Developing A Multi-Directional Single-Leg Jumping Assessment which Incorporates Technical, Physical and Perceptual Components of Performance
Jennifer K. Hewit, PhD
United States Military Academy at West Point.
Developing a comprehensive athlete profile can provide coaches and clinicians with a variety of valuable information regarding individual players’ performance and capabilities. Creating an assessment that is not only reliable, but also addresses the three primary components of agility (technical, physical and perceptual) is needed to better assess individual player strengths and weaknesses. Unilateral performance measures across multiple directions can be used to detect directional-specific asymmetries which may provide valuable information regarding those players that are at an increased risk of injury or that may not be ready to return to play following a lower limb injury. A percent difference in performance measures between legs that exceeds 15% in any of the three directions is thought to place the athlete at greater risk of injury. Additional characteristics associated with alignment, muscle activation patterns and relative joint angles throughout the movement can also be indicative of high risk movement patterns. Further research is needed to assess the reliability and develop normative data for such an assessment.
Keywords: Leg Power; Lower Limb Injury; Asymmetry; Single-Leg Jumping; Agility
Abbreviations: ASI- Average Symmetry Index
Figure 1. Deterministic model of agility (modified from )Of interest in this article is the development of a single-legjumping assessment across multiple directions that is able to detect differences in performance through a variety of technical, physical and reactive elements. When these variablesare excessively high or differ substantially between limbs, theathlete is considered to be at an increased risk of lower limbinjury [5-16]. Therefore, an easily administered and reliable assessment that is able to identify such characteristics whenperforming sport-specific tasks would seem to be of great value to coaches and clinicians.
A common measure of leg strength and power in sport is thevertical jump assessment. This is primarily due to its relativelysimple testing procedures and high reliability of performance results . However, in sport, a player’s movements are notconfined to a single direction (e.g. vertical) but are performed across multiple directions throughout the entirety of the competition.Additionally, it has been shown in recent researchthat a player’s leg strength capabilities are not uniform across these various directions [8,17-19]. Therefore, using only themaximum vertical jump assessment as a means of developing a player profile for those athletes that perform multi-directional movements (vertical, horizontal and lateral) in their sport creates an inaccurate representation of the player’s strengthand power capabilities . An assessment of leg power that can be performed across multiple directions can provide coachesand clinicians with valuable information regarding baseline values, minimum standard values (e.g. performance indicators),and a means of monitoring player progress (whether injured or not) . Additionally, shared variances (rangingfrom 13 – 62%) reported in 3 separate studies [18,20,21] investigating multi-directional jumping have indicated that eachdirection measures relatively independent leg qualities of each other; further supporting the inclusion of horizontal and lateralhopping into the standard vertical jump assessment.
Dynamic movements in sport are not always performed onboth legs simultaneously (i.e. bilaterally). Players are oftenrequired to jump, land, change direction, accelerate, etc. using only one leg at a time (i.e. unilaterally). As such, the legs maydiffer substantially in strength, power and technical characteristics.When a single leg is used to generate or absorb large ground reaction forces (characterized in particular by jumptake-off and landing, respectively), any muscular imbalances will increase the strain placed on the single leg and may detrimentallyaffect the performance [5,7,17,22]. By isolating one leg at a time during the movement task, a measure of symmetry(ASI = average symmetry index) between limbs can easily be calculated using the following equation .
ASI = [1 – (dominant limb/non-dominant limb)] x 100
ASI = [1 – un-injured limb/injured limb)] x 100
It is important to note that some researchers use the absolutevalue of the ASI measure which masks valuable informationregarding which leg is actually performing better. By eliminating the absolute value component of the equation (as shownabove), a positive ASI value will be representative of the dominant/ un-injured limb having superior strength while a negative ASI value will indicate that the non-dominant/injuredlimb had superior strength and power .
When an ASI is calculated for a given movement performance,the magnitude of the imbalance can be an indicator of an increased potential for injury. This is of particular interest whenclearing a player to return to their respective sport following an injury. There is no solid threshold of ASI magnitude thatseparates injured players from non-injured; however a magnitude that exceeds 15% is often associated with players whohave recently sustained an injury to their lower limb, while normative data for various un-injured populations of athletestend to present ASI values below 10% [5,6,8-14]. Therefore, the grading scale outlined in Table 1 can be used as a generalguide for determining the severity of an ASI magnitude. It is important to note, however, that these classifications are notan absolute. For example, an athlete presenting an ASI measure of 17 in one direction may not necessarily incur a lowerlimb injury, while a player presenting an ASI measure of 6 in one direction may. This scale is designed to identify those playersthat are at a greater risk of injury due to their increased imbalances between limbs in one or more movement directions.Insert Table 1 here.
Table 1. Classification of average symmetry index (ASI) thresholds.
Multi-directional Unilateral Assessment
Performing a single-leg countermovement jump into the vertical,horizontal and lateral directions can provide highly reliabledata (ICCs ranging from 0.82-0.96, CV% < 7.2 [9,21,22]) and a more comprehensive profile regarding a player’s legstrength and power output. Additionally, depending on the resources available, such a comprehensive assessment canreflect more sensitive measures of force and power (derived from force plate analysis) or less sensitive measures of jump distance/height (via manual measurement or video analysis). Regardless of the resources available, the single-leg countermovementassessment will provide valuable feedback on thecurrent status of each individual player with relatively high reliability.
Technical Performance Indicators
The strategies used to successfully complete a given task willoften vary across players and genders. There are, however, various body positions and techniques that are thought to be associatedwith an increased incidence of injury to the lower extremities (see Table 2). A kinematic analysis of the movementpatterns used when performing the multi-directional leg assessment may provide further insight into specific movementpatterns that predispose an athlete to injury or a subsequent injury following recovery and medical clearance.
Table 2. Characteristics of movement performances identified as possiblemechanisms for lower extremity injury.
A 3-D video analysis of the multi-directional single-leg assessmentshould be used in order to analyze the movementpatterns being performed. When comparing previously injured athletes to un-injured athletes, those athletes that havemore recently sustained a lower limb injury will likely present additional altered techniques to compensate for the lackof strength, coordination and confidence in the injured limb . As that limb becomes stronger, those previously identifiedcharacteristics will likely dissipate. However, if they fail to diminish over time, the athlete will be at an even greater riskfor injury (in either limb).
Creating a comprehensive player profile must take into accountas many components of agility as possible. However,many assessments of this nature do not measure all three components. Therefore, to create a complete profile of the athlete’sabilities, it is important to include a sport-specific reactive element to the assessment. In the multi-directional single-legjumping assessment that this paper has been centered around, a reactive element can easily be included by having the athlete react to a signal (auditory or visual) by jumping into the designateddirection. Another option is to have the athlete perform multiple jumps into one direction, stopping immediately on the researcher’s command. This would provide additionalinformation concerning balance and control as well as time to stabilization (a factor identified in Table 2).
Player’s movements in sport are not confined to only one directionand are commonly performed off of a single leg. To create a complete profile of athletes’ performance proficiencies, areliable assessment is needed that incorporates not only single- leg multi-directional movements, but also kinematic analysisof movement techniques as well as a reactive component. Highly valuable information gathered from such a comprehensiveassessment includes: direction-specific performances, asymmetry magnitudes, alignments upon landing, contacttime (if consecutive jumps are performed), time to stabilization, muscle activation patterns, and reaction time/accuracy.Reliability of such an assessment is needed, as well as normative measures for both genders and across various sports andperformance levels.
Cite this article: Hewit J K. Developing A Multi-Directional Single-Leg Jumping Assessment which Incorporates Technical, Physical and Perceptual Components of Performance. J J Sport Med. 2015, 2(1): 009.