Athletes have been in pursuit of superior athletic ability for a very long time. One aspect of athleticism that has been at the forefront has been the athlete’s ability to accelerate and sprint. This importance is observed in soccer where most crucial moments, such as goal scoring and goal saving tackles are preceded by sprinting and acceleration actions (Ramírez-Campillo et al., 2015; van Ingen Schenau, Bobbert, & Rozendal, 1987). There are many methodologies available to help an athlete develop their sprinting and acceleration abilities including strength training, speed work and power work, however, my personal favorite has always been the use of plyometrics. Plyometrics, which is derived from the meaning of plio (more or longer) and metric (to measure), is in its purest form the utilization of the stretch-shortening cycle (SSC). Plyometrics, was coined by Fred Wilt. Wilt was a runner, who with his coach Michael Yessis, applied and translated the works of the Soviet Union track athletes under the supervision of Dr. Yuri Verkhoshansky. Dr. Verkhoshansky developed a jumping method that saw a considerable rise in the Soviet Union athlete’s abilities. Plyometrics can help to increase muscle and tendon stiffness, aid in the storage and distribution of elastic energy and help reduce lower extremity injuries, which, in turn, can create a more economical and robust sprinter (Dobbs, Gill, Smart, & McGuigan, 2015; Markovic & Mikulic, 2010).
As the goal of every coach should be to do the best they can for the athlete, it would follow that an understanding of plyometric exercises is an essential component for the continued success and growth of an athlete. Unfortunately, a lot of training methodologies out there are misused or misinterpreted, and plyometrics is not partisan to this misuse. In the following section the building blocks of plyometrics and the particular uses of plyometrics in relation to sprinting will be discussed.
What is the SSC
The SSC consists of three actions; a) an eccentric phase, the amortization phase, and the concentric phase. The SSC is one of the most effective muscular actions that an athlete can perform and is used in a variety of different tasks (Cormie, McGuigan & Newton, 2011). The SSC is an amplification of power that utilizes the Muscle-Tendon Unit (MTU) through the use of the Series Elastic Component (SEC) and the Stretch Reflex (SR). When an MTU is stretched, mechanical work is absorbed and stored in part as potential energy in the Series Elastic Component (SEC), contributing to higher power production (Cormie et al., 2011).
The first phase of the SSC is the eccentric phase. During the eccentric phase of the SSC, the muscle is lengthened and primed for the next step.
The second phase of the SSC is the amortization period (isometric transitional period) (Turner & Jeffreys 2010). This phase of the SSC could be considered the most deciding element for the maximal utilization of the SSC. The amortization phase should be kept to a minimum so that the energy stored during the eccentric phase does not dissipate (McNeely, 2005), however, this will also be dictated by the task that succeeds it.
The third and final phase of the SSC is considered the concentric phase. In this phase, the muscle fibers are shortened, and the force that was generated is released to accomplish the desired task.
Horizontal and Vertical Plyometrics
Horizontal and Vertical plyometrics, as the name states, are plyometrics that utilizes two different directions of force applications. Though similar in muscle sequencing, which employs a proximal to distal muscle sequencing of hip, knee and ankle musculature, they also differ in particular areas (Jones & Caldwell, 2003; Ridderikhoff, Batelaan, & Bobbert, 1999). In the below chart are examples of the similarities and differences.
1. Larger knee extension at take-off
2. Larger knee and ankle angular velocity
3. Larger vertical peak forces
4. Larger peak magnitude of GRF
5. Greater Glute activation towards takeoff (In the horizontal jumps this may be a mechanism to allow for preparation to land)
1. Joint moments are adapted to the direction of the jump
2. Both use a proximal to distal muscle sequencing
3. Both use the biarticular hip extensors to delay knee extension and allow for greater hip extension
1. Has a rotation phase prior to load and take-off
2. Larger hip extension during take-off
3. Larger hip angular velocity
4. Larger horizontal peak force
5. Greater hip flexion and greater hamstring activation
6. Greater Hamstring activation the more forward the jump
(Dobbs et al., 2015; Jones & Caldwell, 2003; Ridderikhoff et al.,1999)
How to Apply This
The prescription of plyometric exercises will always be dependent on the needs and skill level of the athlete you are working with is. When utilizing plyometrics for speed improvements, the below figures are excellent examples of the differences that need to be considered. Figure 1 diagram shows the first 25 steps of a sprint progression. In this sequence, you can see that the figure is directing their ground reaction force (GRF) horizontally in the first 6-10 steps and then alters that pattern after the 6-10th step to transition into a more upright position. The figure, as it achieves the upright posture, starts to redistribute the GRF production more vertically. Also, Figure 2 shows how horizontal work begins to deplete with each successive step, and what is not show in this figure, but has be demonstrated before, is that the vertical GRF rises substantially with each successive step (Mero, Komi, & Gregor, 1992). It would appear the change of force distribution throughout acceleration should be considered as crucial variable when prescribing plyometric exercises.
Figure 1. Shows the runners from 1st step to the 25th (Nagahara, Matsubayashi, Matsuo, & Zushi, 2014)
HORIZONTAL, HORIZONTAL…… HORIZONTAL! It would appear that we need to prescribe mostly, if not only, horizontally focused plyometric exercise to improve 0-10m speed (Dobbs et al., 2015; Loturco et al., 2015). Dobbs et al. (2015) suggested that sprinting has a strong correlation to horizontal mean and peak force production. In addition, they posit that the majority of horizontally driven jump tests strongly correlate to acceleration ability. In Loturco et al. (2015) study the authors demonstrated that when elite level soccer players were divided into a vertical jump group and a horizontal jump group, the horizontal jump group was the only group that improved initial acceleration abilities. This would appear to be common sense in the fact that both initial acceleration and horizontal plyometrics are accelerating the body’s center of mass in a horizontal direction. Additionally, horizontally driven plyometrics have similar muscle sequencing as is seen in acceleration, especially during initial acceleration of 0-10m. However, there has been opposing advice to these findings. Ramírez-Campillo et al. (2015) showed that after 6 weeks of vertical, horizontal and combined plyometric training, 10m speed did not improve with any one combination. Additionally, Salaj and Markovic (2011) caution that since plyometric exercises in nature, revolve around the SSC mechanics, that concentric only action, as is seen in initial acceleration, may not be the best option to improve initial sprinting ability. Kugler and Janshen (2010) echo the previous statement suggesting that even though there is a similar horizontal force distribution, unlike plyometrics sprinting does not require maximal force application. With that said, Dobbs et al. (2015) did find that squat jumps (concentric only action) strongly correlated to 5m speed. It may be suggested that, in addition to the SSC horizontal plyometrics, the use of concentric only jump actions could be prescribed.
For improvements in 10m + speed, it would appear that a combination of vertical plyometrics (VP) and horizontal plyometrics (HP) are the best way to go. More specifically, Ramírez-Campillo et al. (2015) showed improvements of up to 3% over 6 weeks of training to 30m speed. In addition to speed improvements, a combination of VP and HP improved the balance between the posterior and anterior lower extremity musculature, as well as 15m speed and ball control. This once again should be fairly obvious when we observe what the demands of sprinting outside of initial acceleration require.
In summary, when deciding which plyometrics to choose I would follow these two simple formulas:
1) Horizontal Plyometrics + Concentric Only Plyometrics = Improvements in 0-10m sprinting
2) Vertical Plyometrics + Horizontal Plyometrics = Improvement in 10m+ sprinting
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