Volleyball is a sport involving rapid and forceful movements of the body as a whole, both horizontally and vertically. Some studies have already focused on an epidemiological analysis of injury patterns in volleyball (3,4,26,45,46,48,49).
Seemingly, volleyball athletes are at a high risk of acute ankle injuries and overuse conditions of the knee and shoulder joints (1,4,5,9,38,46). Bahr and Bahr (4) found 89 injuries among 272 volleyball players during 46,837 h of training and 5751 h of match play. The total injury incidence was 1.7 ± 0.2 per 1000 h of play, 1.5 ± 0.2 during training, and 3.5 ± 0.8 during match play (4).Verhagen et al. (45) reported that of any injured body part, shoulder injuries resulted in the longest duration of time lost from training or competition (mean = 6.2 wk). Measures to prevent sports injuries form part of the “sequence of prevention” as described by van Mechelen et al. (44). First, the extent of the sports injury problems must be identified and described. Second, the factors and mechanisms that play a part in the occurrence of sports injuries (risk factors) need be identified. The third step is to introduce measures that are likely to reduce the future risk and/or severity of sport injuries. The fourth step is to evaluate the effectiveness of the injury prevention measures introduced by repeating the first step (44).
Reeser et al. (34) divided risk factors for shoulder pain into two main categories: first, intrinsic risk factors, classified as anatomy, biomechanics, core stability, glenohumeral internal rotation deficit, previous injury, scapular dyskinesis, and sex; and second, extrinsic risk factors, defined as competitive situation and load.
In the current literature dedicated to the identification of risk factors for shoulder injury, the only prospective study is provided by Wang and Cochrane (47). This study relied on a small sample (16 players) and showed an association between shoulder muscle strength imbalance of rotators and shoulder injuries in elite volleyball athletes. Given this finding, the aim of our study was to highlight the intrinsic factors that could potentially put volleyball players at risk of shoulder injury, such as rotator cuff maximal strength, passive glenohumeral mobility, posterior rotator cuff stiffness, scapular resting position, or a forward presenting shoulder.
MATERIALS AND METHODS
This prospective cohort study was carried out during the 2008–2009 indoor volleyball seasons. Eligibility criteria included (1) being considered fit for competitive volleyball activity by the team’s medical staff and (2) being normally involved in training sessions through the start of the new season. Players were recruited from a total of nine first and second division volleyball teams from Belgium, France, the Netherlands, and Luxembourg. Sixty-six volleyball players (34 men and 32 women; age = 24 ± 5 yr, weight = 76 ± 12 kg, height = 184 ± 15 cm; mean ± SD) agreed to participate in the study. Two teams refused to participate in the study because of the lack of access by participants to isokinetic devices during the study; two players were excluded after preseason isokinetic assessment because of their complaints regarding inaccurate eccentric testing. Forty-three of the total number of participants (66) were spikers; the others were setters or liberos. Fifty-seven players were right-handed, and all the participants had played volleyball for 12.3 ± 4.2 yr. The participants were playing, on average, 13.7 ± 7.1 h·wk−1 in practice and game, during the in-season registration period. Of the participants, 60.6% (74% of the men and 47% of the women) were involved in regular resistance training workouts in addition to their volleyball training. The study was approved by the medical ethics committee of the University of Liege, and written informed consent was given by each participating player.
Before the season started, all players completed preparticipation forms, including information on previous playing experience (practice time, playing career, playing positions, and national team participation) and a questionnaire to report their previous shoulder pain or injury. This standardized preseason questionnaire included questions about the onset and cause of previous shoulder pain, previous injuries, previous treatment, diagnosis received, and any reinjury. Before the season started, all players (66) underwent an isokinetic evaluation of both shoulders and morphostatic measurements (preseason assessments).
During the subsequent 6 months of the main competition period (from October to March), the players completed (with the help of a physiotherapist or a member of the medical staff) a weekly questionnaire (in-season questionnaire) to report any shoulder pain and sports time lost due to shoulder pain. This enabled us to group symptoms into categories. In the questionnaire, players were asked to describe the characteristics of any shoulder pain, any examinations sustained, and the diagnosis given. Where a player had experienced shoulder pain, they were asked to describe any treatment received. No information was given to the players regarding their isokinetic results, and the players did not benefit from isokinetic rehabilitation during the season.
Before the start of the volleyball season, isokinetic and morphostatic assessments were performed by one experienced examiner in each medical staff team. Isokinetic and morphostatic protocol assessments were standardized for each examiner, who received very precise and standardized instructions. A previous study (personal unpublished data) had established the high level of reliability between examiners regarding the measurements taken during isokinetic and morphostatic assessments, with an intraclass correlation coefficient ≥0.890 for all measurements taken in that study.
Shoulders on both sides (dominant [D] and nondominant [ND]) of the 66 players were assessed using a Cybex Norm dynamometer (Henley Healthcare, Sugarland, TX). Measurements focused on the shoulder internal rotators (IR) and external rotators (ER). Players were placed in a supine position, with the arm abducted at 90° in the frontal plane and the elbow flexed at 90° (Fig. 1). The range of motion was standardized at between 50° of internal rotation and 70° of external rotation (12). The isokinetic speeds selected were 60°·s−1 (three repetitions of testing) and 240°·s−1 (five repetitions of testing) in the concentric mode and 60°·s−1 (four repetitions of testing) in the eccentric mode. These testing sequences were preceded by familiarization at 120°·s−1 and by three submaximal trials at the selected speed. Successive testing velocities were separated by 1 min of rest (14,16).
The isokinetic testing procedure enabled the measurement of absolute peak torque (PT; N·m) and body mass relative to PT (per kg; N·m·kg−1). Agonist–antagonist ratios (ER/IR) were calculated using the same speed and contraction mode for the agonist and antagonist muscle groups (14,16). In addition to the usual “concentric” ratios, a mixed ratio (combining ER PT in the eccentric mode at 60°·s−1 and IR PT in the concentric mode at 240°·s−1) was designed to approximate more specifically the relationship between the shoulder muscles during the throwing motion, as proposed by Scoville et al. (39).
Morphostatic bilateral assessments.
Internal and external passive glenohumeral rotations (°)
The player lay in a supine position to better stabilize the scapula, with shoulder at 90° of abduction in the frontal plane with the elbow flexed at 90°. The examiner passively mobilized the glenohumeral joint up to a maximal position of rotation. The examiner used a goniometer to record the maximal rotations, just before the scapula began to elevate off the examination table (internal rotation) or the back arched (external rotation) (24,35).
Scapular static position on the thorax
The subject stood, with arms at their side in resting condition. The examiner measured the distance (cm) between the spine of the scapula proximal border and the corresponding spinous process (13,22).
Posterior rotator cuff stiffness
The subject lay laterally on the assessed shoulder, in the sleeper stretch position (90° shoulder flexion, elbow flexed at 90°). The examiner effected a maximal internal passive rotation and measured with a tape the distance (cm) between the radial styloid and the table (13,28).
Forward presenting shoulder
The player was supine, with arms at their side, palms facing downward. A measurement was taken to quantify the distance (cm) between the posterior edge of the acromion and the table (18,27,31,32,43).
During the volleyball season that followed (6 months of indoor season), all the players filled in a weekly form about any shoulder pain that they experienced. The in-season questionnaire clarified the onset cause of the shoulder pain and the localization of the pain and painful movements with the aim of informing about the categories of symptoms. The questionnaire asked whether the player had received a specific diagnosis and whether he had benefited from complementary examinations and/or specific treatment. The player was also asked to describe his condition on returning to play in the case of absence from sport. The severity of injury was defined on the basis of sporting time lost: minor injury if absence from sport was less than 1 wk, moderate injury if absence from sport was between 1 and 3 wk, and severe injury if the absence was longer than 3 wk (37).
Mean and SD were calculated for all variables. The Shapiro–Wilk normality test was used to check the normal distribution of the data.
A two-way ANOVA, completed by a Bonferroni post hoc test, was used to identify the significant differences between D and ND shoulders and groups of volleyball players (male and female) for different strength and anthropometric variables. In the retrospective part of the study, mean values were compared by an unpaired Student t-test (independent values) between players with and without a history of lesions. Results were considered to be significant at the 5% critical level (P < 0.05).
Unvaried logistic regression models were used to identify significant independent predictors of shoulder injury outcome. The odds ratios (and 95% confidence interval) were calculated for each model.
Statistical analyses were carried out using SAS (version 8.02 for Windows; SAS Institute Inc., Cary, NC).
Dominant versus nondominant
The morphostatic measurements were as follows:
- External passive glenohumeral rotation of the D shoulder, assessed in the lying supine position, with shoulder at 90° of abduction in the frontal plane, averaged 98° ± 9.5°, with significant (P < 0.001) differences in comparison with the ND side (94.5° ± 9.9°). The internal passive rotation of the D shoulder (54.2° ± 14.3°) was significantly (P < 0.001) lower in comparison with the ND side (58.6° ± 16.2°). Interestingly, the total arc of rotational motion (external + internal passive rotations) was not significantly different between D and ND shoulders.
- The D shoulder was found to be significant (P < 0.01) in a more forward position than the ND side, with an average distance between the acromion and the table in the lying supine position of 6.1 ± 1.6 cm versus 5.7 ± 1.4 cm on the ND side.
- We measured a significant (P < 0.001) posterior rotator cuff stiffness on the D side in comparison with the ND, with an increased distance in the sleeper stretch position on the D side (19.5 ± 4 vs 17.4 ± 4.3 cm on the ND side).
- The scapula of the D shoulder was significantly (P < 0.01) more abducted when compared with the ND scapula. The average distance between the spine of the scapula and the spinous process was 8.3 ± 2 cm on the D side versus 7.6 ± 1.5 cm on the ND side when players had their arms at their side in a resting position.
The isokinetic assessment was as follows:
- The isokinetic performance of the D and ND shoulders is shown in Table 1. There was a highly significant (P < 0.001) difference between both sides when comparing the PT developed by the IR: the D shoulder was stronger through all the isokinetic conditions of assessment. By contrast, no significant difference was found concerning the PT of the ER between the D and the ND shoulders. All the different agonist–antagonist ratios were very significantly lower (P < 0.001) on the D side compared with the ND.
Men versus women
The morphostatic measurements were as follows:
For the D shoulder, there was no difference between men and women concerning the internal and external passive glenohumeral rotations (97.6° ± 13.2° for external rotation and 53.7° ± 17° for internal rotation for men versus, respectively, 98.4° ± 11.8° and 54.6° ± 1.5° for women) when assessed at 90° of abduction in the frontal plane.
Men showed a more forward presenting shoulder (P > 0.0099) on the D side compared with women on the D side: 6.8 ± 1.7 cm for men versus 5.5 ± 1.2 cm for women.
On the D side, men showed a more abducted scapula than women (P < 0.001) (length between the spine of the scapula and spinous process was, on average, 8.8 ± 2.2 cm for men as compared with 7.7 ± 1.1 cm for women). Fifty percent of the men and 41% of women showed a scapula asymmetry between the D and the ND sides.
No significant difference was found when we compared the posterior cuff measurement between men and women for the D and ND sides (the distance during the sleeper stretch measurement of the D shoulder was 19.2 ± 5 cm for men and 20 ± 3 cm for women).
The isokinetic assessment was as follows:
Table 2 shows results regarding body mass relative to peak torque and the different agonist–antagonist ratios for the D shoulder of men and women. Men were found to be highly significantly (P < 0.001) stronger when comparing body mass relative to PT for all the conditions of isokinetic evaluation on the D side. Men showed significantly lower ER/IR ratios for the concentric ratios at 60°·s−1 (P < 0.001), the concentric ratios at 240°·s−1 (P < 0.01), and the mixed ratio (P < 0.001). The ND shoulder of men and women showed similar significant (P < 0.01) differences for relative PT (men stronger than women) and ratios (lower ER/IR ratios for men) than for the D shoulder.
Shoulder Pain History
At the beginning of the season, 34 (52%) of the 66 players involved in our study (56% of the men and 47% of the women, respectively) reported a history of shoulder pain and/or injury in the D shoulder. Seemingly, the players who had previously experienced shoulder pain or had a history of injury were frequently able to play during practice and games, and only 6% had stopped their sports activity for a period of at least 1 wk because of shoulder injury. Previous experience of shoulder pain and/or a history of shoulder injury were related to rotator cuff tendinopathy, requiring complementary radiological examination for 17 of 34 players. One of the 34 players had experienced a long thoracic nerve injury and 3 of 34 players had sustained a traumatic acromioclavicular lesion (2) or a labral lesion (1) before the appearance of rotator cuff symptoms.
The players with a pathological history in their D shoulder showed a significantly more marked forward presenting D and ND shoulder compared with the healthy players at the beginning of the season. For D shoulders, the distance between the posterior edge of the acromion and the table in the lying supine position was 6.5 ± 1.6 versus 5.7 ± 1.4 cm (P = 0.0419) for players with and without a pain history; the distance for ND shoulders was 6 ± 1.5 versus 5.3 ± 1.2 cm (P = 0.03). There was no difference in glenohumeral mobility (internal and external passive rotations) between players with and without a pain history, and there was no difference concerning posterior rotator cuff stiffness or the scapula position on the thoracic wall. No significant difference was found through the isokinetic results (PT and ratios) between players with and without a shoulder pain history during the preseason isokinetic assessment. There was a trend (P = 0.06) in the lower mixed ratio for players with a pain history (1.19 ± 0.29 vs 1.34 ± 0.34), but the difference was not significant.
With respect to the in-season follow-up, 23% (15 of 66 players) of the volleyball players involved in our study (38% of the women and 9% of the men) experienced D shoulder pain during the ongoing season. Of the 15 players, 13 (87%) were spikers. Of these, 2 women (6%) and 1 man (3%) were obliged to stop their sports activity because of shoulder pain for 1 to 3 wk (moderate injury). Men were six times more protected than women from further pain in their D shoulder during the ongoing season (odds ratio = 0.161, P = 0.04). All the shoulder pain reported was related to rotator cuff tendinopathy; there was no traumatic shoulder injury during the ongoing season. Of the 15 players with shoulder pain during the postseason, 13 had already experienced the same shoulder injury in the past. The players who had experienced shoulder pain or injury in the past were at nine times more risk of experiencing further pain in their D shoulder (odds ratio = 9.286, P = 0.006). Diagnosis was established on the basis of the results of specific clinical tests and, for 8 of 15 players, on the results of complementary radiological examinations. Of the 15 players with shoulder pain, 9 (including the 3 players who had been obliged to stop their sports activity) benefited from specific treatment (ice, massage, shoulder stretching, and scapular and rotator muscles strengthening).
Interestingly, the players with no shoulder pain during the season were found to be stronger on the IR and ER in the eccentric mode at 60°·s−1 through the isokinetic assessment. The odds ratio calculated showed that the eccentric contraction of the IR and ER was a protective factor (odds ratio < 1). Indeed, each increase of 1 N·m developed by the IR and ER in the eccentric mode decreased by 1% the risk of shoulder pain (respective odds ratios = 0.946, P = 0.01 and 0.940, P = 0.05) (Table 3).
We did not find any risk factors involved in passive glenohumeral motion (P = 0.9 for passive external rotation, P = 0.53 for passive internal rotation), in stiffness of the posterior rotator cuff (P = 0.92), in showing a forward presenting shoulder (P = 0.06), or in presenting a scapular static position (P = 0.27).
The aim of our study was to identify, both prospectively and retrospectively, risk factors for D shoulder pain among high-level volleyball players (66 subjects: 34 men, 32 women, 57 right-handed). At the preseason assessment, 34 subjects had already experienced D shoulder pain related to rotator cuff tendinopathy. However, the pain caused a low functional impairment, as only 6% of these subjects had had to stop their practice for more than a week. These players showed only a more marked forward presentation of the shoulders. No other morphostatic or strength characteristics were found to be different in comparison with pain-free players.
Concerning the retrospective part of this study, 15 players showed shoulder pain (due to rotator cuff tendinopathy), 13 of whom had previously experienced the same symptoms. When comparing prospectively these 15 players to those without pain (51), we found, first, that men were more protected than women for shoulder pain. Second, those with a history of shoulder pain had a ninefold higher risk of developing new pain. Third, an increase in eccentric PT of IR and ER was a protective factor. No morphostatic measure was found to be associated with the onset of pain.
Isokinetic assessment represents a valid and reproducible method to evaluate the maximal strength developed by shoulder muscles (2,10,16,17). The installation and the shoulder position of the subject for shoulder testing were chosen on the basis of reproducibility and specificity criteria (10,14–17). A systematic literature search in October 2009 concluded that the seated position with 45° of shoulder abduction in the scapula plane seemed the most reliable for IR and ER (11). More recently, we showed (16) that the lying installations, arm abducted at 45° and 90° in the frontal plane, were associated with the lowest coefficient of variation (7.1%–11.8%), with the highest reproducibility being for the 90° of abduction installation. We did not recommend the application of the seated position as we found this offered relatively poor reproducibility for ER PT and the highest coefficient of variation for the ER/IR ratios (16). The isokinetic assessment of IR and ER, in the present study, was performed in lying supine at 90° of abduction in the frontal plane on the basis of reproducibility and specificity of overhead sports. The eccentric and concentric modes of contraction and mixed ratio used in our protocol reflected the different modes of contraction used during a throwing motion, although testing speeds during isokinetic evaluation remain far lower than those during throwing.
The morphostatic measurements were selected on the basis of specific shoulder features of athletes, that is, scapular dyskinesis, tightness of the posterior rotator cuff, and a more forward presenting shoulder with a tight pectoralis minor (9,12,13,19,26,33,48).
In the preseason evaluation, the D shoulder of the volleyball players showed a modification in passive glenohumeral mobilization. In accordance with the literature (29,47,40,51), we observed an increased range of external rotation (commonly called external rotation gain) and a decreased range of internal rotation (commonly called glenohumeral internal rotation deficit). Wilk et al. (50) have referred to this rotational arc shift phenomenon as the “total motion concept.” For throwing sports, a greater range of external rotation allows for more arm cocking, thereby providing a greater ball velocity during the acceleration to the ball-release phase of the throw (12).
Our study also demonstrated a forward presenting shoulder and a more abducted scapula in the throwing shoulder in a resting position. Thoracic and shoulder resting posture has a biomechanical basis for its relevance to shoulder and scapular dysfunction (8,20–22,27,31,42,43). Some authors have used the term “scapular dyskinesis” to describe such an altered scapular position at rest or during movement (23,28,36,40). Borstad (8) provided evidence to support a proposed model linking posture, pectoralis minor muscle length, scapular malpositioning, and shoulder impairment. In patients with subacromial impingement, Lewis et al. (27) showed that changing posture, after postural taping, had a significant effect on the pain. Kugler et al. (26) observed in players at rest that the spinous process of the thoracic spines and the medial border of the scapula were significantly widened in volleyball attackers with shoulder pain versus attackers without shoulder pain. On the other hand, Nijs et al. (32) found no association between the outcome of clinical tests as regarding resting position of the scapula and self-reported pain severity or disability. In our study, although 50% of the men and 41% of the women showed scapular asymmetry between both shoulders in the preseason assessment, no association was shown between scapular asymmetry in resting condition and shoulder pain, neither retrospectively nor prospectively. This is in line with the results of Wang and Cochrane (47), who found no significant association between injury and mobility impairment and scapular asymmetry. Indeed, the scapula altered position should result from physiological adaptation to the sports features and is not a response to painful shoulder pathology. On the other hand, it might have been interesting to add observational analysis or measurement of scapular dynamic control, giving possible information regarding the relationship between injury and dynamic scapular motion assessment (42,43).
In the present study, morphostatic measurement revealed a significant posterior rotator cuff stiffness in the D shoulder in comparison with the ND side. In their study, Kugler et al. (26) showed that the playing shoulder of volleyball attackers presented a shortened inferior and posterior part of the shoulder muscles and capsule in comparison with the opposite shoulder. The authors postulated that tightened posterior and inferior structures combined with shoulder lateralization of the scapula lead to a disturbance in the gliding and rolling motion of the humeral head, thereby causing pain (26). As for scapular asymmetry, no relationship was found either retrospectively or prospectively between posterior rotator cuff stiffness and shoulder pain. Once again, this could be more of a physiological adaptation of the sports gesture than a response to pathological context.
As a result of the retrospective part of this study, we found that the players with previous shoulder pain or injury showed amore forward presenting shoulder on the D side. Some authors have already postulated that a forward presenting shoulder caused mainly by tightness of the pectoralis minor could be related to internal or subacromial impingement (6,13,19,23,25,27,40). The prospective part of this study did not evidence the possession of a forwarded presenting shoulder as a risk factor; the players who sustained a new injury during the season did not show a more forwarded presenting shoulder in comparison with healthy players. The forward presenting shoulder evidenced retrospectively for players with a history of tendinopathy could have represented a long-term aftereffect of shoulder pain history. Anyhow, this morphostatic feature must be treated by rehabilitation corrective measures as pectoralis minor stretching and scapular muscle strengthening.
In the present study, male players were highly significantly stronger than women for all rotator muscle assessment conditions. They were characterized by lower ER/IR ratios, in particular the mixed ratio in the D shoulder, as also described in the study by Wang et al. (48). These low ratios resulted from greater IR strength for the men’s D shoulder without a concomitant modification in ER maximal strength. Interestingly, no significant difference was found through the isokinetic results (PT and ratio) between players with and without shoulder pain history. There was only a trend of lower mixed ratio for players with history of shoulder pain, with no significant difference. Stickley et al. (41) observed a significant lower mixed ratio for adolescent female volleyball athletes with a shoulder injury history. They recommended a shoulder strengthening program focusing on eccentric strength deficits (41). In the prospective part of the present study, ER/IR ratio imbalance did not represent a risk factor for shoulder pain. Players with rotator cuff tendinopathy symptoms did not show lower ratios than players without shoulder pain.
Concerning the prospective analysis, 15 of 66 players (12 women and 3 men) experienced D shoulder pain during the subsequent 6 months of the competition period. Among players with pain, only 2 women (6%) and 1 man (3%) were obliged to stop their sports activities for a period of 1–3 wk. This highlights the fact that, as in the retrospective part of the study, the pain related to rotator cuff tendinopathy showed low functional impairment with 2% of players having to stop their practice more than a week. Of the 15 players with shoulder pain, 9 (including the 3 players who stopped their sports activities) benefited from specific sessions of rehabilitation (ice, massage, shoulder stretching, and scapular and rotator muscles strengthening). Players with a previous history of shoulder complaints had nine times more risk of experiencing pain again in their D shoulder (odds ratio = 9.286, P = 0.006). This could indicate that the injury had not been correctly diagnosed or had not completely healed, or that a previously treated injury established the conditions for a separate injury upon further exposure. This also strongly suggests that the criteria for return to play had not been clear. By inference, the preventive approach should be given top priority as a way of avoiding shoulder tendinopathy.
Of 15 players with shoulder pain, 13 were spikers. No traumatic injury was recorded for these 13 players. However, volleyball athletes are, in general, at great risk of overuse shoulder injuries (34,35,45). Reeser et al. (34,35) noted that the shoulder girdle is exposed to a tremendous cumulative load as the result of repetitive spiking and serving. Interestingly, in the present study, women were six times more at risk of experiencing pain on D shoulder with playing than men (odds ratios = 0.161, P = 0.04). Verhagen et al. (45) found no differences between men and women were found for total, training, and match injury incidence during one volleyball season. In their study of knee sports injury, Myer et al. (30) showed a relationship between hamstrings strength deficit and anterior cruciate ligament injury, giving a much higher incidence of this sports injury among female athletes. Our findings from the preseason isokinetic rotator assessment showed that women were weaker than men in this regard; moreover, only 47% of the women (vs 74% of the men) were involved in regular training workouts apart from their volleyball training. The best level of strength developed by the men, in comparison with the women, could protect them against shoulder pain.
Of the different measurements performed before the season started, eccentric maximal strength developed by the rotator cuff muscles seemed to play a key role. In our study, the eccentric maximal strength developed by the IR and the ER was found to represent a protective factor in volleyball players. Through the odds ratio analysis, each increase of 1 N·m decreased by 1% the risk of shoulder injury during the ongoing volleyball season (respective odds ratios = 0.946 and 0.940). In their study of elite volleyball athletes, Wang and Cochrane (47) found that the average eccentric external strength was weaker in the D arm compared with the concentric internal strength and that this was associated with shoulder injury or pain (Fisher’s exact test, P < 0.05). The authors postulated that an increase in ER eccentric strength could possibly prevent shoulder injury. Indeed, the protective role of eccentric contraction has been suggested by many authors (12,19,47,52). The weakness of strength developed by the IR in eccentric contraction, in addition to the increased external range of motion in the throwing shoulder, could lead, at the end of the cocking phase of the throw, to anterior and inferior (subtle) instability and to internal or secondary subacromial impingement (7). The repetitive ER eccentric overload during the follow-through stage could lead to musculotendinous microtrauma or suprascapular nerve injury (47,52). In a previous study (14), we showed a relationship between isokinetic maximal strength developed by the IR in the concentric mode (60°·s−1°, 240°·s−1) and the speed of the ball during a spike test (standardized field test). Seemingly, the concentric mode of contraction (IR) is related to throwing, although it is likely that the eccentric mode of contraction (IR and ER) protects the shoulder from pain or injury.
The identification of risk factors is of paramount importance and requires, in particular, the evaluation of rotator muscle strength through isokinetic eccentric assessment before the start of the season. The results of the present study indicate that a preventive program with controlled eccentric exercises should be advocated for individual volleyball players. The effectiveness of such preventive exercises could then be assessed through the monitoring of any subsequent occurrence of shoulder pain during the season.
The authors thank A. Depaifve for her kind and efficient technical assistance, Mr. Pirenne and L. Duysen for their essential involvement, and L. Seidel from Prof. A. Albert’s department for assisting with statistical analysis.
The authors declare no funding and conflict of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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