# Validation and Application of Two New Core Stability Tests in Professional Football
## 1 Introduction  
The \"Core musculature\" term refers to the combination of muscles that surround and comprise the luminopelvic region, and act synergistically to stabilize the trunk and hip, contributing to the movement control and stability of more distal joints [1]. On the other hand, core stability, defined as the ability to control the position and motion of the trunk over the pelvis, governs optimal force production, transfer and application to more distal segments in many functional athletic activities [2]. The core muscles are considered to play a key role in sport performance as they seem to provide \"proximal stability for distal mobility\" [1, 3] throughout the entire kinetic chain. Moreover, core stabilization precedes gross motor movement, as the central nervous system activates the trunk musculature before limb movement to provide the stability and stiffness of the trunk and pelvis in anticipation of the forces produced at this level [3]. \"Core stability\" is accomplished through a complex interaction of neuromuscular coordination, proprioception, strength and endurance of the trunk and hip musculature. This inherent complexityhas been the focus of a wide range of studies employing different measurement techniques for core stability evaluation in recent years [3]. In this way, there is a lack in the literature of a gold standard for core stability evaluation in sports. Therefore, the assessment of trunk stability in the field setting could become even more complex because it requires the combination of different variable measurements, such as force, endurance, etc. [4; 5]. Considering this multi-characteristic approach, a wide variety of testing methods have been described to evaluate core stability performance, both in laboratory and in clinical settings. In the laboratory, the most common testing method to measure core strength has been developed by the use of isokinetic dynamometers, whereas trunk stability tests have been performed through the employment of custom-designed devices [6; 7]. Beside these expensive and time-consuming tests, \"clinical tests\" are the preferred choice for evaluating core stability for \"in the field conditions\". No gold standard for core stability evaluation has been established, until recently. These tests have also involved vague or unclear scoring systems and require expensive instrumentations or the development of individually customized equipment. The definition of a gold standard test for core stability evaluation has become challenging, as there is not a widely accepted conclusive definition for core stability. In fact, there are numerous muscles that participate in the body core's dynamic stabilization. Several reliable and easy to use methods have been proposed to assess core musculature function. These include the prone bridging test, the Biering-Sorensen test, the double leg lowering test, prone plank stability], the side plank bridging test], the front abdominal power test (FAPT), the side abdominal power test (SAPT) [3; 8; 9; 10; 11; 12] and the flexion-rotation test [13]. Some of the limitations of these tests are as follows: (a) they isolate one aspect of this complex interaction, such as core strength or endurance; (b) they are linked to a subjective scoring or evaluation system; and (c) they asses a more complete picture of this interaction, but not in a functionally relevant position, aligned with the sport-specific core region's biomechanical and or functional requirements [3]. Furthermore, these tests have also reported vague or unclear scoring systems and/or require expensive equipment, or they require the development of individually customized measurement devices which limit the extrapolation of the results obtained to other populations. The interaction among the lumbopelvic and hip muscles makes it difficult for researchers to develop a single test that could encompass all muscles and structures [12].