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Article

Sport-Specific Shoulder Rotator Adaptations: Strength, Range of Motion, and Asymmetries in Female Volleyball and Handball Athletes

by
Manca Lenart
,
Žiga Kozinc
* and
Urška Čeklić
Faculty of Health Sciences, University of Primorska, SI-6310 Izola, Slovenia
*
Author to whom correspondence should be addressed.
Symmetry 2025, 17(8), 1211; https://doi.org/10.3390/sym17081211
Submission received: 5 June 2025 / Revised: 21 July 2025 / Accepted: 22 July 2025 / Published: 30 July 2025
(This article belongs to the Special Issue Application of Symmetry in Biomechanics)
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Abstract

This study aimed to compare isometric strength, range of motion (RoM), and strength ratios of shoulder internal and external rotators between female volleyball and hand ball players Twenty-five volleyball players (age = 21.8 ± 4.8 years, height = 178.5 ± 7.1 cm, mass = 69.3 ± 7.7 kg) and twenty-four handball players (age = 19.5 ± 2.9 years, height = 169.7 ± 6.4 cm, mass = 67.6 ± 8.4 kg), all competing in the Slovenian 1st national league, participated. Maximal isometric strength and passive RoM of internal and external rotation were measured bilaterally using a handheld dynamometer and goniometer, respectively. A significant group × side interaction was observed for internal rotation RoM (F = 5.41; p = 0.024; η2 = 0.10), with volleyball players showing lower RoM on the dominant side (p = 0.001; d = 0.89), but this was not the case for handball players (p = 0.304). External rotation strength also showed a significant interaction (F = 9.34; p = 0.004; η2 = 0.17); volleyball players were stronger in the non-dominant arm (p = 0.033), while handball players were stronger in the dominant arm (p = 0.041). The external-to-internal rotation strength ratio was significantly lower on the dominant side in volleyball players compared to handball players (p = 0.047; d = 0.59). Findings suggest sport-specific adaptations and asymmetries in shoulder function, emphasizing the need for sport-specific and individually tailored injury prevention strategies. Volleyball players, in particular, may benefit from targeted strengthening of external rotators and flexibility training to address imbalances.

1. Introduction

Volleyball and handball are among the most popular team sports for women both in Slovenia and globally, involving repetitive overhead movements such as spiking, serving, and throwing. These actions place high mechanical demands on the shoulder joint, making shoulder pain and injury particularly prevalent among female athletes. In volleyball, shoulder injuries represent 16–32% of all injuries [1,2], while in handball, chronic shoulder pain affects 19–45% of players during the season [3,4]. Given the high participation rates and injury burden, particularly in female athletes [5], sport-specific screening of shoulder function is essential for injury prevention and performance optimization.
During repetitive ballistic movements, such as throws or spikes, the rotator cuff muscles are stressed in both concentric conditions (contributing to the throw or swing during the acceleration phase) and eccentric conditions (decelerating the movement and stabilizing the joint). The shoulder joint is most stressed during the phases of maximum external rotation and deceleration in the swing phase. In throwing, the limb moves from an abducted position (above the head) through extreme external rotation, followed by elbow extension, internal rotation, and adduction. During the acceleration phase of the swing, the internal rotators of the shoulder act concentrically, while the external rotators act eccentrically. The role of the external rotators is not only to decelerate the limb eccentrically but also to maintain dynamic stabilization of the shoulder girdle, thus playing a crucial role in injury prevention [6]. In case of injured or undertrained muscles, the balanced relationship between agonists and antagonists is lost, which potentially leads to shoulder instability and pain [7].
A significant predictor of rotator cuff injury is the strength of the shoulder rotators and the ratio between external (ER) and internal rotation (IR), known as the ER:IR ratio [7]. In sports where the dominant shoulder is under higher stress, it is crucial for injury prevention to maintain an optimal balance between the strength of the internal and external rotators, as well as the flexibility of the shoulder girdle [8]. Several studies have examined the ER:IR strength ratio and reported that athletes exposed to high unilateral shoulder loading often develop strength and mobility asymmetries between the dominant and non-dominant limbs, likely as a result of sport-specific adaptations. The strength ratio in the dominant limb is typically altered due to the greater strength of the internal rotators compared to the non-dominant limb [9,10].
Evaluating the ER:IR ratio is important for joint stabilization and injury prevention, as maintaining a proper balance between agonists and antagonists is essential for shoulder safety. The ER:IR ratio can be calculated by dividing the average maximal isometric strength of each muscle group [10,11]. The mean values of ER:IR ratios reported in previous studies vary slightly due to differences in methodology, such as the use of isometric or isokinetic dynamometers, the population studied, and the measurement position and procedure. Regardless of the exact ER:IR ratio values, athletes with higher loads on their dominant shoulder exhibit asymmetry between their dominant and non-dominant limbs [10]. The ER:IR ratio in a healthy general population was found to range from 0.86 to 0.99, with no significant differences between the dominant and non-dominant limbs [12].
In volleyball players with increased shoulder loading in the dominant limb, internal rotation strength is 3–9% greater in the dominant limb compared to the non-dominant limb. Conversely, external rotation in the dominant limb is 0–14% lower than in the non-dominant limb [5]. Studies indicate that volleyball and handball players should maintain a functional eccentric external rotator (ER) to concentric internal rotator (IR) strength ratio greater than 1 to optimize movement control and reduce injury risk [7,13]. A lower ratio correlates with decreased control and a higher likelihood of injury. This reference value is essential for designing effective fitness and rehabilitation programs. It is important to recognize that changes in rotator cuff muscle strength and range of motion are normal adaptations to the demands of these sports. Generally, athletes with increased load on the dominant shoulder should aim for an external-to-internal rotator strength ratio of approximately 2:3 (or 0.66–0.75), meaning the external rotators should be about two-thirds as strong as the internal rotators [7,13]. Athletes can achieve this ratio through preventive exercises, which can reduce the likelihood of injury [14].
Despite all this, there is limited comparative research directly examining the ER:IR ratios and shoulder strength asymmetries between volleyball and handball players. Understanding these differences is crucial for developing sport-specific training and rehabilitation programs. The aim of this study is to analyze and examine the isometric strength and maximum range of motion in internal and external rotation of the shoulder joint, and to determine the ER:IR ratio in the dominant and non-dominant limbs of female volleyball and handball players. Given the similar repetitive ballistic movements of the dominant limb in volleyball (serving and spiking) and handball (throwing), we sought to determine whether there are differences between the two groups. The added value of our research lies in its contribution to understanding the specific differences in isometric strength in two sports; the study provides a direct comparison between volleyball and handball players, two sports with high shoulder joint loads. Based on the sport-specific demands, we hypothesized that (1) volleyball players would demonstrate lower internal rotation RoM and external rotation strength on the dominant limb compared to handball players; (2) volleyball players would exhibit greater inter-limb asymmetry in strength and RoM; and (3) the ER:IR strength ratio would be lower on the dominant side in volleyball players compared to handball players.

2. Materials and Methods

2.1. Participants

Our sample consisted of twenty-five volleyball athletes (age = 21.80 ± 4.81 years, body mass = 69.32 ± 7.74 kg, body height = 178.52 ± 7.05 cm, BMI = 21.7 ± 1.64 kg/m2; training years = 13.44 ± 3.19; weekly training hours = 686.40 ± 132.00) and twenty-four handball athletes (age = 19.54 ± 2.92 years, body mass = 67.63 ± 8.44 kg, body height = 169.71 ± 6.44 cm, BMI = 23.46 ± 2.50 kg/m2; training years = 12.21 ± 2.72). The average weekly training volume was 686 ± 132 min (11.4 ± 2.2 h) for volleyball players and 469 ± 65 min (7.8 ± 1.1 h) for handball players. In the volleyball group, the positional distribution was as follows: opposites (n = 2), setters (n = 4), outside hitters (n = 8), middle blockers (n = 6), and liberos (n = 5), and in the handball group, there were right backs (n = 2), right wings (n = 5), pivots (n = 3), left backs (n = 1), left wings (n = 6), center backs (n = 3), and goalkeepers (n = 4). Inclusion criteria for our sample were to play in the 1st volleyball or handball national league and no skeletal, muscle, nerve, or connective tissue injuries during the last 12 months. All participants included in our study were from female clubs from the coast region, which played in the 1st national league (two volleyball and two handball clubs). The study was conducted in accordance with the Declaration of Helsinki. The research methods and interventions used were non-invasive and approved by the Commission of the University of Primorska for Ethics in Human Subjects Research (4264-25-7/23). Coaches, subjects, and their parents/legal guardians were informed about the testing procedures and provided written informed consent prior to the study.

2.2. Study Design

The study was conducted in the gyms of clubs in Izola, Koper, and Ankaran municipalities in January 2024. All participants at each club were tested in one afternoon, with each test session lasting approximately 20 min per participant. Participants first completed a questionnaire regarding general information and training characteristics. Following this, they engaged in a 3 min walk on a stepper, dynamic stretches for the upper limbs, and an activation exercise using an elastic band, consisting of 10 repetitions with both limbs (horizontal and vertical arm abduction and adduction, internal and external rotation). Before measuring shoulder strength and range of motion (ROM) in internal and external rotation, we measured each participant′s forearm length from the olecranon process to the styloid process, which was used to calculate the torque from recorded force values. The order of ROM and strength measurements for the dominant and non-dominant shoulders was randomly determined for each participant. The dominant arm was defined as the arm with which the participant typically threw (handball) or spiked (volleyball) a ball. Of the participants, forty-six reported their right hand as dominant, while only three (handball players) were left-handed.

2.3. Range of Motion Assessment

After the participants finished with warm-up, we conducted measurements of maximal range of motion (ROM) internal rotation (IR) and external rotation (ER) on dominant and non-dominant limbs with standard goniometric procedures. Participant was lying on a massage table, the limb was in 90° of abduction and modified neutral for shoulder rotation, with the elbow flexed at 90° and palm in neutral position [13], while the non-tested arm was lying next to the body. One assistant stabilized the scapula and, with their other hand, passively moved the participant’s arm in IR or ER. The other assistant used a handheld goniometer to test ROM of IR or ER. The pivot point of the goniometer was placed on the lateral epicondyle, while the moving part was aligned with the ulna; the fixed part was parallel with the floor. We tested IR and ER on both the dominant and non-dominant limbs.

2.4. Strength Assessment

We determined the maximal internal rotation (IR) and external rotation (ER) isometric strength of the dominant and non-dominant upper limbs (Figure 1). We used a digital dynamometer (EasyForce®, Meloq AB, Stockholm, Sweden), externally fixed to a stable sport ladder via a strap. This setup allows for valid and reliable measurements of shoulder rotator strength [15,16,17]. During the ER, participant was lying on the massage table and facing the sport ladder. Lower limbs were placed on the sport ladder, so that the knee angle was set to 90° (0° = full extension) and hips were set at 90° (0° = neutral position). During the IR, participant was facing away from the sport ladder, lower limbs were fully extended on the massage table. The non-testing limb was next to the body, lying on a massage table. During all tests, the limb was in 90° of abduction and modified neutral for shoulder rotation, with the elbow flexed at 90°. During each trial, one examiner manually stabilized the participant’s upper arm to minimize compensatory trunk or scapular movement, while the other monitored limb alignment and instructed the participant. The dynamometer was externally fixed onto the sport ladder (on one side) and the cuff (on the other side). During the ER strength testing, the dynamometer was positioned on the participant’s dorsal surface of the wrist, and the volar surface during the IR testing. The participants were instructed to perform the tasks “as fast and as strong as possible” and to maintain the maximal effort for approximately 5 s. After the familiarization, the participants performed 3 maximal voluntary contractions (MVC) per task (IR and ER) unilaterally, in a random order. The participants were loudly verbally encouraged throughout the trial in order to facilitate maximal effort. Between each trial with the same limb and when they needed to switch the arm, the participant rested for 60 s. The outcome measures of IR and ER strength we normalized with the body weight of participants.

2.5. Statistical Analysis

A priori power analysis was conducted using G * Power 3.1 (University of Düsseldorf, Düsseldorf, Germany) for a two-way mixed ANOVA with interaction (group × side), with two groups and two measurements (dominant and non-dominant limbs). Assuming a medium effect size (f = 0.25), α = 0.05, and power (1 − β) = 0.80, the required total sample size was estimated at 34 participants. Our sample of 49 participants (25 volleyball and 24 handball players) thus provides sufficient power to detect moderate effects and group × side interactions. Inter-limb asymmetry (%) is calculated by taking the difference between the values of the stronger limb and the weaker limb, dividing that difference by the value of the stronger limb, and then multiplying the result by 100 to express it as a percentage. Further Statistical analysis was conducted with IBM SPSS Statistics 29 (IBM, New York, NY, USA). For all outcome measures, we calculated descriptive statistics (mean value ± standard deviation, minimum and maximum value). We used the intraclass correlation coefficient (ICC) to test the intra-rater reliability of the strength measurements, which reflects the variation of data measured by 1 rater. ICCs were interpreted as follows: ICC > 0.90 = excellent, 0.75–0.90 = good, 0.50–0.74 = moderate and <0.50 = poor [18]. Before analyzing the differences, we tested normality of distribution using the Shapiro–Wilk test. A two-way analysis of variance with side (dominant, non-dominant) as within-participant factor and group (VG, HG) as between-participant factor was run. In cases where a statistically significant main effect or interaction was observed, post hoc testing with Bonferroni correction was applied to explore specific differences between sides and groups. Effect sizes were calculated using eta-squared (η2) for ANOVA, with values interpreted as small (0.01), medium (0.06), or large (0.14), and as Cohen’s d for t-tests, with values interpreted as trivial (<0.2), small (0.2–0.5), medium (0.5–0.8) and large (>0.8) [19].

3. Results

3.1. Reliability

The reliability for internal rotation for the dominant arm and both rotations for the non-dominant arm was excellent (ICC > 0.9; range = 0.92–0.94), while the reliability of the dominant arm for the external rotation was good (ICC = 0.74–0.90).

3.2. Range of Motion

RoM results are shown in Figure 2. For the IR RoM, there was a statistically significant effect of side (F = 13.22; p = 0.001; η2 = 0.22), group (F = 4.86; p = 0.032; η2 = 0.09), as well as interaction between side and group (F = 5.41; p = 0.024; η2 = 0.10). Further testing revealed that IR RoM was lower in the dominant limb compared to the non-dominant limb only in volleyball players (p = 0.001; d = 0.89), but was not different between the dominant and non-dominant limbs in handball players (p = 0.304; d = 0.23). Volleyball players had lower IR RoM on the dominant limb (p = 0.003; d = 0.91), whereas there were no differences between the groups in IR RoM in the non-dominant limb (p = 0.628; d = 0.14). Accordingly, the volleyball group had a larger mean inter-limb asymmetry in IR RoM (10.24 ± 13.31°) compared to handball players (2.25 ± 10.49°) (p = 0.024; d = 0.67).
For the ER RoM, there was as statistically significant effect of side (F = 26.24; p < 0.001; η2 = 0.36), but no main effect of group (F = 0.47; p = 0.496; η2 = 0.01) nor interaction between side and group (F = 0.06; p = 0.805; η2 < 0.01). In both groups, the dominant limb exhibited larger ER RoM compared to the non-dominant limb (p = 0.001–0.005; d = 0.81–0.82). There were no differences in the mean inter-limb asymmetry score between the groups (volleyball: 7.64 ± 8.4°; handball: 8.42 ± 13.11°; p = 0.805)

3.3. Maximal Strength

Maximal strength results are shown in Figure 3. For IR maximal strength, there was a statistically significant effect of side (F = 5.24; p = 0.026; η2 = 0.10), whereas there was no statistically significant effect of group (F = 0.06; p = 0.808; η2 < 0.01) and no interaction between side and group (F = 1.25; p = 0.276; η2 = 0.02). Post hoc testing revealed a statistically significantly greater IR strength in the dominant compared to the non-dominant side in volleyball players (p = 0.044; d = 0.27), whereas there was no statistically significant difference between sides in handball players (p = 0.326; d = 0.10). There was also no statistically significant difference in terms of mean inter-limb asymmetries between volleyball (9.2 ± 8.0%) and handball players (6.1 ± 5.3%) (p = 0.117; d = 0.47).
Regarding ER maximal strength, there was a statistically significant interaction between group and side (F = 9.34; p = 0.004; η2 = 0.17), with no main effects of side (F = 0.49; p = 0.484; η2 = 0.01) and group (F = 0.15; p = 0.701; η2 < 0.01). Post hoc testing revealed that the interaction in the absence of other main effects was present because there were statistically significant side differences in both groups, but in opposite directions. Specifically, volleyball players had higher maximal ER strength in the non-dominant limb (p = 0.033; d = 0.50), whereas handball players had greater ER maximal strength in the dominant limb (p = 0.041; d = 0.33). Volleyball players also exhibited greater inter-limb asymmetries compared to handball players (17.1 ± 11.9% compared to 10.7 ± 10.1%; p = 0.05; d = 0.57).

3.4. ER:IR Ratio

Results for the ER:IR ratio are shown in Figure 4. There was a statistically significant interaction between group and side (F = 9.80; p = 0.003; η2 = 0.17), with no main effects of side (F = 2.44; p = 0.124; η2 = 0.05) and group (F = 0.124; p = 0.727; η2 < 0.01). Post hoc testing revealed that the ER:IR ratio was lower in the dominant compared to the non-dominant hand in volleyball players (p = 0.010; d = 0.59). In contrast, there was no statistically significant difference between the limbs in the handball players group (p = 0.153; d = 0.26). Furthermore, volleyball players had lower ER:IR ratios compared to handball players when considering the dominant limb (p = 0.047; d = 0.59), whereas there were no differences between the groups in terms of ER:IR ratio on the non-dominant side (p = 0.249; d = 0.33).

4. Discussion

The aim of this study was to analyze and examine the isometric strength and maximum range of motion in internal and external rotation of the shoulder joint, and to determine the ER:IR ratio in the dominant and non-dominant limbs of female volleyball and handball players. While our findings are broadly consistent with previous studies on overhead athletes, this study provides added value by directly comparing female volleyball and handball players using a standardized bilateral assessment. Importantly, we employed accessible tools—handheld dynamometry and goniometry—that can be easily implemented in applied settings. This makes our protocol highly relevant for coaches and clinicians seeking practical, low-cost methods to monitor shoulder strength, range of motion, and inter-limb asymmetries in field conditions.
In overhead sports, such as volleyball and handball, we have to consider the asymmetric nature of shoulder movements that can cause strength imbalances that present in the form of asymmetries between the dominant and non-dominant limb and abnormal strength ratios between the ERs and IRs, known as the ER:IR ratio [5]. This is because maintaining a proper balance between agonists and antagonists is essential for shoulder joint stability. Several studies have revealed that athletes with increased shoulder joint loading exhibit asymmetry between the dominant and non-dominant limbs. The strength ratio in the dominant limb is typically altered due to the greater strength of the internal rotators compared to the non-dominant limb [5,9,10]. Regardless of the exact ER:IR ratio values, athletes with higher loads on their dominant shoulder exhibit asymmetry between their dominant and non-dominant limbs [10]. In this study, we investigated the RoM of internal (IR) and external rotation (ER) on dominant and non-dominant limbs between female volleyball and handball players. We expected that the participants would have decreased IR RoM on the dominant limb, but larger ER RoM compared to the non-dominant limb. Further testing revealed that IR RoM was lower in the dominant limb compared to the non-dominant limb only in volleyball players, while in handball players, there were no statistically significant differences between limbs. In previous research [2,20,21,22,23,24] where volleyball and handball players were compared, similar conclusions were reached, as they found less IR RoM and increased ER RoM on the dominant limb. The authors explain that these differences arise from the specific demands of each sport. During actions such as hitting and serving in volleyball and throwing in handball, the dominant shoulder is repeatedly placed in extreme external rotation (ER) positions. This repetitive exposure contributes to greater ER range of motion (RoM) in the dominant limb compared to the non-dominant one. In support of this, Benda et al. [20] demonstrated that young volleyball and handball players already exhibit increased dominant-arm RoM in external rotation, extension, and horizontal adduction, alongside decreased internal rotation and increased local hypermobility in the glenohumeral joint. Importantly, Guney et al. [21] further showed that glenohumeral internal rotation deficit (GIRD) is associated with a significantly reduced functional ER:IR ratio, indicating that loss of IR mobility may also compromise neuromuscular control. Together, these findings underscore the relevance of monitoring and addressing RoM asymmetries not only as sport-specific adaptations but also as potential contributors to shoulder dysfunction and injury risk.
Our hypothesis about differences between RoM in observed sports is partially supported by the results, as we found that volleyball players reached statistically significant lower IR RoM, but not ER RoM compared to the handball group. Our results are partially in contrast with a study of Benda et al. [20] that found no statistically significant difference in the RoM of IR and ER between volleyball and handball. A reduced range of IR RoM and an increased range of ER RoM is a common phenomenon in athletes where the shoulder joint is more stressed due to the nature of the sport. Reeser et al. [25] reported that volleyball players have a range of IR on the dominant limb approximately 10° smaller than on the non-dominant limb, which coincides with our findings (10.24°). Meanwhile, a study by Ceballos-Laita et al. [26], conducted on young male handball players (aged between 14 to 16 years old), found statistically significant differences between limbs (approximately 10°), which is in contrast with our results (2.25°).
Maximum IR isometric strength was not statistically significantly different between the groups. We found statistically significant differences only in the ER strength between volleyball and handball groups, with the handball group showing higher results compared to the volleyball group (0.59 Nm/kg vs. 0.54 Nm/kg; p = 0.038). Few studies have examined in detail the comparison of shoulder strength across multiple sports that involve high loading of the shoulder joint. However, some evidence suggests that volleyball players may be more susceptible to suprascapular nerve compression, which in turn can lead to infraspinatus atrophy and compromised external rotation strength. Reeser et al. [27] demonstrated that volleyball-specific overhead motions, particularly spiking and serving, involve greater shoulder abduction and horizontal adduction at ball contact compared to baseball pitching or tennis serving. These unique kinematic patterns may increase traction forces on the suprascapular nerve at the spinoglenoid notch, predisposing volleyball athletes to cumulative nerve injury. Further support is provided by Contemori et al. [28], who showed that volleyball players with isolated infraspinatus atrophy exhibit significantly impaired shoulder position sense and greater joint repositioning errors, suggesting sensorimotor deficits due to suprascapular nerve dysfunction. These neuromuscular impairments could contribute not only to diminished ER strength, as observed in our volleyball group, but also to a heightened risk of instability and injury. Thus, the relatively lower ER strength observed in our volleyball players may reflect both structural and functional adaptation specific to the mechanical demands of their sport. It is also worth considering that relatively lower external rotator strength in volleyball players may reflect a functional adaptation. Excessive co-contraction from strong external rotators during overhead swings could potentially reduce arm velocity. While purely speculative, this perspective invites further investigation into whether such imbalances may serve sport-specific performance needs.
In the differences between dominant and non-dominant limbs in the volleyball group, we obtained statistically significant differences in both rotations. IR strength was statistically significantly higher in the dominant limb, where the non-dominant limb showed statistically significantly higher ER strength, which is similar to previous findings [5,9]. Meanwhile, the handball group showed statistically significant differences between the limbs only in ER strength, where the dominant hand was stronger. Similar findings were reported by Clarsen et al. [29] in a study on handball players, where greater ER strength was observed in the dominant limb. The authors explain that this occurs mainly due to frequent strain on the dominant hand during throwing, where both muscular and bone changes or adaptations can occur. When comparing inter-limb asymmetry in IR strength between the groups, the difference did not reach statistical significance (p = 0.117). However, the moderate effect size (d = 0.47) suggests a potential practical difference that may be relevant in clinical or sport-specific contexts and warrants further investigation in larger samples.
Many repetitive movements, such as throwing, serving, and spiking in overhead sports, can cause shoulder injury. One possible mechanism leading to shoulder injury may be a strength imbalance between IR and ER muscles that are responsible for dynamic stabilization of the glenohumeral joint [2,5,24,30]. Differences in IR and ER strength ratios appear to be related to injury in almost all players whose sports involved overhead moving (throwing, spiking, and serving), such as handball, baseball, water polo, tennis, and volleyball [24,29]. We compared the ER:IR strength ratio between sports. We assumed that the volleyball group would show lower ER:IR ratios on the dominant limb, compared to the handball group. With more detailed analysis, we showed that the difference in the dominant hand ER:IR ratio between sports is statistically significant. Similarly, Hadžić et al. [5] found a lower ratio on the dominant than on the non-dominant hand in volleyball players, while another study also found a higher ratio on the dominant hand in handball players [31]. We came to similar conclusions, but the aforementioned studies obtained lower ratio values than we did, namely between 0.60 and 0.75. The values from our study can be better compared with the study by Cools et al. [9], who measured the ER:IR ratio from 0.59 to 1.02 in volleyball, handball, and tennis players. The lower the ER:IR ratio and the weaker the external rotators are on the dominant hand in volleyball players or athletes with a loaded shoulder joint, the higher the probability of achieving comparable concentric strength of the internal rotators, which is not followed by equivalent eccentric strength of the external rotators. This represents a high risk of injury in the high number of impacts, as is typical for volleyball players [9,30].
Cools et al. [9] measured strength in volleyball, handball, and tennis players using isometric and isokinetic dynamometers. The functional ER:IR ratio (the ratio between ER eccentric and IR concentric) reaches values between 0.97 and 1.31, and the isometric ER:IR ratio, measured with a hand dynamometer, between 0.59 and 1.02. Some authors suggest that the functional ER:IR ratio in volleyball and handball players should be greater than 1 [7,13]. A lower ratio is potentially associated with poorer movement control and a greater risk of injury. This reference value can be useful in developing a fitness or rehabilitation program. Our participants achieve isometric ratios between 0.97 and 1.11 in favor of the external rotators, indicating a similar strength in IR and ER. A commonly recommended benchmark for athletes with high shoulder loading is an external-to-internal rotator strength ratio of approximately 2:3, or 0.66–0.75. This implies that the external rotators should possess about two-thirds the strength of the internal rotators. Such ratios may be achieved through targeted preventive exercises aimed at minimizing strength imbalances and, consequently, lowering injury risk [14]. The relatively favorable ratios observed in our sample, particularly among handball players, may reflect effective neuromuscular adaptation to sport-specific loading and effective prevention strategies, which suggest a lower injury risk.
This study is not without limitations. First, the sample size was relatively small and limited to female athletes competing in the Slovenian 1st national league, which may affect the generalizability of the findings to broader or more diverse athletic populations. While a priori power analysis indicated sufficient statistical power for detecting moderate effects, larger samples would enable more robust subgroup comparisons (e.g., by playing position or injury history). Second, although we included a range of positions in both sports, we did not analyze shoulder characteristics by position due to limited numbers in each subgroup. Future research should consider stratified sampling and include male athletes, youth populations, or athletes from different competitive levels to extend the applicability of these findings.

5. Conclusions

This study highlights distinct sport-specific adaptations in shoulder strength and range of motion among female volleyball and handball players. Volleyball players demonstrated greater inter-limb asymmetries and lower external-to-internal rotation (ER:IR) strength ratios on the dominant side, which may increase their risk of shoulder injury. In contrast, handball players exhibited more balanced profiles, likely reflecting different movement patterns and muscular demands. These findings have several practical implications. For volleyball players, targeted strengthening of the external rotators and flexibility training for internal rotation should be emphasized in both preseason and in-season programs to reduce imbalance-related injury risks. Handball players, while generally more balanced, may still benefit from periodic strength ratio monitoring to detect early signs of maladaptation. Sport-specific screening protocols and individualized prevention programs are recommended to address the specific demands of each sport. Additionally, coaches and clinicians should consider inter-limb asymmetries when designing return-to-play criteria and rehabilitation plans. Future research should focus on longitudinal studies to assess whether the identified asymmetries and strength deficits are predictive of injury. Intervention trials evaluating the efficacy of rotator-specific strength and flexibility training in reducing asymmetry and improving ER:IR ratios would also provide clinically meaningful insights. In addition, future studies should consider integrating advanced measurement technologies to capture dynamic, real-time shoulder function during sport-specific tasks like spiking or throwing. This could complement static strength and RoM assessments by providing ecologically valid insights into neuromuscular adaptations in vivo, thus enhancing the translational value of shoulder profiling in athletic populations.

Author Contributions

Conceptualization, M.L. and U.Č.; methodology, M.L. and Ž.K.; software, Ž.K.; validation, Ž.K. and U.Č.; formal analysis, Ž.K.; investigation, M.L.; resources, U.Č.; data curation, M.L.; writing—original draft preparation, M.L.; writing—review and editing, Ž.K. and U.Č.; visualization, Ž.K.; supervision, U.Č. and Ž.K.; project administration, Ž.K.; funding acquisition, Ž.K. All authors have read and agreed to the published version of the manuscript.

Funding

The study was partially supported by the Slovenian Research Agency through the research program KINSPO—Kinesiology for the effectiveness and prevention of musculoskeletal injuries in sports (P5-0443).

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by Commission of the University of Primorska for Ethics in Human Subjects Research (approval number: 4264-25-7/23) on 11 July 2023.

Data Availability Statement

Raw dataset for this study can be accessed freely on the Zenodo database (Link: https://zenodo.org/records/15600034, accessed on 21 July 2025).

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
BMIBody Mass Index
CoPCenter of Pressure
ERExternal Rotation
ER:IRExternal-to-Internal Rotation Strength Ratio
HGHandball Group
ICCIntraclass Correlation Coefficient
IRInternal Rotation
MVCMaximal Voluntary Contraction
RoMRange of Motion
VGVolleyball Group

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Symmetry 17 01211 g001
Figure 1. Participant positioning for internal rotation (left) and external rotation (right) isometric strength measurement.
Figure 1. Participant positioning for internal rotation (left) and external rotation (right) isometric strength measurement.
Symmetry 17 01211 g001
Symmetry 17 01211 g002
Figure 2. Range of motion across groups and sides. * indicates a statistically significant difference between dominant and non-dominant limbs.
Figure 2. Range of motion across groups and sides. * indicates a statistically significant difference between dominant and non-dominant limbs.
Symmetry 17 01211 g002
Symmetry 17 01211 g003
Figure 3. Muscle strength across groups and sides. * Indicates a statistically significant difference between dominant and non-dominant limbs.
Figure 3. Muscle strength across groups and sides. * Indicates a statistically significant difference between dominant and non-dominant limbs.
Symmetry 17 01211 g003
Symmetry 17 01211 g004
Figure 4. External-to-internal rotation maximal strength ratio. * indicates a statistically significant difference between dominant and non-dominant limbs.
Figure 4. External-to-internal rotation maximal strength ratio. * indicates a statistically significant difference between dominant and non-dominant limbs.
Symmetry 17 01211 g004
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MDPI and ACS Style

Lenart, M.; Kozinc, Ž.; Čeklić, U. Sport-Specific Shoulder Rotator Adaptations: Strength, Range of Motion, and Asymmetries in Female Volleyball and Handball Athletes. Symmetry 2025, 17, 1211. https://doi.org/10.3390/sym17081211

AMA Style

Lenart M, Kozinc Ž, Čeklić U. Sport-Specific Shoulder Rotator Adaptations: Strength, Range of Motion, and Asymmetries in Female Volleyball and Handball Athletes. Symmetry. 2025; 17(8):1211. https://doi.org/10.3390/sym17081211

Chicago/Turabian Style

Lenart, Manca, Žiga Kozinc, and Urška Čeklić. 2025. "Sport-Specific Shoulder Rotator Adaptations: Strength, Range of Motion, and Asymmetries in Female Volleyball and Handball Athletes" Symmetry 17, no. 8: 1211. https://doi.org/10.3390/sym17081211

APA Style

Lenart, M., Kozinc, Ž., & Čeklić, U. (2025). Sport-Specific Shoulder Rotator Adaptations: Strength, Range of Motion, and Asymmetries in Female Volleyball and Handball Athletes. Symmetry, 17(8), 1211. https://doi.org/10.3390/sym17081211

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