Trunk Function Correlates Positively with Wheelchair Basketball Player Classification Sileno da Silva Santos, MS, Chandramouli Krishnan, PhD, PT, Angelica Castilho Alonso, PhD, and Júlia Maria D’Andréa Greve, MD, PhD Objective: The aims of this study were (1) to identify differences in trunk muscle strength and balance among various classes of wheelchair bas- ketball (WCB) players and (2) to determine if trunk muscle strength and balance correlate with the current observation-based classification of WCB players. Design: Isometric trunk strength and balance (limits of stability) were objectively quantified in 42 male WCB players. Principal component anal- ysis was used to synthesize a battery of strength and balance measures into a single, composite score of trunk function. The K-means clustering algorithm was then used to generate an objective classification system by stratifying players into 4 classes based on their trunk function. Results: Results indicated that there were significant differences in trunk muscle strength and balance between various classes of WCB players (P < 0.05), such that the mean peak trunk extensor and flexor torque and limits of stability indices increased progressively according to the players’ classes. There was also a significant correlation between observation-based WCB classification and principal component analysis cluster analysis–based WCB classification (ρ = 0.785, P < 0.05). Conclusions: This study provides novel evidence indicating that trunk strength and balance differ among various classes of WCB players, and objective measures of trunk function correlate positively with the current observation-based WCB classification system. Key Words: Cluster Analysis, Isometric Strength, Polio, Spinal Cord Injury, Wheelchair Basketball Classification (Am J Phys Med Rehabil 2017;96:101–108) W heelchair basketball (WCB) is a highly competitive para- lympic sport and is very popular among people with physical disabilities. 1–5 Here, athletes with various physical disabilities due to conditions such as spinal cord injury, ampu- tations, postpoliomyelitis sequelae, cerebral palsy, and others join a team to play WCB. 6 To ensure that a team’s total func- tional potential is matched to its opponent, the International Wheelchair Basketball Federation (IWBF) has developed a player classification system. 7 Simply put, WCB classification is a process in which players are grouped into categories (classes) by assigning points according to their functional capacity. 8 Ac- cording to the current classification system, the player’s playing point ranges between 1.0 (being the player with least physical function) and 4.5 (being the player with most physical function) (Supplementary Table 1; http://links.lww.com/PHM/A267). 7 The classification of WCB players is performed by a panel of trained/certified classifiers based on the observation of a player’s movement and stability in their playing chair and on the basketball court. When performing this observation-based WCB classification, several factors such as an athlete’s (1) trunk function, (2) lower-extremity function, (3) upper-extremity func- tion, and (4) hand function are taken into consideration to arrive at a classification. While the current classification system does not include any objective assessments, there is some evidence to suggest that there is a good relationship between players’ clas- ses and their physiological characteristics and field performance measured in controlled environments. 9–13 Furthermore, evi- dence suggests that objectively measured upper-extremity function correlates with WCB performance. 14,15 Collectively, these results support the notion that observation-based WCB classification system is a valid approach to categorize players into different functional groups. However, several studies have also pointed to the fact that there is substantial overlap in functional capacity metrics be- tween players of different classes. 10,11,16 In other words, players in different classes are not mutually exclusive across perfor- mance domains. As a result, these authors have suggested con- solidating the current levels of classes into a lower number of classes (preferably to 2 or 3 levels). It is important to note that many of these studies have used arm/hand function metrics or upper-body skill metrics, but have rarely incorporated strength, range of motion, or stability indices of the trunk, which form the basis for observation-based WCB player classification. 7 Trunk muscle strength, balance, and range of motion play an important role on players’ functional capacity. For example, players frequently execute trunk movements to recover a ball in the front or on the side of a wheelchair, to receive lateral passes, and to perform wheelchair locomotion on the court. As a result, it is likely that there may be a strong relationship between trunk function and WCB classification. However, despite the impor- tance of trunk strength and stability in WCB sport, there are virtually no studies that have evaluated trunk strength and From the Institute of Orthopedics and Traumatology, Movement Study Laboratory, São Paulo, Brazil (SSS, ACA, JMDG); and Department of Physical Medicine and Rehabilitation, Medical School (CK), School of Kinesiology (CK), and Deparment of Biomedical Engineering (CK), University of Michigan, Ann Arbor, Michigan. All correspondence and requests for reprints should be addressed to: Chandramouli Krishnan, PhD, PT, Neuromuscular & Rehabilitation Robotics Laboratory (NeuRRo Lab), Department of Physical Medicine and Rehabilitation, University of Michigan, 325 E Eisenhower Pkwy (Suite 3013), Ann Arbor, MI 48108. SSS and CK contributed equally to this study. Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.ajpmr.com). Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0894-9115 DOI: 10.1097/PHM.0000000000000548 ORIGINAL RESEARCH ARTICLE American Journal of Physical Medicine & Rehabilitation • Volume 96, Number 2, February 2017 www.ajpmr.com 101 Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.