Hip, Trunk, and Shoulder Rotational Range of Motion in Healthy Japanese Youth and High-school Baseball Pitchers

ABSTRACT

Objective: The rotational range of motion (ROM) in the upper extremities, trunk, and lower extremities is important for throwing motion. However, unlike for the shoulders, the differences relating to age and throwing-side in trunk and lower extremity ROMs in baseball pitchers are unknown. This study examined the effects of age and dominance on the ROMs of the trunk and upper and lower extremities. Methods: The study included 356 young baseball pitchers aged 9–17 years who participated in off-season baseball camps. The subjects comprised 155 youth pitchers (aged 9–14 years) and 201 high-school pitchers (aged 15–17 years) who were able to throw at full force without pain. The neck, shoulder, trunk, and hip rotational ROMs on the dominant and non-dominant side were measured by well-trained physical therapists. The differences between throwing sides and between age groups were examined using two-way analysis of variance. Results: Shoulder external rotation on the dominant side was greater than that on the non-dominant side. Shoulder external and internal rotational ROMs were maintained regardless of age, whereas the trunk rotational ROM significantly increased with age. Conclusions: The effects of age and dominance on ROMs of the neck, trunk, and upper and lower extremities in Japanese youth and high-school baseball pitchers were clarified. These data could be used as a specific reference and as target values for the rehabilitation of throwing injuries in young athletes.

INTRODUCTION

The throwing motion of baseball pitchers is a total body activity that requires significant coordination of the lower extremities, trunk, and upper extremities for proper execution. Sports, such as baseball, in which the throwing motion is performed repeatedly and the trunk is rotated to throw the ball in the throwing direction,^1,2) can lead to adaptive changes in the rotational range of motion (ROM) of the trunk and hip joints, leading to differences between the throwing and non-throwing sides.^3,4) There have been studies on the characteristics and left–right differences of shoulder rotational ROM,^5,6,7,8) but there are few detailed reports on the characteristics and left–right differences in the ROMs of the neck, trunk, and lower extremities for throwing athletes.⁹⁾

Because of increased participation in sports and the potential for sports-related injuries in young athletes, the treatment and prevention of injury has become an important topic in sports medicine.¹⁰⁾ Sports injuries often arise during the pubertal growth period,¹¹⁾ which usually lasts for several years, beginning around age 11 years for girls and 13 years for boys; the shoulder and elbow joints are particularly susceptible to injury in young baseball players. Injuries are particularly common in pitchers, who have many throwing opportunities.¹²⁾ Moreover, the muscle power and rotational ROM of each joint are important to prevent throwing injuries and to facilitate continued pitching. Generally, the ROM of each joint is considered to decrease on both sides during the growth period.^13,14) However, there have been few detailed reports on the effects of age and handedness (right-handed versus left-handed) on bilateral differences in ROM of the neck, trunk, and lower extremities for throwing athletes.⁶⁾

For injured athletes, basic conservative treatment, including rehabilitation, has been performed.^15,16) During rehabilitation for shoulder and elbow injuries in athletes, it is important not only to evaluate the ROM of the injured shoulder and elbow, but also the ROM of the trunk and lower extremity, which could be the main cause of the pathology. Consequently, understanding the physical attributes of healthy young baseball players in terms of ROM characteristics can provide important basic information that will serve as a reference when evaluating athletes with throwing injuries.

We hypothesized that similar ROM characteristics of the neck, shoulder, trunk, and hip of pitchers would be observed in young baseball pitchers as they age. Our objective was to examine the characteristics of handedness differences in young baseball pitchers and to compare the bilateral difference in these ROMs between youth and high-school baseball pitchers.

METHODS

Subjects

Baseball skill camps are held annually in Kyoto Prefecture during the off-season. The study participants were 356 male baseball pitchers who were recruited at these camps. The age range of the participants was 9–17 years (youth pitchers 9–14 years; high-school pitchers 15–17 years). The height range of the study participants was 127–190 cm (youth 127–176 cm; high school 161–190 cm). The weight of the study participants ranged from 24 to 86 kg (youth 24–79 kg; high school 48–86 kg). The age at commencement of pitching ranged from 3 to 13 years (youth 5–12 years; high school 3–13 years), and pitching experience ranged from 1 to 14 years (youth 1–8 years; high school 3–14 years). All 356 pitchers who could throw at full force without pain and had no pathological signs at the time of the medical checkup were included. Individuals were excluded if they reported a history of significant upper or lower extremity injury, shoulder or elbow surgery in the previous year, or limitations in passive hip or shoulder ROM attributable to pain or an empty end-feel.

This study was approved by the Ethical Review Board of Kyoto Prefectural University of Medicine (Protocol Number: C-1197). Participants were informed of the objectives, methods, and the anticipated hazards and inconveniences related to the experiment. Each participant gave written consent thereafter. Consent was also obtained from the guardians and team managers of the participants.

Procedures

Shoulder external rotation (ER) and internal rotation (IR) (with the shoulder joint abducted to 90°), hip ER and IR (with the hip and knee flexed to 90°), and neck and trunk rotation were assessed by a physical therapist (MH) while two other therapists fixed the adjacent joints to avoid compensatory motion and another physical therapist measured the passive ROM with a bubble goniometer. These procedures were based on the methods of the Japanese Orthopaedic Association, the Japanese Association of Rehabilitation Medicine,¹⁷⁾ and Kibler et al.¹⁸⁾

Shoulder ER and IR angles were measured with the subject in the supine position with the scapula fixed, the shoulder joint abducted to 90°, and the elbow joint flexed to 90°. The angle formed by the ulna and the line perpendicular to the frontal plane passing through the elbow was measured. The neck rotation angle was measured while the subject sat upright. The angle formed by the line connecting both acromions and the line connecting the bridge of the nose and the external occipital protuberance was measured. Trunk rotation angle was measured in the sitting position with the pelvis fixed. The angle formed by the line connecting both posterior superior iliac spines and the line connecting both acromions was measured. For neck and trunk rotation in right-handed pitchers, left rotation was defined as the dominant side (throwing direction), and right rotation was defined as the non-dominant side (the opposite direction). Hip ER and IR angles were measured in the supine position with the pelvis fixed, and the hip and knee joints flexed to 90°. The angle formed by the line descending from the patella and the centerline of the lower leg (the line connecting the center of the patella with the point between the medial malleolus and lateral malleolus) was measured (Fig. 1). For the ROM of the lower extremities in right-handed pitchers, the right lower extremity was defined as the dominant side (stance leg), and the left lower extremity was defined as the non-dominant side (lead leg). Angles were measured in 1° increments using a standard goniometer.

Fig. 1

Measurement method of ROM by a four-member team. Therapists a and b fixed the adjacent joints to avoid compensatory motions. Therapist c measured the passive ROM with a bubble goniometer, and therapist d recorded the angle.

Intra- and Inter-rater Reliabilities

To prevent compensatory movements during measurements, the extremities were moved or fixed based on the method of Wilk et al.¹⁹⁾ A four-member team measured and recorded the angles. All four members confirmed the movable arm, stationary arm, and measured values. The techniques were practiced thoroughly before the day of the evaluations.

All ROM measurements of 10 healthy pitchers were performed twice over a 2-week period by two independent certified physical therapists of the four-member team who were not informed about the conditions of the pitchers.

Statistical Analysis

SPSS for Windows version 21.0 (IBM, Armok, NY, USA) was used for the data analysis. The effects on the ROM data of dominance (dominant; non-dominant) and handedness (right-handed; left-handed) were analyzed using two-way repeated measures analysis of variance (ANOVA) (dominance * handedness). Two-way ANOVA was performed for each motion. When a significant interaction between the dominance and the handedness was observed, Fisher’s least significant difference (LSD) post hoc testing was used to determine significant differences between the dominance and the handedness.

The effects of sidedness (right; left [dominant]) on the ROM data collected for both age groups (youth; high school) were analyzed using two-way repeated measures ANOVA (dominance * age). Two-way ANOVA was performed for each motion. When a significant interaction between the dominance and the age was observed, Fisher’s LSD post hoc testing was used to determine significant differences between the dominance and the age.

Correlation analyses were performed under two conditions: condition 1 involved the dominant and non-dominant ROM and condition 2 included the ROM for each joint. These separate analyses were based on the hypothesis that no relationships would be observed between the dominant and non-dominant ROM. For the purposes of this study, all correlation coefficients (r values) were interpreted as follows: 0.00–0.25 represents little, if any correlation; 0.26–0.49 represents low correlation; 0.50–0.69 represents moderate correlation; 0.70–0.89 represents high correlation; and 0.90–1.00 represents very high correlation.²⁰⁾ The level of statistical significance was set at P<0.05 (two-sided).

RESULTS

Reliability

The interclass correlation coefficient^1,3) was 0.817 (95% confidence interval [CI], 0.774–0.904) for the evaluation of ROM, indicating good inter-rater reliability. The intraclass correlation coefficient was 0.88 for the evaluation of ROM, indicating good intra-rater reliability.

The study included 356 participants who completed the ROM evaluations. There were 74 left-handed pitchers (youth 28; high school 46). All players were male; the average height, weight, age, age at commencement of pitching, and pitching experience are shown in Table 1.

Table 1.  Physical characteristics of right-handed and left-handed youth and adolescent pitchers (n = 356)

	Right-handed			Left-handed
	n = 282			n = 74			P
Age, years	14.2	±	2.4	14.7	±	2.3	0.15
Height, cm	163.8	±	15.1	164.2	±	12.9	0.84
Weight, kg	55.1	±	14.5	54.9	±	12.8	0.91
BMI, kg/m2	20.5	±	8.7	20.0	±	2.3	0.63
Age at commencement of pitching, years	8.0	±	1.7	8.3	±	1.8	0.18
Pitching experience, years	6.2	±	2.6	6.4	±	2.3	0.62

Data are mean ± SD.

BMI, body mass index.

Data relating to right-handed versus left-handed group differences in pitchers are shown in Table 2. The shoulder ER showed a significant interaction between the dominance and the handedness (P<0.001). Shoulder ER was significantly larger on the right side of right-handed pitchers (P<0.001) and on the left side of left-handed pitchers (P<0.05) by post hoc analysis with Fisher’s LSD. Shoulder IR also showed a significant interaction between the dominance and the handedness (P<0.001). Shoulder IR was significantly larger on the left side of right-handed (P<0.001) subjects by post hoc analysis with Fisher’s LSD. Neck rotation showed a significant main effect on the dominant and non-dominant side (P<0.001). For neck rotation, there was no significant interaction between the dominance and the handedness.

Table 2.  ROMs in right- and left-handed pitchers

		Right-handed			Left-handed			Dominance	Handedness	Interaction
		n = 282			n = 74			P	P	P
Shoulder external rotation at 90°, deg	Dominant side	126.0	±	12.0	123.4	±	11.4	<0.001	0.71	<0.001
	Non-dominant side	119.0	±	12.5	120.5	±	9.9
Shoulder internal rotation at 90°, deg	Dominant side	34.4	±	11.7	42.9	±	11.7	<0.001	0.75	<0.001
	Non-dominant side	50.5	±	11.9	42.9	±	11.6
Neck rotation, deg	Dominant side	82.8	±	10.9	78.3	±	9.7	<0.001	0.29	0.17
	Non-dominant side	80.4	±	8.4	82.4	±	11.4
Trunk rotation, deg	Dominant side	52.6	±	11.1	53.6	±	13.2	0.10	0.96	0.02
	Non-dominant side	52.2	±	11.6	51.3	±	11.7
Hip external rotation, deg	Dominant side	59.6	±	11.2	59.1	±	11.0	0.61	0.60	0.34
	Non-dominant side	59.4	±	11.0	58.4	±	10.5
Hip internal rotation, deg	Dominant side	39.3	±	13.1	38.3	±	12.1	0.68	0.65	0.04
	Non-dominant side	40.4	±	14.9	39.9	±	10.7

Data are mean ± SD.

Interaction was calculated by repeated two-way ANOVA with the dominance as an intra-subject factor and handed-ness group as an inter-subject factor.

Table 3 shows differences in the dominant versus the non-dominant side and differences between the youth group and the high-school group. Shoulder ER and IR had a significant main effect on the dominant and non-dominant sides (P<0.001); however, there was no significant interaction between dominance and age. Neck rotation had a significant main effect with respect to age (P<0.001); however, there was no significant interaction between dominance and age. Trunk rotation demonstrated a significant interaction between dominance and age (P<0.001). Post hoc analysis with Fisher’s LSD showed that trunk rotation was significantly larger in high-school (P<0.001) players, and on the dominant side of youth players (P<0.001). Hip ER had a significant main effect with respect to age (P<0.01); however, there was no significant interaction between dominance and age. Hip IR showed a significant interaction between dominance and age (P<0.05). Post hoc analysis with Fisher’s LSD showed that hip IR was significantly larger in the youth group (P<0.05), especially, in the non-dominant side of the youth group (P<0.001).

Table 3.  ROMs in youth and high-school pitchers

		Youth			High-school			Dominance	Age	Interaction
		9–14 years old			15–17 years old
		n = 155			n = 201			P	P	P
Shoulder external rotation at 90°, deg	Dominant side	125.5	±	14.4	125.4	±	9.5	<0.001	0.38	0.13
	Non-dominant side	120.4	±	13.2	118.5	±	11.0
Shoulder internal rotation at 90°, deg	Dominant side	35.4	±	14.4	36.7	±	10.1	<0.001	0.06	0.31
	Non-dominant side	47.3	±	13.6	50.1	±	10.9
Neck rotation, deg	Dominant side	84.6	±	9.8	79.8	±	11.1	0.03	<0.001	0.73
	Non-dominant side	83.3	±	9.0	78.9	±	8.7
Trunk rotation, deg	Dominant side	49.7	±	12.6	55.2	±	10.0	0.27	<0.001	0.00
	Non-dominant side	47.2	±	12.4	55.7	±	9.5
Hip external rotation, deg	Dominant side	61.2	±	12.2	58.2	±	10.1	0.38	0.01	0.57
	Non-dominant side	60.6	±	12.8	58.0	±	9.1
Hip internal rotation, deg	Dominant side	42.0	±	13.4	36.9	±	12.1	0.01	<0.001	0.02
	Non-dominant side	44.5	±	15.1	37.0	±	12.3

Data are mean ± SD.

Interaction was calculated by repeated two-way ANOVA with dominance as an intra-subject factor and age group as an inter-subject factor.

The relationship between dominant side and non-dominant side in the players and the relationship between each ROM are shown in Tables 4, 5. The correlations between dominant and non-dominant ROM for condition 1 ranged from r=0.37 to 0.76 (P<0.01) (Table 4). Because there was a significant and low-high positive correlation between dominant and non-dominant ROM, we selected the dominant ROM. The correlations between each ROM for condition 2 in the youth group ranged from r= –0.31 to 0.38 (P=0.000 to 0.93) (Table 5). In the youth group, there was a significant and low-positive correlation between shoulder ER and hip ER, trunk rotation and hip ER/IR, and hip ER and hip IR. There was a significant and low-negative correlation between shoulder IR and trunk rotation. The correlations between each ROM for condition 2 in the high-school group ranged from r= –0.16 to 0.21 (P=0.002 to 0.76) (Table 5). In the high-school group, there was a significant and low-positive correlation between shoulder ER and neck rotation, shoulder ER and hip ER, shoulder IR and trunk rotation, and neck rotation and trunk rotation. There was a significant and low-negative correlation between shoulder ER and shoulder IR.

Table 4.  Correlations between dominant side and non-dominant side

	r
1 Shoulder external rotation	0.58	**
2 Shoulder internal rotation	0.37	**
3 Neck rotation	0.56	**
4 Trunk rotation	0.72	**
5 Hip external rotation	0.76	**
6 Hip internal rotation	0.76	**

**Statistically significant correlation (P<0.01).

Table 5.  Correlations between ROMs for youth and high-school pitchers

	1	2	3	4	5	6
1 Shoulder external rotation	–	0.06	0.10	0.10	0.32**	0.01
2 Shoulder internal rotation	–0.16*	–	–0.01	–0.31**	0.06	–0.07
3 Neck rotation	0.20**	0.09	–	0.09	–0.06	–0.08
4 Trunk rotation	0.11	0.21**	0.19**	–	0.26**	0.38**
5 Hip external rotation	0.15*	0.10	0.10	0.13	–	0.24**
6 Hip internal rotation	0.02	0.09	0.08	0.06	–0.09	–

Statistically significant correlations: *P<0.05 and **P<0.01.

Correlation coefficients for youth pitchers are to the top right of the diagonal, and those for high-school pitchers are to the bottom left of the diagonal.

DISCUSSION

The present study sought to examine differences resulting from handedness and age in neck, shoulder, trunk, and hip rotational ROM in healthy baseball pitchers.

Reliability of the Range of Motion Measurement

Measuring ROM is a basic method of evaluation in physiotherapy. The interclass correlation coefficients for the measurements conducted by four researchers in this study were high, indicating good reliability of measurements. Kouyoumdjian et al.²¹⁾ reported interclass correlation coefficients of 0.83 for measurements of hip IR and 0.66 for ER, both measured with the subject in the prone position. Wilk et al.,¹⁹⁾ in measurements of shoulder IR ROM, found a coefficient of 0.51 with the scapula not fixed and 0.62 with the scapula fixed. To note the fixation status is important in ROM measurements for each extremity. Further, it is considered important that the measurement process be observed by another staff member to prevent compensatory movements.⁶⁾ The fact that the measurements were conducted by four people in this study might have led to the high intra- and inter-rater reliabilities obtained.

Right-handed versus Left-handed Pitchers

In the throwing arms of baseball pitchers, it is known that shoulder ER is large and shoulder IR is small.^5,6,7,8) Comparing right-handed pitchers with left-handed pitchers, shoulder ER was significantly larger on the right side in right-handed pitchers, and on the left side in left-handed pitchers. Shoulder IR was significantly larger on the left side in right-handed pitchers. In a report targeting professional baseball players, in left-handed pitchers, the shoulder IR did not show a significant difference between the dominant and non-dominant sides.²²⁾ Similar to that report, this study revealed that shoulder IR did not exhibit any difference between the dominant and non-dominant side in left-handed pitchers. Left-handed pitchers often might use the right hand dur-ing activities of daily life. It would be necessary to analyze pitching biomechanics and examine differences between right and left-handed pitchers.

The ROMs of trunk and hip joints were significantly different between left-handed pitchers and right-handed pitchers, but the difference was less than 2°, providing little insight to explain any clinical significance.

Age and Bilateral Differences of Rotational Angles

Shoulder ER was larger than IR on the throwing side in this study. The shoulder rotational ROM profiles were consistent with previously published profiles of healthy baseball players.^5,6,7,8) Generally, the ROM of each joint decreases with age because of increasing rigidity of connective tissue, particularly in and around the muscles and tendons.^13,14) However, the shoulder ER and IR showed no interaction between youth and high-school pitchers. The repetition of pitching may have overridden the effects of age on the range of shoulder rotation.

In addition, the trunk rotation angle was significantly larger in high-school pitchers than in youth pitchers. Ishida et al. reported that trunk rotation in the throwing direction from wind-up to foot-contact and in the opposite directions from maximal external rotation to ball-release were necessary for pitching.²³⁾ Stodden et al. reported that during throwing motion,²⁴⁾ the rotation angles in the throwing direction from the upper trunk to the pelvis increased if ball speed increased. Lorson et al. reported that high-school pitchers threw using a more developed pattern, with the lower extremities and trunk effectively rotated.²⁵⁾ The trunk is rotated to the non-throwing direction in the early cocking phase and to the throwing direction from the late cocking to the follow-through phase during throwing,^1,2) which might lead to adaptive change in the trunk rotational ROM. The repetition of pitching may have overridden the effects of age on the range of trunk rotation.

Neck rotation in the throwing direction was significantly larger than in the non-throwing direction in youth and high-school pitchers. However, this difference was less than 1°, which might be of little clinical significance. Neck rotation angle generally decreased with age,^26,27) as seen in our results.

The hip ER of the youth group was significantly larger in the standing leg, and hip IR was significantly larger in the lead leg. However the differences were approximately 1°, with likely little clinical significance.

Correlation of Shoulder, Neck, Trunk, and Hip Rotation

Correlation was significant between the dominant and non-dominant sides. In youth and high-school pitchers, the correlations were significant but weak between shoulder, neck, trunk, and hip rotation. In youth and high-school pitchers, the correlation was significant between shoulder and hip rotation. Scher et al.²⁸⁾ reported that there was significant correlation between shoulder ER and hip extension in pitchers with throwing disorders and no correlation between shoulder ER and hip extension in healthy pitchers. There was no correlation between shoulder rotation and hip IR between the players with or without throwing disorder. Sauers et al. ²⁰⁾ reported that there was a weak correlation between hip rotation and shoulder rotation in professional baseball players. There was little, if any, correlation between hip rotation and shoulder rotation in youth and high-school pitchers in this study, and this was consistent with the findings of previous studies.^20,28) The correlations between trunk and hip rotation ROM were low and ranged from r =0.26 to 0.38 (P<0.01) for youth pitchers, although there was no significant correlation in high-school pitchers. This result might be affected by the fact that trunk rotation was higher in high-school pitchers. Because relational adaptations in each ROM might be considered part of a pathologic cascade, future research is needed to evaluate the relationships between ROM and throwing biomechanics in pitchers with shoulder or elbow injuries.

CONCLUSIONS

The effects of age and bilateral differences on the trunk and upper and lower extremities in Japanese youth and high-school baseball pitchers during the growth period were clarified. Laterality was observed in shoulder rotation. In terms of age-group differences, high-school pitchers exhibited lower ROM values in the extremities and neck, although shoulder IR and trunk rotation were greater on the non-throwing side. Laterality and age-group differences in ROM, as well as increases in ROM among high-school pitchers, are considered to result from changes that occur during the growth process and are regarded as characteristics of ROM. These results are uniquely practical in two ways: first, they could be used as specific reference and target values for stretching during rehabilitation for throwing injuries in the young athlete; second, they could be used as reference values for giving instructions for conditioning to prevent future throwing injuries in the young athlete.

Limitations

We presently clarified the ROM range of athletes with no throwing disorders. However, this study is a cross-sectional study. The characteristics of the ROM of players who are likely to develop throwing disorders remain unknown. In the future, it will be necessary to carry out longitudinal research to advance disability prevention.

CONFLICTS OF INTEREST

The authors declare that there are no conflicts of interest regarding the publication of this article

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