Is the Force Plate with You?

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Sport’s organizations are constantly aiming to protect and develop their most valued assets – the athlete. These efforts are generally reflected through the adoption and/or investments in various testing tools as well as methods of evaluation. Consider the use of the force plate in today’s sports environment. These rectangular metal platforms outfitted with special devices called piezoelectric or strain gauge transducers can cost up to 30,000$. Despite the monumental costs, these devices are quietly creeping into training facilities all of the world. And for good reason, the force plate can be an effective resource and investment for developing performance in athletes and protecting them from potential injury.

Force plates have a wide range of applications in sports measurement and analysis. To understand the scope of its utility, one must first understand the function of the force plate. A force plate is a platform which measures force exerted by a subject. This force can be denoted through several movements such as a jump, a step, a shift in weight and even subtle movements during a single leg stance. The concept of force plate measurement is based on Newton’s third law of motion which states “for every action, there is an equal and opposite reaction”.

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In other words the force plate measures the force acted on it by a subject and/or gives an indication of the force exerted by platform to the subject.  The ability to measure these forces provides a litany of opportunities, methods and perspectives to understand force exertion by the athlete and its relationship to movement, athletic and injury potential. 

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        With the increasing presence of force plates in athletic spaces, researchers and various sports authorities are beginning to accumulate meaningful data that may be important to the development and safety of athletes in sport. Additionally, we are beginning to see the rise of criterion -reference standards based on force plate data that are being used for the development of athletes to attenuate injury and improve performance.

Researchers from the Human Performance Laboratory at the University of Calgary used a force plate to measure single-limb stance of 50 individuals aged 16 – 26. These subjects were instructed to stand as still as possible in the center of the force platform on one leg with their arms relaxed at their sides and to focus on a point in front of them. Measurement for this test are taken from the ground reaction forces garnered from a single-limb stance. Thus a simple step on a force plate produces quantifiable data which can be used for predicting injury risk and for comparison between injured and uninjured limbs (Baltich et al, 2015). Investigators in this particular study indicated that injured participants showed a greater medial/lateral excursion and greater 95% ellipse area of the center of pressure and demonstrated a longer entropic half-life in the medio-lateral direction(Baltich et al, 2015). In laymen terms, individuals with previous injury swayed more and showed less control of themselves in the presence of potential change. The conclusion reached from this study was that those individuals with a history of previous intra-articular knee injury demonstrated balance deficits up to 3–10 years following injury (Baltich et al, 2015).  This information can be effective for sports organizations to use as part of their evaluation for athletes in regard to health, safety and as a foundation for program design or return to performance.

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         In a 2006, authors Chen, Shiang, Jan & Lin used similar strategies to understand and develop criteria that can impact risk of injury in the ankle of high school basketball players. They studied forty-two adolescent players competing in first league of the High School Basketball Association without a history of injury in the lower extremities (Wang, Chen, Shiang, Jan & Lin, 2006). Researchers in this study similarly to the aforementioned study utilized the 1-leg standing postural sway assessment to identify risk of injury in the ankle. These investigators however, demonstrated that high variations of postural sway in 1-leg standing test could be used to understand the risk of ankle injury in basketball players. In particular these researchers identified a particular criterion which showed that high variation of postural sway in both anteroposterior and mediolateral directions corresponded to occurrences of ankle injuries (Wang, Chen, Shiang, Jan & Lin, 2006). In more simple terms, those individuals who showed a greater relative change in various planes of motion while attempting to perform a movement which requires stability are at greater risk for injury (in regards to the ankle).  1_xiyV3Zdct6Q79D9SxRBuCA   Researchers have also used the force plate as a neuromuscular screening tool for other tests such as a single leg counter movement jump, a vertical drop test, a single leg countermove the jump test and a hop test.  Measurements like peak vertical ground reaction force and variances in asymmetry can be reliably assessed using aforementioned tools such as the hop and Single leg countermovement jump test. The wide array of applications to them force plate have resulted in a battery of movement tests that have produced useful screening tools for sports scientists (and coaches alike) wishing to understand more about their athletes. 

      It’s important to understand that these studies reflect just one of the many ways in which force plates are being used currently in the world of sports performance  screening and rehabilitation. The results of these studies are increasingly providing sports organizations with useful criterions to help predict, evaluate and treat athletes in regard to injury. Additionally, these devices are also useful in providing quantitative measures for predicting various measures of athletic performance. While these devices are increasingly demonstrating their value the manner in which they are used is equally important for the production of meaningful data and useful application the athlete. Some movements or tests are more valuable than others when using the force plate.     2010-tim-tebow-077567612.jpg         The vertical jump for instance is a well-studied and commonly used assessment of lower-body neuromuscular performance in athletes. Authors have previously noted the existence of a relationship between vertical jump and performance factors such as increased playing time (Hoffman, 1996).  It is commonly understood as a reflection of commonly expressed athletic qualities such as “explosive movement.”  In addition, there is a strong relationship between vertical jump and various field measures such as straight-line sprinting (Cronin & Hansen, 2005; Marques, Gil, Ramos, Costa, & Marinho, 2011; Peterson, Alvar, & Rhea, 2006), and change of direction movements (Barnes et al., 2007; Brughelli, Cronin, Levin, & Chaouachi, 2008; Peterson et al., 2006).  Thus, insights into the vertical jump of an athlete can provide insight to a myriad of components important to athletic performance. 

As evidence for this fruitful relationship between movement and device, the force plate provides an indication of jump heieght through measures of  the calculation of factors such as flight time, impulse and the work-energy (Linthorne, 2001).  These factors are also able to provide intrinsic characteristics of a jump which can help performance specialists understand the biomechanical processes taking place during a jump. This insight is useful as  it allows individuals to understand elements of a jump that can be monitored and/or manipulated through training.

        Jump shot.jpgEvidence for the value of this insight was most noticeably reflected in a recent study by authors at the University School of Physical Education, Wrocław, Poland.  These researchers sought to understand the various biomechanical differences between basketball players performing a jump shot and a jump commonly used for expressing maximal vertical jump height.  Specifically, these individuals sought to investigate the characteristics of lower limbs during the take-off and landing phases achieved when performing a jump shot and a maximum countermovement achieved without an arm swing (Struzik,Pietraszewski & Zawadzki, 2014). 

        The use of a force plate allows researchers to analyze the differences in ground reaction forces generated by basketball players during these fundamentally similar jumps. The differences in these jumps are manifested through various force changes concerning the phases of take-off and landing (Struzik, Pietraszewski, & Zawadzki, 2014). Investigators demonstrated that when basketball players performed the jump shot, they had improved take-off times and peak powers and an overall improved mean power in the take-off phase and relative mean power relative to counter movement jump. Despite these differences, statistical analysis of the jumps revealed no significant differences between the two types of jumps in regard to jump height (Struzik, Pietraszewski, & Zawadzki, 2014). 

         Force Plate - 1.jpg            Thus, while a counter movement jump with an arm swing may be more effective at producing a maximal jump height, authors of this study conclude that a counter movement jump without an arm swing is a good indication of maximal jump height during a jump shot (Struzik, Pietraszewski, & Zawadzki, 2014).  The ability to reach this conclusion is the result of an intrinsic understanding of jumping biomechanics garnered from a force plate.  This information can help sports organizations make important decisions in the evaluation of athletes who expressed much of their talents through the action of a jump shot.  The benefits of a force plate are multifaceted and highly resourceful for the sports organization interested in limiting injury, improving and evaluating athletic performance. They are also a valuable tool for monitoring important factors of athletic performance – neuromuscular fatigue.
      48079_cpf While we have identified the vertical jump performed on force plate as useful means of measuring lower body strength, power, and a manner to provide perspective to the integrity of the musculotendinous pre-stretch, or countermovement stretch shortening cycle, this combination of movement and device has also proven to be an effective tool for monitoring fatigue.  In fact, authors recently published a  meta – analysis in the journal of science & medicine in sport, where they concluded that an average of counter movement jump heights was an effective measure to evaluate for neuromuscular fatigue (Claudino, et al., 2017).  It is believed that the relative changes which take place at the neuromuscular actions level during the eccentric and concentric phases of the counter movement jump  during various periods in a season can reflect fatigue of the athlete (Gathercole, Sporer, Stellingwerff, Sleivert, 2015).  Researchers at the School of Exercise and Health Sciences  Centre for Exercise and Sports Science Research  at Edith Cowan University identified factors important to the expression of a force plate jump such as flight time to contraction time as an important and highly sensitive measure for detecting neuromuscular fatigue in female basketball athletes (Spiteri, Nimphius, Wolski, Bird, 2013). These researchers demonstrated that there are more insightful cues to neuromuscular fatigue than simply measuring jump height.

            Screen Shot 2018-05-24 at 4.35.45 PM.png        This study is part of the growing value of force plates to sports performance facilities as a tool for providing athletes with various measures dedicated to limiting injury, improving athletic potential and facilitating decision making in the complex world of exercise and/or load management.  The force plate provides a meaningful view to jumping performance as well as as neuromuscular aspects of this movement such as single leg stance and measures of sway. These tests are just some of the more valuable pieces that can allow athletes to reach greater levels of success in today’s highly competitive landscape. If the force plate is not a tool in which you currently use in your training facility, you should consider the multitude of applications and benefits garnered from understanding the force that lies within your athletes.

References:

Baltich, J., Whittaker, J., Tscharner, V., Nettel-Aguirre, A.,  Nigg, B., Emery, C.,  (2015). The Impact of Previous Knee Injury on Force Plate and Field-Based Measures of Balance. Journal of Clinical Biomechanics. 30.

Cheah, P. Y., Cheong, J. P., Razman, R., & Abidin, N. E. (2017). Comparison of Vertical Jump Height Using the Force Platform and the Vertec. IFMBE Proceedings 3rd International Conference on Movement, Health and Exercise, 155-158.

Claudino, J. G., Cronin, J., Mezêncio, B., Mcmaster, D. T., Mcguigan, M., Tricoli, V., . . . Serrão, J. C. (2017). The countermovement jump to monitor neuromuscular status: A meta-analysis. Journal of Science and Medicine in Sport, 20(4), 397-402.

Gathercole, R.; Sporer, B.; Stellingwerff, T.; Sleivert, G. Alternative countermovement-jump analysis to quantify acute neuromuscular fatigue. International Journal of Sports Physiology Perform. 2015, 10, 84–92.

Hoffman, J. R., Tenenbaum, G., Maresh, C. M., & Kraemer, W. J. (1996). Relationship Between Athletic Performance Tests and Playing Time in Elite College Basketball Players. Journal of Strength and Conditioning Research, 10(2), 67-71.

Read, P., Oliver, J. L., De Ste Croix, M.B., Myer, G. D., & Lloyd, R. S. (2016). Consistency of field based measures of neuromuscular control using force plate diagnostics in  youth soccer players. Journal of Strength and Conditioning Research, 30(12), 3304–3311

Struzik, A., Pietraszewski, B., & Zawadzki, J. (2014). Biomechanical Analysis of the Jump Shot in Basketball. Journal of Human Kinetics42, 73–79.

Spiteri, T.; Nimphius, S.; Wolski, A.; Bird, S. (2013). Monitoring neuromuscular fatigue in female basketball players across training and game performance. Australian Journal of Strength and Conditioning. 21, 73–74.

Wang, H., Chen, C., Shiang, T., Jan, M., & Lin, K. (2006). Risk-Factor Analysis of High School Basketball–Player Ankle Injuries: A Prospective Controlled Cohort Study Evaluating Postural Sway, Ankle Strength, and Flexibility. Archives of Physical Medicine and Rehabilitation, 87(6), 821-825.

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