12th Oct, 2018
Buali Sina University
Question
Asked 25th May, 2018
Are Leg Extension Exercises Beneficial or Dangerous?
Some articles claim that the leg extension exercise is harmful for knee, because this exercise can damage ACL and stretch it.
and so....
Most recent answer
Dear Mostafa,
Prior to any response to your question, I should state three most important things:
First, each movement at different articulation will be produced with some amount of co-contraction. This process is the foremost technique that the human body utilizes to stabilize the joint during different movement. This means that we have co-contraction even within the leg extension exercise.
Second, the improvement in the co-contraction during two different movements should not be deduced as the safety accretion. It is important to note that co-contraction enhancement can be obtained when the increment in joint load appeared. Increasing the amount of load more than the safety factors of human knee articulation or applying the normal amount of force in excessive direction can cause injuries of knee structures including the ligament and meniscus although the amount of co-contraction will arouse.
And third, the probability of vulnerability to injury is high during movement like deep squat as well. As it is presented in previous literature, most prevalent injuries within the weightlifters appear at the knee articulation (most of the professional weightlifters never exploiting the knee extension movement and their training time highly consist of deep squad exercise)
Finally, the probability of the leg extension exercise injuries are dependent to the amount of load put on the joint, the amount of extension the athletes use, the speed of the movement, and most importantly the position of the fulcrum during this exercise.
If the movement performs without the rotation, prohibiting of the joint from being locked (close pack position), and lower amount of load, the vulnerability of the knee articulation to the ACL rupture will be attenuated. However, improving the load on the knee articulation during this type of exercise proliferate the vulnerability to ACL rupture exponentially as a result of sheer force improvement in the knee articulation. However, using the deep squat and normal inclined leg press can be dangerous for amateur athletes as well.
Therefore, it has been suggested that the amateur trainers should use the seated level leg press machines or the leg extension with lower loads and higher repetitions (specifically lower than 50 percent of the 1RM).
Best regards
Alighanbari
All Answers (6)
The knee is locked in full extension leading to no more of it possible normally . It is hyperextension that is proposed as one of the mechanism of ACL injury apart from sudden deceleration and pivoting.
Hyperextension in my view is less common than other mechanisms of injuries to ACL but may be a feature in the settings of abnormal morphology of knee.
Besides it only partial rupture is usually possible as one of the two described part of the ACL is tight in extension while the other one is relaxed.
1 Recommendation
It is a very interested question . I agree with Ganesh answer
Also these links may help yoy
2 Recommendations
Hyperextension is dangerous and is a part of ACL trauma mechanism. Extension exercises in the frame of normal ROM are not harmful.
Thank you for your answers
In my opinion the best and safe exercise for knee is close kinetic chain movements because quad and hamstring are active at same time and co-contraction of these muscles help knee stability.
furthermore, it harms the quad to hamstring strength ratio
and
it s not natural to load the knee while the foot travels through space with open chain movement.
Leg extension also maximize shearing force on knee and patella.
It is known that part of the ACL is getting tight at the extension position as it is locking. It is known that the mechanism of ACL rupture is the combined movement of extension and rotation. All is explained in the nicest way above.
Dear Mostafa,
Prior to any response to your question, I should state three most important things:
First, each movement at different articulation will be produced with some amount of co-contraction. This process is the foremost technique that the human body utilizes to stabilize the joint during different movement. This means that we have co-contraction even within the leg extension exercise.
Second, the improvement in the co-contraction during two different movements should not be deduced as the safety accretion. It is important to note that co-contraction enhancement can be obtained when the increment in joint load appeared. Increasing the amount of load more than the safety factors of human knee articulation or applying the normal amount of force in excessive direction can cause injuries of knee structures including the ligament and meniscus although the amount of co-contraction will arouse.
And third, the probability of vulnerability to injury is high during movement like deep squat as well. As it is presented in previous literature, most prevalent injuries within the weightlifters appear at the knee articulation (most of the professional weightlifters never exploiting the knee extension movement and their training time highly consist of deep squad exercise)
Finally, the probability of the leg extension exercise injuries are dependent to the amount of load put on the joint, the amount of extension the athletes use, the speed of the movement, and most importantly the position of the fulcrum during this exercise.
If the movement performs without the rotation, prohibiting of the joint from being locked (close pack position), and lower amount of load, the vulnerability of the knee articulation to the ACL rupture will be attenuated. However, improving the load on the knee articulation during this type of exercise proliferate the vulnerability to ACL rupture exponentially as a result of sheer force improvement in the knee articulation. However, using the deep squat and normal inclined leg press can be dangerous for amateur athletes as well.
Therefore, it has been suggested that the amateur trainers should use the seated level leg press machines or the leg extension with lower loads and higher repetitions (specifically lower than 50 percent of the 1RM).
Best regards
Alighanbari
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