What is moment arm

This, over time, will encourage the quadriceps to become stronger and the gluteals to develop only a little. Unfortunately it will teach the person to squat with their thighs and not use their gluteals in a normal way. It will eventually bias the movement pattern and over time could cause knee injury or low back problems.

You can also see the line of force is on the heels and not the mid-foot. This is not a natural position. Although the torso is in good posture here, you usually see a flat back in the clubs. Also, the bar is stopping the person moving forward as they can hang on to it, so there is little requirement for the trunk extensors to be active.

Very few stabilisers will be used as the exercise has eliminated most natural sagittal plane requirements due to the fixed bar and virtually all front and transverse plane requirements. If a person were to fail on this exercise it would be around the lumbar for stability. None of this seems reasonable when you understand the biomechanics. The best way to help clients build up to free weight squatting is through teaching bodyweight squats with a range of movement that suits each individual client.

One final point. When you do this squat the further you put your feet out the more the knee extensors quadriceps become active and the less the hip extensors gluteals do.

As this occurs a force vector that creates knee shearing develops and increases such that if used over time the knee joint is almost guaranteed to get injured.

The line of force is marked going down through the centre of mass in blue. The base of support is a long way from the line of force and the centre of mass will be around the very top of the thighs. The knee moment arm is in green — basically this exercise is all quadriceps, and very little gluteals if any given there is virtually no moment arm for them to act around.

Because of the moment arm of the quadriceps and because the person must constantly push backward to keep the ball on the wall, there is constant shearing force at the knee joint.

In order to cope with the quadriceps activity the inner unit of the knee will be constantly challenged the inner unit includes the cruciate ligaments, lateral and collateral ligaments, and hamstrings. The torso is dormant as it is resting on the ball if anything only the erector spinae may be active to hold the torso on the ball , and the gluteals are dormant as they have no way of contributing to the exercise.

Even though the hip moment arm is longer, most likely this high-bar back squat will work the quads and the glutes fairly equally , given the differential in muscle strength of the two groups. Why do front squats emphasize the quads more than the glutes? A cursory glance at this diagram makes it clear. The moment arm to the knee is equal to that of the hip and certainly longer than in the high-bar back squat position , requiring more force output from the knee joint, and consequently, making the quads work harder to extend the knee.

What about a low -bar back squat? This is when the bar is pulled down over the scapulae rather than resting on the upper traps. Pulling the bar down lower forces the torso to lean forward more, changing the force placed on the hips and knees to demand more of the glutes and lower back.

I can tell you, I have recently switched out my low-bar back squat for a front squat to save my lower back which is congenitally dysfunctional. It has helped me tremendously, in that, my back is less stressed, my quads are more stressed they needed it! Squats are a movement where moment arms are easily visualized and understood. So are bicep curls, leg extensions and shoulder raises. The bar on the hip, for instance, is only one force. So are the floor and the bench your upper body is resting on.

As I mentioned, changing from the back squat to the front squat personally helped me spare my lumbar spine while still challenging my quads and satisfy my desire to lift heavy things. Torque is by no means a bad thing in and of itself, but it is a variable we need to think about! This is why lifters tend to miss lifts when the bar drifts away from them. This is also why many elite level powerlifters have lifted with rounded upper backs it shortens the moment arm. The moment arm joint relationship is illustrated in the image of the 1st pull in a clean below:.

In the squat, the moment arms are slightly different because the bar is no longer in front of both the knees and the hips, rather it sits between them, this splits the single arm into two related arms. Folks that say this may be well meaning, but they are not necessarily correct. The torques produced at the hips and the knees have a relationship the ankles are involved too, but to keep it simpler we will focus on just hips and knees for now. Sign in via your Institution.

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