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How fast are you performing your concentric, (positive) and eccentric (negative) motions during a particular exercise? Do you emphasize slow negatives, and forceful positive muscle contractions while lifting weights?
Regarding weight training for general power you should perform exactly that; slow negatives and forceful positive motions to maximize the effect of each repetition for increased power.

The most important factor prior to doing this is that the movement is done correctly, and the athlete maintains a Five Point Contact position, when appropriate with correct mechanics of the lift being performed. So, practicing the lift with good form should be a prerequisite. Once the athlete has the form mastered, then they may incorporate this technique.

Concentric contractions are when the muscle fibers shorten by either pushing or pulling weight against gravity, where the external forces act in the opposite direction of the motion. Eccentric contractions are when the muscle lengthens under tension, where external forces act in the same direction as the motion, lowering weight in the same direction of gravity.

There are several good reasons to perform slow negatives, typically 5-8 seconds in duration. Slow negatives help control the exercise being done by minimizing any unnecessary swinging or movement through good eccentric control. Slow negatives place less stress on the joints and prevent ballistic movements (bouncing), and muscles can handle higher weight loads during the eccentric contraction. For example, if an athlete were to perform the bench press at 225 lbs until muscle failure, the point to where they could no longer press the barbell back to the starting point. They would still be able to perform several negative repetitions, or lowering of the weight with control. Of course the athlete would need a spotter to help bring the weight back to starting position.

Performing fast positive motions innervates more type II muscle fibers, and increases the power output of the muscles involved. This allows for near maximal contractions in the muscles involved in the lift. I usually prefer to call the positives, forceful movements rather than fast, because as the athlete moves on to heavier weights for lower repetitions in the 6-10 range, the positive motions will not actually be fast. Although the effort is at maximal exertion, the weight may not move so rapidly causing the force capability of the muscle to decline, and with an increased speed of contraction, the muscle power increases.

Force production is reciprocally related to velocity of muscle fiber shortening during concentric contractions. During faster movements less force production is possible, and when lifting heavier loads, the slower the speed of movement becomes, even though the weight is being pulled or pushed as forcefully as possible. This phenomenon is different in the eccentric action. As the velocity of eccentric contractions increases, the force production increases in the muscle. Studies have shown that the eccentric force capabilities are 120% to 160% greater than compared to concentric contractions. Studies have also found that when only concentric actions were performed, twice the amount of work had to be performed to get the same effects when eccentric actions were included. Therefore when overloading muscles eccentrically an athlete would require a greater weight load than in a concentric action.

As a note, strength should not be associated with low speeds and power with high speeds. Strength is the maximal capacity that a given muscle group can exert force at any given speed or velocity, and power is the product of force and velocity at whatever the speed, or time rate of doing work. Force is defined as the difference between strength and power at given speeds, or it can be defined as an instantaneous measure of the interaction between two bodies. Force is characterized by magnitude, direction, and point of application.

This is not a replacement for power lifting, but this type of training is a good method of increasing overall power, by just adjusting the speed in which you perform exercises that you may already do. Power lifting may not always be an option for an athlete, due to space and equipment limitations. Prior to attempting any explosive power lifting or Olympic stlye lifts, one should be supervised by a strength and conditioning coach to learn proper power lifting techniques.

Jon Torerk, CSCS