Exercises that extend your knees are important for maintaining overall leg strength and balancing ability. Strict knee extension exercises use only the four quadriceps muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius, which are essentially the anterior thigh muscles. The American College of Sports Medicine's Guidelines for Exercise Testing and Prescription advise you to breathe normally while doing strength exercises, rather than holding your breath, to prevent excessively high blood pressure. They also recommend taking a break between exercises so that you can perform the next set with good form.
Leg Extensions
Leg extensions are the classic knee extension exercise because the only movement is bending and straightening of your knees. Leg extension exercise machines make this exercise simpler, but you can do them while sitting on a chair and wearing ankle weights too. To use a machine, sit on the seat with your ankles behind the shin pads. Straighten your knees to lift the weights. Adjust the weight stack to change the intensity.
Leg Press
Leg press exercises involve extension of your hips as well as your knees, meaning that you are using additional muscles. "Strength Training Anatomy," by Frederic Delavier, suggests placing your feet close together and low on the foot plate to emphasize the quadriceps muscles. Adjust the weight stack as necessary and avoid arching your back or locking your knees to prevent injury. Extend your knees and hips while exhaling to lift the weights correctly.
Squats
Since squats extend both thighs and hips, they use gluteus muscles as well as quadriceps. However, you can isolate your knee extension muscles through exercise variations. When performing regular squats, "Strength Training Anatomy" suggests placing a low block under your heels to focus exertion on your quadriceps. Working in a squat frame allows you to lean back further, which also isolates your knee extenders. Avoid bending your knees past a right angle or allowing your knees to move forward past your toes; both of these lead to knee injuries.
Squat Variations
Perform front squats by relocating the weight bar from your upper back to your chest. Keep your feet a shoulder width apart and perform squats as usual. "Strength Training Anatomy" states that this technique "focuses a greater part of the effort onto the quadriceps." Dumbbell squats are similar to regular and front squats except you hold dumbbells down at your sides. Executing dumbbell squats while leaning back against a wall will also isolate your knee extension muscles.
References
- "ACSM's Guidelines for Exercise Testing and Prescription"; American College of Sports Medicine; 2006
- "Strength Training Anatomy"; Frederic Delavier; 2006
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