This is an excerpt from Velocity-Based Training by Nunzio Signore & Nunzio Signore.
Intention to move a barbell or the body as fast as possible is one of the most important factors for increasing strength and power, and it relies on neural adaptations to achieve this. The increase in neural drive allows the athlete to feel what true explosiveness is all about. It not only requires a great application of force during the concentric portion but also involves selecting the correct exercise to maximize the type of concentric contraction needed. First, let’s briefly focus on what a concentric contraction actually is.
A concentric contraction uses energy and will result in acceleration of an object. When a muscle is activated and required to lift a load that is less than the maximum tension it can generate, the muscle begins to shorten. This is referred to as a concentric contraction. Two good examples of concentric contractions are raising the weight during a biceps curl (see figure 2.3a) and coming out of the bottom of a bench press (see figure 2.3b).
However, the speed at which we perform these concentric movements distinguishes whether we are focusing more on strength or power. To increase power, we must train both force (strength) and velocity (the ability to apply this strength). This requires using heavier loads (force) and lighter loads (velocity). During the concentric portion of a movement, the body as a protected device, must reduce the velocity and force of the concentric portion of the rep to guard against jerking the tendons or creating undue stress on the joint when coming to an abrupt stop at the end range of motion. On the other hand, when training the force side of the power equation, there is little deceleration because we are using loads greater than 60 percent of 1RM. Due to the heavier load and slower speed, there is no need for a longer range of deceleration. However, when training with loads less than 60 percent, a larger portion of this concentric portion must be used to decelerate the movement in order to protect the body as mentioned. Therefore, to most efficiently train the velocity side of the equation, athletes use ballistic exercises such as jumps and throws. Because the body is being thrown into the air, it does not need to decelerate the load. As a result, higher velocities can be attained because there is no deceleration.