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Balance Performance in Male and Female Collegiate Basketball Athletes: Influence of Testing Surface

Sabin, Matthew J1; Ebersole, Kyle T2; Martindale, Alan R3; Price, Jimmy W3; Broglio, Steven P1

Journal of Strength and Conditioning Research: August 2010 - Volume 24 - Issue 8 - p 2073-2078
doi: 10.1519/JSC.0b013e3181ddae13
Original Research
Free

Sabin, MJ, Ebersole, KT, Martindale, AR, Price, JW, and Broglio, SP. Balance performance in male and female collegiate basketball athletes: Influence of testing surface. J Strength Cond Res 24(8): 2073-2078, 2010-The Star Excursion Balance Test (SEBT) is a simple and cost-effective balance test. Information on SEBT performance in athletic populations and under varying testing surfaces is needed to fully elucidate the clinical and training utility of this task. The purpose of this study was to examine SEBT performance in division I, collegiate basketball athletes (men = 9, women = 7) and in a healthy nonathlete control group (men = 7, women = 9). Each participant performed the SEBT with their dominant and nondominant limbs on stable and unstable testing surfaces while reaching in the anterior, medial, and posterior directions. No significant differences resulted between the dominant and nondominant limbs (p > 0.05). Significant differences were found between the basketball and control groups in all directions (p < 0.01) and the average reach score (p < 0.01) with the control group reaching 6-7% farther than the basketball group. A significant main effect for gender (collapsed across group and limb) was present in the posterior direction (p = 0.02). The SEBT performance in the medial and posterior directions and the average score were significantly (p < 0.01) reduced during testing on the unstable surface. These results suggest that athletic status may be a factor to consider when interpreting SEBT reach performance. Future research should examine the influence of SEBT testing in other athletic populations. Further, use of an unstable surface provided a greater challenge to balance. Additional research may provide insight into the role of using an unstable surface with the SEBT as part of an injury risk assessment and its use in identifying limb differences between injured and uninjured limbs.

1Department of Kinesiology, University of Illinois, Champaign, Illinois; 2Department of Human Movement Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; and 3Department of Intercollegiate Athletics, University of Illinois, Champaign, Illinois

Address correspondence to Matthew J. Sabin, msabin2@illinois.edu.

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Introduction

The importance of balance assessment lies in the potential relationship between balance ability and injury incidence. Poor balance has been linked to an increased risk for injury such as those resulting from falls in the older adult population (13). In an athletic population, balance, as assessed by sway index, has been demonstrated to predict injury in high-school basketball athletes (15) and in Australian football athletes (12). The results from these studies suggest that individuals with poor static balance may be more likely to experience ankle injuries. The potential link between balance ability and injury risk has resulted in increased interest in developing less-instrument intensive balance assessment tasks that may guide the development of intervention programs to improve balance and minimize the potential for injury.

The Star Excursion Balance Test (SEBT) is an example of a reliable, simple, and noninstrumented test for assessing lower-extremity balance and neuromuscular control (5,19). The SEBT uses a single-leg stance to maintain a stable base of support while performing a maximum reach of the free leg in specific directions (5,6,9,10,19,21,24). Performance on the SEBT is quantified by measuring the distance reached with the free leg and greater reach distance has been suggested to be associated with greater postural control (9,19,21). For example, individuals with chronic ankle instability have been reported to have decreased SEBT reach distances in comparison to a healthy population. Similar results have also been reported in individuals with anterior cruciate ligament (ACL) deficiencies where the ACL group reached significantly less than the healthy control group (8). Nakagawa and Hoffman (17), however, reported an absence of difference in SEBT scores between the injured and uninjured limbs in a population with a history of recurrent ankle sprains. More recently, Plisky et al. (21) reported that healthy boy and girl high-school basketball athletes with limb differences in SEBT performance were 2.5 times more likely to sustain a lower-extremity injury during the season.

The simplicity of the SEBT makes it an ideal task to be used by clinicians or strength coaches to assess balance within an athletic population. Few studies, however, have included an athletic population as part of SEBT testing. Bressel et al. (3) examined SEBT performance in National Collegiate Athletic Association (NCAA) division I collegiate female basketball, gymnasts, and soccer athletes and reported that female collegiate basketball athletes had inferior SEBT performance where as the soccer group had the greatest SEBT performance. This study, however, did not report the results for a comparative nonathletic female population. Thorpe and Ebersole (24) reported that the SEBT performance in healthy division I collegiate female soccer athletes was less than that of a healthy nonsoccer female group. Thus, it appears that the influence of athletic status on SEBT performance is unclear. Furthermore, no prior studies, to our knowledge, have examined SEBT performance in male collegiate athletes.

None of the previous studies using the SEBT have incorporated the use of an unstable testing surface. The balance and ankle injury literature has suggested that using an unstable surface to assess balance increases the challenge of the task and may better discriminate between different populations (2,4). The Balance Error Scoring System uses both stable and unstable testing surfaces to determine balance related deficits associated with a head injury (7). Decreases in balance (i.e., more errors) have been reported with the progression of stance and testing surface difficulty, indicating that maintaining balance becomes more difficult as the surface moves from stable to unstable (4). Incorporation of an unstable surface with SEBT testing may provide a more challenging task that ultimately improves the SEBT as a meaningful test to assess postural control changes associated with injury and training programs. To date, however, the SEBT literature has used a testing protocol involving only a stable surface.

The purpose of this study was to examine the SEBT response in healthy division I collegiate basketball athletes (men and women) during testing on a stable and unstable surface.

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Methods

Experimental Approach to the Problem

The SEBT is a simple task designed to measure postural control and may be a useful tool to screen for balance deficit that may be associated with injury risk and response to rehabilitation or conditioning programs. It is possible that the sensitivity of this task may be enhanced by the addition of an unstable testing surface. However, no current literature has incorporated an unstable testing surface with the SEBT. Furthermore, the response of healthy collegiate basketball players on the SEBT has not been previously explored. This study will extend the current SEBT-related literature and provide novel insight for future research and implementation of the SEBT as a tool to assess balance.

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Subjects

Sixteen NCAA division I collegiate basketball athletes (n = 9 men, 19.5 ± 1.7 years, 93.5 ± 8.0 kg, and n = 7 women, 20.3 ± 1.1 years, 78.4 ± 12.8 kg) and 16 recreationally active, nonbasketball college-aged students (n = 7 men, 21.0 ± 1.0 years, 83.1 ± 8.1 kg and n = 9 women, 21.2 ± 0.9 years, 65.0 ± 9.4 kg) volunteered to participate in this study. This investigation was approved by University Institutional Review Board for Human Subjects and all participants completed a self-report health history questionnaire and signed a written informed consent before testing. All participants were screened for lower-extremity (ankle, knee, hips) bone and joint injuries and abnormalities and for conditions (i.e., concussion, vestibular disorders, upper respiratory infection, etc.) that may influence balance. Any participant self-reporting the presence of any injury or condition was excluded from the study. The healthy, control participants were recruited from a general collegiate student population and were recreationally active (3-4 d·wk−1) in fitness activities (i.e., running, resistance exercises, swimming) but not involved in competitive basketball. The basketball group participants were all from the same NCAA division I, Big 10 team. Collegiate basketball players were used in this study because this population has been previously identified as having a high risk for lower-extremity injury (1,14,16,18) and, therefore, may benefit from future development of the SEBT as an injury screening tool.

The data collection for all participants was completed relative to the off-season time period for the basketball group (July to August) and before the start of any formal preseason conditioning program.

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Star Excursion Balance Test Protocol

To minimize the potential for a learning effect, each participant was required to visit the laboratory on 2 separate days. The first session was an orientation and practice session in which the participants completed the required paperwork, were given instructions for the SEBT, and allowed to practice a minimum of 3 reaches in each direction or until they felt comfortable with the task. No measurements were taken during the first session. At the second session, participants warmed up for 5 minutes on an exercise bike at a self-selected pace and then performed the SEBT with the reach distances being recorded. A minimum of 24 hours separated each session.

The SEBT was administered as previously described in the literature (9,24). However, only the anterior (A), medial (M), and posterior (P) reach directions were used in this study (Figure 1). An Airex (Alcan Airex, Sins, Switzerland) balance pad (50 × 41 × 6 cm) was used to create the unstable testing surface. The Airex pad was marked with perpendicular pieces of tape so that the pad could be placed on top of the stable surface design (ground) without altering the alignment of the reaching directions or starting position for the foot. Previous test-retest reliability from our laboratory for SEBT reach indicated that for 10 participants measured 48-72 hours apart, the intraclass correlation coefficient values during the stable condition were 0.916 (anterior direction) and 0.837 (posterior direction) and 0.936 (anterior direction) and 0.947 (posterior direction) during the unstable condition.

Figure 1

Figure 1

While maintaining a single-leg stance, the participants were asked to maximally reach along the identified line with the contralateral limb and lightly touch the line with the distal part of the foot. All reach trials began with both feet in contact with the ground and the stance leg appropriately positioned in relation to the center of the SEBT grid. The participants were instructed to keep their hands on their hips while performing this task. Failed test criteria included the following: (a) if the reach foot was placed in contact with the ground for support, (b) the stance foot was moved or lifted, (c) equilibrium was lost during any part of the reach or return phase, and (d) the point of contact was to either side of the taped line. A total of 5 test reaches were performed in each direction. Reach distance was quantified by measuring the distance (cm) from the center of the crosshairs to the point of distal foot-ground contact marked in ink by the investigator. A 1-minute rest was allowed between directions. The order of the reach direction and starting limb were counterbalanced for all participants.

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Statistical Analyses

The Star Excursion Balance Test performance for each direction was represented by the reach trial resulting in the greatest reach for each direction (A, M, P). To account for variations in limb length, all reach distances were normalized as a percent of the reaching leg's length as determined by measuring the distance from the ASIS to the ipsilateral medial malleolus. In addition, an average (AVG) score was calculated by averaging together the maximal reach for each direction. All statistical analyses were completed with Statistical Package for Social Science (SPSS, version 16.0, Chicago, IL, USA).

To examine surface (stable, unstable), group (basketball, nonbasketball), limb (right, left), and gender (men, women) differences in normalized SEBT reach performance, separate repeated measures, mixed factorial analyses of variance (limb × surface × gender × group) were performed for each reach score (A, M, P, AVG). Pairwise follow-up tests, implementing a Bonferroni correction, were carried out when appropriate. An alpha of 0.05 was used for all analyses.

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Results

Anterior Reach

For reach distance in the anterior direction, there were no significant interactions for limb, surface, gender, or group (p > 0.05). There was no significant main effect for limb, testing surface, or gender. There was, however, a significant between-group effect (p < 0.01, 1 − β = 0.84; Figure 2). Follow-up analysis revealed significant differences between the basketball group (=0.96 ± 0.06 cm) and the control group (=1.03 ± 0.06 cm) with the control group reaching 7% farther.

Figure 2

Figure 2

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Medial Reach

Analysis of the medial reach distances revealed a significant 3-way interaction between limb, surface, and group (p = 0.02, 1 − β = 0.66) but no significant 2-way interactions (p > 0.05). Follow-up analysis of the interaction resulted in no significant differences in limb (p > 0.05). However, significant differences were found between groups (p = 0.01; Figure 2) and surface type (p < 0.01, Figure 3) where the control group reached (= 1.00 ± 0.05 cm) 6% farther than the basketball group (= 0.94 ± 0.07 cm). In addition, a significant difference between testing surface was found (p < 0.01, 1 − β = 1.00; Figure 3) with a 4.5% greater reach distance on the stable surface (= 0.99 ± 0.07 cm) than the unstable surface (= 0.94 ± 0.07 cm).

Figure 3

Figure 3

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Posterior Reach

Analysis of the posterior reach direction indicated a significant gender × group interaction (p = 0.04, 1 − β = 0.53) with follow-up analyses revealing significant differences between genders (p = 0.02; Figure 4) and groups (p < 0.01; Figure 2) when collapsed across all other variables. The men (= 0.87 ± 0.07 cm) reached 5% farther than women (= 0.82 ± 0.09) and the control group (= 0.88 ± 0.06 cm) reached 7% farther than the basketball group (= 0.81 ± 0.091 cm).

Figure 4

Figure 4

There was no significant main effect for limb (p > 0.05); however, there was a significant main effect for surface (p < 0.01, 1 − β = 1.00; Figure 3). Follow-up analysis indicated that reach distance was 9% farther on the stable surface (= 0.89 ± 0.08 cm) than on the unstable surface (= 0.80 ± 0.09 cm).

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Average Score

No significant interactions were noted in the AVG reach scores. Analyses of the AVG score indicated a significant between-group effect (p < 0.01, 1 − β = 0.91; Figure 2). Follow-up analysis indicated that reach was 7% farther in the control group (= 0.97 ± 0.05 cm) than the basketball group (= 0.90 ± 0.06 cm). There was also a significant main effect for surface (p < 0.01), 1 − β = 1.00; Figure 3) with a 5% farther reach distance on the stable surface (= 0.96 ± 0.07 cm) than the unstable surface (= 0.91 ± 0.07 cm). There was no significant difference between limbs or genders.

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Discussion

To our knowledge, the use of an unstable testing surface during the SEBT was unique to this study. One finding of this study indicated that performance during the SEBT, as measured by reach distance, is greater on a stable surface than on an unstable surface in all directions with nonsignificant results only in the anterior direction. The magnitude of the significant differences ranged from 5 to 10% depending on the direction of the reach. An unstable testing surface has been speculated to challenge the somatosensory mechanism of postural control (22) increasing the difficulty to maintain balance. As a result, trunk sway, and therefore center of mass, increases while balancing on a foam surface (2). Although trunk sway was not quantified in the present investigation, the change in surface (i.e., foam) resulted in decreased reach distance indicating that a more challenging task was indeed created. Because the groups of this study consisted of healthy individuals, we can only speculate on the ability of the foam surface to differentiate those with and without a pathological condition or those simply at risk for future injury. The results of this study however lay a foundation for further research that would elicit more specific conclusions about the use of unstable surfaces during balance testing with the SEBT.

Analysis of mean group performance (collapsed across limb and testing surface) revealed significant differences between the basketball and control groups in all directions and the average reach score (Figure 2). Across all directions, the control group reached 4-8% farther than the basketball group when reach scores were normalized to leg length. The methodological constraints of this investigation lead us to speculate on the underlying reasons for these differences. It is possible that, individually or in combination, the level and the specific nature of prior training, current strength, flexibility or the presence of pathological condition may alter “normal” SEBT performance or the perception of function in basketball athletes resulting in differences between the groups. Because recent lower-extremity and pathological condition was controlled for as part of the criteria for inclusion, it is possible that group differences in the level of training and lower-extremity strength were, in part, responsible for group differences in SEBT reach.

Level of training comparisons must be drawn from research comparing an athletic population to a healthy control group, typically not involved in specific sport training, because currently no known research has compared different levels of the same sport on SEBT performance. Supporting research for training differences between healthy populations in general is limited. Only one known investigation has previously examined the SEBT in a healthy, collegiate athletic population when compared to a healthy control group. Thorpe and Ebersole (24) used a division 1, collegiate soccer population and a healthy control group reporting recreational activity with no soccer experience. The authors reported increased performance, as measured by reach distance, in the soccer population compared to the control group. Although the results of the current study seem to be in conflict with those of Thorpe and Ebersole (24), direct interpretation is difficult as the control groups performed quite differently in these 2 studies. Despite these differences in the results, it can be speculated that sport-specific function and possibly training variations between the collegiate soccer and basketball populations may account for the differences in the findings of the 2 studies. Increased SEBT reach distances in a soccer population compared to a basketball population have been previously reported and speculated as a result of differing sport-specific demands (3). Soccer uses unilateral stance and balance with contralateral reaches that are less common in basketball participation, which may enhance the necessary postural control used to increase SEBT reach distances in the soccer population.

Although the current study did not examine strength characteristics, strength differences between the basketball and nonbasketball groups may have also contributed to the SEBT results of the current study. Based on the current clinical literature where those with ACL deficiency (8) performed more poorly on the SEBT than their healthy counterparts, it seem reasonable to assume that strength differences may be a contributing factor to the sensitivity of the SEBT to injury status. Thorpe and Ebersole (24), however, reported that although the collegiate female soccer group was significantly stronger then the nonsoccer control group, reach distance for the soccer athletes was significantly less and negatively correlated to lower-extremity strength. A recent study by Sato and Mokha (23) reported nonsignificant increases in SEBT reach distance after a 6-week core strength training program in competitive runners. Thus, the influence of strength on SEBT performance remains unclear.

When the current results are considered with those of prior studies involving athletes (3,23,24), it is possible that SEBT performance and the contributing factors may vary across different athletic populations. Previous studies comparing different populations have suggested that reach distance and balance increase as “function” increases (injured to noninjured (8,9,19) and weak to strong (20,24). This appears to hold true in a soccer population as shown by Thorpe and Ebersole (24); however, it is plausible to think that the sport-specific differences in basketball athletes (i.e., demands of sport, type of training) may, in part, account for the apparent inferior balance performance in the basketball athletes (when compared to the controls) from the current study.

The results of this study indicate that there were no limb differences in SEBT reach performance for any group or testing surface. This similarity in limbs, independent of group or testing surface, is consistent with previous literature (3,9,24) and provides further support that healthy limbs will perform in a similar manner during SEBT performance. Healthy limb symmetries have been observed during a unilateral postural control task on a force platform where sway area and sway path length demonstrated nonsignificant differences between functionally dominant and nondominant limbs (11). Nonsignificant differences between limbs were expected in this study because it is assumed that in healthy populations, reach distances from the 2 limbs will be equal in the absence of pathology (9,24). These findings support the notion that the SEBT may be sensitive to detecting limb asymmetries within an individual when one limb is injured (6) or at risk for future injury (21).

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Practical Applications

Similar SEBT reach performance between both limbs in athlete and nonathlete populations has been previously reported and further confirmed with the results of the current study. Performance of the SEBT on an unstable surface did not change this finding of clinical and methodological importance. As such, when a known or unknown injury is present, the SEBT will likely demonstrate limb asymmetries in SEBT reach distance. Furthermore, balance ability, as defined by SEBT reach distance, was decreased in the basketball group compared to the nonbasketball groups, despite the absence of known lower-extremity injury. This finding raises questions relative to how SEBT reach distance is interpreted and whether performance can be generalized across healthy populations and sport. Comparison between healthy populations may be influenced by differences in levels of strength, training, and sport-specific requirements.

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Keywords:

dynamic balance; SEBT; reach distance

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