The Influence of Task Constraints on the Glenohumeral Horizontal

Breslin, Garner, Rudisill, Parish, St. Onge, Campbell,Development and Weimar Research Note—Motor Research Quarterly for Exercise and Sport ©2009 by the American Alliance for Health, Physical Education, Recreation and Dance Vol. 80, No. 2, pp. 375–379

The Influence of Task Constraints on the Glenohumeral Horizontal Abduction Angle of the Overarm Throw of Novice Throwers Casey M. Breslin, John C. Garner, Mary E. Rudisill, Loraine E. Parish, Paul M. St. Onge, Brian J. Campbell, and Wendi H. Weimar

Key words: shoulder, throwing, young children

T

he action of the throwing arm during the development of the mature overarm throwing pattern has garnered much attention in recent years. Many of these studies have incorporated Newell’s (1986) developmental model into the description of the organismic (e.g., Halverson, Roberton, & Langendorfer, 1982; Langendorfer & Roberton, 2002) and/or environmental constraints placed upon the thrower (e.g., Thomas & French, 1985; Thomas, Michael, & Gallagher, 1994). According to Newell, three types of constraints—the organism, environment, and task—must be considered when investigating factors related to motor development and learning. These factors and their interactions are included in Newell’s triangular model as key sources of constraint when examining motor development at any age. Constraints are usually defined as facilitative channeling of movement, or limitations thereof, implying that constraints either encourage or limit motor development depending on the characteristics of the constraints (Haywood & Getchell, 2005). Organismic constraints involve the genetic makeup and an individual’s unique characteristics, such as height, limb length and mass, attentional focus, motivation, and arousal level. Because of organismic constraints, people Submitted: December 11, 2006 Accepted: March 28, 2008 Casey M. Breslin, John C. Garner, Mary E. Rudisill, Loraine E. Parish, Paul M. St. Onge, Brian J. Campbell, and Wendi H. Weimar are with the Department of Health and Human Performance at Auburn University.

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performing the same task in identical environments may achieve various degrees of success (Haywood & Getchell, 2005). Environmental constraints include those that describe the setting in which an organism lives and thrives. For example, light, temperature, humidity level, air quality, nutritional opportunities, laws, cultural beliefs and practices, and normative views regarding acceptable behavior represent environmental constraints (Haywood & Getchell). Task constraints are controls that are placed upon the execution of the skill, such as skill criteria, equipment used, and the task itself (Haywood & Getchell). Only a few studies have accounted for the third axiom of Newell’s model, which is the task constraint (Cross, 2004; Southard, 1998). For instance, several studies have investigated how various populations of children respond to different instructional strategies when learning the skill of throwing (e.g., Goodway & Branta, 2003; Goodway, Rudisill, & Valentini, 2002; Valentini & Rudisill, 2004a, 2004b), but the majority of the studies have not reported or described the size or weight of the throwing implement. The failure to report and/or standardize task constraints, such as ball size and weight, makes comparisons across studies difficult, due to evidence that the size and weight of the ball influence the mechanics of overarm throwing (Alexander, 1991; Cross; 2004). Therefore, this study aimed to determine the influence of task constraints on the horizontal abduction angle of the overarm throw of novice throwers. Specifically, the study attempted to determine whether increasing the inertial components of the distal portion of the throwing arm forces the arm into an increased glenohumeral horizontal abduction angle. In an attempt to define the effects of task constraints on the overarm throwing motion, Alexander suggested

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Breslin, Garner, Rudisill, Parish, St. Onge, Campbell, and Weimar

that more massive and larger objects elicit a more nearly simultaneous, rather than sequential, movement pattern (Alexander, 1991). Southard (1998) and Cross (2004) expanded on Alexander’s postulation by investigating the influence of different inertial properties on humeral lag in adult throwers. Specifically, Southard found that mature throwers were more susceptible to external increases in segment mass of the throwing limb (Southard, 1998). Cross (2004) continued this line of research by examining the maximum object speeds and release angles of different masses and found that more massive objects are thrown at higher angles to the horizontal than less massive objects (Cross, 2004). Therefore, previous research on adults leads to the hypothesis that throwing objects of different size and mass will influence specific pattern parameters (i.e., horizontal angle) in children. The purpose of this study was to determine the effects of three baseballs and softballs of different masses (.113 kg, .198 kg, .340 kg) and regulation diameters (22.86 and 30.48 cm, respectively) on the glenohumeral horizontal abduction angle of an overarm throw performed by young children who were novice throwers. Glenohumeral horizontal abduction angle was operationally defined as a relative angle greater than 180° between the humerus and the trunk (determined by a line from the lateral epicondyle to the acromion and the line between the acromions). Based on past research using adult throwers, it was hypothesized that the glenohumeral horizontal abduction angle would differ with the balls of various sizes and masses. Specifically, it was hypothesized that the increased mass of the ball would increase the mass (inertia) of the hand, making the hand-ball system more resistant to a change in its motion, from the drawing back of the arm, to the ballistic movement forward. Theoretically, a more massive hand would force the more proximal segments to proceed posteriorly during the cocking phase of the throw. This increased posterior movement would result in an increased angle between the trunk and upper arm, indicating a greater glenohumeral horizontal abduction angle. In addition, it was speculated that the increased size of the ball would produce less glenohumeral horizontal abduction angle, because the participants would move the object closer to the midline and adopt a more pushlike (simultaneous) motion (Alexander, 1991).

considered novice throwers based on researcher observation during outdoor physical play. Informed consent was obtained from parents, and assent was obtained from the children, prior to data collection. Equipment A digital camera (Canon GL2, Canon USA, Inc., Itasca, IL), filming at 30 Hz, was located 8 feet (2.4 m) above the ground. It was positioned above the participants and into the transverse plane along the polar axis. Video data were analyzed using video analysis software (Dartfish Motion Analysis Corporation, Marietta, GA). The software allowed the researchers to determine the humeral angle as defined previously. The glenohumeral horizontal abduction angle was measured at one frame before initiation of horizontal adduction of the throwing arm, as this would be the position of maximum glenohumeral posterior movement in the transverse plane (see Figures 1 and 2). Design A within-participants design was implemented to determine whether the glenohumeral horizontal abduction angle differed when balls of various sizes and masses were thrown. All participants were asked to throw baseballs and softballs of three different masses twice each. The six balls of different sizes and masses were randomly assigned to avoid learning effects.

Glenohumeral horizontal abduction angle c a

b Head

Method Participants The participants in this study were 15 African American preschool-age children (M = 4.69 years, SD = 0.64), consisting of 7 girls and 8 boys enrolled in an accredited daycare serving low income children and located in a small city in the southeastern U.S. All children were

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Figure 1. Visual display of the angle created during Dartfish data analysis. The labels in the drawing indicate the anatomical landmarks used to construct the angle measured: a. = acromion of the nonthrowing arm; b. = acromion of the throwing arm; and c. = lateral epicondyle of the throwing arm. The arrow on the left indicates the direction of the throw.

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Procedures During data collection, each participant was independently assessed using the following procedures. First, to determine throwing arm, the researcher held a ball in the palm of the hand at the participant’s midline, and the hand the participant used to reach for the ball was the arm with which the child threw during data collection. The child was then outfitted with reflective markers placed on the acromion processes of both scapulas and the lateral epicondyle of the elbow of the throwing arm. This created lines representing the humerus (lateral epicondyle to acromion of throwing arm) and the trunk (acromion to acromion). These lines formed the humeral angle and were used to represent the glenohumeral horizontal abduction angle. If the humerus broke the plane of the body (acromion to acromion) posteriorly, then an angle greater than 180o was created, indicating a more mature glenohumeral horizontal abduction angle. This angle was chosen because it was hypothesized that increasing the inertial components of the hand would cause a larger glenohumeral horizontal abduction angle at front facing, thus indicating a more mature overarm throwing pattern. Time was not used as a dependent measure, because the researchers felt that segmental position was a stronger indicator of the influence of environmental constraints than time. After the reflective markers were securely in place, the participant was asked to stand in the camera view. A research assistant then demonstrated a mature overarm throw and asked the participant to throw the ball “hard as you can.” The participant performed three practice trials with a .071 kg baseball and then was asked to throw all balls in random order, with the sequence repeated for

a total of two trials for each ball. The humeral angle obtained at each size and mass was collapsed before statistical analysis. Each trial was reviewed during capture, and in the event that the participant’s throw was not captured by the camera, he or she was repositioned and immediately instructed to throw that same ball again.

Results All statistical analyses were performed using SPSS version 13 statistical software package (SPSS, Inc., Chicago, IL). Statistical significance was established a priori at α = .05. The glenohumeral horizontal abduction angle was analyzed using a 2 (ball size: baseball, softball) x 3 (ball mass: .113 kg, .198 kg, .340 kg) within-participants repeated measures analysis of variance. There were no significant changes seen in the humeral angle of the participants with the changes in size (p = 0.962, power = .050), mass (p = 0.683, power = .102), or an interaction between the two (p = .778, power = .071), suggesting that ball mass and size did not affect the glenohumeral horizontal abduction angle. The variable of interest was averaged across participants, producing the following mean values: .113 kg baseball = 144.12° + 18.21°; .198 kg baseball = 140.14° + 17.27°; .340 kg baseball = 144.60° + 13.66°; .113 kg softball = 142.69° + 14.67°; .198 kg softball = 142.91° + 15.08°; and .340 kg softball = 143.53° + 26.30°. See Figure 3 for a graphical representation of the mean humeral angle as measured by relative horizontal shoulder abduction as a function of ball size and mass.

Discussion

Figure 2. Visual display of the camera view. The labels in the drawing indicate the marker location of the anatomical landmarks used to construct the angle measured: a. = acromion of the nonthrowing arm; b. = acromion of the throwing arm; and c. = lateral epicondyle of the throwing arm. The arrow on the left indicates the direction of the throw.

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The purpose of this study was to examine the effect of the ball size and mass on the glenohumeral horizontal abduction angle of novice throwers. The novice throwers in the present study failed to achieve demonstrable change in the glenohumeral horizontal abduction angle, which may be attributed to the relatively small angle between the trunk and the upper arm produced by novice throwers. This is consistent with the implication that there will be more of a pushlike simultaneous motion in these throwers, rather than the sequential whiplike motion typically demonstrated with a temporal and spatial lag in the forward movement of the humerus. In addition, the dramatic variability of the performance of the novice throwers, demonstrated by the high standard deviations of the relative glenohumeral horizontal abduction angle, further indicates that a consistent throwing pattern had not yet been achieved by the participants. This may have been the result of inconsistencies in ball size, grip size, grip strength, and/or the restriction of degrees of

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freedom of the participant in an attempt to perform an overarm throw under new task constraints. Specifically, we hypothesized that the increased mass of the ball would increase the mass (inertia) of the hand, making the hand-ball system more resistant to a change in its motion, from the drawing back of the arm, to the ballistic movement forward, resulting in an increased glenohumeral horizontal abduction angle, which may be one of the defining characteristics of humeral lag. The results failed to statistically support the aforementioned hypothesis. This finding, while counterintuitive, enhances the generalizability of previous literature. The results of the current study suggest that previous findings regarding the development of the overarm throw can be compared across studies in which implements of different size and weight were thrown. However, the findings of the present study do not support previous research by Southard (1998) and Cross (2004), which suggested that throwing motions are changed with the addition of an external mass, because altering the inertial properties of the system changes the kinematics of the overarm throw, per the suggestions of Alexander (1991). It appears that the findings described by Southard (1998) and Cross (2004), which included mature throwers, cannot be generalized to novice throwers.

As throwers grow, the inertial properties of the limb segments change, making the limbs more resistant to changes in rotational motion. The present study attempted to elicit this resistance to changes in motion by increasing the inertia of the novice thrower’s arm by increasing the weight of the hand and, in turn, distributing larger mass farther away from the axis of rotation. These conclusions should be read with some caution. As is the case with most research conducted on novice performers, the variability in performance based on standard deviations was considerable. In addition, these novice throwers demonstrated an extremely limited glenohumeral horizontal abduction angle, suggesting that the cocking phase of the throw was not developed enough to generate the momentum required for increased inertia of the hand to draw the arm back. Although the observed statistical power was low, it is unlikely that a larger sample size would have yielded different results. Regardless of the object thrown, the skill level of the participants lacked the mechanical capability to exploit the inherent inertial properties of balls with increased size and mass. Future research should advance the understanding of the role of inertial properties that contribute to the overarm throwing pattern of both mature and novice

Relative Shoulder Horizontal Abduction vs. Ball Size & Mass 180

Relative Humeral Angle

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Standard Deviation Mean

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0 .113 kg BB

.198 kg BB

.340 kg BB

.113 kg SB

.198 kg SB

.340 kg BB

Ball Size & Mass

Figure 3. Graphical representation of the mean humeral angle as measured by relative horizontal shoulder abduction as a function of ball size and mass.

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performers. Care should be taken in future research to report the size and mass of all throwing implements in any study that incorporates throwing motion. This contribution will afford future researchers the ability to directly compare and analyze research across methodological and theoretical constructs. In addition, attention should be given to the method by which this inertial influence is measured. Specifically, the role of the glenohumeral horizontal abduction should be further analyzed as a necessary component of the current understanding of both temporal and spatial humeral lag. Furthermore, future research should attempt to identify the qualifying variables, such as glenohumeral internal/external rotation, horizontal adduction/abduction, or humeral angle, that provide a consistent measure of the kinematic parameters of the overarm throw. Conceptually, in order to effectively and easily compare research across populations, there is a need to develop a single variable that combines the overall actions in each of the planes of motion and reliably quantifies the change in kinematics.

References Alexander, R. (1991). Optimum timing of muscle activation for simple models of throwing. Journal of Theoretical Biology, 150, 349–372. Cross, R. (2004). Physics of overarm throwing. American Journal of Physics, 72, 305–312. Goodway, J. D., & Branta, C. F. (2003). Influence of a motor skill intervention on fundamental motor skill development of disadvantaged preschool children. Research Quarterly for Exercise and Sport, 74, 36–46. Goodway, J. D., Rudisill, M. E., & Valentini, N. C. (2002). The influence of instruction on catching: A developmental approach. In J. E. Clark (Ed.), Motor development: Research and reviews (Vol. 2; pp. 96–119). Reston, VA: National Association for Sport and Physical Education. Halverson, L. E., Roberton, M. A., & Langendorfer, S. (1982). Development of the overarm throw: Movement and ball

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velocity changes by seventh grade. Research Quarterly for Exercise and Sport, 53, 198–205. Haywood, K., & Getchell, N. (2005). Lifespan motor development (4th ed.). Champaign, IL: Human Kinetics. Langendorfer, S. A., & Roberton, M. A. (2002). Individual pathways in the development of forceful throwing, Research Quarterly for Exercise and Sport, 73, 245–256. Newell, K. M. (1986). Constraints on the development of coordination. In M. G. Wade and H. T. A. Whiting (Eds.), Motor development in children: Aspects of coordination and control (pp. 341–361). Amsterdam: Martinus Nijhoff. Southard, D. (1998). Mass and velocity: Control parameters for throwing patterns. Research Quarterly for Exercise and Sport, 69, 355–367. Thomas, J. R., & French, K. E. (1985). Gender differences across age in motor performance: A meta-analysis. Psychological Bulletin, 98, 260–282. Thomas, J. R., Michael, D., & Gallagher, J. D. (1994). Effects of training on gender differences in overhand throwing: A brief quantitative literature analysis. Research Quarterly for Exercise and Sport, 65, 67–71. Valentini, N. C., & Rudisill, M. E. (2004a). Effectiveness of an inclusive mastery climate intervention on the motor skill development of children. Adapted Physical Activity Quarterly, 21, 285–294. Valentini, N. C., & Rudisill, M. E. (2004b). Motivational climate, motor-skill development, and perceived competence: Two studies of developmentally delayed kindergarten children. Journal of Teaching Physical Education, 23, 216–234.

Author’s Note This article is based on an abstract presented at the 2006 North American Society for the Psychology of Sport and Physical Activity, Denver, CO. We thank J. Ross Zorn for his assistance with data collection and Mark G. Fischman for his help in editing the manuscript. Please address all correspondence regarding this article to Casey M. Breslin, 2050 Memorial Coliseum, Auburn University, Auburn, AL, 36849-5323. E-mail: [email protected]

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