This is an excerpt from Developing Power by NSCA -National Strength & Conditioning Association & Mike McGuigan.
In simple terms, what differentiates exercises that develop strength from exercises that develop power is whether the performance of the exercise entails acceleration of a load throughout the majority of the ROM; this results in faster movement speeds and thus higher power outputs. Power exercises are characterized by high-velocity movements that accelerate the athlete's body or an object throughout the ROM with a limited braking phase and little, if any, slowing of contractile velocity. A comprehension of full acceleration and movement speed is important within the paradigm of power training because athletes are often instructed to move a load as fast as possible, often using lighter relative loads in order to be powerful. However, the problem with conventional resistance training techniques is that even when using lighter loads, power decreases in the final half of a repetition in order for the athlete to decelerate the bar and for the bar to achieve zero velocity. This is so an athlete can maintain his or her grip on the bar and bring the bar to a static position under control at the end of the ROM. When resistance exercises are performed in this traditional fashion, Elliot et al. reported that the deceleration of a bar accounts for 24% of the movement with a heavy weight and 52% of the movement with a light weight. Furthermore, this deceleration phase is accompanied by a significant reduction in electromyogram (EMG) activity of the primary agonist muscles recruited in the movement. Therefore, in any one movement, a quarter to half of the full ROM is actually spent slowing rather than trying to generate explosive contractile characteristics.
Ballistic training refers to when an athlete attempts to accelerate a weight throughout the full ROM of an exercise, which often results in the weight being released or moving freely into space with momentum. Examples of ballistic exercises are shown in table 8.1 and are described in more detail in chapters 5 and 6. Investigating the ballistic bench throw exercise, Newton et al. report that ballistic movements produce significantly higher outputs for average velocity, peak velocity, average force, and, most important, average power, and peak power than traditional methods. Furthermore, during ballistic training, the bar can be accelerated for up to 96% of the movement range, causing greater peak bar velocities and allowing the muscles to produce tension over a significantly greater period of the total concentric phase. Even when performed under heavier loading conditions (e.g., >60% of 1RM) which would severely limit an athlete's ability to release a weight into free space, the intent to propel a load into the air is superior to traditional resistance training methods for the development of maximal power output.
Training to maximize power output for advanced training should entail not only slower heavy-resistance exercises for strength development, but it should also involve high-velocity ballistic exercises in which acceleration of an external load is promoted throughout the entire ROM. The most common ballistic exercises used in athletic performance training are the loaded countermovement jump (CMJ) for the lower body (e.g., jump squat), and the Smith machine bench throw for the upper body. Plyometrics and Olympic weightlifting can also be considered ballistic in nature because they too encourage full acceleration. In the case of weightlifting, bar velocities are affected only by gravity. For example, the slow contractile velocities involved in powerlifting (back squat, deadlift, and bench press) have been shown to generate approximately 12 W/kg of body weight in elite weightlifters. In comparison, the second pull of Olympic weightlifting movements, such as the snatch or the clean, produce on average 52 W/kg of body weight in the same population of athletes. These data are largely a consequence of the ballistic nature of Olympic weightlifting movements, where athletes try to accelerate a barbell for up to 96% of the movement (e.g., clean, snatch) in an attempt to impart momentum into the bar before dropping under it as it continues to rise in free space, thus allowing the athletes to move into the catch, or receiving, position.
The mean velocities of ballistic movements are greater than those of nonballistic movements because there is no deceleration or braking phase in ballistic movements. This is supported by Frost et al., who observed that significantly higher power measures are found during ballistic exercises, largely as a result of their higher mean velocity. Lake et al., however, challenged the superiority of lower body ballistic exercises for power development. Studying moderately well-trained men, the authors suggest that while higher mean velocity (14% greater) is seen in ballistic exercise, there is no difference between ballistic and traditional training methods when comparing the RFD during an exercise. Data such as these continue to challenge our understanding of the kinematics related to ballistic training methods. What is apparent, however, is that consideration must be given to the manner in which ballistic exercises are interpreted. If instantaneous Ppeak is recorded, it is likely that the impact of ballistic exercise on power characteristics may be equivocal between moderately trained and well-trained people. If, however, Pmax is a more important variable to pursue, Frost et al. suggest this may better differentiate well-trained athletes when compared to moderately trained people. Such comparisons potentially lead us to conclude that ballistic training methods are better suited to advanced athletes who already possess high levels of muscular strength and require substantial complexity and variation within their training program in order to augment the desired adaptation in force - velocity characteristics.
When developing advanced training strategies, athletes and coaches should consider the time available within discrete motor skills in which to produce peak force. While the majority of weight room - based strength training exercises take several seconds to complete a single repetition, rarely in sport is time sufficient within athletic movements to achieve maximal force, with instantaneous peak force (Fpeak) instead largely occurring between 0.101 s and 0.300 s (table 8.2). Therefore, velocity specificity should be a central consideration when training to develop muscular power, with the physiological adaptations being velocity dependent and the greatest adaptations occurring at or near the training velocities. Owing to recent technological advancements and improved diagnostic techniques, the opportunity to gain insight into the force - velocity characteristics of discrete exercises and movement patterns has increased. As a result, velocity-based training (VBT) is becoming a popular way to determine optimal resistance training loads through real-time biometric feedback that reports repetition-to-repetition performance. More specifically, monitoring repetition velocity helps to dictate the speed at which a training exercise should be performed. When combined with moderate to high external loads, the intent to move at high speeds can enhance the relative and absolute power output in the concentric phase of muscle actions.
Why Velocity-Based Training?
Historically, strength and conditioning practitioners have prescribed resistance training loads based on a percentage of a previously determined 1RM. Exercises are performed and progress at various submaximal intensities (e.g., loaded CMJ at 40% of 1RM back squat). While sound in principle, using % 1RM can be challenging from a practical perspective. Unless daily 1RMs are established, training at a specific % 1RM may be flawed. Testing for 1RM can take a significant amount of time, making it logistically difficult to schedule into a program regularly. Furthermore, the accuracy of 1RM testing is affected by daily levels of motivation. Add to this the potential change over time in 1RM performance that may occur as a consequence of training, and accurately gaining a measure of true max can be challenging at best. In comparison, VBT relies on rep-to-rep instantaneous feedback relating to the velocity of a barbell or weight. This allows variation in training loads across a training phase so long as the athlete consistently maintains a specified bar speed threshold. This bar velocity, or velocity-based training, can then be related to the stimulus for a specific strength quality (figure 8.6).
Figure 8.6 Velocity-based training curve illustrating the relationship between specific strength qualities and associated bar velocities during resistance training.
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