The leg extension is a resistance weight training exercise that targets the

quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) 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 ...

muscle (m. quadriceps femoris) 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. Most gym and weight rooms will have the machine in their facility. 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 or

deadlift The deadlift is a weight training exercise in which a loaded barbell or bar is lifted off the ground to the level of the hips, torso perpendicular to the floor, before being placed back on the ground. It is one of the three powerlifting exercises, ...

. The exercise consists of bending the leg at the knee and extending the legs, then lowering them back to the original position.

Risk of injury

Some fitness professionals and coaches advise people to not use an isolating leg extension machine due to the unnatural pressure it places on the knees and ankles.. However, this is a fitness myth based on largely anecdotal evidence rather than peer-reviewed research. Whilst there is some evidence that the leg extension's unnatural

moment arm In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of ...

places constant tension on the

anterior cruciate ligament The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are also called "cruciform" ligaments, as they are arranged in a crossed formation ...

(ACL), there is no evidence to suggest that this constant tension increases injury risk outside of individuals with pre-existing ACL injuries. The leg extension is a good exercise for isolating muscular contraction in the quadriceps, but as with all isolation exercises, should be included in a holistic resistance training program working all muscles, especially

antagonistic muscle Anatomical terminology is used to uniquely describe aspects of skeletal muscle, cardiac muscle, and smooth muscle such as their actions, structure, size, and location. Types There are three types of muscle tissue in the body: skeletal, smooth, ...

pairs (such as the quadriceps,

hamstrings In human anatomy, a hamstring () is any one of the three posterior thigh muscles in between the hip and the knee (from medial to lateral: semimembranosus, semitendinosus and biceps femoris). The hamstrings are susceptible to injury. In quadrupe ...

, and

gluteal muscles The gluteal muscles, often called glutes are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus, gluteus medius and gluteus minimus. The three muscles originate from the ilium and sac ...

), to avoid muscular imbalances, which are associated with increased injury risk.

References

Weight training exercises {{sports-stub