Changes in Overhand Throwing Patterns as a Function of Ball Size

Pediatric Exercise Science, 1992, 4, 50-67

Changes in Overhand Throwing Patterns as a Function of Ball Size

Allen W. Burton, Nancy L. Greer, and Diane M. Wiese

Ten males and 10 females in each of four gradelage groups threw styrofoam balls of six different diameters as hard as possible at a wall 6.7 m away. Each ball size was thrown four times. The first hypothesis, that the levels of the five components of the one-hand overhand throw would be quite stable for individuals for throws of a particular ball size, was supported. Ball sizes at which the component levels were unstable marked the beginning of a transition to a new component level 70.6% of the time. The second hypothesis, that five components would change from higher to lower levels for most of the subjects as ball size was scaled up, was supported only for the backswing and forearm components. These components were more likely to be affected by increasing ball size because the higher level components required a firm, one-hand grip on the ball, which became more difficult as ball diameters exceeded the subjects' hand widths. The results indicate that practitioners need to recognize that different ball sizes may elicit different throwing patterns, and specifically that a critical ball diameter may be reached when it is equal to hand width.

Objects such as balls can be thrown many ways. A throw may vary by the number of hands used (one or two), the vertical position of the hands relative to the shoulder (underhand or overhand), or the horizontal position of the hands relative to the midline (from the midline, as in a chest pass, or from one side). Despite the number of throwing pattern options, research with adults and with children from 3 years of age and up has shown that most persons, when given a choice, prefer to use a single pattern-one-hand overhand from the side-to perform a variety of tasks including throwing for accuracy, throwing for maximum distance, and throwing for maximum force (1, 8, 16). There may be some situations in which other throwing patterns are preferred, such as tasks involving very heavy objects, but the many possible within-pattern variations of the one- hand overhand throw allows it to be used for many different tasks by persons with a wide range of physical and motor attributes. It is not surprising, then, that the one-hand overhand throw has been studied more extensively than any other throwing pattern.

The authors are with the Division of Kinesiology, 1900 University Avenue S.E., University of Minnesota, Minneapolis, MN 55455-0155.

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52 - Burton, Greer, and Wiese

ing the one-hand overhand throw, should not be labeled developmental but rather should be considered a continuum of specific patterns that may vary as a function of performer, task, or environmental constraints.

Two studies designed to examine the effect of task constraints on the patterns used to perform a one-hand overhand throw were reported by Langendorfer (14) and Roberton (24). Langendorfer sought to determine whether the developmental status of the individual components of the one-hand overhand throw in fourth graders and young adults would be altered by changing the goal of the task from accuracy to force. In the accuracy condition, the subjects were instructed to hit the center of an 8-ft diameter vertical target, marked with a red dot, with a tennis ball from a distance of 6 m (children) or 10 m (adults); in the force condition, the subjects were instructed to throw the ball as hard as possible from the same distances with the target still in place.

Langendorfer (14) found that the mean levels of four of the five components (all except the backswing) were significantly higher in the force condition for the males. However, the only effect of the shift to a force task for the females was a significant increase in the mean level of the feet component in the fourth-grade girls. Langendorfer (14) suggested that the differential effects of the task manipu- lation on males and females may have been related to differences between the sexes in the relative force demands of the same throwing distances. These results are important because they show that task constraints such as the goal have a substantial effect on the component levels, and thus on the overall pattern of the one-hand overhand throw.

Roberton (24) had boys and girls from 3 to 8 years of age throw beanbags for force from 8 feet (younger children) to 11 feet (older children) in four target conditions: (a) no target, (b) a stationary target, (c) a stationary target changing location between trials, and (d) a stationary target changing location within a trial. She found that the component levels of the humerus, forearm, trunk, and feet of the children as a group did not change as a function of the environmental manipulations. However, changes in projectile velocities indicated that "some adjustments to the moving environment were occurring within developmental levels, but that the adjustments were not drastic enough to evoke the movement reorganization typical of a change in level" (24, p. 12).

A task constraint more likely to elicit changes in the component levels of the one-hand overhand throw may be object diameter. In an experiment involving young men throwing, for maximum distance, ball-like objects varying in both weight and diameter, Bingham et al. (1, Exp. 2) reported that the largest diameter object (5 in.) tended to be thrown with a one-hand overhand pattern, with less elbow flexion and less wrist extension than the smaller objects. Also, Broer and Zernicke (2) assert that if a ball is too large to be grasped, the throwing pattern must be adjusted to a push, which puts the hand behind the ball (p. 261).

If indeed the component levels of the one-hand overhand throw are con- strained by larger ball diameters, then the lower component levels documented for younger children (6, 19, 20) may be partially accounted for by the fact that younger and smaller children were required to use relatively larger balls than older and larger children (same absolute diameters, different relative diameters). The scenario of using objects of the same size for subjects of different ages and sizes in describing developmental progressions of prehension patterns has been verified by Newell et al. (18). Thus the general lack of regard for ball size in

Changes in Throwing Patterns - 53

developmental studies of the one-hand overhand throw leaves this possibiIity open to question and calls for a careful examination of the interaction between performer and task constraints, particularly hand size and ball size.

The present study was part of a project designed to explore the interactive effects of three performer variables, gradelage, sex, and hand width, and one task variable, ball size, on the movement patterns used to grasp a ball and throw it with maximum force. In the first phase of this project, the absolute and relative ball diameters, at which basic grasping and throwing patterns emerged as ball diameter was scaled up from 2 to 12 inches, were documented for male and female kindergartners, second graders, fourth graders, and adults. The percentage of one-hand overhand th&s relative to d l throws across all ball sizes increased with age, from 56.3% for kindergartners to 97.2% for adults, and was higher for males (86.0%) than for females (76.7%). The focus of the present report was on the changes in the components of those one-hand overhand throws as ball diameter increased. The component changes were analyzed from a dynamical systems perspective (9, 11, 12, 13, 27, 29, 30), emphasizing the stability of movement behavior across ranges of performer or task constraints (or control parameters) and the abrupt transitions that may occur at a critical value of one or more constraints.

The predictable sequence of movement skills patterns demonstrated across age can be viewed from a dynamical systems perspective as emerging from attractor states that "evolve and dissolve" as performer, task, and environmental constraints change in nonlinear and asynchronous ways over time (30, p. 263). In this context, the term "attractor state" refers to an equilibrium point, or stable behavioral configuration, which is optimal for solving a movement problem within certain boundary conditions.

When one or more constraints are changed up to a critical value, stability is maintained as the system converges back to the preferred pattern, or attractor (13). However, when one or more constraints exceed a critical value, the internal cohesiveness of the system may be disrupted, leading to a dynamic transition whereby the system reorganizes as it is drawn to a new level of stability with a different attractor (30). In addition, the emergence of a new stable pattern may be preceded by a short period of instability during which several patterns may be exhibited as the system shifts from one attractor state to another (10, 13, 27). Thelen (30) argues that "only a dynamical, emergent view can account for the nonlinearity of the process and the ability of the motor system to continually recalibrate for growth and the inevitable contextual changes that come with add- ing new skills" (p. 276).

Hypotheses for the present study relate to two aspects of the dynamics of the components of the one-hand overhand throw: (a) stability of component levels within ball diameters, and (b) transitions between component levelsas a function of increasing ball diameter. First, the steps or levels for each component shown by each subject were expected to be quite stable for a particular ball diameter. Consistent with this hypothesis, Roberton (20) found that 76 children from kindergarten to second grade who were filmed performing 10 one-hand overhand throws for force using a tennis ball two or three times (a total of 214 testings) always demonstrated the same component category for the humerus and forearm on at least 8 of the 10 trials. Second, the component levels were expected to change from higher, more mature patterns to lower, less mature patterns as ball


diameter was scaled up for most of the subjects. Indeed, the larger ball diameters used in this study (up to 12 in.) were specifically chosen for their potential to elicit changes in the throwing pattern.

Methods Subjects

A total of 80 subjects, 10 males and 10 females in each of four gradelage groups, participated in the experiment. The four gradelage groups included kindergartners (5-6 yrs), second graders (7-8 yrs), fourth graders (9-10 yrs), and young adults (19-33 yrs). The children were students at one elementary school in suburban Minneapolis, and the adults were students at the University of Minne- sota. Informed consent was obtained from each subject or hislher parent or guard- ian. See Table 1 for detailed information regarding the subjects' ages, heights, and hand widths.

Apparatus

The equipment used in this experiment included styrofoam balls, gymnastic mats, a videocamera, and instruments for measuring body length. There were six sizes of styrofoam balls: 1.9, 4.1, 5.8, 7.8, 9.6, and 11.6 inches in diameter. The increments in ball diameter were planned to be 2.0 inches, but manufacturing variability caused them to range from 1.7 to 2.2 inches. Styrofoam balls were used to minimize the effect of weight (2, 24, 85, 109, 211, and 360 g, respec-

Table 1

Age, Height, and Hand Width for Each AgeISex Group

Mean age Mean height Mean hand width (yrs-mos) ( i n~hes )~ ( i n~hes )~

Group N M SD M SD M SD

Kindergarten Boys Girls

Second grade Boys Girls

Fourth grade Boys Girls

Adult Men Women

a~ubject height and hand width are expressed in inches rather than centimeters to be compatible with standard ball size units.


tively), but the covariance of diameter and weight must be acknowledged. The denting of the rather fragile styrofoam balls was controlled by placing mats on the floor and wall surfaces where the ball might land. The subjects' throwing patterns from a side view were recorded on videotape with an SVHS videocamera mounted on a tripod.

Despite the clear differences in ball weights, studies on the sizelweight illusion show that an object that is the same weight as another object but larger will be perceived as lighter than the other (1, 3). An application of power laws of the sizelweight illusion reported by Bingham et al. (1) and Cross and Rotkin (3) indicate that the perceived differences between the weights of the different- sized styrofoam balls should be much less than the differences in the absolute weights. Thus the subjects' perception of the task constraints, as well as actual physical properties of the task constraints, may affect their throwing patterns.

Procedures

Subjects were asked to pick up a styrofoam ball from the floor and throw it as hard as possible at a wall 6.7 m away. Balls of six different sizes were presented four times each in random order for a total of 24 trials. Subjects started with their back to the target wall, picked up a ball that was on or in a 13cm diameter rubber ring, turned around and stepped into a taped rectangle (137 x 91 cm) designating the throwing space, and threw the ball as hard as possible at the wall. The experimenter gave no verbal or visual clues on throwing form (e.g., with one or two hands). In addition, on three trials before and after the main set of 24 trials, subjects were asked to pick up and throw any one of the six different-sized balls that had been placed in a hula hoop (81.3 cm in diameter) on the floor. At the end of the experiment session, each subject's standing height with shoes on was measured with a tape measure against a wall, and his or her maximum hand width from thumb to fifth finger was measured with a ruler.

Experimental Design and Analysis

This experiment involved two between-subject independent variables, gradelage (four levels) and sex (two levels), and one within-subject independent variable, ball size (six levels). The range of absolute ball diameters was the same for all subjects, but the range of ball diameters relative to each subject's hand width was greater for youngerlsmaller subjects than for olderllarger subjects. Thus, ball diameters in the analyses were expressed both in terms of absolute (inches) and relative (ball sizelhand width) size.

The focus of this report was on the one-hand overhand throw, although other throwing patterns were demonstrated by many subjects. A throw was considered to be one-handed when the entire forward motion of the throw was carried out with only one hand in contact with the ball; thus, in a one-hand throw, two hands could have been in contact with the ball during the backswing. One-hand throws were considered to be overhand when the path of the hand was above the shoulder for most of the forward motion, accounting for 98.4% of all overhand throws across all agelsex groups. Only 1.6% of all overhand throws were coded as underhand or sidearm.

Given this focus on the one-hand overhand throw, the primary dependent variables were the developmental steps of five components of the one-hand over-


Table 2

Developmental Sequences for the One-Hand Overhand Throw for Force

Component Level / description

Backswing 1. No backswing 2. Ball moves to position behind or alongside head via upward flexion of

shoulder and concomitant elbow flexion 3. Circular, upward backswing with elbow extended 4. Circular, downward backswing

Humerus 1. Humerus oblique to transverse plane 2. Humerus aligned with transverse plane and, when shoulders are parallel

with frontal plane, has moved ahead of outline of body 3. Humerus aligned with transverse plane and, when shoulders are parallel

with frontal plane, has lagged back within or behind outline of body Forearm 1. No forearm lag

2. Forearm lag is greatest before shoulders are parallel with frontal plane 3. Greatest forearm lag is not reached until shoulders are parallel with

frontal plane Trunk 1. No trunk action (only arm active)

2. Total trunk rotation 3. Differentiated trunk rotation with pelvis preceding upper spine

Feet 1. No step, or step not beyond outline of opposite foot 2. lpsilateral step beyond outline of opposite foot 3. Contralateral step beyond outline of opposite foot

Note. Adapted from Roberton (23).

hand throw, as summarized by Roberton (23, 24). These components include action related to the backswing (four levels), humerus (three levels), forearm (three levels), trunk (three levels), and feet (three levels, excluding Roberton's, 23, fourth level) (see Table 2). These developmental sequences have been supported by validation studies (6, 19, 20) and other related work (15, 31). The components for the feet were coded for both one- and two-hand throws.

The modal component level (1-4) for each set of four trials with a particular ball size was identified. If there were two each of two different component levels, the highest level was used. A score of 0 indicated that the throw was made with two hands.

Reliability

Test-retest and interrater reliability of the identification of modal throwing patterns for each of the five components of the one-hand overhand throw was estab- lished on a sample of 10 subjects (4 kindergartners, 4 second graders, and 2 fourth graders, balanced by sex). The proportion of perfect agreement between two raters (trained undergraduate students) across the 10 subjects was greater than -72 for all components (the mean proportion across the two testings). The proportion of perfect agreement between the two testings across the 10 subjects


was greater than .82 for all components (the mean proportion across the two raters). The results presented in the following section were based on data coded by Rater 1 only.

Results Component Stability Within Ball Diameters

The degree of stability of the component levels within ball diameters for each subject was quantified for each component by the number of times the modal component appeared over the four trials (2, 3, or 4). The grand mean was 3.46 (SD = 0.74) for the backswing, 3.37 (0.76) for the humerus, 3.56 (0.67) for the forearm, 3.67 (0.61) for the trunk, and 3.67 (0.66) for the feet.

The main and interactive effects of age (4), sex (2), and ball size (6) were statistically examined using separate repeated-measures ANOVAs for each component. Because the use of five ANOVAs increased the probability of making Type I errors, a relatively conservative alpha value of .O1 was chosen. In addition, the degrees of freedom for the within-subjects variable, ball size, were adjusted using the Greenhouse-Geisser method (5).

There were significant age effects for the humerus, F(3,72) = 8.60, fi.0001, and the feet, F(3,72) = 1 1.22, fi.0001. Tukey pairwise comparisons indicated that the stability of the humerus component levels was significantly less for the second graders (3.17) and fourth graders (3.20) than for the kindergartners (3.63). Significant main effects for sex were found for the trunk, F(1,72) = 7.93, fi.01, and the feet, F(1,72) = 11.60, p<.01, with the females (3.57 and 3.52, respectively) demonstrating less component level stability than the males (3.78 and 3.83). For the forearm there was a significant ball size effect with component level stability decreasing as ball size increased, F(2.90,209.06) = 4.09, p<.01. Further, there was a significant Age x Ball Size interaction for the trunk, F(3.67, 264.23) = 3.93, with a subsequent simple-effects analysis showing that only the second graders' component level stability was significantly affected by increasing ball size w . 0 1 ) . For the backswing there were no significant main effects or interactions.

Component Transitions as a Function of Ball Size

The primary purpose of this study was to determine whether changes in component levels of the one-hand overhand throw can be elicited by manipulating ball size. The data indicated that the mean percentage of subjects who showed a transition from a higher to a lower component level as ball size increased, without a regression back to a higher level, was 53.3 % for the backswing, 25.0% for the humerus, 6 1.3 % for the forearm, 0 % for the trunk, and 2.5 % for the feet.

Transitions from a higher to a lower component level and then to a two- hand throw without any regression also were included in these percentages. Fig- ure 1 depicts the percentage of subjects in each age group demonstrating a transition from a higher to a lower one-hand component level, including eventual transitions to a two-hand pattern, for each component. The age and sex effects of these two types of throwing pattern transitions were examined for each component using chi square analyses. As in the previous set of analyses, the alpha value was set at .O1 to minimize the probability of making Type I errors over repeated tests.

58 - Burton, Greer, and W i s e

backswing

forearm trunk

I feet

Kindrgrtn 2nd grade 4th grade Adult

Age group

Figure 1 - Percentage of subjects in each age group demonstrating a transition from a higher to a lower one-hand component level, including eventual transitions to a two-hand pattern.

For the backswing, the percentage of subjects showing a transition from a higher to a lower component level significantly varied by age, X2(3, N = 80) = 42.21, p<.001, but not by sex. The percentage of kindergartners who demonstrated a high-to-low transition (15.0%) was much lower than that for the other three groups (mean percentage = 66.7 %) (see Figure 1). For the other four components there were no significant age or sex effects. No subjects in any age group demonstrated a transition from a higher to a lower trunk component level, and only two girls, one kindergartner and one second grader, switched from a higher to a lower level for the feet component.

As ball size increased, many subjects did not change from a higher to a lower component level. Some demonstrated (a) a transition from a lower to a higher component level (mean across all agelsex groups and components = 1.3 %); (b) a transition from a higher to a lower component level (or two-handed pattern) and back to a higher level, or from a lower to a higher component level and back to a lower level (or two-hand pattern) (17.5%); (c) a transition from a single one-hand component to a two-hand pattern (16.5%); and (d) the same throwing pattern across all six ball sizes (36.0%).

The results reported so far provide clear evidence that increasing ball size from 1.9 to 11.6 inches in diameter (and 2 to 360 g in weight) can elicit transitions from a higher to a lower one-hand component level, particularly in the backswing, humerus, and forearm components. Given this information, the next logi- cal question might be, at what ball diameters do these transitions occur? To answer this question, the absolute ball diameters at which the high-to-low component transitions occurred for individual subjects were identified and then con- verted to relative diameters by dividing them by the subject's hand width (relative ball diameter = absolute ball diameterlhand width). The use of relative rather than absolute ball diameters controlled for differences between subjects in hand


size, which is a key physical constraint in throwing. Because there were so few transitions for the trunk and feet components, the mean relative transition diameters were calculated across all subjects only for the backswing, humerus, and forearm components.

For the backswing, 50 one-hand transitions were identified for individual subjects, including (a) 30.0% from Levels 4 to 3, (b) 16.0% fmm Levels 4 to 2, (c) 52.0% from Levels 3 to 2, and (d) 2.0% from Levels 2 to 1. The mean relative diameters for these four transitions were 0.90 (SD = 0.16), 1.07 (.30), 1.12 (0.04), and 1.43 (n = I), respectively. For the humerus, 20 transitions were identified, with 10.0% from Levels 3 to 2 and 90.0% from Levels 2 to 1. The mean relative diameters for these transitions were 0.54 (0.01) and 1.04 (0.28). For the forearm, 51 transitions were identified, including 3.9% from Levels 3 to 2 and 96.1 % from Levels 2 to 1. The mean relative diameters for these transitions were 0.85 (0.02) and 1.14 (0.24).

Another type of analysis was used to help identify the relative ball diameters at which abrupt changes in component levels were made. The mean modal component score for each set of four trials at a particular ball size (0 = two-hand throw, 1-4 = one-hand overhand component score) was calculated by age group for each component. Figures 2 through 6 plot these mean modal component scores for each age group against mean relative ball diameters (MRBD). In addition, a 4 X 2 X 6 (Age X Sex x Ball Size) repeated-measures ANOVA was used to statistically analyze these data. As with the previous ANOVAs, an alpha value of . O l was chosen to guard against Type I errors, and the degrees of freedom for the ball size factor were adjusted using the Greenhouse-Geisser

Backswing

0 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Mean relative ball diameter

-

-

* Kindrtn - + 4th gr + Adult

l - l ~ l ~ t ~ l ~ l ' l -

Figure 2 - Mean modal component score across subjects presented as a function of mean relative ball diameter for the backswing.


Humerus


Figure 3 - Mean modal component score across subjects presented as a function of mean relative ball diameter for the humerus.

Forearm

-

- * Kindrtn

+ Adult 1 . 1 . 1 ' 1 ' 1 ' 1 ' 1 .


Figure 4 - Mean modal component score across subjects presented as a function of mean relative ball diameter for the forearm.


Trunk

.+c Kindrtn + 2nd gr + 4th gr * Adult


F i e 5 - Mean modal component score across subjects presented as a function of mean relative ball diameter for the trunk.

Feet I

* K - male + K - female

- + 2nd -male + 2nd - female + 4th - all + adult - all

~ ' l ~ l ~ l ' 1 ~ 1 ' 1 ' ~


F i e 6 - Mean modal component score across s u b j d presented as a function of mean relative ball diameter for the feet.


method (5). Note that fractions of component levels do not exist, but that the mean modal component scores across subjects, which may be nonintegers, repre- sent the relative distribution of the component levels for a particular subject group.

For the backswing there were significant main effects for age, F(3,72) = 26 .63 , f l . (300 1 , and ball size, F(2.8 1, 202.60) = 12 1.09,fl.OOO 1, as well as an Age x Ball Size interaction, F(8.44,202.60) = 4.30, fl.0001. A subsequent simple-effects analysis showed that the mean modal component scores significantly varied with ball size at each age level @<.0001) (see Figure 2). Tukey painvise comparisons indicated that significant (p<.0001) decreases in the component scores occurred for all four age groups only at a ball diameter of 8 inches (MRBD = .96-1.28). In addition, there was a significant difference between the mean modal component scores for males (2.49) and females (2.07), F(1,72) = 14.76, p<.OOl.

For the humerus, as for the backswing, there were significant main effects for age, F(3,72) = 17.15, p<.0001, and ball size, F(3.99, 287.31) = 45.02, p<.0001, as well as an Age x Ball Size interaction, F(11.97, 287.31) = 3.02, p<.001. A subsequent simple-effects analysis showed that the mean modal component scores varied significantly with ball size for kindergartners, second graders, and fourth graders @<.0001) (see Figure 3). Tukey pairwise comparisons revealed significant @<.01) decreases in the component scores for kindergartners and second graders at 6 and 8 inches (MRBD = 0.89-0.96 and 1.19-1.28), and for fourth graders at 10 inches (MRBD = 1.39). Also, there was a significant main effect for sex, F(1,72) = 8.65, p<.01, with higher mean modal component scores for males (1.36) than for females (1.11).

For the forearm there were significant age effects, F(3,72) = 21.09, p<.0001, and ball size effects, F(2.53, 181.83) = 127.37, p<.0001, and an Age X Ball Size interaction, F(7.58, 181.83) = 7.07, p<.0001. A follow-up analysis of simple effects showed that the mean modal component scores varied significantly with ball size at each age level @<.001) (see Figure 4). Tukey painvise comparisons indicated that there were significant @<.0001) decreases in the component scores for kindergartners at 6 and 8 inches (MRBD = .96 and 1.28), for second graders at 6 inches (MRBD = 1.19), and for fourth graders at 8 and 10 inches (MRBD = 1.11 and 1.39). There was no main effect for sex.

For the trunk there were significant main effects for age, F(3,72) = 25.39, p<.0001, and ball size, F(3.36, 242.16) = 20.71, p<.0001, as well as an Age X Ball Size interaction, F(10.09,242.16) = 5.12, p<.0001. A follow-up simple- effects analysis showed that the mean modal component scores varied significantly with ball size for kindergartners and second graders @<.0001) (see Figure 5). Tukey pairwise comparisons showed significant @<.01) decreases in the component scores for both of the youngest age groups at 6 inches (MRBD = 1.19-1.28). In addition, there was a significant difference between the mean modal component scores for males (1.71) and females (1.25), F(1,72) = 26.65, p<.o001.

For the feet there was a significant main effect for age, F(3,72) = 6.60, 6 . 0 0 1 , and significant interactions for Age x Ball Size, F(11.98, 287.52) = 3.19, p<.001, and Age x Sex x Ball Size, F(11.98, 287.52) = 3.16, p<.001. A subsequent analysis of simple interaction effects showed that there were significant Sex X Ball Size interactions for kindergartners (p<.001) and second graders QK.01). The nature of these interactions is shown in Figure 6.


Discussion

The results of this study clearly showed that changes in the components of the one-hand overhand throw can be elicited by changes in ball size. Although ball diameter was the manipulated variable in this study, the corresponding changes in weight may have had a separate or interactive effect on the components of the one-hand overhand throw. The following issues will now be addressed: component stability within ball sizes, component transitions as a function of ball size, and implications for practitioners.

Component Stability Within Ball Sizes

The stability of the components of the one-hand overhand throw for a particular person at a given time was emphasized in the prelongitudinal screening procedures proposed by Roberton (19,20,21). She argued that unless the stability of a stage across trials first can be demonstrated, longitudinal procedures should not be used to validate the concept of stages in fundamental motor skills. In the present study, stable patterns (three or more of the four trials at a given ball diameter with the same component level) were demonstrated on 88.4% of the trial sets across all agelsex groups, ball sizes, and components. To compare, Roberton (20) found that the 76 children in her study always demonstrated the same component category for the humerus and forearm on at least 8 of the 10 trials.

The instability within the sets of four trials for a particular ball size (only half of the trials at a given ball diameter with the same component level) that was found for 11.6% of the ball diameters was not inconsistent with dynamical systems theory. Kelso and his colleagues (10, 13,27) have hypothesized and shown in other experiments that a transition to a new pattern may be preceded by a short period of instability during which several patterns may be exhibited as the system shifts from one attractor state to another. Thus, at ball diameters just preceding a shift to a different component level, some degree of instability may have been expected. Indeed, the stable component levels (three or more the same) at ball sizes that both preceded and followed one or more consecutive ball sizes with unstable component levels (only two the same) were different 70.6% of the time, indicating that unstable component levels at a particular ball size usually marked the beginning of a transition to a new component level.

Thus the significant age and sex effects found for the stability values most likely reflected a greater degree of change in component levels occurring at specific ages or for only one sex group. For example, the significantly lower stability values for second and fourth graders compared to kindergartners for the humerus matched a higher percentage of second and fourth graders, demonstrating a transition from a higher to a lower component level (see Figure 1). Simi- larly, the significantly lower stability values for kindergartners compared to fourth graders and adults for the feet matched a higher percentage of kindergartners, demonstrating feet component transitions (see Figure 1).

There was a significant ball size effect for stability values only for the forearm which, again applying a dynamical systems argument, suggests that more subjects should have shown transition in forearm component levels than other component levels. This indeed was the case, with more subjects demonstrating forearm component transitions (62.5 %) than any other component transitions (0.0-53.8%) (see Figure 1).


Component Transitions as a Function of Ball Size

The data indicated that the mean percentage of subjects who showed a transition from a higher to a lower component level as ball size increased, without re- gressing back to a higher level, was greatest for the forearm (61.3 %) and backswing (53.3%), and least for the trunk (0%) and feet (2.5%). The backswing. and forearm components were affected by increasing ball size more than the other components, most likely because the higher level components required a firm, one-hand grip on the ball, which became difficult as ball diameters exceeded the subjects' hand widths (i.e., relative ball diameters of 1.0). Significant shifts in mean modal component scores for the backswing and forearm occurred between mean relative ball diameters of 0.96 and 1.39 for all age groups (see Figures 2 and 4).

When a performer used a circular upward or circular downward backswing (Levels 3 or 4, see Table 2), or showed forearm lag (Levels 2 and 3), centrifugal force was pulling the ball away from his or her hand, necessitating a firm grip to avoid dropping the ball. Thus, as relative ball diameters exceeded 1.0, most subjects (a) used a shorter path to raise the ball to a position near the head (the most common backswing transition was from Levels 3 to 2), (b) eliminated forearm lag (the most common forearm transition was from Levels 2 to I), and1 or (c) controlled the ball with two hands for at least part of the backswing. Remember that in this study the distinction between a one-hand and two-hand throw was only based on the number of hands in contact with the ball as it was projected forward. Again, the increasing weight of the ball also should be acknowledged as a possible contributing factor to these transitions.

Statistical analysis of the transition percentages for the backswing revealed a significant effect for age, with lower percentages for kindergartners than for the other three age groups (see Figure 1). Many kindergartners shifted to lower level backswing components, most likely using two hands to control the ball, but then also proceeded to project the ball forward with both hands. Consequently these backswing transitions were not included in the analysis of one-hand overhand throws, reducing the percentage of subjects showing component transitions, but they are reflected in decreasing mean modal component scores depicted in Figure 2. Most of the older subjects showed the backswing shift but maintained a one-hand overhand throwing pattern. There was no effect of age or sex for the transition percentages of any of the other four components.

The percentage of subjects who showed component transitions for the humerus was about half that for the backswing and forearm (see Figure 1). This can be explained by the lower number of subjects at all ages who performed with higher level humerus components, which reduced the number who could demonstrate a transition from higher to lower levels (compare Figure 3 with Figures 2 and 4). At Levels 2 and 3, the humerus was aligned with the transverse plane (see Table 2).

No subjects in any agelsex group showed a component transition for the trunk (see Figure 1); however, a transition from a one-hand throw, using only a single trunk component, to a two-hand throw was demonstrated by 55.0% of the kindergartners, 35.0% of the second graders, 15.0% of the fourth graders, and 5.0% of the adults. This accounts for the significant decrease in mean modal component scores across increasing ball sizes for the two youngest groups (see


Figure 5). The same component level was shown across all component levels by 56.3 % of the subjects.

Two children shifted from higher to lower components for the feet as ball size increased, and four others shifted from lower to higher feet components. However, 83.8% of the subjects, including all of the fourth graders and adults, showed the same component level across all ball sizes (remember that feet components were coded even for two-hand throws). The very low percentage of trunk and feet transitions, which Was contrary to the hypotheses guiding this study, might be attributed to the anatomical position of the trunk and feet relative to the position of the ball and the invariance of the objective of the task (i.e., to throw the balls as hard as possible). First, the trunk and feet were more distal to the ball during the throw than the arm components and, consequently, were less likely to be directly affected by increasing ball diameter. Also, trunk rotation and an ipsilateral step apparently were important in maintaining a high level of force with larger balls, particularly when arm components may have been disrupted. Changes in the trunk and feet may be more sensitive to manipulations of task constraints (force vs. accuracy; see 14) than ball diameter.

implications for Practitioners

Some suggestions have been offered in the motor development literature on how practitioners should manipulate ball size for throwing activities for children, but this information has been too general to be very useful. For example, Herkowitz (7) has suggested that "children should progress from lightweight, easily held balls to larger, heavier balls in throwing activities" (p. 155). However, the purpose of these manipulations is not clear. Is this progression to larger, heavier balls designed to improve distance, accuracy, or form, or to just provide experi- ence with various ball sizes? Further, there is no empirical basis for using particular ball sizes even if the purpose of the activity is clearly specified.

The results of this study provide practitioners with some initial information on how to manipulate ball diameters to elicit certain throwing patterns. First, teachers should consider ball diameters not in absolute terms but relative to an appropriate body parameter, such as hand width, to control for physical differences between students (4). Balls of equal relative diameters should be used across age groups to ensure common performance conditions and standardized assessment procedures. This may be difficult to do with large classes, but the average hand width for each class can be used as a guide in selecting balls for each instructional unit. In addition, students may be allowed to choose from a variety of ball sizes and can be taught how to make appropriate choices.

Second, teachers should recognize that a critical relative ball diameter is reached when it is equal to hand width. When the relative ball diameter exceeds 1 .O, young children are likely to demonstrate two-hand throwing patterns, and subjects who continue to use a one-hand pattern are likely to show regressions in the backswing and forearm components. The most mature one-hand overhand throwing patterns are elicited with the smallest ball diameters, at least down to relative diameters of about 0.20. There is some evidence that balls with a diameter greater than a performer's hand width may be useful in eliciting higher level components for the trunk and feet, particularly in girls, but this needs to be tested further.


And third, teachers should understand that the one-hand overhand pattern is an "attractor" for the task of projecting an object as hard as possible. For balls with relative diameters less than 1.0, all throws by all subjects were performed with just one hand, and 98.4% of all throws made with one hand were considered to be overhand. The use of a movement pattern other than a one-hand overhand throw within the present range of ball sizes most likely reflects some type of performer constraint, such as immaturity, poor strength, inadequate expe- rience, or even perhaps a neuromuscular disorder. The nature of the performer limitation might be explored further by manipulating the other task or environmental variables, and observing the preferred movement solutions (4).

References

1. Bingham, G.P., R.C. Schmidt, and L.D. Rosenblum. Hefting for a maximum distance throw: A smart perceptual mechanism. J. Exp. Psychol. : Hum. Percept. Pe?f: 151507-528, 1989.

2. Broer, M.R., and R.F. Zernicke. Eficiency of Human Movement (4th 4.). Philadel- phia: W .B. Saunders, 1979.

3. Cross, D.V., and L. Rotkin. The relation between size and apparent heaviness. Percept. Psychophys. 18:79-87, 1975.

4. Davis, W.E., and A.W. Burton. Ecological task analysis: Translating movement behavior theory into practice. Adap. Phys. Act. Q. 8: 154-177, 1991.

5. Dixon, W.J. (Ed.). BMDP Statistical Software. Berkeley, CA: University of Califor- nia Press, 1983.

6. Halverson, L.E., M. A. Roberton, and S. Langendorfer. Development of the overarm throw: Movement and ball velocity changes by seventh grade. Res. Q. Exer. Sport 53: 198-205, 1982.

7. Herkowitz, J. Developmentally engineered equipment and playgrounds. In: Motor Development During Childhood and Adolescence, J.R. Thomas (Ed.). Minneapolis: Burgess, 1984, pp. 139-173.

8. Hicks, J.A. The acquisition of motor skill in young children: A study of the effects of practice in throwing at a moving target. Child Dev. 1:90-105, 1930.

9. Karnrn, K., E. Thelen, and J.L. Jensen. A dynamical systems approach to motor development. Phys. Therapy 70:763-775, 1990.

10. Kelso, J.A.S., J.P. Scholz, and G. Schoner. Nonequilibrium phase transitions in coordinated biological motion: Critical fluctuations. Phys. Lett. A. 118:279-284, 1986.

11. Kugler, P.N. A morphological perspective on the origin and evolution of movement patterns. In: Motor Development in Children: Aspects of Coordination and Control, M.G. Wade and H.T.A. Whiting (Eds.). Dordrecht: Martinus Nijhoff, 1986, pp. 459-525.

12. Kugler, P.N., J.A.S. Kelso, and M.T. Turvey . On the concept of coordinative struc- tures as dissipative smctures: I. Theoretical lines of convergence. In: Tutorials in Motor Behavior, G.E. Stelmach and J. Requin (Eds.). New York: North-Holland, 1980, pp. 3-47.

13. Kugler, P.N., J.A.S. Kelso, and M.T. Turvey. On the control and coordination of naturally developing systems. In: 7he Development of Movement Control and Co- ordination, J.A.S. Kelso and J.E. Clark (Eds.). New York: Wiley, 1982, pp. 5-78.

14. Langendorfer, S. Motor-task goal as a constraint on developmental status. In: Ad-


vances in Motor Development Research (Vol. I), J.E. Clark and J.H. Humphrey (Eds.). New York: AMS Press, 1987, pp. 16-28.

15. Leme, S.A., and G.M. Shambes. Immature throwing patterns in normal adult women. J. Human Mvmt. Stud. 4:85-93, 1978.

16. Morris, A.M., J.M. Williams, A.E. Atwater, and J.H. Wilmore. Age and sex differences in motor performance of 3 through 6 year old children. Res. Q. Ejcer. Sport 53:214-221, 1982.

17. Newell, K.M. Constraints on the development of coordination. In: Motor Develop- ment in Children: Aspects of Coordination and Control, M.G. Wade and H.T.A. Whiting @Is.). Dordrecht: Martinus Nijhoff, 1986, pp. 341-360.

18. Newell, K.M., D.M. Scully, F. Tenenbaum, and S. Hardirnan. Body scale and the development of prehension. Dev. Psychobiol. 22: 1-13, 1989.

19. Roberton, M.A. Stability of stage categorizations across trials: Implications for the 'stage theory' of overarm throw development. 3. Human Mvmt. Stud. 3:49-59, 1977.

20. Roberton, M.A. Longitudinal evidence for developmental stages in the forceful overarm throw. J. Human Mvmt. Stud. 4: 167-175, 1978.

21. Roberton, M.A. Stages in motor development. In: Motor Development: Issues and Applications, M.V. Ridenour (Ed.) . Princeton, NJ: Princeton Book, 1978, pp. 63- 81.

22. Roberton, M.A. Describing "stages" within and across motor tasks. In: 7Ke Devel- opment of Movement Control and Co-ordination, J.A.S. Kelso and J.E. Clark (Eds.). New York: Wiley, 1982, pp. 293-307.

23. Roberton, M .A. Changing motor patterns during childhood. In: Motor Development During Childhood and Adolescence, J.R. Thomas (Ed.). Minneapolis: Burgess, 1984, pp. 48-90.

24. Roberton, M.A. Developmental level as a function of the immediate environment. In: Advances in Motor Development Research (Vol. l), J.E. Clark and J.H. Humphrey (Eds.). New York: AMS Press, 1987, pp. 1-15.

25. Roberton, M.A. The weaver's loom: A developmental metaphor. In: Advances in Motor Development Research (Vol. 2), J.E. Clark and J.H. Humphrey (Eds.). New York: AMS Press, 1988, pp. 129-141.

26. Roberton, M.A. Developmental sequence and developmental task analysis. In: Future Directions in Exercise and Sport Science Research, J. S. Skinner, C .B. Corbin, D.M. Landers, P.E. Martin, and C.L. Wells (Eds.). Champaign, IL: Human Kinetics, 1989, pp. 369-381.

27. Schoner, G., and J.A.S. Kelso. Dynamic pattern generation in behavioral and neural systems. Science 239: 1513-1520, 1988.

28. Seefeldt, V., and J. Haubenstricker. Patterns, phases, or stages: An analytical model for the study of developmental movement. In: The Development of Movement Control and Co-ordination, J.A.S. Kelso and J.E. Clark (Eds.). New York: Wiley, 1982, pp. 309-318.

29. Thelen, E. Self-organization in developmental processes: Can systems approaches work? In: Systems and Development: The Minnesota Symposia on Child Psychology (Vol. 22), M.R. Gunnar and E. Thelen (Eds.). Hillsdale, NJ: Erlbaum, 1989, pp. 77-117.

30. Thelen, E. Evolving and dissolving synergies in the development of leg coordination. In: Perspectives on the coordination of movement, S.A. Wallace (Ed.). Amsterdam: Elsevier Science, 1989, pp. 259-28 1.

31. Wild, M.R. The behavior pattern of throwing and some observations concerning its course of development in children. Res. Q. 9:20-24, 1938.

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Changes in Overhand Throwing Patterns as a Function of Ball Size

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