High performance in many sporting endeavors is characterized by the ability to display high amounts of muscular power. Power is the product of muscular force and velocity and can be expressed as a measure of anaerobic capacity over the duration of a specific event or as an instantaneous value during a given movement. The latter, often referred to as peak power (PP), is typically associated with explosive movements such as sprinting, jumping, and Olympic weightlifting and may be an important variable associated with success in a given discipline. The measurement of PP by strength and conditioning coaches is an important consideration in the training process. Changes in PP throughout the annual plan may be indicative of training status or adaptation to the workload and could be used to plan or adjust the training program based on the athlete’s performance.
Vertical jump
One method of power measurement proven to be a reliable and effective predictor of sporting success is the measurement of a vertical jump. Two types of vertical jump measurements are commonly used—the countermovement jump (CMJ) and the squat jump (SJ). The CMJ is the most recognizable type of vertical jump tested by strength and conditioning coaches. It begins from an upright standing position. Athletes then self-select an optimal eccentric depth or knee bend and then immediately jump vertically. A less common type of jump is the SJ where the athlete starts from a stationary, semi-squatted position. The athlete is instructed to hold a knee angle of approximately 90 degrees for a three count and then jump vertically. The jumper doesn’t employ a downward phase (i.e. a countermovement or rebound). Most athletes can jump 3–6 cm higher in a CMJ than in the SJ.
Vertical jumps can be measured in several different ways, all with their associated advantages and disadvantages. To specifically analyze lower body power and eliminate differences in jump technique, it may be valuable to eliminate the arm action used during testing. The elimination of arm action during jumping may allow the athlete to concentrate on leg and hip explosiveness and minimize jumping technique differences. Testing without arm mechanics is typically performed with the athlete assuming a “hands on hips” approach or with a light barbell or stick placed across the athlete’s upper back. The method of holding a light bar/stick across the upper back in the same fashion as a back squat exercise is the ideal method to remove any contribution from arm action in both jumps. An alternative method is to place both hands on the hips and hold this position throughout the duration of the jump. However, the light bar/stick method may be a more familiar body position to jump from if back squats or jump squats are a regular part of the athlete’s training program.
Starting position for an athlete performing a squat jump.
When eliminating the arm mechanics associated with vertical jump testing, the use of flight time or the length of time the athlete spends in the air during a maximal vertical jump may be an effective method of vertical jump testing. An electronic switch mat (or jump mat) is a commonly used method of determining vertical jump height and peak power from flight time. The jump mat is portable and may be obtained at a much lower cost relative to a force plate or accelerometer. The jump mat, similar to a force plate, measures flight time as the amount of time the athlete spends in the air during the vertical jump. Jump height is derived from flight time using the common formula: Jump height (m) = [9.81 X flight time (s) X flight time (s)] / 8.
Flight time is determined through the duration of time the athlete spends in the air during a maximal vertical jump.
PP is determined from a vertical jump by measuring the mechanical work performed during the vertical jump using the equation developed by Sayers et al (1):
Peak power (W) = (60.7) X jump height (cm) + 45.3 X body mass (kg) – 2055.
Eccentric utilization ratio
In addition to PP, the measurement of a vertical jump using both SJ and CMJ may provide strength and conditioning coaches with an additional piece of information related to sports performance. The eccentric utilization ratio (EUR) can be calculated using vertical jump height or peak power. Only one countermovement jump and squat jump result is needed to determine an athlete’s EUR. Dividing the CMJ height (or PP) by the SJ height (or PP) will generate the EUR. The SJ, CMJ, and resulting EUR calculation can be completed in a matter of minutes. An additional benefit of the EUR is that it will result in very little fatigue and have an insignificant impact on an athlete’s present training regimen.
The SJ is thought to be an indicator of concentric strength of the lower body while the CMJ is an indicator of lower body reactive ability or reactive strength. Traditionally, the CMJ produces greater jump heights and power outputs compared to the SJ. The difference in jump height and power output between the two jumps is due to the use of the stretch shortening cycle (SSC) employed with the CMJ. The ability to utilize the SSC efficiently is a critical factor in many sports. The EUR could potentially expose an athlete’s ability or lack thereof to efficiently utilize the SSC. Most athletes will have a EUR of one or greater. Athletes generally can jump higher during a CMJ than a squat jump due to the storage of elastic energy and increased muscle activity that occurs during the eccentric phase of the CMJ. This additional force potential isn’t available during a squat jump because the countermovement is removed.
A high EUR means that an athlete has a high capacity to store potential energy in the elastic components of the tendons and muscle and then release this energy when the tendon and muscle is shortened. Because very few sporting activities are purely concentric in nature, this is a desirable quality for an athlete. Conversely, a low EUR means that an athlete has a low capacity to store potential energy in the elastic components of the tendons and muscle and express this energy when the tendon and muscle is shortened. In most instances, this is an undesirable quality. If athlete A and athlete B have identical squat jump heights or PP, the athlete with the more efficient stretch shortening cycle will jump higher during the CMJ jump.
The EUR has been proposed as an indicator of SSC ability in various sports and during different phases of training. Data produced by McGuigan et al (2) determined that athletes from the sports of soccer and football (rugby) have greater EUR values when compared to other sports. This data may suggest that performance in these sports is dependent on greater reliance on the SSC. This could also reflect that athletes from these sports are more highly trained or use an increased amount of power training and SSC activities in their annual training plan.
Just as training status has an affect on power production, the training phase during the annual plan may also affect the EUR. Additional data by McGuigan et al (2) demonstrated a significant difference between the EUR measured during the off-season and the EUR measured during the pre-season period for field hockey players with the higher values recorded immediately pre-season (1.26 versus 1.05). The argument can be made that the pre-competitive or special preparation phase of training for many sports incorporates a greater volume of plyometric training than any other training phase throughout the year. The aim of most plyometric training programs is to increase the efficiency and magnitude of the SSC in sporting activities. In doing so, the EUR should be increasing as these adaptations occur and as an athlete’s readiness to perform his sport is also high at this time of year. If an athlete’s readiness to perform his sport is high with his ability to efficiently utilize the SSC, the EUR could be a tool to indicate performance. Coaches could quickly and easily conduct the necessary jump tests to determine an athlete’s EUR and predict the athlete’s readiness for competition.
Practical applications
Strength and conditioning professionals can find a high level of utility by incorporating EUR testing into their athletes’ physical assessment protocols. The negligible amount of time and effort required to perform EUR testing make it a great complement to strength and conditioning coaches’ current physical assessment protocols. The use of the CMJ in physical assessment protocols is very widespread. With the addition of a SJ and a very simple equation, a whole new picture of an athlete’s expression of power may be evaluated. The ability to store and express elastic energy could be a characteristic that separates many distinguished athletes from the undistinguished.
If stringent jump testing is employed, the EUR testing data will provide valid and reliable data regarding power production. For a conditioned athlete, performing a maximal effort CMJ and SJ isn’t physically demanding. While physical testing provides the strength and conditioning professionals with a wealth of information that they can use to create and manipulate training programs, it sometimes comes at the expense of training sessions. Training sessions are sometimes abbreviated prior to and after testing sessions because of the physical toll incurred during the tests. An optimal physical test is one that provides useful data to the strength and conditioning professional without impacting the athlete’s training plan. A EUR test can be conducted at any time with little or no adverse effects on the athlete’s current training regimen.
EUR testing results may help strength and conditioning professionals address an athlete’s power output limitations and program for improvement. If an athlete has a low EUR, there may be some value in adding additional plyometrics to his training plan. An athlete who can produce a SJ nearly equal in magnitude to his CMJ is almost exclusively reliant on his concentric force producing capabilities. The athlete’s lack of reactive ability leaves much to be gained from training devoted toward increasing the efficiency of the SSC. This is where adding plyometric training to the athlete’s current training plan may help to improve upon this weakness. In contrast, the athlete who has a high EUR already has a highly efficient SSC. This athlete’s limitation isn’t his ability to take advantage of the elastic properties of the muscle and tendon. There will need to be an improvement in lower body force production for gains in jump magnitude to be realized. Strength training will be very beneficial for this type of athlete.
Physical testing is critical in the talent identification process, and EUR testing may be a valuable indicator for coaches to examine. While strong athletes are in abundance, finding athletes with high levels of reactive power are less commonplace. Athletes exhibiting a high EUR may be able to achieve higher power outputs than their counterparts who can’t. Developing an athlete’s ability to produce force is less difficult to train than an athlete’s ability to utilize stored elastic energy. If coaches can identify and recruit those athletes who already have a highly efficient SSC, the potential for these athletes to become very powerful by increasing their strength levels is realistic. Athletes who already possess a great deal of strength but lack an efficient SSC may have a more difficult time developing the same degree of reactive power as their counterparts. This type of athlete’s efficiency improvements in the SSC may not be able to equal performance improvements seen by the highly reactive athletes who increase their strength levels.
References
- Sayers SP, et al (1999) Cross-validation of three jump power equations. Med Sci Sports Exerc 31:572–77.
- McGuigan MR, et al (2006) Eccentric utilization ratio: Effect of sport and phase of training. J Strength Cond Res 20:992–9.