Design
This study was a Pre-test – post-test quasi-experimental cohort design with a control group aiming to investigate the effect of an eight-week 11 + S programme on shoulder proprioception and stability in young male volleyball players. Two teams were randomly divided into intervention and/or control group.
Participants
Two teams consist of Thirty-two young male volleyball players (mean age 17.5 ± 1.47 years) Were selected by available methods from thirteen teams of the Iranian Youth Volleyball Premier League volunteered to participate in this study during the pre-season. Block randomization method was used to create a random sequence. In this method, 4 blocks of all possible combinations (6 possible modes AABB, ABAB, ABBA, BBAA, BABA, BAAB) were created. Then these blocks were numbered and randomly selected and placed one after the other, thus, the participants were divided into two groups A (intervention = 16) and B (control = 16). MZ generated all the steps of random allocation sequence, enroll and assignment of participants to the interventions. The sample size was estimated based on the findings of previous studies [15, 26,27,28]; so that using the G-Power software with 95 % power at the 0.05 level of significance the expected number of participants was estimated (Considering a full factorial ANOVA and using small effect size (h = 0.53), confidence level (a = 0.05), and desired power (95 %) for 2 measurements, a test power analysis was performed and the required total sample size was calculated to be 32 subjects).
In such studies, blinding cannot be performed completely and therefore, in the present study, a single-blind method was used where only participants were tried to be blinded from the study. For this purpose, both intervention and control groups were given warm-up exercises. The warm-up exercises of the intervention group were the main exercises of 11 + S, while the warm-up exercises of the control group were the same as their normal warm-up exercises.
Inclusion criteria for the study were as following: (1) Having no severe injuries (more than three weeks absence from exercise) over the past six months, (2) Having at least three years playing experience in volleyball, (3) Exercising approximately three sessions per week including matches and training. The absence in two consecutive training sessions, and conducting any systematic injury prevention programme leaded to players’ exclusion from the investigation.
Ethical considerations
This study was approved by research ethics committee of sport science research institute of Iran. Written consent was obtained from the participants before participation at the study. Participants had the right to withdraw from the study at any time without any consequences.
Procedures
Demographic data
All the participants filled into the questionnaires on the age, height and weight, previous shoulder injuries, their specific game post, game level and training hours.
Proprioception measurement
The Biodex System 4 dynamometer (Biodex Medical Systems, New York, USA) was used to measure the proprioception of the dominant shoulder. Two methods of TTDPM and JPS in passive mode were used to measure proprioception. We used the passive protocol for both because the proprioception measurement is reported to have a greater reliability )ICC values ± SD: 0.92 ± 0.07 (in the passive protocol compared to active protocol (ICC values ± SD: 0.34 ± 0) [10]. The dominant side was determined using the Edinburgh questionnaire [29, 30]. The subjects did not perform any exercise the day before the test. Before each testing session, the dynamometer was set in accordance with the manufacturer’s recommendations. A standardized testing protocol was followed. Tests were conducted in the sitting position. To provide stability and prevent extra movements, participants were fixed with straps around the shoulders, chest, and hip. To remove visual feedback and auditory feedback the blindfold and headphones were used during the test and subjects listened to white noise during the test. In order to familiarize the participants with the levels, the test was performed twice before the start. All tests were performed between 9 am and 2 pm. For each individual, pre and post tests were taken approximately at the same time of the day with the same manner and order.
To determine the JPS, shoulder internal/external rotation were measured at 2 degrees per second in passive mode. The rationale for choosing these velocities was based on previous studies in which comparable velocities were used [11].
The dominant shoulder was positioned at 90 degrees of abduction and 0 degrees of external rotation (ER) in the scapula plane (30 degrees ahead of the frontal plane), as the measurement of the proprioception of internal and external rotators at this angle has high validity [10]. The elbow flexed 90 degrees. The forearm was in internal rotation (IR); see Fig. 1. The target angle was 45 degrees of IR (from neutral to 45 degrees of IR) and 75 degrees of ER (from neutral to 75 degrees of ER). The limb moved up to 45 degrees of IR by the device and the shoulder was kept in this position for 10 s and the participant was then asked to focus on the position. Then the manual key was given to the participant and the device information on the motion was inactivated by 45 degrees of IR and 75 degrees of ER, and the participant was asked to press the key at any angle he felt that he reached to the target angle. Three repetitions for IR and three repetitions for ER were performed and the magnitude of the difference between the reconstructed angles and the target angle was calculated and considered as the angle reconstruction error [11].
To determine the TTDPM, shoulder internal/external rotators muscles were measured at 0.25 degrees per second in passive mode. The dominant shoulder position was similar to the JPS test (Fig. 1). Then the manual key was given to the participant and the shoulder passively started from 0 degree to the IR direction and the person was asked to press the key as soon as the movement was detected. Then the onset test and the mean motion detection threshold were recorded 3 times in the test [31]. The same protocol was then repeated for ER.
Dynamic stability measurement
The Upper Quarter Y Balance Test (UQYBT) was used to measure the dynamic stability of the dominant shoulder. The UQYBT is a valid and reliable test (with ICC coefficients ranging from 0.80 to 1.0 for test-retest as well as intra-rater reliability) [32, 33] for measuring unilateral (dominant hand) upper extremity performance and stability in a closed-chain position. It can identify upper extremity motor limitations and asymmetry and therefore can be used to predict injury in athletes [33].
To perform this test, the participant was asked to place the thumbs on the palms of the fingers and elbows open, keeping the spine and lower limbs in one position. The location of the thumb was indicated by a line and the legs were about the shoulder-width apart (the legs were not more than 30 cm apart). In this situation, the participant was asked to maintain the position of the support arm, trunk, and lower limb, to reach the medial, supero-lateral and infero-lateral directions[34] as far as possible with his free hand (Fig. 2). In order to be able to compare the results of this study with others, The player’s upper limb length reach values (the seventh cervical vertebra to the end of the longest finger at 90 degrees shoulder abduction and extension of the elbow, wrist, and toe) were normalized [35]. While maintaining the push up position the ability to reach all three directions was measured without rest and without touching the ground. The participant was allowed, after each round of reaching all 3 directions, to place the free hand on the ground and rest [33]. Before the test, each participant was allowed to perform two practice trials. Three consecutive trials in all three directions were performed on the dominant arm. In each direction, the highest reach was recorded and was calculated in the following formula to calculate the overall composite score [35]:
$$\mathrm{Combined}\;\mathrm{score}\;=\;(\mathrm{middle}\;\mathrm{access}\:+\:\mathrm{lower}-\mathrm{external}\;\mathrm{access}\:+\:\mathrm{upper}-\mathrm{external}\;\mathrm{access})\;\div\;(\mathrm{upper}\;\mathrm{limb}\;\mathrm{length}\;\times3)$$
Intervention programme
The 11 + S programme was developed by an international group of experts, including orthopedics, physiotherapists, and sports rehabilitation specialists. The programme focuses on core stability, neuromuscular control, eccentric rotators’ strength, and shoulder agility. It consists of three parts: general warm-up (part I); strength and balance training for the shoulders, elbows, wrists, and fingers (part II); core stability and muscle control exercises (part III). The second part of the programme has three levels of difficulty and to achieve that elastic bands at three resistance levels (blue [low], black [medium], and gold [high]) are used. Prior to the implementation of the 11 + S programme by the participants of intervention group, several educational sessions were organized for the coaches by the researcher to familiarize the coaches with the exercises and how they are implemented, this was done in order to ensure that the programme would be properly implemented by the coaches, Informative posters were also provided. The researcher supervised the training at intervention group at each session to validate the implementation of the 11 + S injury prevention programme. The content of the training and participants’ progress was monitored by the researcher every two weeks during the intervention period.
All players started training from level one and moved on to the next level if they were able to do error-free training determined by coaches under standard conditions. The participants at the intervention group performed 11 + S exercises three times per week as their warm-up protocol. The 11 + S programme was usually taken about 20–25 min.
The control group also performed their normal warm-up for 25 min, including 5 min of stretching exercises for the whole body, then dynamic warm-up exercises for 10 min, including running and jumping movements, and finally 10 min of exercises with the ball, including spiking, etc.
In order to avoid the effect of fatigue on the proprioception due to increased intramuscular concentrations of lactic acid, bradykinin, arachidonic acid, and serotonin after fatiguing contractions which may affect the muscle spindle system, and, thus, proprioceptive acuity [28], players performed JPS and TDDPM tests with an isokinetic dynamometer before the UQYBT test. Before the pre-test and post-test, the players performed a standardized 5-minute warm-up on an arm-cycle ergometer (Monarch Model 894E, Sweden) at a self-determined cadence (between 80 and 110 rpm) with the workload set to 75 W. Participants then familiarized with the dominant shoulder test to learn how to perform a proprioception test with an isokinetic device. They tried to do the UQYBT test, did the test twice in three directions. The proprioception and UQYBT tests for the dominant shoulder were conducted in standard conditions. All tests were conducted three days before and three days after the intervention programme at the Shahid Beheshti University Sport Laboratory.
Statistical analysis
All statistical analyses were performed by SPSS 24.0 software (IBM corp. Amork, NY). Descriptive data are provided as mean and standard deviation. The demographic characteristics of the participants of two groups at baseline were analyzed using the independent samples T-test. Measurements of proprioception in internal and external shoulder movement (for JPS and TTDPM) have been reported. Two-factor ANOVA test (condition factor: “pre” and “post” and group factor: intervention vs. control) with a group x condition interaction was used to analyze the within and between group evaluation over the eight-week intervention period at 95 % significance level with alpha equal or less than 0.05. To limit the possibility of getting a statistically significant result, Bonferroni adjustment for multiple comparisons was used for post hoc test. To analyze the effect of the intervention on the different proprioception measures, we calculated the mean differences and the ∆%between the intervention group and the control group. The effect size was calculated using Cohen’s d value. An effect size between 0.2 and 0.5 was considered a small effect, between 0.5 and 0.8 a medium effect, and greater than 0.8 a large effect [36].
