Deceleration during acceleration in the weight room?

Although often forgotten the mechanical profile of an exercise and its variations can be decisive to strength/power development.

First of all, it should be clarified that there is no difference between strength training or power training. We should not infer that, for example, power training is associated always with low loads and high speed. Power is defined as the rate of doing work, or more commonly as the product of Force and Velocity. It is true that greater displacement velocity during a certain movement under the same load will result in higher power outputs – the main goal of training for the majority of sports. However, under a certain load, more velocity is dependent on more force application. If someone becomes faster under the same load, it means he applied more force during that movement.

When doing “power training”, or using a more adequate term, low load/high velocity training, athletes and professionals should be aware of kinetics/kinematics of that particular exercise. If this aspect is not taken into account, the final result could be below the expectations for that program.

In a particular movement, we can identify 2 main components during a concentric action: acceleration phase and deceleration phase. When learning Physiology and Biomechanics 101, we learn that concentric actions will result in acceleration of an object, and eccentric actions in deceleration of an object. While this is true, during some concentric actions, especially during explosive actions under low loads, we can also have a deceleration phase, sometimes up to more than 50% of the entire range! This means that during an exercise such as bench press, which is the main exercise to develop upper body push strength, someone can in fact spend more time pulling the bar towards the chest than pushing the bar towards the ceiling. It also means that during the bench press, someone could be only pushing during the first half of the exercise. On the other hand, most sports where upper body actions are important, require more capacity during the second half of the movement. So this raises a fair question: is our training matching our goals?

During explosive actions using low loads, we can get a long deceleration phase, sometimes up to 50% or more of the total ROM.

Using again the bench press as an example, since it is one of the easiest to understand – however this also applies to other exercises with the same characteristics -, the deceleration phase has an inverted correlation with the amount of load during that particular movement: less load equals to greater deceleration, and vice versa. In fact, loads over 70/75% RM should involve minimal to zero deceleration. While this is true, these higher loads also mean lower velocities, which result in lower power outputs. So, if the goal is to maximize power output or movement velocity, on one hand we should avoid low load/high velocity bench press since it involves a marked deceleration phase, but on the other hand, high load/low velocity bench press, although it avoids the deceleration problem, the speed is simply too low to result in high power outputs. So what should we do when our goal is to maximize power output?

Fabio Bench
By using a load equivalent to ~55%RM, we observed that the acceleration or propulsive portion of the lift (the most important during the lift) was only 49% of the total ROM. Is our training matching our goals?

The answer to this question relies on modifying the inherent mechanics of an exercise, or changing the exercise itself. We can solve the problematic of the deceleration phase while keeping high power outputs by changing the movement profile to full acceleration, and I am going to highlight and analyze 2 different ways of doing it for the sake of this article: throw/release of implements and accommodating resistance.

▪️Throw/release of implements:
Probably the most effective way of achieving full acceleration during a concentric action under low/medium loads while using high velocities. By throwing an object, like a medball, a barbell or something similar, or throw a punch against a heavy bag, we eliminate the deceleration phase. In this case, there’s no need to decelerate the movement to avoid joint, tendon or muscle injury, like it happens during a low load/high velocity bench press. Apart from medball throwing, the Bench Throw is one of the most effective exercises, allowing us for reliable power quantification using devices such as LPTs (linear position transducers). The only drawback is that we need to use a Smith machine to execute this movement (I strongly recommend the use of a Smith machine for safety reasons, but some people still do it with a barbell), but the vast majority of weight rooms have this equipment, so it should not represent a problem at all.

We can also include in this category some upper body plyometric calisthenics, such as plyometric push ups. Instead of throwing/releasing an external implement, the implement in this case will be bodyweight itself.

Fabio bench throw
Using a full acceleration (i.e., absent deceleration phase) exercise, we get the biggest benefit from training with high speed/low load exercises.

▪️Accommodating resistance:
This is accomplished by altering the mechanical profile of a particular exercise. We can do that by using bands, chains, or other devices like pneumatic/air resistance. That reinforces the need to extend the acceleration phase of the bar, minimizing deceleration. In the particular example of using bands in order to accommodate resistance, the more stretched the band is, the more resistance it will offer. This will result in the need of keeping acceleration towards the end of the concentric action, in order to overcome the resistance.

Fabio bench band
By adding a band that can give us around extra 10kg by the end of the concentric phase (lockout), we changed the mechanical profile of the exercise, resulting in shorter deceleration phase. (21% against 51% seen during the traditional bench press, as shown before)

Using a LPT, we did a basic experiment to demonstrate the several aspects presented during this article – you can check it in the previous graphs.

I should say that I don’t think it’s wrong to do things like speed squat or speed bench press using low loads/high velocities. However, and given what was exposed during this article, there are other ways that can be potentially more effective and more specific to fit the needs of our goals.

It’s not necessarily wrong to do speed squats or speed bench presses using low loads. However, we should be aware that probably there are other strategies that can be more effective.

Rule of thumb:
✅ Intention to move the barbell as fast as possible is one of the most important factors to increase strength and power due to neural factors;
✅ When aiming for anatomical adaptations and skill acquisition, moderate to low speeds of movement are desired, so low loads can be used during structural exercises without worrying about deceleration;
❌ If we try to move a light barbell during a structural/core exercise such as squat or bench press, we will get a long deceleration phase, which is not ideal;
✅ Introducing full acceleration exercises such as throws, jumps, or using accommodating resistance can be effective for strength/power development under high speed/low load.

Luís Mesquita

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