Measurement of Power

The following is an exclusive excerpt from the book Developing Power, published by Human Kinetics. All text and images provided by Human Kinetics.

Much of the strength and conditioning research measuring system power has focused on the Ppeak and Pmean produced during a variety of discrete movements (e.g., squat, jump squat, bench press throw) (22) instead of continuous movements such as cycling or rowing, where power output is measured over repeated efforts. A criticism of using and calculating power only during these discrete movements is that the value does not explain or predict actual performance (22). However, what may be of interest to many practitioners is the change in Ppeak or Pmean, which can reflect adaptations to training when interpreted in conjunction with other variables, such as force or velocity or performance variables such as jump height. The curve produced during a common ballistic movement, a countermovement jump, is shown in figure 2.1.

Figure 2.1 provides the information needed to understand the relationship between commonly measured variables (displacement, velocity, and force) and their relationship to the derived variable of power. To understand how the figure relates to aspects of the jump, consider the displacement curve (figure 2.1) and imagine this curve represents an athlete standing, lowering, jumping to maximum height, landing (then absorbing), and returning to standing height. With this understanding of the phases of the jump relative to the displacement curve, it will be easier to consider the eccentric versus concentric jump phase with respect to power, or any other variable. Further, this particular athlete has two peaks of the force curve (figure 2.1) before take-off. The first peak represents the force exerted to brake the lowering of the body during the countermovement, while the second peak represents the maximal dynamic strength where the athlete summates the forces of the hip, knee, and ankle during the concentric phase of the jump. Such an understanding can be applied to loaded ballistic jumps as well as bench press throws that include a countermovement.

Eccentric and Concentric Phase

The phases of the jump are often described as the portion of the jump with negative change of displacement or positive change of displacement (6). The eccentric phase of the jump (countermovement) has a negative Ppeak and Pmean and commences when the force begins to decrease (figure 2.1). It ends when velocity goes from negative to positive (crosses zero). Simultaneously, this indicates the start of the concentric phase that subsequently ends at takeoff or when force is zero (19).

To derive the power curve shown in figure 2.1, one multiplies the force and velocity data for each sample. The power curve has been isolated in figure 2.1b, where the portions of the power curve that are used to calculate the mean concentric and mean eccentric power values are labeled. The actual calculation of power is relatively simple when velocity and force are directly measured; however, as will be discussed, many methods of measurement can be used to derive the power curve, each with its own advantages and disadvantages.

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