Tip of the Month -- October 2006

Power Development

By. Andrew Wilson MS, CSCS, USAW

The desired combination of maximum speed and strength to produce movement is known as power (Chu, 1996). Power can be expressed as force multiplied by distance (work), divided by time (Newton & Kraemer, 1994). The rate at which power can be generated and applied is determined by several factors (slow and high velocity strength, rate of force development, intermuscular coordination and skill, stretch shortening cycle) in the development of explosive power (Newton & Kraemer, 1994).

Slow and high velocity strength training are two factors used to increase total power, but with different principles. Slow velocity strength is primarily used with heavy resistance strength training (Newton & Kraemer, 1994). An increase in maximal strength is achieved through the use of heavy resistance training and slow concentric muscle actions. High velocity strength is the exact opposite of slow velocity strength. High velocity strength involves decreasing the amount of resistance used and increasing the speed of the concentric muscle action. Improvements in strength are reduced at higher velocities, because the amount of resistance is no longer at the same magnitude with slow velocity training (Newton & Kraemer, 1994).

The slow and high velocity of strength application is directly linked to the rate of force development since a muscle must exert as much force in the shortest amount of time (Newton & Kraemer, 1994). Slow strength training is not considered a key factor in improving an athlete’s rate of force development. Since the movement is too slow in heavy resistance training a decrease in the muscle’s ability to develop force rapidly may occur. Since slow strength training only increases maximum strength this factor of training does not positively affect the rate of power development. On the contrary movements that do rely on high velocity actions with resistance of 30–60% of a 1 RM do increase the ability of rate of force development (Newton & Kraemer, 1994).

Since there is a high velocity component in power development, the intermuscular coordination and skill of an athlete is quite important (Yessir, 1994). The explosive action of the muscle requires a high level of stimulation of the nervous system to coordinate the movements for optimal firing of the muscles in a short time frame. When an explosive movement is performed the inertia from the movement carries it through its acceleration and deceleration phases, while requiring the involvement of several joint actions of the body (Yessir, 1994). Within the several joint actions of the body during an explosive movement lies the ability of the muscle to utilize intrinsic properties of elasticity (Chu, 1998).        

The potential for a muscle to generate power comes from the muscle’s property of elasticity. The property of elasticity gives a muscle the ability to return to normal resting length after an external force has distended the muscle (Chu, 1998). When a muscle is stretched eccentrically (negative phase), the muscle begins to store elastic energy within its elastic components. Once the muscle has reached a desired level of stretch, the muscle must rapidly contract concentrically (positive phase) in order to utilize the stored energy so the energy will not be lost as heat. The process of moving from an eccentric contraction to a concentric contraction is also known as the stretch shortening cycle (SSC). The ability of a muscle to store and utilize elastic energy depends on the speed of the stretch, length of the stretch, force at the end of the stretch, and length of time the stretch is held.

Force is a direct application of power because production will increase, as the resistance increases, but the speed of the movement will subsequently decrease (Stone et al., 2003). Peak power is produced during a movement when both force and velocity are at optimum levels, but not necessarily at peak levels. The highest values of peak power recorded are at 30% of peak isometric force during isolated movements and at about 30-60% of the 1 RM (Newton & Kraemer, 1994). Consequently different levels of force production are affected by the amount of resistance and speed of the movement.

In conclusion there are several factors that affect the development of power.  The use of resistance training and plyometrics are two methods strength coaches use to increase power output in athletes.  Different training protocols will develop power in different ways, but all are successful approaches as long as the goal to increase power production is achieved. 

References

Chu, D. A., (1996). Explosive power and strength. Champaign, IL: Human Kinetics.

Chu, D. A., (1998). Jumping into plyometrics. Champaign, IL: Human Kinetics.

Newton, R. U., & Kraemer, W. J. (1994). Developing explosive muscular power: implications for mixed methods training strategy. Journal of Strength and Conditioning, 16(5), 20-31.