The leg extension is a resistance weight training exercise that targets the quadriceps muscle (m. quadriceps femoris) [1] in the legs. The exercise is done using a machine called the Leg Extension Machine. There are various manufacturers of these machines and each one is slightly different. The leg extension is an isolated exercise targeting one specific muscle group, the quadriceps. It should not be considered as a total leg workout, such as the squat [2] or deadlift.[ citation needed ]
Align the backrest to support a straight posture and adjust the seat so that the knees align with the fulcrum. [3] Align the lower moving pads so that they rest against the front of the shin. The upper support pad should be lowered until it places gentle pressure on the thighs. [4]
Sit on the edge of a stable and flat bench/chair. While holding onto the sides of the seat, extend one leg outward to a straightened or slightly bent position. Hold that position for 1-2 seconds and reset to the starting position. Repeat on the same or other leg and complete repetitions for the set. The goal is resistance in the quads building throughout the sets, holding for a longer time or adding different forms of resistance to build strength. [5]
Initiate the movement by extending the legs up against the moving pad, raising the weight until the legs are parallel to the ground. Then, slowly lower the weight in a controlled manner while bending the knees until the user returned to the initial position. [6]
Common mistakes to avoid while performing the exercise include Incorrectly setting up the machine. Not adjusting the machine to fit the body is a common error that can lead to feeling uncomfortable, slowing progress, and injury risk. Another common mistake is an incomplete range of motion. Setting up the machine at 90 degrees and then pressing the legs up to 45 degrees is the recommended range of motion. Another common mistake is using too much weight. Using more weight than the user can handle can lead to using body momentum, which can hurt prevent results and place unnecessary strain on the joints. [6]
Can be used with a weight bag or resistance band attached to the user’s ankle on the leg in use to increase the difficulty and strengthen quadricep muscles. [7]
The exercise consists of bending the leg at the knee and extending the legs, then lowering them back to the original position. The exercise engages all four heads of the quadriceps, the vastus lateralis, vastus intermedius, vastus medialis and rectus femoris. The vastus lateralis has been shown to engage more during the movement when toes are pointed inward. The rectus femoris engages more when the toes are pointed outward. [8] Research has shown, that performing the leg extension with the hip flexion at a 40-degree angle rather than the typical 80-degree angle can promote more rectus femoris activation. [9] [10] [1] This is because the rectus femoris attaches to the hip, and leaning backward stretches the muscle more. [11] Additionally, angling the arm of the machine closer to the seat places the quad muscles in a more stretched position, potentially causing more muscular growth. [11] However, if this position is uncomfortable, adjust the arm of the machine to the most comfortable angle.
Some fitness professionals and coaches advise against using an isolating leg extension machine because they believe it puts unnatural pressure on the knees and ankles. [12] [ better source needed ]. However, this concern is based more on anecdotal evidence than on solid research. Whilst there is some evidence that the leg extension's unnatural moment arm places constant tension on the anterior cruciate ligament (ACL), [13] there is no proof that this increases the risk of injury, except for those with pre-existing ACL issues. The leg extension is a good exercise for isolating muscular contraction in the quadriceps, [14] but as with all isolation exercises, should be included in a holistic resistance training program working all muscles, especially antagonistic muscle pairs (such as the quadriceps, hamstrings, and gluteal muscles), to avoid muscular imbalances, which are associated with increased injury risk. [15]
The leg extension exercise is for different purposes in many different workout routines.
The leg extension is a staple in the majority of bodybuilding programs. The exercise excels in isolating all four heads of the quadriceps when performed with good technique and control. The exercise is convenient to setup when a machine is provided, and the machine provides a lot of stability. Bodybuilding programs look for exercises that can increase mass and strength, the leg extension is good for that purpose. 
The quads are a muscle that is proven to be beneficial to train when excelling in running and most sports. Leg extensions are a beneficial exercise to isolate the quadriceps. Leg extensions can be performed to maximize endurance and hypertrophy (mid-high rep ranges) or explosive strength (mid-lower rep ranges). [16] [17]
In a physical therapy context, patients can perform leg extension variations to build muscular quad strength. Many physical therapists use this exercise to help patients rehabilitate after knee surgery and to address knee pain. Many physical therapists refer to leg extensions as Long Arc Quads and Short Arc Quads. Long Arc quads are similar to the leg extension exercise described in this article. Patients sit at the end of a bench or platform, placing their knees at a 90-degree angle. The patient then extends their leg and then slowly lowers back down to 90 degrees. Short Arc Quads are variations performed by laying the leg flat and then placing an elevated platform under the knee. Then extending the elevated knee to perform a shorter range of motion leg extension. [18]
The leg extension machine was created by American fitness guru Jack LaLanne in the 1950s [19] . The first prototype is recognized to have been made under Gustav Zander, but labeled the machine as a form of “mechanotherapy” along with other machines that extended the knee and ankle. [19] The machine was made to target the quadriceps. The exact method of inventing the leg extension machine is not consistently recorded, but in most cases, it is attributed to LaLanne. [19]
The leg is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or buttock region. The major bones of the leg are the femur, tibia, and adjacent fibula. There are 60 leg bones in each leg.
In anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the lower limb.
The gluteus maximus is the main extensor muscle of the hip in humans. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. It is the single largest muscle in the human body. Its thick fleshy mass, in a quadrilateral shape, forms the prominence of the buttocks. The other gluteal muscles are the medius and minimus, and sometimes informally these are collectively referred to as the glutes.
The quadriceps femoris muscle is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur. The name derives from Latin four-headed muscle of the femur.
A squat is a strength exercise in which the trainee lowers their hips from a standing position and then stands back up. During the descent, the hip and knee joints flex while the ankle joint dorsiflexes; conversely the hip and knee joints extend and the ankle joint plantarflexes when standing up. Squats also help the hip muscles.
The vastus medialis is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group.
The vastus intermedius (Cruraeus) arises from the front and lateral surfaces of the body of the femur in its upper two-thirds, sitting under the rectus femoris muscle and from the lower part of the lateral intermuscular septum. Its fibers end in a superficial aponeurosis, which forms the deep part of the quadriceps femoris tendon.
The vastus lateralis, also called the vastus externus, is the largest and most powerful part of the quadriceps femoris, a muscle in the thigh. Together with other muscles of the quadriceps group, it serves to extend the knee joint, moving the lower leg forward. It arises from a series of flat, broad tendons attached to the femur, and attaches to the outer border of the patella. It ultimately joins with the other muscles that make up the quadriceps in the quadriceps tendon, which travels over the knee to connect to the tibia. The vastus lateralis is the recommended site for intramuscular injection in infants less than 7 months old and those unable to walk, with loss of muscular tone.
The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius, and the vastus lateralis. All four parts of the quadriceps muscle attach to the patella by the quadriceps tendon.
Lombard's paradox describes a paradoxical muscular contraction in humans. When rising to stand from a sitting or squatting position, both the hamstrings and quadriceps contract at the same time, despite them being antagonists to each other.
An anterior cruciate ligament injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn. The most common injury is a complete tear. Symptoms include pain, an audible cracking sound during injury, instability of the knee, and joint swelling. Swelling generally appears within a couple of hours. In approximately 50% of cases, other structures of the knee such as surrounding ligaments, cartilage, or meniscus are damaged.
The tuberosity of the tibia, tibial tuberosity or tibial tubercle is an elevation on the proximal, anterior aspect of the tibia, just below where the anterior surfaces of the lateral and medial tibial condyles end.
The anterior compartment of thigh contains muscles which extend the knee and flex the hip.
A patellar dislocation is a knee injury in which the patella (kneecap) slips out of its normal position. Often the knee is partly bent, painful and swollen. The patella is also often felt and seen out of place. Complications may include a patella fracture or arthritis.
The leg raise is a strength training exercise which targets the iliopsoas. Because the abdominal muscles are used isometrically to stabilize the body during the motion, leg raises are also often used to strengthen the rectus abdominis muscle and the internal and external oblique muscles.
Terrestrial locomotion by means of a running gait can be accomplished on level surfaces. However, in most outdoor environments an individual will experience terrain undulations requiring uphill running. Similar conditions can be mimicked in a controlled environment on a treadmill also. Additionally, running on inclines is used by runners, both distance and sprinter, to improve cardiovascular conditioning and lower limb strength.
The vastus muscles are three of the four muscles that make up the quadriceps femoris muscle of the thigh. The three muscles are the vastus intermedius, the vastus lateralis, and the vastus medialis located in the middle, on the outside, and inside of the thigh, respectively. The fourth muscle is the rectus femoris muscle a large fleshy muscle which covers the front and sides of the femur.
A kick is a skill in association football in which a player strikes the ball with their foot. Association football, more commonly referred to as football and also known as soccer, is a sport played world-wide, with up to 265 million people around the world participating on a yearly basis. Kicking is one of the most difficult skills to acquire in football. This skill is also vitally important, as kicking is the way in which passes are made and the primary means by which goals are scored.
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