Gym biomechanics: how to build muscle using the principle of leverage

If you train with a barbell and dumbbells, then you have probably heard the basic rules and tips: "When doing deadlifts, you need to keep the barbell close to your feet", "If you take your pelvis back in a squat, the buttocks are loaded more" or "Press the bar with a narrow grip shifts the emphasis on the triceps ".

And these rules really work. But why does this happen and how to shift the load in lesser-known exercises? The simplest mechanism - a lever - will help to understand this.

How the principle of leverage is implemented in our body

A lever is a body that can rotate around a fixed support. It helps you lift more weight with less effort. It has a fulcrum and an axis of rotation. There is a force that is applied to its end, and the shoulder of the force is the shortest distance from the axis of rotation to the point of application of the force.

Torque = force × force shoulder

And the longer the shoulder, the more torque.

All of our joints work on the principle of a lever. Muscles are attached to bones with the help of tendons, contract and pull them, making movement. For example, two heads of the biceps, the biceps brachii, are attached to the radius. When you flex your arm, the biceps contract (force) and create torque at the elbow joint (pivot). The thicker your biceps, the more torque increases. And this is understandable: a pumped-up athlete will lift more than a thin girl.

The principle of leverage in the work of the biceps of the shoulder

At the same time, the shoulder of force is also important - the distance from the point of rotation to the place of application of the force. Therefore, the greater the distance from the joint to the point of attachment of the tendon, the stronger the person. However, these are physiological features of the structure that cannot be changed. And the differences between people in this regard are not so great.

Another thing is the shoulder to the point of application of the opposing force, for example, a kettlebell, barbell, or your own body weight. Let's take the same example with the elbow flexion, just add a dumbbell for clarity.

Shoulder strength from dumbbell to elbow

When you bend your arm, the axis of rotation is at the elbow joint (green dot). The point of application of the force is a dumbbell that pulls the arm downward under the influence of gravity (red dot). And the shoulder of force is the perpendicular from the elbow to the axis along which the dumbbell runs (green line).

When you lower your arm, the shoulder strength decreases, and with it the load on the biceps. The shoulder strength is maximum when the forearm is parallel to the floor, which means that at this point the load on the muscles is the strongest.

How to apply the principle of leverage in the gym

By evaluating your shoulder strength from the bar or dumbbell to the joint, you will always know how to flex your limbs or core to maximize the load on the desired muscles and prevent overload if it is undesirable.

Find out at which point in the exercise the muscle load is greatest

The longer the strength shoulder, the more load the muscle receives. So, in lifting a dumbbell for biceps, the shoulder of strength increases as you raise your arm, and reaches its maximum length when the arm is bent at the elbow at an angle of 90 °. Further, the load begins to decrease again until it reaches a minimum at the top point.

Let's take another exercise: a narrow grip bench press. Here, the load on the triceps will be maximum at the bottom and minimum at the top.

But in the bench press with a regular grip, on the contrary, shoulder strength and load decrease at the bottom point when the wrist is above the elbow, and at the top it rises.

In the deadlift, the load is also maximum at the bottom point, because the shoulder of force from the hips to the bar is the longest. By the way, that's why you need to keep the bar close to your feet and lead it up, almost touching your shins: this way you reduce the shoulder of strength to the hip joint and reduce the load, which can be critical when lifting a lot of weight.

Take hyperextension. The shoulder of force to the hip joint is maximum when the body is parallel to the floor. In an attempt to increase the stress on the back and buttocks, people pick up a pancake or place it on their back. However, it will be much more effective to keep it pressed to the head: in this case, the shoulder strength from the weight to the hip joint will be greater, which means that you will get the same effect with less weight.

By determining at which point the muscles are straining more, you will regulate the load. For example, you can slow down the movement at the point of maximum load and accelerate where the shoulder force and load are minimal.

In addition, you will not shorten the range of motion where it could affect the effectiveness of the exercise. For example, doing biceps curls from parallel and higher, or throwing a barbell after the deadlift, instead of smoothly passing both the lift and lower.

Shift the focus to the right muscles in different exercises

Let's take a look at the barbell squat. There are several types of this exercise: with a barbell on the back, on the chest, on the Smith machine. Let's look at all of these positions in terms of leverage.

When you squat with a barbell on your back, the shoulder strength to the hip is greater than the shoulder strength to the knee. That is, the quadriceps, the knee flexor, in this case does less work than in the version with a barbell on the chest. This is confirmed by a study using electromyography.

Moreover, the back squat increases the shoulder of force from the equipment to the lower back, so that the lumbar spine is more stressed than the chest squat. And, the stronger the forward lean, the higher the load and the greater the risk of injury.

Now let's look at Smith Machine Squats.

The shoulder of strength to the knee is simply huge, but to the pelvis it is almost nonexistent. Here the gluteal muscles do not swing in any way, only the quadriceps. This, of course, increases the load on the knees. It turns out that this exercise is great for pumping quads, but for the buttocks it is useless.

Many girls in the gym like to do dumbbell lunges to work their hips and buttocks. I must say that this is not the best way to pump the ass: there is an exercise that is much more effective. But even in them, you can increase the load on the buttocks.

Let's look at the shoulders of strength. If you lunge with a straight body, the shoulder of force from the point of application of the force to the knee joint is maximal, and to the buttocks is minimal. Therefore, all the load goes to the quadriceps. Indeed, research shows that lunges pump all quadriceps heads well.

If you want to load your glutes more, you need to increase your shoulder strength from the barbell or dumbbells to the hip joint - just tilt the body forward.

Let's take some upper body exercises now. For example, a standing press. Often, during its execution, they circle the head, fearing of touching the chin. I touched in the jerk and it is very unpleasant. Therefore, some people wrap their heads around the sports equipment, but this increases the load and does not allow you to take more weight.

Let's look at the trajectory of the bar: if it runs in a straight line, the shoulder of force is minimal, if it goes around the head, it increases and it is much more difficult to keep it.

Bench press from the chest while standing

Thus, you can adjust the load by assessing the distance from the joint to the point of application of the force, and shift it to the desired muscle groups.