The issue of the safety of the leg Extension exercise is a very hot topic and one that will surely raise some discussion – however here is a simple summary of the issues with this exercise.
1. Shearing Forces
In the majority of ground based leg exercises – such as squats and lunges – the resistance to movement runs through the knee joint – basically compressing and stabilizing the knee itself. However – in an exercise such as the Leg Extension the resistance is at 90 degrees to the shin – as this is where you are pushing against to raise the shin pad.
The resistance is at 90 degrees to the long axis of the bone (the tibia) – which has the effect of producing shearing forces across the knee – compared to a squat where the resistance runs along the long axis of the bone.
2. No Co-contraction:
In conventional squats and lunge type movements there is contraction of the quadriceps ( to extend the knee) at the same time as there is contraction of the hamstring group ( to extend the hip ) – this is termed co-contraction.
In the Leg Extension exercise there is contraction of the quads with limited hamstring involvement – again promoting shearing forces across the knee and reducing muscle involvement.
3. Functional Transfer:
The actual motion of the Leg Extension exercise produces limited functional carry over to real life sports and daily tasks – compared to squatting and lunging movements that are common patterns in everyday life.
4. Reduced Muscle Involvement:
The majority of PT clients are time poor and are better off doing an exercise involving a large number of muscle groups compared to smaller isolated groups – simply from a time management and results perspective.
That being said – I think the actual risks of doing the leg extension exercise are somewhat exaggerated however it comes down to time efficiency and getting your client the best results in the shortest possible time.
For a full analysis of the Leg Extension and knee rehabilitation in general I suggest you check out my “Knee Injury Prevention and Rehabilitation for Health Professionals” which can be previewed at:
You can get full acces to the full presentation and more than 50 hours of other exercise rehabilitation and injury prevention videos at www.PhysioProfessor.com