In the field of health and fitness, and to a lesser extent, strength, and conditioning, muscular power appears to be a misunderstood topic. Many practitioners in the field claim to offer muscular power as a training modality but then train the body in a contradictory manner. It is the author's experience that aerobic and muscular endurance-based training circuits in group environments are believed to develop muscular power, even though the training regimen adopted in these circumstances fails to address critical concepts of muscular power. The rest of this article will define and explore power as a training concept and provide some examples of its application in training.
By definition, muscular power is the body's ability to produce as much force as possible in as little time as possible. It is the product of two distinct training variables, namely, force and velocity. The force-velocity relationship best depicts what avenues can be used to increase power, as there is both velocity and force specific adaptations that can result from training. The force-velocity relationship states that when there are increases in force, there are subsequent decreases in velocity and vice versa. Low-velocity training, for example, bench-press, deadlift, squat, etc. are traditional resistance training activities that can increase force related aspects of power. High-velocity training e.g., Olympic weightlifting, jump squats, and med ball throws, develops the ballistic capabilities of clients and affects the velocity component of this relationship.
This relationship is exceptionally significant when discussing performance enhancement because the two modes mentioned above each offer a very different training stimulus and consequently provide unique training adaptations (Channell & Barfield, 2008; Cormie, McGuigan, & Newton, 2010; Cronin, McNair, & Marshall, 2003). Traditional resistance training exercises like the bench press, the deadlift, and the squat typically employ heavy loads (>85% 1RM) to improve an individual's maximal strength. Muscular power is said to progress with maximal strength training and can be used to increase a client's performance characteristics significantly, i.e., countermovement jump height (Cronin et al., 2003).
Performance can improve in this instance due to the high levels of force produced, which develops an individual's neural capabilities, i.e., motor unit recruitment, rate coding, and synchronization. This neural component and other subsequent adaptations like muscle size are organism level constraints that, when improved, is said to be advantageous. Especially to relatively weak and untrained individuals because of the long term benefit that they offer (Cormie et al., 2010; Cronin et al., 2003). In a sporting context, advantages of traditional resistance training lie in the understanding of Newton's first law: the law of inertia, which states that the greater the mass of an object, the greater the resistance needed to perturb that object's linear motion. Therefore, the stronger athlete is harder to move and their momentum is tough to stop, which is a specific requirement of American football and rugby players. External forces experienced in a competition can be replicated with traditional resistance training.
Traditional resistance training is potentially disadvantageous to athletes in sports like football and basketball due to the low movement velocity not being conducive to the specific tasks those athletes perform (Cronin et al., 2003). Additionally, the end range of motion can be undertrained due to a loss of acceleration during the concentric phase of these lifts (Newton, 2008). Olympic lifts and ballistic exercises like the snatch or med ball throws are an alternative training model that is immensely valuable to trainers as they explore ways to enhance the performance of their clients. Ballistic exercise allows for the individual to accelerate the training implement (bar, medicine ball, etc.) or their body through a full range of motion and project themselves or the load into the air (Cronin et al., 2003). The acceleration produces superior power outputs at higher velocities, which is something that cannot be achieved optimally with traditional resistance training. For example, a jump squat or jumping to complete a burpee is advantageous due to the velocity of the movement. It is also specific to many sports, i.e., basketball players projecting themselves into the air to slam-dunk.
Olympic and ballistic exercises draw upon an eccentric pre-stretch of the musculature involved; this pre-stretch supplements a rebound effect called the stretch-shortening cycle (SSC). The SSC is responsible for more significant initial impulses, greater peak bar velocities, a higher rate of force development, and consequently, results in increased power and movement velocities which can transcend previous jump and sprint performances (Cormie et al., 2010; Cronin et al., 2003). This training modality is advantageous for the conditioning of clients who have a rich training history by optimising the use of the SSC and developing power at the other end of the force-velocity relationship. For the improvement of performance in this aspect of conditioning, a spectrum of moderate loads (30-60% 1RM) is considered optimal for power development (Channell & Barfield, 2008; Cronin et al., 2003; Hatfield et al., 2006).
Suggestions for trainers would be to utilise the spectrum of loads and start at the light end of the spectrum, i.e., 30% RM load and progress based on the client's ability. Doing so will limit the potential for injury and allow a safe environment for the client to learn. For ballistic lifts like the jump squat, they are generally performed on a smith machine limiting the involvement of the stabilisers. Notwithstanding these disadvantages, the heightened injury risk observed in a study by Hall (1985) is difficult to ignore. Hall (1985) compared movement velocities over a spectrum of loads and determined that shear and compressive forces at the L5/S1 vertebral joint are higher when the movement velocity is more considerable. Subsequently, the SSC elicits high levels of mechanical stress due to the rapid nature of its involvement.
Traditional resistance training, Olympic lifts, and ballistic lifts can all elicit positive adaptations in clients. It is crucial to consider the individual's training history when prescribing conditioning exercises as relatively untrained/weak individuals may benefit more from traditional resistance training due to the nature of the adaptations having a long term benefit. In contrast, the more experienced client seeking power development as a training goal may profit from high-velocity exercises as they can enhance the functionality of the SSC. The higher the movement velocity, the greater the risk of injury to the spine, this is something that trainers need to consider as sound training progressions and excellent core stability guard the spine. Consequently, both training modes should be utilised heavily by trainers as the training adaptations differ but are both advantageous and attack different ends of the force-velocity relationship to enhance muscular power.
