10 reps per leg.
Rest for one to two minutes and repeat the superset two to three more times. You may substitute the lunge exercise in step two with bodyweight squats or step-ups in the second and third supersets.
You can use any power exercise in the power and strength superset for which you perform one set of high-intensity exercise followed by a lower-intensity exercise. This can help you burn more calories in less time while strengthening your legs and hips. Other power exercises include jump-rope double unders, power lunges, vertical jumps and shuttle runs. Mix-and-match various exercises to see which ones you prefer.
If you plan to do each leg exercise individually without using the circuit training or superset format, the National Academy of Sports Medicine recommends that you perform four to six sets of one to five reps at 85 to 100 percent of your maximum intensity if you want to train for maximum strength. Work with a qualified exercise professional if you're new to strength training before working out on your own.
Do not train when you feel pain in your back, hips or legs. See your physician or physical therapist immediately before you resume training.