Overview
Developing an athlete’s ability to generate power is the primary goal of most strength and conditioning (S&C) programmes and is usually the final phase and foci during a periodised programme when peaking is imperative (Haff and Nimphius, 2012; NSCA, 2016). Successful achievement of such an outcome, however, is based on a sound understanding of the scientific principles related to power. This development can be enhanced through manipulation of the force-velocity curve (FVC), whereby an athlete first increases force output (i.e., maximum strength – magnitude) and then the ability to apply this force during progressively time-constrained movement skills specific to their sport (i.e., rate of force development). In Part 1 of this blog, we will examine the physiological and biomechanical theories that govern the efficacy of power training, including the force-velocity curve, and exercise considerations to developing force-velocity characteristics. And in Part 2, we will review the effect of strength training and ballistic training on power development while examine the training strategies and principles of training to maximise power development through a periodised training programme.
What is Power?
Power is a generic neuromuscular or athlete performance characteristic (Turner et al., 2020), but quantitatively, mechanical power can be described as work per unit of time, or often, more specific to sport, force multiplied by velocity and is a scalar quantity (i.e., magnitude but not direction) (Turner et al., 2020). Therefore, an increase in either variable (i.e., force or velocity) will increase power if the other variable remains constant; however, force is a more trainable quality (Haff and Nimphius, 2012; Haff and Stone, 2015). Explosivity is often used to describe power; however, this term is incorrect as nothing explodes in the human body (Winter et al., 2016), but in simple terms for athletes and coaches it does facilitate a greater understanding and is a good coaching term to use (Turner et al., 2020). Conversely, impulsive (based on the impulse-momentum relationship) is a more suitable and scientifically correct term to use. Table 1, adapted from Turner et al. (2020), provides an overview of key mechanical definitions and practical terminology.
Siff (2003) suggests that it is not difficult to corroborate the interdependence of strength and power by using the formula: v = F x t/m (where F = force; m = mass; a = acceleration; v = velocity; t = time). This equation represents a rearrangement of Newton’s second law of motion: F = ma → F = m x v/t → v = F x t/m. The equation (v = F x t/m) reveals that to increase velocity (v), it is necessary to increase the magnitude or duration of the force applied (or both), or decrease the mass of the body. However, not all of these are possible as the athlete may be unable to decrease the mass of their body or sports apparatus, or increase the duration of movement. Consequently, only one option remains in this instance: namely, to increase force (i.e., strength). Additionally, the rearrangement of Newton’s second law of motion is also imperative: a = F/m. Therefore, by increasing force output, decreasing the mass or both, acceleration and velocity can be improved. Finally, the impulse-momentum equation is also an important consideration for power activities. Although much interest has been placed on power, the ability to move and accelerate a mass (i.e., own mass or external), is underpinned by the impulse-momentum relationship, and is summarised in the below Figure 1. Thus, increasing net impulse is key. Net impulse is associated with better performance in movement tasks, and as long as net force increases over the time interval, momentum, and thus, velocity will increase (Turner et al., 2021). The equation, impulse = momentum = average force × time force is applied shows that a large impulse is needed to produce a large change of momentum. Again, force must predominate because of the short duration of most sports movements.
What is the Force-Velocity Curve?
Our understanding can be further enhanced by the use of the force-velocity curve (FVC; Figure 2), sometimes known as the load-velocity curve, which illustrates that maximum force is developed during low velocity activities and conversely, when maximal velocity is achieved, force production is low (Hill, 1950). Thus, an inverse relationship exists between these two variables and peak power output (PO) occurs at a compromise between force and velocity (Figure 2, a). This is based on the seminal work of Hill (1950) who looked at the force-velocity characteristics in single muscle fibres based on concentric muscle actions, demonstrating the hyperbolic curve of force-velocity characteristics. Human muscle velocity of shortening is limited because as the speed of movement increases, the number of crossbridges formed at the same time and the number of crossbridge attach-detach cycles decreases while also influencing enzymes kinetics which reduces force / tension capacity (Haff and Nimphius, 2012; Haff and Stone, 2015; Suchomel and Comfort, 2018; Cormie et al., 2011). Additionally, there is also reduced time to recruit motor units and rate coding (tetanisation); therefore, less force can be generated when time is limited and velocity is high. That is one reason why we lift very heavy weights slowly to recruit the appropriate high threshold motor units (i.e., size principle) and permit cross-bridge cycling. This has led to the recent recommendations to prioritise training focus on rapid force development due to the limited time to express maximal force during most tasks (Haff and Nimphius, 2012; Haff and Stone, 2015; Turner et al., 2021).
Figure 2. graph a) The force-velocity curve for a single muscle fibre (red box indicates that max power occurs at compromise between force and velocity); graph b) theoretical placement of various sports motor skills on the FVC; graph c) Placement of motor skills on the FVC for rugby
As stated above, the FVC is also known as the load-velocity curve, whereby motor skills can be placed on the FVC depending on the mass of the object to be moved as quickly as possible (Figure 2, b). For example, a rugby union scrum requires relatively larger forces than those required to pitch a baseball and are therefore at opposite ends of the curve (Figure 2, b). Furthermore, most sports require a variety of motor skills (e.g., jumping, tackling, and kicking) that may span the entire FVC (Figure 2, c). For example, in rugby, players are required to perform low velocity exertions and tasks which require accelerations of external mass (i.e., opponents). Conversely, they also need to accelerate their own mass during jumping and sprinting activities while performing isolated tasks such as throwing and kicking (Figure 2, c). Therefore, it is encouraged that training programmes target all aspects of the FVC curve at different phases within a periodised training programme by utilising a variety of exercises and training modalities at specific loads / velocities (Haff and Nimphius, 2012; Haff and Stone, 2015; Turner et al., 2021). The FVC may therefore be described as the individual’s athletic journey whereby they initially aim to increase strength and then attempt to apply this increase in force generation capacity under progressively more time constrained (higher velocity) movement skills specific to their sport.
FVC and Exercise Considerations for Power Development
Within S&C, velocity and force are used synonymously with speed and strength, respectively, and thus, power is often referred to as speed-strength (Siff, 2003). Moreover, speed-strength (SPD-STR) and strength-speed (STR-SPD) are also important and separate qualities, with important distinctions when devising S&C programmes. For example, SPD-STR (<30% 1RM) can be defined as: “the ability to quickly execute a movement against a relatively small external resistance and is assessed in terms of speed of movement” (Siff, 2003; Newton and Dugan, 2002). Conversely, STR-SPD (>30% 1RM) is considered: “the ability to quickly execute a movement against a relatively large external resistance and is assessed in terms of load” (Siff, 2003; Newton and Dugan, 2002). These terms are intended to signify a gradual shift in training emphasis from strength (i.e., low velocity) to speed (i.e., high velocity) as the athlete journeys along the FVC curve during a periodised training programme. This can be achieved through appropriate exercise selections such as ballistic exercises, heavy resistance, Olympic weightlifting derivatives, medicine ball throws, and plyometrics (see Table 2 for examples and Figure 2) and the gradual reduction in resistance load (i.e., %1RM) as emphasis shifts from strength, STR-SPD, SPD-STR and finally to speed, typically as part of a phase potentiation periodised model (Stone et al., 2016; Suchomel and Comfort, 2018). A revised schematic (Figure 3) may further enhance the application of power training within S&C programmes.
Power Training Aims and Key Considerations
Most sporting movements have a limited opportunity to express maximum force, generally < 300ms (Turner et al., 2020) (Figure 4, a); therefore, athletes must generate the highest possible net forces (thus impulse) at the appropriate time during a movement. Additionally, jumping, kicking, lunging, and throwing require force production as quickly as possible over a given range of motion (ROM). The greater the force over a given distance or ROM will increase work, and if performed over the same or shorter time epoch will increase power output.
As it takes > 300ms to generate maximal force (Aagaard et al., 2002a; Aagaard, 2002b), improving the rate of force development and magnitudes of force over critical time intervals (i.e., net impulse) are integral to increase acceleration, velocity, and momentum (Figure 4, b) (Stone et al., 2016; Turner et al., 2021). These are considered the primary goals of periodised training programmes (Stone et al., 2016; Suchomel and Comfort, 2018).
Figure 4. a) Adapted from Turner et al. (2021) illustrating the force-time profiles for dynamic tasks; b) Force-time profiles and aims of strength and conditioning is to improve the magnitude and rate at which force is produced; adapted from Haff and Nimphius (2012).
A range of different exercise modalities can be used within S&C programmes to elicit a power / impulsive / RFD training stimulus, and the targeted force-velocity characteristics can be easily manipulated through load (%1RM). For example, exercises typically performed at higher percentages of 1RMs during ballistic and Olympic weightlifting derivatives generally overload force characteristics to a greater extent, whereas a reduction in load, and exercises performed at reduced %1RMs tend to overload velocity characteristics to a greater extent. Example exercises are illustrated in the videos below. For example, Olympic weightlifting derivatives can be performed from mid-thigh, hang, and the floor, and as such are effective exercises that elicit high power outputs during a sport-specific and transferable action (i.e., lower-limb triple extension). Although typically performed with a catch (front or overhead squat position for clean and snatch, respectively), pulling variations can be performed (i.e., without the catch phases) which can provide an easy to teach and equally or potentially more effective training stimulus to develop power output and force-velocity characteristics (Suchomel et al., 2015). While catching variations are technically more challenging exercise, and potentially challenging the trunk stabilisers to a greater extent, pulling derivatives provide an attractive and simple option which potentially overcomes some of the complexities of teaching Olympic lifts for athletes, typically in time-constrained environments. Some benefits include (Suchomel et al., 2015; 2017):
- Less complexity and quicker to teach and learn
- Reduced mobility requirements (i.e., wrist, elbow, shoulder)
- Some athletes may achieve greater / full triple extension / intent and thus greater force-velocity characteristics. Pertinent for athletes who do not complete full hip extension and are concerned about dropping and catching the bar
- Can be used with injured athletes who are unable to adopt catch position safely
- Key! – Loads > 100%1RM can be used to overload force / RFD characteristics. This is pertinent for athletes specifically where their ability to catch the bar is a limiting factor
Ballistic exercises, where the aim is to rapidly accelerate an external resistance whereby the mass of interest can become a projectile, are also affective and simple solutions to develop the explosive properties of athletes. Some examples are illustrated in the video below. However, with these variations, it is imperative that athletes have sufficiently landing mechanics, particular with external load. Athletes who are uncomfortable landing with external load in back squat position, and want to avoid spinal loading, may prefer to perform loaded jumps with a trap-bar / hex bar to reduce the compressive forces. Finally, med-ball throws and lower-limb plyometrics (i.e., high impact tasks that involve the stretch-shortening cycle – typically hopping, bounding, and jumping activities) are also effective modalities for improving power. We will discuss plyometric training in a future blog.
Summary
Overall, irrespective of the exercise, practitioners should focus on the adaptation they are trying to elicit (i.e., power, force, velocity) which conform to the principles of specificity. In this article, we have highlighted key mechanical terminology related to power development and discussed the underpinning physiology and biomechanical theories applicable to power development. In part 2, we will discuss power training strategies and programming considerations to enhance your athlete’s neuromuscular power as part of a periodised S&C training programme.
References
Aagaard, P., Simonsen, E. B., Andersen, J. L., Magnusson, P. & Dyhre-Poulsen, P. 2002a. Increased rate of force development and neural drive of human skeletal muscle following resistance training. J Appl Physiol, 93, 1318–1326.
Aagaard, P., Simonsen, E. B., Andersen, J. L., Magnusson, P. & Dyhre-Poulsen, P. 2002b. Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses. J ApplPhysiol, 92, 2309–2318.
Haff, G. G., & Nimphius, S. (2012). Training principles for power. Strength & Conditioning Journal, 34(6), 2-12.
Haff, G. G., & Stone, M. H. (2015). Methods of developing power with special reference to football players. Strength & Conditioning Journal, 37(6), 2-16.
Haff, G. G., & Triplett, N. T. (Eds.). (2016). Essentials of strength training and conditioning 4th edition. Human kinetics.
Hill, A. V. (1950). The dimensions of animals and their muscular dynamics. Science Progress (1933), 38(150), 209-230.
Newton, R. U., & Dugan, E. (2002). Application of strength diagnosis. Strength and Conditioning Journal, 24(5), 50-64.
Siff, M. C. (2003). Supertraining. Supertraining Institute.
Stone, M. H., Cormie, P., Lamont, H., & Stone, M. (2016). Developing strength and power. Strength and conditioning for sports performance, 230-260.
Suchomel, T. J., Comfort, P., & Stone, M. H. (2015). Weightlifting pulling derivatives: Rationale for implementation and application. Sports Medicine, 45(6), 823-839.
Suchomel, T. J., Comfort, P., & Lake, J. P. (2017). Enhancing the force-velocity profile of athletes using weightlifting derivatives. Strength & Conditioning Journal, 39(1), 10-20.
Suchomel, T. J., & Comfort, P. (2018). Developing muscular strength and power. Advanced Strength and Conditioning-An Evidence-based Approach, 13-38.
Turner, A. N., Comfort, P., McMahon, J., Bishop, C., Chavda, S., Read, P., … & Lake, J. (2020). Developing powerful athletes, Part 1: mechanical underpinnings. Strength & Conditioning Journal, 42(3), 30-39.
Turner, A. N., Comfort, P., McMahon, J., Bishop, C., Chavda, S., Read, P., … & Lake, J. (2021). Developing Powerful Athletes Part 2: Practical Applications. Strength & Conditioning Journal.
Winter, E. M., Abt, G., Brookes, F. C., Challis, J. H., Fowler, N. E., Knudson, D. V., … & Yeadon, M. R. (2016). Misuse of “power” and other mechanical terms in sport and exercise science research. The Journal of Strength & Conditioning Research, 30(1), 292-300.
