Abstract
This systematic review aims to provide normative values for internal and external glenohumeral rotation strength in rugby players. From the inception to March 2021, the search strategy was (strength OR torque) AND shoulder AND rugby using PubMed, Scopus, Web of Science, and SPORTDiscus databases, with no language restrictions. This systematic review includes 15 articles involving 573 rugby players and presenting internal or external glenohumeral rotation strength values. Two main methods are used to assess glenohumeral rotation strength in rugby players: isokinetic and isometric methods; in the isometric method, the upper arm is abducted at either 0° or 90°. Owing to differences in isokinetic procedures and a lack of studies assessing isometric strength when the upper arm is in a neutral position, normative internal or external glenohumeral rotation strength values are only provided for isometric contractions when the upper arm is abducted at 90° based on 311 shoulders of 163 male rugby union players, with 2.04 ± 0.15 N.kg−1 and 2.11 ± 0.13 N.kg−1 for internal and external glenohumeral rotation strength, respectively. These findings may help strength and conditioning coaches and physical therapists, provide objective evidence when deciding whether or not rugby union players should return to sport.
Keywords: shoulder, isometric assessment, isokinetic assessment, collision sports
Introduction
The shoulder region of rugby players is subject to traumatic injuries, particularly glenohumeral dislocation and subluxation, 1 because of the high frequency of contact during training sessions 2 and matches. 3 Despite high adherence to rehabilitation programs in rugby players, 4 nonoperative management of glenohumeral injuries does not prevent recurrence and anterior shoulder instability in these players. 5 Shoulder stabilization surgery yields excellent functional outcomes with low recurrence in rugby players6,7; however, the time between surgery and return to rugby competition remains uneven (ranging from 3 to 24 months).6,7 Producing objective markers for shoulder assessment could aid clinical practitioners in monitoring players’ progress toward regaining adequate shoulder functional status and returning to rugby competition.
Several specific rugby skills require the use of the shoulder region,8,9 and some of them are the major causes of glenohumeral injury.10,11 About 85% of shoulder dislocations are caused by four mechanisms, with tackles being the most common. 11 A technical determinant of tackle performance is the active front-on shoulder tackle, 8 in which the tackler's shoulder makes first contact with the opponents. 12 In laboratory conditions, this approach involves impact forces of about 1600 N at the shoulder joint. 12 Despite the importance of dynamic muscle control around the shoulder complex in establishing normal joint function, 13 it is vital for a rugby player to have the ability to develop high muscle strength at the glenohumeral joint to serve the dual functions of mobility and stability.
The anatomy of the glenohumeral joint allows for great mobility but limited stability, making it difficult to keep the humeral head centered in the glenoid and maintain congruence. 14 Although passive structures may contribute to preventing humeral head translation, 15 subluxations and dislocations commonly cause the ligaments that stabilize the glenohumeral joint to distend or rupture. 16 In such situations, active structures play a critical role in overcoming passive structure deficits and ensuring glenohumeral joint stability. One goal of rehabilitation and return-to-sports programs is to restore joint stability within surrounding muscular tissues, particularly the glenohumeral rotator muscles. 17 The contralateral uninjured shoulder is commonly used as a reference when the strengths of both shoulders are regularly assessed during rehabilitation procedures. 18 Such an approach may be convenient, but it may also be ineffective if the strength reference value for rugby practice remains inadequate. Consequently, determining internal and external glenohumeral rotation strength levels in rugby players may be relevant to provide objective strength outcomes for the return to sport.
Reference values are useful in clinical decision making, particularly when deciding whether or not a rugby player should return to collision/contact sport after a shoulder injury. This study aims to provide normative values for internal and external glenohumeral rotation strength in rugby players based on a systematic literature review.
Methods
Data sources and search strategy
The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. 19 From the inception to March 2021, a comprehensive search was conducted in the scholarly electronic databases PubMed, Scopus, Web of Science, and SPORTDiscus, with no language restrictions. The primary search strategy was (strength OR torque) AND shoulder AND rugby, which was tweaked to meet the requirements of each database.
Eligibility criteria and study selection
The inclusion criteria were studies involving rugby players of any sex, age, rugby level, or experience, with players who were unable to play rugby at the time of assessment being excluded (e.g. players assessed during the rehabilitation process). A study had to have assessed the internal and external glenohumeral rotation strength or torque to be included. Studies were deemed ineligible when the values of the desired outcomes were not available.
The titles, keywords, and abstracts were screened to determine which studies were eligible. Thereafter, the full-text articles were analyzed according to the predefined criteria. The reference lists of the included studies were also screened to include all relevant studies missed during the original search. The first and last coauthors independently conducted the selection process. In the event of a disagreement, the second author made the final selection decision.
Methodological quality assessment
Two raters (first author and last coauthor) independently assessed the methodological quality of each selected article employing the scales used by Kotte et al. 20 for isometric assessment and those used by Castro et al. 21 for isokinetic assessment. The scales consisted of 19 items for both types of assessment and 6 additional items for isokinetic assessment, and they were divided into 3 sections: (i) population description, (ii) strength measurement procedures, and (iii) result presentation (Table 1). Each item was rated using the grades “yes,” “no,” “unclear,” and “not applicable.” Cohen's κ coefficients and percentage of agreement (%A) were then calculated to evaluate the interrater agreement by article and by item, with κ < 0.40 and %A < 15% for minimal agreement, 0.40 ≤ κ < 0.60 and 15% ≤ %A < 35% for weak agreement, 0.60 ≤ κ < 0.80 and 35% ≤ %A < 63% for moderate agreement, and κ ≥ 0.80 and %A ≥ 64% for strong agreement. If there was a moderate or low level of agreement, a discussion was held to obtain a consensus, and if necessary, a third rater (second author) was consulted. When more than one-third of the items were graded “no” or “unclear,” the methodological quality was deemed low, but when two-thirds of the items were graded “yes,” the methodological quality was deemed acceptable. 21
Table 1.
Methodological quality of the included studies with grades n for no, uc for unclear, y for yes, and na for not applicable.
| Topic | Explanation | Bolton et al. (2013) | Coetzee et al. (2002) | Davies et al. (2016) | Edouard et al. (2009) | Haines et al. (2018) | Haines et al. (2019) | Horsley et al. (2012) | Kadlec et al. (2020) | McDonough et al. (2014) | Ogaki et al. (2014) | Ogaki et al. (2016) | Rogowski et al. (2020) | Tadiello et al. (2017) | Walch et al. (2021) | Zelinski et al. (2019) | Cohen's kappa coefficient | Percentage of agreement (%) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1. | Was the sample size adequate? | Yes for a squad at minimum/no for other | y | n | n | n | y | y | n | y | n | y | y | n | n | n | y | 1.00 | 100 |
| 2. | Was the description of selection criteria presented? | Yes for inclusion or exclusion criteria | ya | na | ya | y | y | y | y | na | y | y | y | y | ya | uca | ya | 0.00 | 0 |
| 3. | Was the sex of population described? | Female/male | y | uca | na | n | na | na | n | y | n | n | n | y | y | y | y | 0.50 | 25 |
| 4. | Was the age of the population described? | Mean or range | y | y | y | y | y | y | y | y | y | y | y | y | y | y | y | 1.00 | 100 |
| 5. | Was the body mass of the population described? | Mean or range | y | y | y | y | y | y | n | y | y | y | y | y | y | y | y | 1.00 | 100 |
| 6. | Was the body height of the population described? | Mean or range | y | y | y | y | y | y | n | y | y | y | y | y | y | y | y | 1.00 | 100 |
| 7. | Was the type of rugby described? | Union/League/seven | y | na | y | n | y | y | y | y | y | y | y | y | uca | na | y | 0.49 | 24 |
| 8. | Were the level of rugby practice described? | Professional/semi-professional/amateur | ya | y | y | y | y | y | y | n | y | y | y | uca | y | y | y | 0.55 | 30 |
| 9. | Was the upper limb dominance considered? | Left/right dominant upper limb | y | y | n | y | n | n | n | n | n | n | n | n | y | y | n | 1.00 | 100 |
| 10. | Was the shoulder health presented? | Healthy/asymptomatic/history of problems/injured | y | y | na | y | y | y | y | n | y | y | y | y | n | y | y | 0.77 | 59 |
| 11. | Were warm-ups and familiarization protocol performed? | Yes/no | y | y | ya | y | y | y | n | y | y | n | n | y | y | y | y | 0.82 | 67 |
| 12. | Was the body position of subject described? | Standing/sitting/supine/prone | y | n | uc | y | y | y | n | y | y | y | y | y | y | y | y | 0.80 | 64 |
| 13. | Was the arm position relative to the thorax described? | Degrees of flexion/extension/abduction | y | y | y | y | y | y | y | y | y | y | y | y | y | y | y | 1.00 | 100 |
| 14. | Was the position of the elbow described? | Degrees of flexion/extension | y | n | n | y | n | n | n | y | n | y | y | y | y | y | y | 1.00 | 100 |
| 15. | Was the measurement device described? | Commercial model | y | y | y | y | y | y | y | y | y | y | y | y | y | y | y | 1.00 | 100 |
| 16. | Were measures of reliability presented? | Yes for ICC, SEM or MDC a values/uc when citation | n | n | na | uca | y | y | n | uc | n | y | y | uc | n | n | y | 0.79 | 62 |
| 17. | Were the measurements repeated? | Yes for two or more repetitions/no for 1 repetition | y | y | y | y | y | y | uc | y | y | n | n | y | y | y | y | 1.00 | 100 |
| 18. | Did participants receive the encouragement during the test? | Yes/no | y | y | n | y | y | y | na | na | n | n | n | n | y | y | n | 0.76 | 58 |
| 19. | Were the outcome measures clearly described? | Mean strength/mean torque | y | y | y | y | y | y | na | y | na | uc | uc | y | y | y | y | 0.36 | 13 |
| 20. | Was the type of muscle action described? | Concentric/eccentric | y | y | – | y | y | y | – | – | y | – | – | – | y | y | – | 1.00 | 100 |
| 21. | Was the sequence of action described? | Concentric-concentric/eccentric-eccentric | n | n | – | uca | y | n | – | – | y | – | – | – | y | y | – | 0.90 | 81 |
| 22. | Was the velocity of movement described? | Yes/no | y | y | – | y | y | y | – | – | y | – | – | – | y | y | – | 1.00 | 100 |
| 23. | Were the order of tests randomized? | yes for velocities or upper limbs | na | y | – | y | n | n | – | – | n | – | – | – | n | y | – | 1.00 | 100 |
| 24. | Was gravity correction considered? | Yes/no | n | n | – | y | y | y | – | – | y | – | – | – | n | y | – | 0.90 | 81 |
| 25. | Were data extracted from the isokinetic load range? | Yes/no | n | n | – | n | n | n | – | – | n | – | – | – | n | na | – | 0.88 | 77 |
| Cohen's kappa coefficient | 0.69 | 0.75 | 0.43 | 0.77 | 0.87 | 0.88 | 0.82 | 0.80 | 0.91 | 0.90 | 0.90 | 0.87 | 0.82 | 0.36 | 0.84 | ||||
| Percentage of agreement (%) | 48 | 56 | 18 | 60 | 75 | 78 | 67 | 64 | 83 | 81 | 81 | 76 | 66 | 13 | 70 | ||||
| Methodological quality (Acceptable/Low) | A | L | L | A | A | A | L | A | L | A | A | A | A | A | A |
Agreement was obtained after discussion.
ICC: Intraclass Coefficient of Correlation; MDC; Minimal Detectable Change; SEM; Standard Error of Measurement.
Collected information and data
Data extraction included the country of the rugby players, population (sample size, mean ± SD age, body mass, and body height by groups if any), type of rugby practice (union, league, or seven), level of practice (professional/semiprofessional or amateur), time of assessment (precompetitive or competitive season), type of strength assessment (isokinetic or isometric), instrumentation (device model), body position (standing, sitting, prone, or supine), upper limb position (arm elevation in degrees and arm elevation plane, such as frontal, scapular, or sagittal plane), mode (concentric, eccentric, or isometric) and speed (in °/s), and outcome measures (maximal torque, maximal strength, or ratio) with units (kg, N, kg/body mass, or N/body mass).
Statistical analysis
When strength values with similar experimental protocols were provided in three or more studies involving methodologies of acceptable quality and players who played the same type of rugby, demographic and strength (or torque) data were pooled, and mean values with 95% confidence intervals (CI95%) were calculated using random-effects models.22,23 Heterogeneity between groups of players was assessed using Cochrane's Q statistic with p-value ≤ 0.05 and the I2 statistic, which was classified as low heterogeneity when I2 < 25%, moderate heterogeneity when 25% ≤ I2 < 75%, and high heterogeneity when I2 ≥ 75%. 24
Results
Systematic review
A total of 683 articles were found in the PubMed, Scopus, Web of Science, and SPORTDiscus databases, while 9 articles were identified through reference lists. Owing to duplication, 118 articles were excluded. After screening titles, keywords, and abstracts, 534 articles were excluded because the eligibility criteria were not met. The remaining 40 articles were read fully. Afterward, 11 articles were excluded because no strength values were provided, 4 because no rugby players were involved, and 10 because the upper limb strength was assessed during polyarticular motions, such as bench press exercise. Finally, 15 articles that provided internal or external glenohumeral rotation strength values were included in the systematic review (Figure 1).
Figure 1.
PRISMA flowchart demonstrating the article selection process.
Methodological quality assessment
Among the 333 items (25 items each from 8 articles focusing on isokinetic assessment and 19 items each from 7 articles focusing on isometric assessment), 307 (92%) had similar grades for both examiners, while 26 required further discussion to reach an agreement (Table 1). In terms of population description, one study omitted the body mass and height characteristics of the players, four studies did not clearly state the type of rugby practice, one study omitted the level of rugby practice, and three studies did not define shoulder health status. In terms of strength measurement procedures, three studies did not describe the body position clearly, but they described the devices and outcome measures adequately. The absence of information about measurement reliability was a major concern in 10 studies. Finally, just one study did not provide mean and SD strength values in numbers. To summarize, 11 studies had acceptable methodological quality, while four studies had low methodological quality (Table 1).
Population
The remaining 15 studies (Table 2) allowed for the identification of 18 groups, which encompassed 573 rugby players who played rugby union (87%) or rugby league (13%) at professional and semiprofessional (60%) or amateur (35%) levels. The mean age was 21.2 ± 3.1 years, the mean body mass was 96.7 ± 11.9 kg, and the mean body height was 182.9 ± 6.3 cm.
Table 2.
Summarized information on the 15 selected studies.
| Population | Rugby | Strength assessment | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Study | Country | n | Groups (n) | Age (years) | Mass (kg) | Height (cm) | Type | Level of practice | Type | Instant |
| Bolton et al. (2013) | South Africa | 91 | Forwards (40) Backs (51) |
20.8 ± 2.7 20.7 ± 3.0 |
103.3 ± 13.3 82.2 ± 8.6 |
186.5 ± 7.9 178.4 ± 6.4 |
Rugby union | Semiprofessional | Isokinetic | Preseason |
| Coetzee et al. (2002) | South Africa | 40 | Forwards (20) Backs (20) |
24.3 ± 3.5 24.5 ± 3.7 |
105.9 ± 8.3 84.1 ± 3.6 |
190.2 ± 6.7 180.3 ± 4.8 |
Rugby union | Professional | Isokinetic | Competitive season |
| Davies et al. (2016) | Wales | 40 | Age-graded first raw (21) Senior first raw (19) |
19 ± 1 27 ± 5 |
109 ± 7 114 ± 6 |
182 ± 5 185 ± 4 |
Rugby union | Professional | Isometry | – |
| Edouard et al. (2009) | France | 14 | – | 25 ± 5 | 91 ± 10 | 181 ± 6 | Rugby union | Amateur | Isokinetic | Preseason |
| Haines et al. (2018) | England | 49 | Professional (25) Semiprofessional (24) |
26.6 ± 3.9 25.9 ± 3.2 |
96.7 ± 11.3 94.1 ± 8.0 |
183 ± 4 184 ± 5 |
Rugby League | Professional/ semiprofessional | Isokinetic | Preseason |
| Haines et al. (2019) | England | 29 | – | 26.8 ± 4.1 | 96.9 ± 12.2 | 183 ± 5 | Rugby League | Professional | Isokinetic | Pre-, in-, post-season |
| Horsley et al. (2012) | England | 28 | – | 25 ± 5 | – | – | Rugby union | Professional | Isometry | Competitive season |
| Kadlec et al. (2020) | New Zeland | 28 | – | 23.9 ± 2.6 25 | 107.1 ± 12.9 | 187.9 ± 6.2 | Rugby union | Professional/ semiprofessional | Isometry | – |
| McDonough et al. (2014) | England | 14 | – | 19.2 ± 1.6 | 9.01 ± 10.6 | 183 ± 2 | Rugby League | Professional/ semiprofessional | Isokinetic | Preseason |
| Ogaki et al. (2014) | Japan | 69 | – | 19.5 ± 1.3 | 83.6 ± 11.2 | 176.0 ± 5.4 | Rugby union | Amateur | Isometry | Preseason |
| Ogaki et al. (2016) | Japan | 28 | – | 19.2 ± 1.6 | 86.7 ± 13.2 | 176 ± 7 | Rugby union | Amateur | Isometry | Preseason |
| Rogowski et al. (2020) | France | 38 | Healthy (21) History of injury (17) |
21.2 ± 1.9 22.2 ± 2.8 |
82.1 ± 15.2 83.5 ± 11.5 |
178 ± 8 179 ± 6 |
Rugby union | Amateur | Isometry | – |
| Tadiello et al. (2017) | Brazil | 12 | – | 24.6 ± 3.2 | 92.3 ± 15.0 | 179 ± 6 | Rugby union | Amateur | Isokinetic | – |
| Walch et al. (2021) | France | 42 | Forwards (29) Backs (13) |
26.9 ± 5.1 26.9 ± 4.7 |
111.0 ± 9.5 89.7 ± 7.0 |
190.0 ± 7.5 181.0 ± 5.5 |
Rugby union | Professional/ semiprofessional | Isokinetic | In season |
| Zelinski et al. (2019) | Australia | 18 | – | 25.3 ± 4.2 | 95.1 ± 10.1 | 182.8 ± 7.8 | Rugby union | Amateur | Isometry | Competitive season |
Strength assessment
Eight studies (Table 3) used isokinetic assessment with four different dynamometers in concentric25,26 or concentric and eccentric modes27–32 to measure the maximal internal and external glenohumeral rotation torques at 60 °/s,25–28,32 120 °/s, 25 180 °/s,26,31 or 240 °/s28–30,32 when the player was standing29,30 or sitting,26–28,31,32 with the arm in a neutral position, 25 or abducted at 30°,28–32 60°, 26 or 90° 27 in the frontal 31 or scapular plane.26–30,32 Four studies provided mean values for dominant and nondominant sides,26–28,32 three studies provided for right and left sides,29–31 and one study combined the mean values for the two sides. 25 The mean peak torque was the main outcome measure in all but one study; this measure was reported in Nm only in five studies25,26,29,31 or in Nm and normalized by body mass in three studies.28,30,32 Six studies25–28,30,32 found ratios between external rotation torque in concentric mode and internal rotation torque in concentric mode, two studies27,30 found ratios between external rotation torque in eccentric mode and internal rotation torque in eccentric mode, and one study 31 found ratios between internal rotation torque in eccentric mode and external rotation torque in concentric mode. Six studies26–30,32 had acceptable methodological quality; however, the required number of three studies assessing glenohumeral rotation strength in similar experimental conditions was not reached, preventing data pooling.
Table 3.
Experimental settings in the eight studies measuring internal and external glenohumeral rotation torques using isokinetic assessment.
| Study | Instrumentation | Body position | Upper limb position | Mode and speed | Outcome measures (mean ± SD) |
|---|---|---|---|---|---|
| Bolton et al. (2013) | Kin-Com 500H (Chattanooga, Tennessee) | Seated | Upper arm abducted at 90° Elbow flexion at 90° In scapular plane |
Concentric at 60 °/s Eccentric at 60 °/s |
ER/IRdominant = 54.55 ± 10.18%; ER/IRnondominant = 64.14 ± 14.41% ER/IRdominant = 61.52 ± 9.73%; ER/IRnondominant = 67.24 ± 11.62% |
| Coetzee et al. (2002) | Cybex 6000 isokinetic dynamometer | – | Neutral position | Concentric at 60 °/s Concentric at 120 °/s |
Forwards: IR = 80.3 ± 10.3 Nm; ER = 44.4 ± 6.0 Nm Backs: IR = 66.5 ± 7.8 Nm; ER = 42.7 ± 6.8 Nm Forwards: ER/IR = 0.56 ± 0.06; Backs: ER/IR = 0.64 ± 0.06 Forwards: IR = 75.1 ± 10.6 Nm; ER = 42.2 ± 5.8 Nm Backs: IR = 60.6 ± 6.7 Nm; ER = 37.2 ± 6.5 Nm Forwards: ER/IR = 0.57 ± 0.07; Backs: ER/IR = 0.61 ± 0.07 |
| Edouard et al. (2009) | Con-Trex ® dynamometer (Con-Trex MJ; CMV AG, Dübendorf, Switzerland) | Seated | Upper arm abducted at 30° Elbow flexion at 90° In scapular plane |
Concentric at 60 °/s Concentric at 240 °/s Eccentric at 60 °/s |
IRdominant = 65.2 ± 13.7 Nm; IRnondominant = 61.2 ± 14.0 Nm IRdominant = 0.73 ± 0.18 Nm.kg−1; IRnondominant = 0.69 ± 0.18 Nm.kg−1 ERdominant = 42.5 ± 6.1 Nm; ERnondominant = 43.3 ± 6.2 Nm ERdominant = 0.47 ± 0.09 Nm.kg−1; ERnondominant = 0.48 ± 0.10 Nm.kg−1 ER/IRdominant = 0.67 ± 0.12; ER/IRnondominant = 0.73 ± 0.14 IRdominant = 53.6 ± 11.4 Nm; IRnondominant = 52.5 ± 11.3 Nm IRdominant = 0.60 ± 0.15 Nm.kg−1; IRnondominant = 0.59 ± 0.15 Nm.kg−1 ERdominant = 33.1 ± 6.7 Nm; ERnondominant = 33.2 ± 8.4 Nm ERdominant = 0.37 ± 0.09 Nm.kg−1; ERnondominant = 0.37 ± 0.10 Nm.kg−1 ER/IRdominant = 0.63 ± 0.12; ER/IRnondominant = 0.65 ± 0.12 IRdominant = 79.9 ± 20.1 Nm; IRnondominant = 75.6 ± 20.9 Nm IRdominant = 0.89 ± 0.26 Nm.kg−1; IRnondominant = 0.85 ± 0.26 Nm.kg−1 ERdominant = 46.1 ± 7.1 Nm; ERnondominant = 47.1 ± 6.3 Nm ERdominant = 0.51 ± 0.10 Nm.kg−1; ERnondominant = 0.53 ± 0.11 Nm.kg−1 |
| Haines et al. (2018) | Cybex HUMAC (HUMan Assessment Computer) NORM Testing & Rehabilitation System | Standing | Upper arm abducted at 30° In scapular plane |
Concentric at 240 °/s Eccentric at 240 °/s |
Professional: IRright = 60.2 ± 20.3 Nm; IRleft = 61.9 ± 21.7 Nm ERright = 33.9 ± 13.6 Nm; ERleft = 32.8 ± 11.1 Nm Semiprofessional: IRright = 45.6 ± 15.5 Nm; IRleft = 47.4 ± 17.3 Nm ERright = 27.6 ± 10.5 Nm; ERleft = 27.0 ± 9.2 Nm Professional: IRright = 87.9 ± 22.1 Nm; IRleft = 86.2 ± 18.9 Nm ERright = 49.6 ± 13.1 Nm; ERleft = 50.1 ± 14.3 Nm Semiprofessional: IRright = 73.3 ± 17.4 Nm; IRleft = 72.7 ± 15.4 Nm ERright = 49.6 ± 8.2 Nm; ERleft = 48.8 ± 1.2 Nm |
| Haines et al. (2019) | Cybex HUMAC (HUMan Assessment Computer) NORM Testing & Rehabilitation System | Standing | Upper arm abducted at 30° In scapular plane |
Concentric at 240 °/s Eccentric at 240 °/s |
IRright = 60.0 ± 19.3 Nm; IRleft = 62.3 ± 20.7 Nm ERright = 33.5 ± 12.7 Nm; ERleft = 34.7 ± 8.9 Nm IRright = 0.62 ± 0.17 Nm.kg−1; IRleft = 0.64 ± 0.19 Nm.kg−1 ERright = 0.34 ± 0.12 Nm.kg−1; ERleft = 0.34 ± 0.11 Nm.kg−1 ER/IRright = 0.59 ± 0.26; ER/IRleftt = 0.54 ± 0.16 IRright = 88.3 ± 22.2 Nm; IRleft = 88.0 ± 18.3 Nm ERright = 50.5 ± 12.5 Nm; ERleft = 51.3 ± 14.7 Nm IRright = 0.92 ± 0.24 Nm.kg−1; IRleft = 0.91 ± 0.18 Nm.kg−1 ERright = 0.52 ± 0.13 Nm.kg−1; ERleft = 0.53 ± 0.14 Nm.kg−1 IRecc/IRcondominant = 2.56 ± 0.71; ERecc/IRconnondominant = 2.87 ± 1.11 |
| McDonough et al. (2014) | Biodex-System III Dynamometer (Biodex Medical, Shirley, New York) | Seated | Upper arm abducted at 30° In frontal plane |
Concentric at 180 °/s Eccentric at 180 °/s |
IRright = 63.3 ± 12.7 Nm; IRleft = 64.5 ± 11.7 Nm ERright = 44.1 ± 6.4 Nm; ERleft = 46.6 ± 9.1 Nm IRright = 87.1 ± 6.4 Nm; IRleft = 83.4 ± 18.4 Nm ERright = 64.5 ± 25.4 Nm; ERleft = 62.3 ± 19.3 Nm IRecc/IRconrught = 1.94 ± 0.29; ERecc/IRconleft = 1.84 ± 0.50 |
| Tadiello et al. (2017) | Biodex System 4®, Biodex Medical Systems, Shieley, Nova Iorque, EUA | Seated | Upper arm abducted at 60° Elbow flexed at 90° In scapular plane |
Concentric at 60 °/s Concentric at 180 °/s |
IRdominant = 65.6 ± 11.9 Nm; IRnondominant = 61.7 ± 12.0 Nm ERdominant = 43.4 ± 4.7 Nm; ERnondominant = 38.9 ± 4.2 Nm ER/IRdominant = 67.48 ± 11.10%; ER/IRnondominant = 64.74 ± 11.39% IRdominant = 59.8 ± 9.0 Nm; IRnondominant = 56.5 ± 11.7 Nm ERdominant = 42.3 ± 7.9 Nm; ERnondominant = 40.6 ± 9.2 Nm ER/IRdominant = 71.62 ± 13.96%; ER/IRnondominant = 72.85 ± 15.27% |
| Walch et al. (2021) | Con-Trex ® dynamometer (Con-Trex MJ; CMV AG, Dübendorf, Switzerland) | Seated | Upper arm abducted at 30° Elbow flexion at 90° In scapular plane |
Concentric at 60 °/s Concentric at 240 °/s Eccentric at 60 °/s |
Forwards: IRdominant = 87.9 ± 18.1 Nm; IRnondominant = 85.1 ± 18.5 Nm IRdominant = 0.80 ± 0.18 Nm.kg−1; IRnondominant = 0.77 ± 0.19 Nm.kg−1 ERdominant = 59.6 ± 16.4 Nm; ERnondominant = 58.3 ± 16.8 Nm ERdominant = 0.54 ± 0.15 Nm.kg−1; ERnondominant = 0.53 ± 0.15 Nm.kg−1 ER/IRdominant = 0.68 ± 0.13; ER/IRnondominant = 0.69 ± 0.14 Backs: IRdominant = 70.2 ± 12.2 Nm; IRnondominant = 72.3 ± 15.1 Nm IRdominant = 0.79 ± 0.14 Nm.kg−1; IRnondominant = 0.81 ± 0.19 Nm.kg−1 ERdominant = 46.3 ± 10.0 Nm; ERnondominant = 50.9 ± 14.9 Nm ERdominant = 0.52 ± 0.11 Nm.kg−1; ERnondominant = 0.57 ± 0.18 Nm.kg−1 ER/IRdominant = 0.66 ± 0.10; ER/IRnondominant = 0.71 ± 0.13 Forwards: IRdominant = 81.2 ± 17.0 Nm; IRnondominant = 78.6 ± 19.5 Nm IRdominant = 0.74 ± 0.17 Nm.kg−1; IRnondominant = 0.71 ± 0.20 Nm.kg−1 ERdominant = 54.0 ± 16.9 Nm; ERnondominant = 52.6 ± 17.9 Nm ERdominant = 0.49 ± 0.16 Nm.kg−1; ERnondominant = 0.48 ± 0.16 Nm.kg−1 ER/IRdominant = 0.67 ± 0.16; ER/IRnondominant = 0.68 ± 0.17 Backs: IRdominant = 65.9 ± 16.3 Nm; IRnondominant = 64.8 ± 17.7 Nm IRdominant = 0.74 ± 0.19 Nm.kg−1; IRnondominant = 0.72 ± 0.19 Nm.kg−1 ERdominant = 42.8 ± 15.1 Nm; ERnondominant = 46.4 ± 16.0 Nm ERdominant = 0.48 ± 0.18 Nm.kg−1; ERnondominant = 0.52 ± 0.19 Nm.kg−1 ER/IRdominant = 0.64 ± 0.11; ER/IRnondominant = 0.72 ± 0.13 Forwards: IRdominant = 105.8 ± 28.0 Nm; IRnondominant = 103.0 ± 26.2 Nm IRdominant = 0.95 ± 0.28 Nm.kg−1; IRnondominant = 0.93 ± 0.25 Nm.kg−1 ERdominant = 70.8 ± 23.1 Nm; ERnondominant = 70.3 ± 21.3 Nm ERdominant = 0.64 ± 0.21 Nm.kg−1; ERnondominant = 0.64 ± 0.10 Nm.kg−1 Backs: IRdominant = 79.0 ± 24.0 Nm; IRnondominant = 87.8 ± 25.9 m IRdominant = 0.88 ± 0.25 Nm.kg−1; IRnondominant = 0.98 ± 0.30 Nm.kg−1 ERdominant = 57.8 ± 16.5 Nm; ERnondominant = 59.8 ± 17.0 Nm ERdominant = 0.65 ± 0.21 Nm.kg−1; ERnondominant = 0.67 ± 0.20 Nm.kg−1 |
con: concentric; ER: External Rotation; ecc: eccentric; IR: Internal Rotation.
Seven studies (Table 4) used isometric assessment to determine the maximal internal and external glenohumeral rotation strength when the player was standing, 33 sitting, 34 or supine.34–37 Three studies reported mean strength values for both the right and left sides,33,35,38 and three studies combined the values for both sides.34,36,37 All the studies reported the maximal glenohumeral rotation strength values, except for one study. 39 Two studies expressed the strength values in kg,33,38 one study expressed them in N, 35 and three studies normalized them by body mass in N.kg−1.34,36,37 Two studies34,37 reported ratios of the external to internal rotation strength. Three studies33,34,38 assessed glenohumeral rotation strength with the arm in a neutral position. One study 38 failed to reach the threshold for acceptable methodological quality, preventing normative strength values from being provided. The other five studies34–37,39 assessed glenohumeral rotation strength when the arm was abducted at 90° in the frontal plane. Since one study 39 had low methodological quality, data from the remaining four studies34–37 with acceptable methodological quality were used to compute the normative strength value.
Table 4.
Experimental settings in the seven studies measuring internal and external glenohumeral rotation strength using isometric assessment.
| Study | Instrumentation | Body position | Upper limb position | Outcome measures (mean ± SD) |
|---|---|---|---|---|
| Davies et al. (2016) | Gatherer System (Gatherer Systems Ltd, Aylesbury, UK), | – | Neutral | Age-graded first raw: IRleft = 36 ± 8 kg; IRright = 37 ± 8 kg ERleft = 25 ± 5 kg; ERright = 26 ± 6 kg Senior first raw: IRleft = 46 ± 11 kg; IRright = 46 ± 12 kg ERleft = 35 ± 6 kg; ERright = 37 ± 7 kg |
| Horsley et al. (2012) | Nottingham Myometer | – | Upper arm abducted at 90° | Maximal IR and ER strength (kg) a |
| Kadlec et al. (2020) | Groinbar (Vald Performance, Newstead, Australia) | Supine | Upper arm abducted at 90° | IRleft = 180 ± 42 N; IRright: 192 ± 41 N ERleft: 183 ± 41 N; ERright: 194 ± 39 N |
| Ogaki et al. (2014) | Micro-FET; Hoggan Health Industries, Draper, UT, USA | (1) Seated (2) Supine |
(1) Upper arm abducted at 0° Elbow flexed at 90° (2) Upper arm abducted at 90° Elbow flexed at 90° |
IR = 3.03 ± 0.6 N.kg−1; ER = 2.81 ± 0.4 N.kg−1 ER/IR = 1.72 ± 0.40 IR = 2.42 ± 0.6 N.kg−1; ER = 2.22 ± 0.4 N.kg−1 ER/IR = 1.10 ± 0.30 |
| Ogaki et al. (2016) | Micro-FET; Hoggan Health Industries, Draper, UT, USA | Supine | Upper arm abducted at 90° Elbow flexed at 90° |
IR = 2.66 ± 0.5 N.kg−1; ER = 2.50 ± 0.5 N.kg−1 |
| Rogowski et al. (2020) | micro-FET; Hoggan Health Industries, Draper, UT, USA | Supine | Upper arm abducted at 90° Elbow flexed at 90° |
Healthy players: IR = 2.32 ± 0.53 N.kg−1; ER = 2.37 ± 0.43 N.kg−1 ER/IR = 1.06 ± 0.23 Players with injury history: IR = 2.40 ± 0.37 N.kg−1; ER = 2.33 ± 0.54 N.kg−1 ER/IR = 1.08 ± 0.27 |
| Zelinski et al. (2019) | HHD; Lafayette Manual Muscle Test System Model 01163, Lafayette Instrument Company, Lafayette, IN) | Standing | Upper arm abducted at 0° Elbow flexed at 90° |
IRleft = 23.4 ± 4.5 kg; IRright = 23.2 ± 4.8 kg ERleft = 17.8 ± 2.5 kg; ERright = 16.5 ± 3.1 kg |
Values are not reported because they were unclear in the original manuscript.
IR: Internal Rotation; ER: External Rotation.
Six groups of shoulders (n = 311) in five groups of rugby union players (n = 163) were identified from the remaining four studies, resulting in a pool of maximal internal and external glenohumeral rotation strength assessed when the arm was abducted at 90° and the elbow was flexed at 90°. The 163 rugby union players had a mean age of 20.3 ± 0.7 years (CI95% [18.9; 21.7]), mean body mass of 88.1 ± 4.5 kg (CI95% [79.3; 96.6]), and mean body height of 179.3 ± 2.2 cm (CI95% [175.0; 183.6]). The three players characteristics had low heterogeneity (I2 = 0%; Q = 5.00, p = 0.42; I2 = 0%; Q = 3.98, p = 0.41; I2 = 7.9%; Q = 4.34, p = 0.36). Figure 2 presents the summary statistics for the shoulder groups in each study included in the meta-analysis. An external/internal glenohumeral rotation strength ratio of 1.03 was determined based on the normative strength values (Figure 2).
Figure 2.
Meta-analysis (bold line) of internal (top) and external (bottom) glenohumeral rotation strength (expressed in N.kg−1 and in N for all) assessed in isometric mode when the arm was abducted at 90° and elbow flexed at 90°.
Discussion
This study aimed to provide normative values for internal and external glenohumeral rotation strength in rugby players based on a systematic literature review. The main findings were that there are two main methods for assessing glenohumeral rotation strength in rugby players, namely, isokinetic and isometric methods. Studies that employed isokinetic assessments used various experimental procedures despite having acceptable methodological quality, making it impossible to compare and pool data. Isometric assessments are performed when the arm is placed in two different positions. Only studies that assessed isometric strength when the arm was abducted at 90° in the frontal plane were sufficiently numerous and of acceptable methodological quality to allow for data pooling to provide normative values for internal and external glenohumeral rotation strength.
This systematic review focuses on studies that assessed the internal and external glenohumeral rotation strength in the rugby player population. Although rugby is a globally popular sport and the shoulder region is the primary site of upper-extremity injury in rugby players,2,3 only 15 studies assessed glenohumeral rotation strength. However, 85% of these studies were published in the last decade, indicating the need for additional information on the shoulder strength of rugby players. Overall, the most recent studies adequately described the studied population and the experimental design used to assess glenohumeral rotation strength and provided numerical strength values in the form of mean ± SD. The major gap is in the essential parameters for evaluating test–retest reliability, such as intraclass coefficient of correlation, standard error of measurement, or minimal detectable change, which are used to assess the consistency of outcome measures. Since numerous previous studies have reported high reliability for either isokinetic40,41 or isometric assessment 42 and the studies included in this meta-analysis provided high reliability of strength measures,33,34,36 we assumed that this item might have a minor influence on pooling data in terms of population and experimental procedure heterogeneity.
Isokinetic assessment is considered the gold standard for objectively evaluating muscle performance 41 despite the variety of device settings and the extensive freedom of motion in the shoulder complex, which results in a wide range of body and arm positions, motion, and isokinetic speeds. Such a wide range is also found for glenohumeral rotation strength assessment in rugby players. Most of the studies used a seated position (60%) with the upper arm elevated in the scapular plane (70%), that is, 30° in front of the frontal plane. The seated position is preferred to the standing position to avoid compensatory strategies, and the scapular plane appears to be more physiological, safe, and comfortable, resulting in high reliability for glenohumeral rotation strength values. 40 However, the position of the arm in abduction ranges from a neutral position to 90°, and assessment speeds range from 60 °/s to 240 °/s, influencing the production of muscle strength due to muscle lever arm, force–length, and force–velocity relationships. 25 Moreover, previous studies have shown that not every athlete reaches the isokinetic phase at speeds greater than 180°/s, particularly for the external glenohumeral rotation 43 and eccentric mode. 44 Isokinetic measures, particularly the strength ratio between the eccentric mode in internal rotation and concentric mode in external rotation for simulating the upper arm resisting hyperextension, are believed to be indicative of the actions encountered during rugby practice. 31 Similar to previously reported isokinetic assessments for hip muscle strength, 21 isokinetic tests for glenohumeral rotation strength in rugby players have high variability in terms of body position, arm position, articular plane, and speed, preventing comparison or pooling of data from previous studies. Thus, these findings suggest that specific experimental isokinetic procedures for assessing strength in internal and external glenohumeral rotation in rugby players may be designed and validated.
Two upper-arm postures were used to assess internal and external glenohumeral rotation strength in rugby players during the isometric assessment. According to the force–length relationship, differences in arm positioning influence muscle ability to produce strength. To conduct the meta-analysis, we required three or more studies that used similar experimental procedures and involved players who played the same type of rugby, in addition to acceptable methodological quality. Four studies that assessed isometric glenohumeral rotation strength when the arm was abducted at 90° in a supine body position met these criteria. Fortunately, these studies exclusively focused on male rugby union players, eliminating any potential differences in shoulder adaptations related to sex or rugby type. Variability in participants’ characteristics may also be due to the player's on-field position, shoulder dominance, and anthropometry, 45 particularly the forearm length. Indeed, the resistance is applied to the styloid process during glenohumeral rotation isometric strength testing. The level of force achieved and the reliability of the measurements may be influenced by generating a lever arm that corresponds to the forearm length. Despite the most effective anthropometric parameter for normalizing strength values is expressing the isometric strength for internal and external glenohumeral rotation relative to body mass, 46 using torque by multiplying strength by moment arm may be a potential optimal quantification of strength. Furthermore, intraclass coefficients of correlation higher than 0.80 and a standard error of measurement lower than 0.17 N.kg−1 indicate that the internal and external glenohumeral rotation isometric strengths are reliable. 47 In addition, no differences in either normalized strength between forward (on-field positions 1–8) and backward (on-field positions 9–15) players 32 or maximal strength between right and left, or dominant and nondominant, shoulders28,38 have been previously observed in rugby union players. Among the four studies from which data could be pooled, the age, body mass, and body height of the players presented low heterogeneity, while one source of heterogeneity remained (i.e. level of practice). Despite the presence of amateur and professional rugby union players, heterogeneity and variability in normalized strength values for either internal or external rotations remained low and were consistent with those reported in a previous meta-analysis of glenohumeral rotation strength in a nonathletic population. 48 Therefore, we assumed that the strength values for all the players, regardless of the level of practice, can be pooled to provide an initial benchmark for shoulder rehabilitation. The normative values obtained by including 10 squads were higher than those reported for students 42 or overhead athletes, 49 indicating that rugby union players require more specialized strength adaptations at the glenohumeral joint than nonathletes 28 or noncollision sports athletes. 37 The similarity in the normative values for internal and external rotation strength also suggested that the goal of a return-to-sports program could be to achieve a balance between the two glenohumeral rotations. 18 Clinical practitioners must know the normative internal and external glenohumeral rotation strength in male rugby union players to use an evidence-based approach when repairing shoulder strength in these players.
This study has some limitations. The first limitation is the small number of groups included in the meta-analysis for providing normative internal and external glenohumeral rotation isometric strength values, which probably skews the statistical assessment of heterogeneity. Second, no risk of bias is provided. Third, the normative isometric strength values are based on retrospective and prospective studies that involved professional/semiprofessional or amateur rugby union players, and professional players may require higher glenohumeral rotation strength than amateur players. Moreover, normative isometric strength values expressed relatively to body mass may not be appropriate because this infers that strength is linearly related to body mass. However, this is the first study to provide normative glenohumeral rotation strength values to aid clinicians in restoring proper shoulder function in male rugby players. Further studies are required to validate experimental isokinetic procedures in rugby players and refine normative glenohumeral rotation isometric strength values as a function of playing levels, rugby type, sex, and age.
In conclusion, this systematic review emphasizes that to pool data from several studies, isokinetic assessments of glenohumeral rotation strength in rugby players must be standardized in experimental procedures. This systematic review also provides normative values for internal and external glenohumeral rotation strength, which were assessed during isometric contractions with the upper arm abducted at 90°. These normative values may aid physical therapists and strength and conditioning coaches in restoring the glenohumeral rotation strength in male rugby union players and authorizing them to return to full rugby sport participation.
Footnotes
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding: The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ramsay Santé (grant number COS-RGDS-2019-12-050).
ORCID iD: I Rogowski https://orcid.org/0000-0002-9159-382X
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