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Fundamentals of Power Development

This is an excerpt from Developing Power-2nd Edition by NSCA -National Strength & Conditioning Association.

The ability to generate high power outputs is facilitated by the ability to generate high levels of force rapidly and express high contraction velocities (74). Examination of the relationship between force and velocity reveals that they are inversely related, as indicated by the force–velocity curve (figure 3.12). See chapter 1 for additional detail regarding the fundamentals of power development.

When examining the force–velocity curve, it is apparent that as the velocity of movement increases, the force that the muscle can produce during the concentric contraction will decrease. Because of the relationship between force and velocity, it is clear that the expression of maximal power outputs occurs at compromised levels of maximal force and velocity (figure 3.13).

When targeting the optimization of power output in a training program, three key elements should be considered. First, maximal strength must be increased, because it has a direct relationship with the ability to express high rates of force development and power output (2, 4, 20, 50, 85, 91, 126, 145). Second, a high rate of force development (RFD) must be achieved; this is the ability to express high forces in short periods of time and is central to the ability to express high power outputs (20, 52, 53, 88, 148), because impulse (force × time) relative to the object’s mass determines velocity (see chapter 1). Finally, it is important to develop the ability to express high forces as the velocity of shortening increases (50). The interplay among these elements is strong, and the athlete’s overall strength serves as the main factor dictating the ability to express higher power outputs (50, 74). Within the scientific literature is evidence of the interrelationship between maximal strength, RFD, and the ability to express maximal power output (45, 52). Based on these interactions, any periodized training plan designed to optimize power must consider the development of each of these key interrelated attributes.

Maximal Strength and Power

As noted previously, one of the foundational elements in the development of power is the athlete’s maximal strength (4, 50, 91, 126, 145). Clearly, stronger athletes demonstrate a greater potential to develop higher power outputs and often express higher power outputs when compared to their weaker counterparts (4, 118, 126). Haff and Nimphius (50) suggest that stronger people are able to generate higher forces at a higher rate when compared to weaker people (3, 4, 19, 79). Support for this contention can be seen in the research literature, which reports that weaker athletes who undertake resistance training targeting the development of maximal strength experience significant increases in muscular power (4, 19), which translates into improvements in athletic performance (19, 118). Once athletes have established adequate strength levels, they are then able to better capitalize on the benefits of specific power development exercises, such as plyometrics, ballistic exercises, complexes, or contrast training methods (50). In fact, stronger athletes exhibit a greater overall responsiveness to power-based training methods (19, 50).
Based on the literature, it is clear that maximization of strength levels is a prerequisite for the development of higher power outputs. However, it is often difficult to determine what an adequate level of strength is for a given athlete or group of athletes. Based on the contemporary body of knowledge, athletes who can squat more than 2.0 × body mass express higher power outputs than their weaker counterparts (1.7 or 1.4 × body mass) (7, 118). Research suggests that athletes between the ages of 16 and 19 years who compete in strength and power sports or team sports should be able to back squat a minimum of 2.0 × body mass (75). Additionally, when using strength–power potentiation complexes or plyometric exercises, it appears that athletes who are able to squat double their body weight are able to optimize the effectiveness of these exercises (108, 109, 128). Maximal lower body strength is also related to the degree of difficulty or intensity of plyometric exercises that maximize performance adaptations, with a minimum back squat of 2.0 × body mass being a prerequisite for maximizing the benefits of higher-level plyometrics, such as depth and drop jumps performed from moderate to high heights (i.e., more than 30 cm [11.8 in]). Based on this literature, Haff and Nimphius (50) suggest that a minimum back squat of 2.0 × body mass is a requirement for undertaking specialized training to optimize lower body power output. Specifically, higher-level plyometric activities, such as depth and drop jumps and loaded ballistic exercises (e.g., squat jump with 40% of the 1-repetition maximum [1RM]), should be reserved for athletes who can back squat a minimum of 2.0 × body mass, because this level of strength allows the athlete to better tolerate these activities and achieve greater training benefits (127, 128). Importantly, this does not mean that athletes who back squat less than 2.0 × body mass should not perform plyometric training. Weaker athletes should perform lower-level plyometric activities (e.g., pogo jumps, repeated countermovement jumps, and hops) as part of their training program, but they should only engage in higher-level plyometrics once their 1RM back squat is a minimum of 2.0 × body mass (128).
Maximal strength levels also seem to be an important prerequisite for the development of higher upper body power outputs (24), with stronger athletes being able to display significantly higher power outputs (4). While high levels of strength are an important factor underpinning the ability to express higher upper body power outputs, there is currently no consensus in the contemporary body of knowledge on the minimal level of upper body strength required when seeking to maximize upper body power development (126). There is, however, an emerging body of evidence suggesting that a bench press of at least 1.35 × body mass may be a minimum requirement for undertaking upper body strength–power potentiation complexes or plyometric exercises (21, 110). As such, until further research is conducted examining the effect of upper body strength on power development, a minimum bench press of at least 1.35 × body mass may be a minimum requirement for specialized training to optimize upper body power output.

Rate of Force Development

The rate at which force is expressed during sporting movement is often referred to as the RFD, or explosive muscular strength (1, 85). In its most simplistic form, the RFD is determined from the slope of an isometric force–time curve (39, 50, 142) (figure 3.14). One can calculate the RFD in a variety of ways, including the peak value in a predetermined sampling window and in specific time bands, such as the slope of 0 to 200 m/s (39, 51). Typically, contraction times of 50 to 250 m/s are associated with jumping, sprinting, and change-of-direction movements. With short contraction times, it is unlikely that maximal forces can be developed, and it has been reported that it may take more than 300 m/s to generate maximal forces (1, 129, 131). With this in mind, several authors recommend ballistic exercises performed with light loads as a method to optimize RFD, and subsequently, the overall power output (20, 50, 53).

When examining the scientific literature, it is clear that performing resistance training exercises with heavy loads results in an increase in maximal strength (20, 101, 125) and RFD in weaker or untrained people (84). While training with heavy loads increases most athletes’ strength reserve and can positively affect their RFD, it is likely that explosive or ballistic exercises may be necessary to optimize the RFD in stronger, more experienced athletes (20, 50, 53). Based on this phenomenon, Haff and Nimphius (50) suggest that varying the training foci has the potential to affect various parts of the force–time curve (figure 3.15) and force–velocity curve (figure 3.16).

Heavy resistance training and explosive or ballistic resistance training have the potential to increase an untrained athlete’s maximal strength and RFD (figure 3.15). Conversely, ballistic training does not increase maximal strength but results in a greater increase in the RFD when compared to heavy resistance training in stronger athletes. When examining the force–velocity relationship, it is clear that heavy resistance training results in increases in the velocity of movement at the high-force end of the force–velocity curve (figure 3.16b), while ballistic movements result in increases in the velocity of movement at the low-force end of the force–velocity curve (figure 3.16c). It is clear that mixed methods that target high-velocity and high-force movements are necessary to exert a more global effect on the force–velocity relationship (figure 3.16a and d) and ultimately increase RFD and power output (50).

More Excerpts From Developing Power 2nd Edition

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