Can leg extensions create knee pain ? Can it really be dangerous for the health of the anterior cruciate ligament ? Is the leg extension for rehabilitation useful? These and other similar doubts are often raised when discussing leg extension machinery in the fitness and bodybuilding environment. Over the years this exercise has certainly acquired a bad reputation in the environment (sometimes together with the Leg Curllying down), often listed as not very functional and risky for the knee. Where is the truth? How much is this reputation deserved and what is the result of superficial slogans? A quick analysis of the exercise and the application of an interesting mix of science and common sense will shed light once and for all, delivering practical information to be brought back to the gym tomorrow.
Leg Extension hurts your knee?
Briefly analyzing the forces acting during the Leg Extension, we easily notice that the ankle-level bearing anteriorly generates an anterior tibia translocation force (subluxation) to which only the anterior cruciate ligament (LCA) is opposed , which it will be put in tension and all stress will be absorbed (lack of co-contraction of the ischiocrural and the gastrocnemius in a not very functional exercise). In support of this not only simple biomechanical analyzes such as this but also scientific evidence (Lutz GE et al, 1993; Mesfar W et al, 1997; Jenkins WL et al, 2008).
In particular, going a bit ‘deeper by consulting some scientific studies of reference:
- during the Leg Extension the cutting forces exist and are different depending on the ROM. At 90 ° of flexion there is a rear cutting force. Between 0 ° and 45 ° of flexion there is a front cutting force with increased stress on the anterior crusader. Between 60 ° and 75 ° of flexion there is instead the lowest stress on the anterior crusader and therefore shear forces of a lower intensity (Grood, 1984; Wilk, 1996; Beynnon, 1997).
An important consideration to do now concerns the context in which the exercise is proposed. Who is performing them? A post-operated crusader, a subject with patellofemoral pain or a healthy boy? A neophyte or an advanced? From here you can start to broaden the mind and schematize all the possibilities that can be proposed in the field.
How to make the leg extension: healthy person
The so-called cutting forces that we have found existed during the Leg Extension are well neutralized by a healthy and integral anterior cruciate ligament in all its structure (useless terrorism: a knee dislocation or a patellar dislocation will never happen). Rather some little advice is useful to give it to insert this exercise (if you want to do it to give emphasis on the vast medial muscle) with more criterion.
- Proposing Leg Extension to a healthy neophyte seems questionable, not so much for the question of “knee health”, but for that “training”. The volume of work must be limited compared to an advanced one and the precedence in this case should therefore be given to exercises such as Squat and Affondi which go to give greater and more complete incentives to the new member.
- If you want to propose Leg Extension to an advanced one it will be better to do it either through high repetitions, or as a complementary exercise at the end of the routine, after more demanding and complex exercises from a motor point of view. In both cases the person will be forced not to load huge loads, reducing stress on the anterior crusader.
- It seems obvious, but the execution must be precise and controlled. Avoid making “dribbles” with the bearings by taking the momentum. If you want to do the Leg Extension do it well, controlling the movement and maybe even reducing the ROM, avoiding working in the last degrees of extension, the most stressful for the patella and the anterior crusader.
How to make the leg extension: a person with a knee problem
There are different considerations regarding the person with ligamentous injury (in conservative treatment, in pre-operative or in post-reconstruction of the crusader with graft), with patellofemoral pain (normally anterior to the knee), patellar tendinopathy or meniscal injury.
- For a person undergoing rehabilitation after ligament injury or reconstruction of the anterior crusader, an intelligent use of Leg Extension is recommended. If you decide to opt for this exercise (always under the guidance of a professional) better perform it at high repetitions in a controlled manner, in the right rehabilitation phase (not recommended in the immediate post-operative) and especially with a movement excursion reduced among the 90 ° and 40 ° of flexion (first half of the movement; Wilk, 1996; Fleming, 2001). Any choice to use a different ROM (0 ° – 30 °, second half of the movement) must always be well justified, with the right timing, the right loads and a rational behind. However, in these cases for muscle strengthening, closed kinetic chain exercises will always be preferred.
- For those with patellofemoral pain or patellar tendinopathy, if you decide to opt for Leg Extension (always under the guidance of a professional), the studies recommend to perform it with a movement excursion reduced between 90 ° and 40 ° of flexion (first half of the movement) to decrease patellar stress by increasing the patellofemoral contact zone (Steinkamp, 1993; Escamilla, 1998). In fact, as the knee extension increases (second half of the movement) the forces in play are discharged on an ever smaller contact surface of the patella, generating increased stress and evocation of the symptoms. Vice versa, with a greater knee flexion (first half of the movement) the forces are distributed in a larger area decreasing the patellar stress.
- For those with a broken meniscus it may make sense to decrease the excursion in the opposite direction. A 1998 Arnoczky study reports less movement and less meniscal stress in a range of motion ranging from 60 ° to 15 ° of knee flexion. In principle it could therefore make sense, always customizing and evaluating case by case, to reduce the executive ROM within this interval especially in those who have undergone meniscal suture surgery. As for post meniscectomy rehabilitation, there are no particular ROM restrictions, as the injured tissue was promptly removed.
Having said that, I always encourage the collaboration between different professionals in the gym. In cases of knee pain, direct confrontation between professionals is essential, avoiding bad spelling of one another and understanding the situation and acting accordingly for the good of the person. The choice of proposing the Leg Extension in any situation between the exercises for the vast medial must always be motivated and an adaptation in terms of excursion in sore knees must always be understood by everyone to avoid misunderstandings (it is essential to have clear objectives and manage correctly the workloads).
See Another Article: Squat: how to do it and when to insert it in training sessions.