DESCRIPTIVE PROFILE OF SHOULDER RANGE OF MOTION AND STRENGTH IN YOUTH ATHLETES PARTICIPATING IN OVERHEAD SPORTS

Abstract

Background:

The unilateral and repetitive nature of overhead sports, often result in a biomechanical overload of the upper extremity. Understanding the musculoskeletal shoulder range of motion (ROM) and strength patterns in the youth sports of baseball, softball, and tennis could assist injury prevention screening and further the development of conditioning and rehabilitation programs.

Purpose:

To generate a descriptive profile of shoulder musculoskeletal characteristics and determine whether bilateral differences in shoulder ROM exist in youth baseball, softball, and tennis athletes. A secondary aim was to determine whether shoulder rotational adaptations are correlated with playing position, sport, or years of experience.

Study Design:

Descriptive Laboratory

Methods:

A total of 136 competitive youth overhead athletes (baseball: n = 51,12.8 ± 0.9yrs; softball: n = 63,12.3 ± 1.1yrs; and tennis: n = 22,12.5 ± 0.9yrs) participated. Bilateral shoulder internal (IR) and external (ER) passive ROM and external rotation strength were measured using an inclinometer and handheld dynamometer.

Results:

Significant differences (p<.001) in bilateral shoulder ROM and ER strength were found between the athletes in the three sports. Post-hoc test revealed tennis athletes had greater bilateral shoulder ROM than both baseball and softball athletes, but baseball and softball athletes had greater bilateral ER strength than tennis athletes. There were no differences between baseball and softball athletes. Additionally, tennis athletes had greater bilateral internal rotation and total ROM but less ER strength than baseball pitchers, baseball positional athletes, softball pitchers, and softball positional athletes. There were no significant differences between positions and baseball and softball athletes. There were no significant correlations between playing position, sport, or years of experience.

Conclusion:

The results of this study showed differences in shoulder passive ROM and strength adaptations between youth tennis, baseball, and softball athletes. The descriptive nature of this study is impactful as it presents specific ROM adaptions seen in this population. Future research is needed to further evaluate if the “at risk” ROM identified in older populations holds true in the youth population.

Level of Evidence:

Diagnosis, Level 3b.

INTRODUCTION

Overhead youth sports (athletes under the age of 18) like baseball, softball, and tennis are popular at multiple competition levels. Recently, the United States National Federation of State High School Associations reported baseball, softball, and tennis as three of the top ten most popular high school sports.¹ During the 2018-2019 season more than 1,193,528 high school athletes participated in either baseball, softball, or tennis.¹ As the numbers of youth participating in overhead sports increases, the awareness of sport specialization as well as injury susceptibility intensifies. As a result, there has been an observed increase in overuse pathologic conditions affecting the upper extremity.²

Injuries to the upper extremity (shoulder and elbow) comprise a vast number of all the injuries occurring across multiple levels of competition, in the sports of baseball, softball, and tennis.^3-9 Residual shoulder pain in overhead athletes is often attributed to sport-specific adaptations in flexibility and strength not only at the glenohumeral joint, but throughout the entire kinetic chain.¹⁰ The cumulation of these biomechanical alterations, due to the unilateral and repetitive nature of these overhead sports, often result in a biomechanical overload of the upper extremity. The torque and forces experienced through the shoulder of an overhead athlete can lead to changes in range of motion (ROM), specifically decreased internal rotation (IR) and increased external rotation (ER), which may result in a glenohumeral internal rotation deficit (GIRD).^11,12 These ROM adaptations have been associated with increased injury susceptibility. In particular, decreases in IR, total rotational motion (TROM), and bilateral ER strength have all been associated with injury risk in adult overhead athletes.^11-15 While the examination of glenohumeral ROM and strength alone does not allow for definitive conclusions, it is postulated that acceptable muscle balance and ROM are critical in the protection of the shoulder during dynamic repetitive upper extremity movements.^16-18 The unilateral aspect of the sports of baseball, softball, and tennis create muscular and ROM imbalances that could result in upper extremity injury.^19,20 Thus, further investigation into ROM and strength patterns in youth baseball, softball, and tennis athletes is warranted.

Several authors have examined ROM adaptations in adult overhead athletes and found increased risk of shoulder and elbow injury if a loss of glenohumeral IR (GIRLoss) of 15 º to 25 º is present in the dominant shoulder compared to the non-dominant shoulder or if a TROM deficit (TROMD) of > 5 º exists between the dominant and non-dominant shoulder.^{11,13,14,21,22} Additionally, it has been postulated that excess glenohumeral ER or an ER gain (GERGain, defined as excessive ER of the dominant shoulder in comparison to the non-dominant shoulder) could also increase injury susceptibility.²³ However, it has been documented that in contrast to GERGain, a glenohumeral ER insufficiency (GERInsufficiency), as defined by having less than 5 º more ER in the dominant shoulder than non-dominant shoulder, has also been associated with injury. Specifically, in an examination of adult baseball pitchers it was found that those with GERInsufficiency were 2.2 times more likely to be placed on the disabled list due to shoulder injury.¹¹

The available literature has focused on ROM adaptations about the shoulder in adult overhead athletes,^{7,8,11,13-15,21-23} while there is a paucity of literature regarding these musculoskeletal adaptations in youth overhead athletes. Bilateral descriptive data for glenohumeral ROM and strength are not available for comparisons within the most popular youth overhead sports of baseball, softball, and tennis. Understanding the musculoskeletal shoulder ROM and strength patterns at the youth level in these sports could assist in the development of injury prevention screening and further the development of conditioning and rehabilitation programs either based on sport-specific demands or the dynamic upper extremity demands of these sports.

The purpose of this study was to generate a descriptive profile of shoulder musculoskeletal characteristics and determine whether bilateral differences in ROM exist in youth baseball, softball, and tennis athletes. A secondary aim was to determine whether shoulder rotational adaptations are correlated with playing position, sport, or years of experience.

METHODS

Participants

This observational descriptive study examined youth overhead athletes participating in baseball, softball, and tennis. Inclusion criteria included youth (ages 10-19) with no injury within the prior six months and no history of surgery to the upper or lower extremity. Prior to data collection, all testing procedures were explained to each participant and informed assent and parental consent were obtained. The Auburn University Institutional Review Board and the Institutional Review Board of Universidade Federal de São Carlos approved all testing protocols.

Procedures

Participants reported to the Sports Medicine and Movement Laboratory or the Training and Performance Center on the day of participation. After an overview of testing procedures, participants completed a health history questionnaire that included documenting their years of competitive experience. Following the completion of the questionnaire, bilateral shoulder IR and ER passive ROM, and bilateral shoulder ER isometric strength were assessed. Shoulder rotational ROM's were measured using digital inclinometers (Fabrication Enterprises, Inc., White Plains, NY and Lafayette Instrument Company, Lafayette, IN), while shoulder ER isometric strength was measured using a hand-held dynamometer (Lafayette Instrument Company, Lafayette, Ind., USA).

Assessments were performed by one of four examiners over the course of a two-year period. High intraclass correlation coefficients were reported for IR and ER ROM (ICC_(3,k) of 0.84-0.98) for all examiners. Shoulder rotational ROM testing was performed using standard passive ROM techniques and the visual inspection technique were used to determine glenohumeral ROM, isolate glenohumeral movement, and control for scapulothoracic movement.^24-26 Participants were supine on a table with the shoulder in 90 º of abduction and elbow in 90 º of flexion with a rolled towel under the distal humerus to maintain humeral position. The inclinometer was placed on the soft tissue contour of the forearm between the olecranon process and the styloid process of the ulna. Range of motion measurements were recorded at scapulothoracic movement during IR and firm capsular end-feel during ER.^24-26 GIRLoss, GERGain, TROM, and TROMD were calculated for all participants as follows:²³

$$\begin{array}{l}\text{GERGain = }\left(\text{dominant shoulder ER}\right)\\ \text{– }\left(\text{nondominant shoulder ER}\right)\\ \text{TROM = }\left(\text{ER}\right)\text{ + }\left(\text{IR}\right)\\ \text{TROMD = }\left(\text{non-dominant shoulder TROM}\right)\\ \text{– }\left(\text{dominant shoulder TROM}\right)\end{array}$$

With the participant in the same position as described for ROM, shoulder ER isometric strength was measured for the baseball and softball participant. The dynamometer was placed on the posterior aspect of the forearm approximately two inches below the line connecting the radial and ulnar styloid. Participants were then instructed to externally rotate their humerus against resistance with gradually increasing effort until maximum effort was reached and to maintain maximum effort until instructed to relax by the examiner.²⁷ Due to the different testing locations, the tennis participants were assessed for shoulder ER strength in a supine position with the humerus in a position of neutral rotation.¹⁶ However, it should be noted that both testing positions are valid and have proven to result in excellent reliability, regardless of the examiner, position of the patient, or position of the shoulder.²⁸

Statistical Analysis

Statistical analyses were performed using IBM SPSS Statistics 25 software (IBM Corp., Armonk, NY). To examine if there are differences in ROM and ER strength between softball, baseball, and tennis athletes a Kruskal-Wallis test was used due to unequal sample size groups and because the data was non-normally distributed. When a significant difference among sports was found, post-hoc Mann-Whitney U tests were used to determine exact difference between the sports. Spearman Rank correlations were used to determine correlations between years of experience, ROM, and ER strength for each sport and then for sport position within baseball and softball. Bonferroni corrections were applied to all statistical test to minimize the effects of type 1 error, setting a priori at α  =  .0045.

RESULTS

Examination between Sports

A total of 136 youth overhead athletes currently on the team's competitive roster of either baseball (n = 51; 12.8 ± 0.9yrs; 165.9 ± 10.3cm; 58.2 ± 10.7kg), softball (n = 63; 12.3 ± 1.1yrs; 163.4 ± 9.1cm; 59.7 ± 12.5kg) or tennis (n = 22; 12.5 ± 0.9yrs; 160.6 ± 8.4cm; 48.7 ± 10.0kg) participated in the study (Table 1). Descriptive demographic data can be found in Table 2. Significant differences were found between the athletes of the three sports (p < .001) in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, non-dominant shoulder ER strength, and GIRLoss. No significant differences were found in dominant or non-dominant shoulder ER ROM. Post hoc testing revealed that tennis athletes had statistically significantly (p < .001) greater bilateral IR ROM and TROM than baseball athletes; however, baseball athletes had statistically significantly greater bilateral ER strength (p < .001). Examining tennis and softball athletes, the post hoc test revealed that tennis athletes had statistically significantly (p < .001) greater bilateral IR ROM, TROM, and GIRLoss than softball athletes; however, softball athletes had statistically significantly greater bilateral ER strength (p < .001) than tennis athletes. There were no significant differences between baseball and softball athletes.

Table 1.

Means and Stand Deviations for Overall Demographic Characteristics

Sport	N	Age (yrs)	Height (cm)	Weight (kg)	Years of Experience
Tennis	22	12.46 ± .86	160.57 ± 8.38	48.68 ± 10.03	3.61 ± 2.49
Baseball	51	12.84 ± .99	165.86 ± 10.3	58.20 ± 10.77	6.02 ± 1.54
Positional	26	12.92 ± .93	166.45 ± 10.70	59.02 ± 10.27	6.00 ± 1.62
Pitcher	25	12.76 ± 1.05	165.26 ± 10.05	57.34 ± 11.40	6.05 ± 1.46
Softball	63	12.73 ± 1.08	163.39 ± 9.05	59.73 ± 12.05	5.37 ± 2.05
Positional	29	13.00 ± .89	163.49 ± 7.66	59.49 ± 11.55	5.10 ± 2.29
Pitcher	34	12.50 ± 1.19	163.30 ± 10.20	59.92 ± 12.62	5.59 ± 1.83

Table 2.

Means and Stand Deviations for Dominant and Non-dominant Shoulder by Sport

Sport	Dominant Shoulder IR (˚)	Dominant Shoulder ER(˚)	Dominant Shoulder TROM(˚)	Non-dominant Shoulder IR(˚)	Non-dominant Shoulder ER(˚)	Non-dominant Shoulder TROM(˚)	GIRLoss (˚)	GERGain (˚)	TROMD (˚)	Dominant Shoulder ER Strength (N/kg)	Non-dominant Shoulder ER Strength (N/kg)
Tennis	64.73 ± 8.41†*	107.60 ± 9.39	172.32 ± 11.16†*	71.41 ± 8.64†*	98.02 ± 10.49	169.43 ± 11.25†*	6.68 ± 8.01	9.57 ± 9.18	-2.89 ± 9.20	1.72 ± .44†*	1.59 ± .56†*
Baseball	43.60 ± 9.16*	108.16 ± 10.28	151.75 ± 13.74*	47.92 ± 7.84*	104.51 ± 9.65	152.43 ± 14.54*	4.32 ± 9.95	3.65 ± 8.42	.68 ± 10.01	2.31 ± .64*	2.41 ± .62*
Softball	45.79 ± 7.95†	105.59 ± 12.56	151.38 ± 14.63†	46.22 ± 8.92†	101.43 ± 12.16	147.65 ± 15.07†	.43 ± 7.60	4.17 ± 10.47	-3.74 ± 12.86	2.0 ± .56†	2.11 ± .66†

IR  =  Internal Rotation, ER  =  External Rotation, TROM  =  Total Range of Motion (ER + IR), GIRLoss  =  (nondominant shoulder IR) – (dominant shoulder IR), GERGain  =  (dominant shoulder ER) – (nondominant shoulder ER), TROMD  =  Total Range of Motion Deficit (nondominant shoulder TROM – dominant shoulder TROM). † denotes significant difference between tennis and softball. * denotes significant difference between tennis and baseball sports within a particular variable.

There were no significant correlations between ROM, sport, years of experience or sex.

Examination of Sport Position

Since tennis does not have sport positions all tennis athletes were included as a single group, while baseball and softball athletes were classified as position player or pitcher. Descriptive data for tennis versus baseball position play and pitcher are presented in Table 3. There were significant differences (p < .001) in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, non-dominant shoulder ER strength, and GIRLoss (p  =  .004) between sport positions. Follow-up tests revealed significant differences (p < .001) between tennis athletes and baseball positional players in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, and non-dominant shoulder ER strength. The tennis athletes had greater bilateral IR ROM and TROM than the baseball positional players; while baseball positional players had greater bilateral ER strength. Additionally, there were significant differences (p < .001) between the tennis athletes and baseball pitchers in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, and non-dominant shoulder ER strength. Tennis athletes had greater bilateral IR ROM and TROM than baseball pitchers, though the baseball pitchers had greater bilateral ER strength. Finally, there were no significant differences between baseball pitchers and baseball positional athletes.

Table 3.

Means and Stand Deviations for Tennis, Baseball Pitchers, and Baseball Positional Athletes

Sport	Dominant Shoulder IR (˚)	Dominant Shoulder ER(˚)	Dominant Shoulder TROM(˚)	Non-dominant Shoulder IR(˚)	Non-dominant Shoulder ER(˚)	Non-dominant Shoulder TROM(˚)	GIRLoss (˚)	GERGain (˚)	TROMD (˚)	Dominant Shoulder ER Strength (N/kg)	Non-dominant Shoulder ER Strength (N/kg)
Tennis	64.73 ± 8.41†*	107.60 ± 9.39	172.32 ± 11.16†*	71.41 ± 8.64†*	98.02 ± 10.49	169.43 ± 11.25†*	6.68 ±8.01	9.57 ±9.18	-2.89 ±9.20	1.72 ± .44†*	1.59 ± .56†*
Baseball Pitcher	42.74 ± 9.31*	110.65 ± 10.81	153.39 ± 12.87*	49.14 ± 6.82*	106.40 ± 9.88	155.53 ± 13.48	6.40 ±9.57	4.26 ±9.13	2.14 ±9.32	2.41 ± .74*	2.39 ± .60*
Baseball Positional	44.42 ± 9.12†	105.75 ± 9.31	150.18 ± 14.6†	46.75 ± 8.68†	102.70 ± 9.26	149.44 ± 15.15†	2.32 ±10.08	3.06 ±7.82	-.73 ±10.62	2.21 ± .53†	2.42 ± .65†

IR  =  Internal Rotation, ER  =  External Rotation, TROM  =  Total Range of Motion (ER + IR), GIRLoss  =  (nondominant shoulder IR) – (dominant shoulder IR), GERGain  =  (dominant shoulder ER) – (nondominant shoulder ER), TROMD  =  Total Range of Motion Deficit (nondominant shoulder TROM – dominant shoulder TROM). † denotes significant differences between tennis athletes and baseball pitchers. * denotes significant differences between tennis atheltes as baseball positional players.

In the examination of tennis to softball athletes, similar results were found (Table 4). There were significant differences (p < .001) between softball positional players and tennis players in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, non-dominant shoulder ER strength and GIRLoss (p  =  .002). Tennis athletes had greater bilateral IR ROM, TROM, and GIRLoss than the softball positional players; while the softball positional players had greater bilateral ER strength. Furthermore, there were significant differences (p < .001) between tennis athletes and softball pitchers in dominant shoulder IR ROM, dominant shoulder TROM, non-dominant shoulder IR ROM, non-dominant shoulder TROM, dominant shoulder ER strength, and non-dominant shoulder ER strength. Again, the tennis athletes had greater bilateral IR ROM and TROM than softball pitchers, while the softball pitchers had greater ER strength. Additionally, there were no significant differences between softball pitchers and positional athletes. Furthermore, examining baseball and softball sport positions, there were no significant differences, nor were there any significant correlations between ROM, sport position, or years of experience.

Table 4.

Means and Stand Deviations for Tennis, Softball Pitchers, and Softball Positional Athletes

Sport	Dominant Shoulder IR (˚)	Dominant Shoulder ER(˚)	Dominant Shoulder TROM(˚)	Non-dominant Shoulder IR(˚)	Non-dominant Shoulder ER(˚)	Non-dominant Shoulder TROM(˚)	GIRLoss (˚)	GERGain (˚)	TROMD (˚)	Dominant Shoulder ER Strength (N/kg)	Non-dominant Shoulder ER Strength (N/kg)
Tennis	64.73 ± 8.41*†	107.60 ± 9.39	172.32 ± 11.16*†	71.41 ± 8.64*†	98.02 ± 10.49	169.43 ± 11.25*†	6.68 ±8.01*†	9.57 ±9.18	-2.89 ±9.20	1.72 ± .44*†	1.59 ± .56*†
Softball Pitcher	46.12 ± 6.98*	106.50 ± 12.96	152.62 ± 14.47*	46.89 ± 9.51*	100.64 ± 12.50	147.54 ± 15.45*	.78 ±7.59	5.86 ±11.82	-5.08 ±14.05	2.01 ± .58*	2.07 ± .61*
Softball Positional	45.40 ± 9.06†	104.53 ± 12.22	149.93 ± 14.94†	45.43 ± 8.25†	102.34 ± 11.89	147.77 ± 14.89†	.03 ±7.75†	2.19 ±8.39	-2.16 ±11.35	1.99 ± .54†	2.14 ± .72†

IR  =  Internal Rotation, ER  =  External Rotation, TROM  =  Total Range of Motion (ER + IR), GIRLoss  =  (nondominant shoulder IR) – (dominant shoulder IR), GERGain  =  (dominant shoulder ER) – (nondominant shoulder ER), TROMD  =  Total Range of Motion Deficit (nondominant shoulder TROM – dominant shoulder TROM). † denotes significant differences between tennis athletes and softball pitchers. * denotes significant differences between tennis atheltes as softball positional players.

DISCUSSION

The current study aimed to generate a descriptive profile of shoulder musculoskeletal characteristics and determine whether bilateral differences in ROM exist in youth overhead athletes participating in baseball, softball, and tennis. A secondary purpose was to determine whether shoulder rotational adaptations are correlated with playing position, sport, years of experience and or sex. It was revealed that between the three sports, tennis athletes had greater shoulder ROM than baseball and softball athletes, though they also had a greater amount of GIRLoss than the softball athletes. Additionally, baseball and softball athletes (positional and pitchers) had greater bilateral ER strength than the tennis athletes.

It is documented that adult baseball pitchers with a GIRLoss of approximately 15 º to 25 º in their dominant shoulder are at a greater risk of injury.^11,13,14,22 Though the overall mean of GIRLoss in the youth tennis athletes was lower than the previously documented range of increased injury risk, in previous reports of adult athletes, it should be noted that 18.2% (n  =  4) of the tennis athletes fell within the adult range for injury risk (Table 5). Additionally, it is worth noting that though there were no significant differences in GIRLoss between the youth baseball and softball athletes, 11.8% (n  =  6) of the baseball and 3.1% (n  =  2) of the softball athletes were in the ‘at risk’ range. The current study is one of the first to present GIRLoss data and though there were not significant differences between sports, the clinical significance of these data is noteworthy.

Table 5.

Number and Percent of Athletes “At Risk”

Sport	GIRLoss (15 °-25 °)		TROMD (>5 °)		GERGain (<5 °)
	N	%	N	%	N	%
Tennis	4	18.2	9	40.9	6	27.3
Baseball	6	11.8	32	62.3	28	54.9
Pitcher	4	16.0	15	60.0	11	44.0
Positional	2	7.7	17	65.4	17	65.4
Softball	2	3.1	39	61.9	39	61.9
Pitcher	1	2.9	19	55.9	18	52.9
Positional	1	3.4	20	67.0	21	72.4

GIRLoss  =  (nondominant shoulder IR) – (dominant shoulder IR), GERGain  =  (dominant shoulder ER) – (nondominant shoulder ER), TROMD  =  Total Range of Motion Deficit (nondominant shoulder TROM – dominant shoulder TROM).

The GERGain reported in the current study was not statistically different between the athletes. However, in contrast to GERGain is ER insufficiency and 54% (n  =  73) of the athletes in the current study had less than 5 º more of ER ROM in the dominant than the non-dominant arm. This indicates the need for further investigation as ER insufficiency has been associated with shoulder injury professional baseball athletes.¹¹

Several authors have described that youth tennis and baseball athletes display less IR ROM and greater ER ROM on their dominant side as compared to their non-dominant side;^14,16,18,29 however, to the authors knowledge there is no documented normative ROM adaptations for youth softball athletes. Total range of motion, as defined as the sum of shoulder IR and ER, should be similar upon bilateral examination in healthy upper extremity athletes.^{14,16,18,29,30} However, TROMD of greater than 5 º when comparing dominant to non-dominate sides, is considered an injury risk regardless of age.^11,13,14,22 Though the current study did not reveal statistically significant differences in TROMD between the baseball, softball, and tennis athletes, the TROMD displayed by these athletes may be considered clinically significant. Specifically, of the 135 athletes examined over 50% demonstrated a TROMD of greater than 5 º (Table 5). It is postulated that the total TROMD adaptation in these unilaterally dominant upper extremity athletes could be a result of capsular adaptions from reduced posterior glenohumeral joint capsule extensibility; musculotendinous adaptations from reduced posterior shoulder muscle/tendon extensibility; and or osseous factors such as increased humeral retroversion.³¹

In addition to ROM adaptions known within athletes who participate in upper extremity sports as well as the ROM adaptations reported in the current study, there is also a concern about strength adaptions. The current study revealed that the baseball and softball athletes had greater shoulder ER strength than the tennis athletes. While examination of ER strength alone does not allow definitive conclusions, it is known that muscle balance and ROM are critical to protect the shoulder during dynamic repetitive upper extremity movements.^16-18 Unilateral sports such as baseball, softball, and tennis create muscular imbalances, specifically glenohumeral IR strength being stronger than ER strength. However, since the current study only examined shoulder ER strength in healthy athletes, no inferences can be made regarding muscular balance or imbalances between IR and ER strength in these youth athletes. The lack of shoulder IR strength data is a limitation, however, one should be mindful of the strength adaptions that are present in dynamic upper extremity sports such as baseball, softball and tennis as it was found that the baseball and softball athletes had significantly greater ER strength than the tennis athletes.

Clinically it is important to understand what ‘typical’ ROM measures are when working with upper extremity athletes such as baseball, softball, and tennis. Particularly, the increase in ER ROM and decrease in IR ROM in the dominant arm as compared to the non-dominant arm as well as similar bilateral TROM values are seen as an adaption that has previously been referred to as necessary for improved performance and decreased injury risk.^32,33 Understanding these ‘normal’ ROM adaptions in upper extremity athletes at all competition levels can help clinicians better assess and develop injury prevention and rehabilitation programs.

Compared to what is known in adult upper extremity athletes these youth participants were healthy and displayed relatively normal findings. Specifically, the athletes in the current study displayed this ‘normal’ ROM adaptation of increased ER ROM and decreased IR ROM, however the presentation of GIRLoss and TROMD requires for further investigation. The generalizability of these results however is subject to certain limitations. While years of experience was assessed workload (hours of practice, rest days, stretching routine, competition level, strength and conditioning routine, pitch count, etc.) was not. Previous research has shown that workload can influence the degree of musculoskeletal adaptions and could of played a role in our results.^9,34-36 However, when there is a deficit in total ROM, the clinician must determine whether the deficit is due to the lack of ER ROM in a retroverted shoulder or lack of IR ROM associated with posterior shoulder tightness.³⁷ Not assessing these musculoskeletal adaptions at a particular point in the season (for each athlete) is also a limitation.²⁵ Additionally, not all athletes lived in a particular region, so environmental factors could also have an impact on the results of the study. Finally, ER strength was measured in all participants while they were supine, however the baseball and softball athletes were in a position of 90 º abduction while the tennis athletes were in neutral. Though these differing positions are a limitation, it should be known that both positions are valid and have proven to result in excellent reliability, regardless of the examiner, position of the patient, or position of the shoulder.²⁸

CONCLUSION

These results of the current study demonstrate that youth tennis athletes have more bilateral IR ROM and TROM than youth baseball and softball athletes. The baseball and softball athletes had increased ER strength as compared to the tennis athletes. No significant differences in outcomes were seen between baseball and softball athletes. These data may contribute to previous literature by providing normative values for youth baseball, softball, and tennis athletes. In lieu of the ‘at risk’ measures of GIRLoss and TROMD for youth athletes, the authors recommend monitoring these measurements prior to a season and throughout the season. To the authors’ knowledge, this is the first report of GIRLoss and TROMD values in youth baseball, softball, and tennis athletes and future investigators should establish whether GIRLoss and TROMD ‘at risk’ ranges established in adult upper extremity athletes are applicable to youth.