Background:
Low back pain (LBP) is a common injury in high school volleyball players. We hypothesized that a prevention program could decrease the incidence of LBP in high school volleyball players. This study was an in-season cluster-randomized controlled trial.
Methods:
We block-randomized 8 high school volleyball teams comprising 70 players aged 15 to 17 years into the intervention (4 teams, 34 players) and control (4 teams, 36 players) groups. The intervention program consisted of 9 physical function tests as well as 1 or 2 self-selected preventive exercises, including dynamic thoracic mobility, trunk stabilization exercises, and static stretching, performed during warm-up. Both groups were followed up for 4 weeks, during which the incidence of LBP was recorded. Physical function tests (back endurance; spinal and back flexibility; active or passive shoulder and trunk range of motion; ankle joint mobility; and iliopsoas, quadriceps, and hamstrings flexibility) were conducted before and after the intervention.
Results:
The intervention group had a significantly lower incidence of LBP (8.8%) than the control group (33.3%) (relative risk, 3.78; 95% confidence interval, 1.17–12.23; P = .017, 1 − β = 0.99). Lumbar extension accounted for nearly 70% of LBP incidences. Most players in the intervention group demonstrated improved physical function associated with the exercises.
Conclusion:
The semi-customized prevention program decreased the incidence of LBP and enhanced the physical function parameter in high school volleyball players.
Keywords: injury, low back pain, randomized controlled trial, volleyball, youth sports
1. Introduction
Volleyball is one of the world’s most popular sports for people of all ages. Notably, volleyball has been found to cause fewer injuries than other sports.[1,2] Nevertheless, despite the beneficial effects of volleyball on health, acute or overuse musculoskeletal injuries have been reported.[3,4] Studies have shown that overuse-related back injuries in volleyball are as common as knee and shoulder injuries.[5–7] Mizoguchi et al[8] found that 48% of high school volleyball players developed low back pain (LBP) due to volleyball. Repetitive spiking, jumping, and other volleyball-related motions may expose the lumbar spine to greater stresses than would normal daily activities. Bahr argued that there are numerous occasions in sports in which athletes complain of pain despite being uninjured,[9] which would not only cause deterioration in players’ sports performance but also make them miss practice sessions. Hence, pain management in sports is important considering that it helps improve players’ performance. A study showed that the prevalence of LBP in athletes engaged in sports on a daily basis increase after the age of 17 years.[10] Another study found that the prevalence of LBP was higher in college volleyball players than in high school volleyball players.[11] Hence, reducing the incidence of LBP in adolescent athletes, who are still skeletally immature, may mitigate the subsequent development of LBP.
A systematic review of musculoskeletal injuries related to volleyball conducted by Kilic et al[4] highlighted the importance of focusing on other specific musculoskeletal injuries besides common knee and ankle injuries in volleyball players. The study indicated that only a few effective prevention methods have been available for musculoskeletal injuries in volleyball players.[4] To avoid overuse injuries, specialized preventive measures are necessary in addition to regular training sessions.[12] A study showed that an injury prevention program of at least 15 minutes, which includes warm-up, agility drills, stretching, or strength/conditioning, was effective in reducing the incidence of injuries in adolescent team sports.[13] Pastor et al[14] reported that individualized preventive exercises based on a functional diagnosis significantly reduced the incidence of injuries when performed under professional supervision prior to the start of the season. Overuse-induced LBP in high school volleyball players has been associated with a history of ankle sprains, reduced horizontal abduction (HAB) range of motion (ROM) of the shoulder joint, and reduced hip flexibility.[8,15] Studies have shown that diverse volleyball-specific movements (e.g., spiking, serving, and digging) with no common factors induce LBP in adolescent players.[8] Therefore, considering individualized exercise regimens based on functional assessments rather than those targeting a physical function is necessary for the prevention of LBP in high school volleyball players. Since many high school teams in Japan do not have physical therapists or trainers, there is a need for a simple evaluation method and program to help high school students manage these back pain-related physical function problems themselves.
Therefore, this randomized controlled trial primarily aimed to evaluate the effects of an exercise program designed to reduce the incidence of LBP in high school volleyball players aged 15 to 17 years. The program is designed to evaluate and improve physical function variables that had been identified in previous research[15] as risk factors for volleyball-induced LBP, and that can be easily mastered by players. This study hypothesized that semi-customized exercises would be effective in preventing LBP in high school volleyball players.
2. Methods
2.1. Study design and recruitment
This prospective cluster-randomized controlled trial followed and completed the Consolidated Standards of Reporting Trials with the subsequent extension to cluster-randomized trials[16] and was registered with the University hospital Medical Information Network Center, Tokyo, Japan (UMIN000027554).
The inclusion criteria were male and female volleyball players aged 15 to 17 years belonging to the top 32 of 243 schools (male: 99 teams; female: 144 teams) included in the Saitama Prefecture High School Volleyball League, Japan (population of approximately 7,300,000), in order to homogenize the players’ competition level as much as possible. This was conducted to standardize the skill level of the athletes as well as the intensity and frequency of their practice, thereby reducing the impact of training program on the effectiveness of the intervention. We invited 16 to 32 elite high school volleyball teams across Saitama, Japan, to participate in this study from June 2017, with each team receiving detailed information regarding the study, including an overview and inclusion and exclusion criteria. The exclusion criteria were players who had a history of surgery in the spine, upper limbs, or lower limbs; had LBP at the start of the study; had neurological symptoms, including pins and needles, numbness, and/or weakness in the lower limbs at the start of the study; had no lumbar spondylolysis, lumbar disc herniation, or other spinal disease; and had all eleven physical function tests in this study negative and had no ROM limitations. We confirmed that none of the participants had routinely performed the exercises used herein prior to the intervention (Fig. 1).
Figure 1.
Flow chart of participants throughout the trial.
2.2. Ethical considerations
This study was approved by the Ethics Committee at the Faculty of Health and Medical Care, Saitama Medical University, Japan (M-73), and was conducted in accordance with the principles of the Declaration of Helsinki. The consent of the teams, players, and their parents was obtained prior to study commencement. The study’s purpose was explained via a letter and verbal communication to the school principal and volleyball club coach of each high school, after which the principal’s written consent was obtained. A similar explanation was also provided to the participants and their parents, after which written consent was obtained.
2.3. Sample size
To determine the sample size needed to achieve statistical significance with 80% power (1 − β), a priori power analysis was performed. The sample size was calculated using power analysis application G*Power 3.1.9.2 (http://www.gpower.hhu.de/). To compare the incidence of LBP between both groups, the effect size was set to 0.3 (α = 0.05, 1 − β = 0.8, Df = 1) in the chi-squared test, ultimately resulting in a sample size of 88. Considering the lack of studies similar to the current one, we estimated that at least 88 cases were needed for this study.
2.4. Randomization procedure
In total, 8 high schools participated in this study. Given that normal randomization could not be employed due to the risk of contamination, cluster randomization using each team as the unit of cluster was performed. Randomization was achieved using the envelope method, assigning an equal number of teams to the intervention and control groups. To ensure concealment of allocation, one of the authors who was blinded to the identities of the teams (HN) performed randomization. This randomization scheme was revealed only after the final team had been recruited. Overall, teams were assigned to 4 intervention groups and 4 control groups (Fig. 1).
2.5. Measurement
The athletes’ data, including questionnaires and physical function tests, were collected in the high school gymnasium using methods similar to those employed in previous studies.[8,15] The survey items comprised demographic details, environmental factors, and physical function. Basic information questionnaires and physical function tests were conducted before and after the intervention.
Demographic details included sex, age (years), height (cm), body weight (kg), dominant hand, and years of experience as a volleyball player. Height and weight data were subsequently used to calculate the players’ body mass index (kg/m2). The dominant hand was determined as the arm used to spike or serve. Vertical jump (cm), spike jump (cm), and block jump (cm) values were measured for each player and were calculated by subtracting the standing reach point from the highest reach point of each jump. Each jump was performed 3 times, with the highest point being recorded.
Environmental factors assessed included the volleyball court position [spiker (strong side, weak side, or middle blocker) or others (setter or libero)], spike form (bow and allow, circular, or straight), average volleyball practice time per week, presence or absence of static stretching after volleyball practice, and average sleep duration. Based on previous research,[8,17] LBP during volleyball practice was defined as pain or discomfort within the region between the lowest rib and buttocks. Players with symptoms associated with menstruation were not classified as having LBP. Players replied with “yes/no” to the question of lower extremity pins and needles or numbness, which was used to identify neurological symptoms. Players answered the questionnaire at a location away from the team’s coaches. If necessary, the authors examined the status of the player’s LBP. In case of LBP during the intervention period, players were requested to record the date and time of each occurrence, type of volleyball movement, location and intensity of the pain, and direction of movement induction on a check sheet distributed individually. Pain intensity was assessed using an 11-point numeric rating scale (NRS). The authors contacted the coach once a week to inquire regarding any disability occurrences, including LBP.
Physical function tests included the Ito test (s),[18,19] backbends in a supine position (BB, cm), finger–floor distance (FFD, cm),[20,21] side FFD (cm),[20,21] modified Thomas test (MTT),[22,23] heel–buttock distance (cm),[24] and full squat test.[25] Active shoulder flexion, external rotation (ER), and HAB ROM (degree), as well as trunk rotation ROM, were measured using a plastic goniometer (GS-100; OG Wellness Inc., Japan) at 5° increments.[26] For trunk rotation, participants were instructed to place in a sitting position with their feet on the floor and knees and hips at 90° of flexion. The goniometer was positioned with the axis fixed in the transverse plane at the level of T1–T2, following the measure recommendations.[27,28] We specified to position the subject to kneel against the wall to reduce the contribution of the lower body on spine rotation. The detailed other physical function test measurements have been described extensively in a previous cross-sectional study.[15] These tests have been shown to be reliable in previous studies,[18–25,27,28] and are useful in determining the occurrence of LBP in volleyball players.[15] To address potential sources of bias, the intervention and control group participants were sampled from the same population of high school volleyball players. Additionally, to reduce measurement error as much as possible, all physical function tests were administered by 2 physical therapists (NS and HN) who were blinded to whether the participants were in the intervention or control group after being instructed on the methods of measurement by another skilled physical therapist (YM) with more than 10 years of experience.
A baseline value was established for each of physical function test (Table 1). The reference values were as follows: 180 seconds for the Ito test, 50 cm for BB, 0 cm for FFD, difference of 5 cm between the left and right sides for side FFD, and difference of 10 cm for heel–buttock distance. For full squat test measurements, the participants squatted on the spot while keeping both hands behind. They were asked to not allow their heels to come off the ground during this test. Participants who fell behind were considered to have positive results. The MTT relied on previous research on the reliability of this test.[22,23] The authors stabilized the participant’s pelvis and observed the proper position of the lumbar spine. Flexing of the hip joint on the test side was considered a positive result.
Table 1.
Physical function test exercises.
| Tests | Baseline | Exercises |
|---|---|---|
| 1) Ito test (s) | 180 s | Trunk stabilization exercises |
| 2) BB (s) | 50 cm | Spinal flexibility exercises |
| 3) FFD (cm) | 0 cm | Jack-knife stretching |
| 4) Side FFD (cm) | 5 cm difference between left and right side | Trunk rotation exercises (on all fours) |
| Shoulder FL ROM (°) | 180° | |
| Shoulder ER ROM (°) | 90° | |
| Shoulder HAB ROM (°) | 30° | |
| Trunk rotation ROM (°) | 40° | |
| 5) MTT | Whether the opposite hip flexes. | Iliopsoas stretching |
| 6) HBD (s) | 10 cm | Quadriceps stretching |
| 7) Full squat test | Whether the heel comes off the ground. | Gastrocnemius stretching |
BB = backbends from a supine position, ER = external rotation in 2nd position, FFD = finger–floor distance, FL = flexion, HAB = horizontal abduction, HBD = heel–buttock distance, MTT = modified Thomas test, ROM = range of motion.
2.6. Intervention
Participants performed exercises based on the physical function assessment (Table 1) during the 4 weeks of team practice. When only 1 exercise was applicable, they selected 1 and performed it for a similar period. Considering that volleyball-related LBP occurs more often during practice than in games,[8,29] this study decided to implement the exercises during the warm-up before practice. In the core stabilization exercise (Fig. 2A), participants raised their right and left upper limbs alternately from a grounded posture with their bilateral forearms and bilateral toes. At this point, we instructed that the thumb on the raised side should face the ceiling, the trunk should not be rotated, and the hip and spine should be kept in the neutral position. This posture was maintaining for 10 seconds per raise and performed 10 times for each side. Spinal flexibility exercises (Fig. 2B) involved participants performing 20 repetitions of slowly alternating anterior pelvic tilt and spinal extension, followed by posterior pelvic tilt and spinal flexion from the all-fours position. Participants were instructed to avoid hyperextending the lumbar spine, if possible, in the anterior pelvic tilt position and to perform scapular abduction and thoracic and lumbar spine flexion, as much as possible, in the posterior pelvic tilt position. In jack-knife stretching (Fig. 2C), participants first squatted with both soles grounded and then grasped both ankle joints with their own hands from the outside. They then stood up and extended both lower limbs as much as possible while ensuring that their chest and thighs were not separated. Care should be taken to not cause pain in the hamstrings. The maximum extension position was held for 5 seconds, and the exercise was performed over 5 sets. In trunk rotation exercises (Fig. 2D), participants were placed on all fours, with 1 hand on the back of their head and their trunk rotated alternately outward and inward. Each maximum position was held for 10 seconds, with the same exercise repeated on the other side (i.e., 10 times for each side). Participants were instructed not to rotate the head and pelvis during the exercise and ensure that no accompanying pain was present. In iliopsoas, quadriceps, and gastrocnemius stretching (Fig. 2E–G), participants maintained the position shown in the figure for 30 seconds on each side.
Figure 2.
Semi-customized prevention exercise. (A) Trunk stabilization exercises. (B) Spinal flexibility exercises. (C) Jack-knife stretching. (D) Trunk rotation exercises (on all fours). (E) Iliopsoas stretching. (F) Quadriceps stretching. (G) Gastrocnemius stretching.
One of the physical therapists (YM) instructed the participants individually on the exercises they selected using a paper containing detailed instructions until they understood the exercise. They were also instructed to indicate whether they performed the exercises on an exercise checklist. Once a week, we contacted coaches and managers representatives to keep track of exercise progress. The interventions employed in this study were assigned according to teams, which allowed for complete blinding of the control and intervention groups.
2.7. Outcomes
The primary outcomes included rate of compliance with the semi-customized LBP prevention exercises provided to each athlete, the incidence and intensity of LBP, and the direction of pain induction in the intervention period. The secondary outcome was longitudinal change in physical function tests.
2.8. Statistical analyses
All statistical analyses were conducted using IBM SPSS Statistics for Windows, Version 25.0 (SPSS; Armonk, NY: IBM Corp Released 2017). Initially, simple tabulation of the questionnaire items was performed, after which the means and standard deviations of continuous variables were calculated. Both groups were then compared according to each item using an independent t test. We also investigated whether the excluded participants, who had no LBP and no problems with physical functioning, had LBP or other disabilities throughout the 4 weeks.
The chi-squared test was conducted to compare the number of LBP incidences, type of volleyball movement, location of pain, and direction of movement induction between the intervention and control groups. To determine the risk of developing LBP, the relative risk for the control and intervention groups was calculated and compared. The Mann–Whitney U test was performed to compare the pain intensity in each group. Ancillary analysis was performed using the Mantel–Haenszel test to identify items that may affect relative risk.
To determine the secondary outcomes, the number of participants in each group who had problems with the physical functioning assessment was first determined and then compared using the chi-squared test. Then, within-group comparisons of physical function items pre- and postintervention were conducted using the paired t test or Wilcoxon signed-rank test. The significance level for all statistical analyses was set at 5%.
3. Results
The investigation period lasted from July to November 2017, during which a convenience sample of 63 male and 60 female volleyball players (age: 15.8 ± 0.7 years) was recruited from 8 public high schools. After excluding 53 players who satisfied the exclusion criteria, a total of 70 players were ultimately included. As a result of randomization, 34 and 36 players were assigned to the intervention (four teams) and control (four teams) groups, respectively (Fig. 1). In the intervention group, few failed to complete more than 3 of the test criteria, resulting in most subjects performed 1 or 2 exercises. As the number of participants was lower than planned, post hoc power analysis was conducted as needed.
3.1. Primary outcomes
This study achieved a 100% questionnaire response rate. No significant differences in basic attributes and positive physical function test results were observed between the intervention and control groups before the intervention (Tables 2 and 3). The intervention group had a training compliance rate of 100%. The intervention and control group conducted 6.7 ± 0.5 and 6.6 ± 0.5 team practice sessions per week during the observation period, respectively, with no significant difference between the groups (P = .39, 1 − β = 0.13). Both groups had no missing data for all items pre- and postintervention.
Table 2.
Basic characteristics of the participants.
| Intervention (n = 34) | Control (n = 36) | P | 1 − β | |
|---|---|---|---|---|
| Sex, n; male/female | 22/12 | 18/18 | .21 | 0.73 |
| Age (yr) | 15.5 ± 0.5 | 15.8 ± 0.8 | .08 | 0.43 |
| BMI (kg/m2) | 20.4 ± 1.9 | 20.3 ± 1.3 | .86 | 0.05 |
| Vertical jump (cm) | 50.8 ± 10.6 | 48.3 ± 10.5 | .33 | 0.17 |
| Spike jump (cm) | 56.2 ± 12.3 | 52.2 ± 12.3 | .18 | 0.27 |
| Block jump (cm) | 41.9 ± 9.0 | 41.3 ± 11.0 | .79 | 0.06 |
| Experience as a volleyball player (yr) | 3.5 ± 1.4 | 3.1 ± 2.1 | .33 | 0.15 |
| Hand dominance, n; R/L | 31/3 | 34/2 | .60 | 0.21 |
| Court position, n; spikers/others | 23/11 | 23/13 | .80 | 0.10 |
| Spike form*, n; bow and allow and circular/straight | 19/4 | 20/3 | .68 | 0.12 |
| Players who participated in the previous tournament, n (%) | 10 (29.4%) | 11 (30.6%) | .92 | 0.05 |
| Practice time/week (h) | 2.9 ± 0.6 | 3.0 ± 0.3 | .53 | 0.14 |
| Static stretching after practice, n (%) | Presence: 24 (70.6%) | Presence: 26 (72.2%) | .88 | 0.06 |
| Sleep time/week (h) | 6.3 ± 0.9 | 6.4 ± 1.0 | .83 | 0.07 |
Mean ± SD.
BMI = body mass index, L = left, others = setter and libero, R = right, spikers = wing spiker and middle blocker.
Only spikers.
Table 3.
Comparison of participants who exhibited problems with physical function assessment before the intervention.
| Intervention (n = 34) | Control (n = 36) | P | 1 − β | |
|---|---|---|---|---|
| Ito test, n (%) | 11 (32.4%) | 10 (27.8%) | .68 | 0.13 |
| BB, n (%) | 10 (29.4%) | 9 (25.0%) | .68 | 0.13 |
| FFD, n (%) | 15 (44.1%) | 12 (33.3%) | .35 | 0.44 |
| Side FFD, n (%) | 3 (8.8%) | 4 (11.1%) | .53 | 0.10 |
| Shoulder FL ROM, n (%) | 5 (14.7%) | 9 (25.0%) | .28 | 0.68 |
| Shoulder ER ROM, n (%) | 1 (2.9%) | 1 (2.8%) | .74 | 0.05 |
| Shoulder HAB ROM, n (%) | 2 (5.9%) | 2 (5.6%) | .67 | 0.05 |
| Trunk rotation ROM, n (%) | 2 (5.9%) | 3 (8.3%) | .53 | 0.14 |
| MTT, n (%) | 12 (35.3%) | 12 (33.3%) | .49 | 0.06 |
| HBD, n (%) | 9 (26.7%) | 10 (27.8%) | .90 | 0.06 |
| Full squat test, n (%) | 15 (44.1%) | 12 (33.3%) | .35 | 0.44 |
BB = backbends from a supine position, ER = external rotation in 2nd position, FFD = finger–floor distance, FL = flexion, HAB = horizontal abduction, HBD = heel–buttock distance, MTT = modified Thomas test, ROM = range of motion.
The incidence of LBP was 8.8% (n = 3/34) in the intervention group and 33.3% (n = 12/36) in the control group, with the former having a significantly lower incidence of LBP than the latter (P = .017, 1 − β = 0.99). The control group had a relative risk of 3.78 (95% confidence interval [CI] = 1.17–12.23). Those who developed LBP in each group did not miss any team practice sessions or consult a doctor during the 4-week period. However, all 15 participants with LBP reported that the pain reduced their subjective performance. The median intensity of LBP according to the NRS was 6.0 (4–7) and 4.0 (3–6) in the intervention and control groups, respectively, with no significant difference between the groups (P = .08, 1 − β = 0.44). With regard to the movement that elicited pain in the intervention group, 1 and 2 participants experienced pain during lumbar flexion and extension, respectively. In the control group, 3, 8, and 1 participant experienced pain during flexion, extension, and rotation of the dominant hand. No significant difference was observed between both groups. With regard to the relationship between pain-eliciting and volleyball-specific movements, those who experienced pain during lumbar flexion experienced increased pain during receiving and landing after spiking, whereas those who experienced pain during extension experienced increased pain during spiking and serving. Those who experienced pain during rotation toward the dominant hand side experienced increased pain during spiking. Among those who experienced LBP, nearly 70% (n = 10/15) were caused by lumbar extension. Among the 53 participants excluded from this study, 27 had no problems with physical function tests, and only 1 (3.8%; n = 1/27) experienced LBP (pain during lumbar extension during spiking) throughout the 4-week period.
3.2. Secondary outcome
A large percentage of participants had problems with the physical function tests, especially with the FFD (38.6%; n = 27/70), full squat test (38.6%; n = 27/70), MTT (34.3%; n = 24/70), and Ito test (31.4%; n = 22/70) (Table 3). Based on the results, participants in the intervention group preferred jack-knife stretching (44.1%; n = 15/34), gastrocnemius stretching (44.1%; n = 15/34), iliopsoas stretching (35.3%; n = 12/34), and trunk stabilization exercises (32.4%; n = 12/34) (Table 4). Participants in the intervention group who performed these exercises showed significant improvements in the corresponding physical function tests after intervention. No significant differences in shoulder and trunk ROM and BB were noted before and after the intervention. The control group exhibited a significant increase in bilateral shoulder joint ER ROM, with no significant differences in other test items.
Table 4.
Comparison of physical function tests in each group.
| Intervention (n = 34) | Control (n = 36) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| n* | Pre- | Post- | P | 1 − β | Pre- | Post- | P | 1 − β | |
| Ito test (s) | 11 | 110.1 ± 45.5 | 177.3 ± 23.1 | <.001 | 0.99 | 162.8 ± 38.2 | 171.1 ± 26.3 | .07 | 0.45 |
| BB (cm) | 3 | 46.3 ± 1.2 | 48.0 ± 4.0 | .44 | 0.09 | 52.7 ± 7.0 | 53.3 ± 8.0 | .56 | 0.08 |
| FFD (cm) | 15 | 11.4 ± 8.7 | 6.1 ± 8.5 | .005 | 0.88 | −7.5 ± 9.8 | −7.6 ± 10.3 | .84 | 0.06 |
| Side FFD (cm) | 8 | ||||||||
| Dominant hand side | 41.8 ± 8.2 | 42.8 ± 4.3 | .64 | 0.07 | 39.8 ± 6.7 | 41.4 ± 3.4 | .06 | 0.48 | |
| Non-dominant hand side | 41.3 ± 8.5 | 42.9 ± 4.9 | .43 | 0.12 | 40.1 ± 5.2 | 41.4 ± 3.7 | .08 | 0.42 | |
| Shoulder FL ROM (°) | 8 | ||||||||
| Dominant hand side | 177.0 ± 6.3 | 177.5 ± 5.4 | .34 | 0.15 | 176.9 ± 5.9 | 177.2 ± 5.5 | .60 | 0.09 | |
| Non-dominant hand side | 179.0 ± 3.2 | 179.5 ± 1.6 | .34 | 0.14 | 177.9 ± 5.1 | 178.3 ± 4.5 | .26 | 0.19 | |
| Shoulder ER ROM (°) | 8 | ||||||||
| Dominant hand side | 115.0 ± 15.1 | 124.0 ± 13.1 | .07 | 0.44 | 114.6 ± 11.7 | 121.7 ± 9.2 | .004 | 0.86 | |
| Non-dominant hand side | 102.5 ± 12.1 | 109.5 ± 14.0 | .07 | 0.45 | 104.3 ± 9.5 | 112.4 ± 9.8 | <.001 | 0.99 | |
| Shoulder HAB ROM (°) | 8 | ||||||||
| Dominant hand side | 55.0 ± 20.0 | 55.0 ± 12.7 | 1.00 | 0.05 | 48.5 ± 13.8 | 49.2 ± 12.3 | .79 | 0.06 | |
| Non-dominant hand side | 61.0 ± 18.4 | 59.0 ± 13.1 | .66 | 0.07 | 58.8 ± 14.2 | 55.0 ± 14.8 | .08 | 0.42 | |
| Trunk rotation ROM (°) | 8 | ||||||||
| Dominant hand side | 53.0 ± 13.6 | 61.5 ± 10.0 | .009 | 0.83 | 69.2 ± 10.2 | 68.2 ± 11.5 | .59 | 0.08 | |
| Non-dominant hand side | 55.5 ± 12.4 | 61.0 ± 7.8 | .12 | 0.33 | 69.3 ± 8.9 | 70.7 ± 10.0 | .45 | 0.12 | |
| MTT, n (%) | 12 | 12 (100%) | 1 (8.3%) | <.001 | >0.99 | 8 (22.2%) | 10 (27.8%) | .59 | 0.13 |
| HBD (cm) | 9 | ||||||||
| Dominant hand side | 11.4 ± 4.0 | 10.3 ± 3.5 | .047 | 0.50 | 6.8 ± 3.7 | 6.8 ± 3.3 | .96 | 0.05 | |
| Non-dominant hand side | 10.9 ± 6.2 | 9.3 ± 6.1 | .042 | 0.59 | 6.7 ± 3.4 | 6.7 ± 3.7 | 1.00 | 0.05 | |
| Full squat test, n (%) | 15 | 15 (100.0%) | 5 (33.3%) | <.001 | >0.99 | 12 (30%) | 12 (30%) | 1.00 | 0.05 |
BB = backbends from a supine position, ER = external rotation in 2nd position, FFD = finger–floor distance, FL = flexion, HAB = horizontal abduction, HBD = heel–buttock distance, MTT = modified Thomas test, ROM = range of motion.
Number of players who performed the exercises corresponding to the physical function test.
3.3. Ancillary analysis
The Mantel–Haenszel test was performed to eliminate the confounding effects of sex in the occurrence of LBP. The 95% CIs for the relative risk according to sex overlapped (0.78–47.69 for males and 0.58–9.38 for females), with no significant difference noted. Hence, we determined that a stratified test would be useful. Accordingly, this test had a χ2 value of 4.04 (P = .04), indicating a significantly higher occurrence of LBP in the control group. The Breslow–Day test had a χ2 value of 0.409 (P = .522), indicating a similar level of relative risk in each stratum. The estimated value of the common odds ratio in the Mantel–Haenszel test was 4.69 (95% CI = 1.18–18.68). Similarly, the Mantel–Haenszel test was conducted using court position, whether the player participated in the previous tournament, and the presence or absence of static stretching after practice as confounding factors, showing an overlap in relative risk within each factor. This analysis obtained χ2 and estimated common odds ratio values of 5.37 (P = .021) and 6.21 (95% CI = 1.46–26.34) for court position, 4.80 (P = .03) and 5.53 (95% CI = 1.33–22.97) for whether the player participated in the previous tournament, and 4.72 (P = .03) and 4.96 (95% CI = 1.28–19.31) for the presence or absence of static stretching after practice, respectively, with each test showing a significantly higher incidence of LBP in the control group. Collectively, our analysis showed that the aforementioned confounding factors did not affect the main results of the study.
4. Discussion
Based on eleven physical function tests, the present study found that 1 or 2 self-selected preventive exercises, including dynamic thoracic mobility, trunk stabilization exercises, and static stretching, performed over 4 weeks reduced the incidence of LBP in high school volleyball players. Among the 7 exercises, jack-knife stretching, gastrocnemius stretching, iliopsoas stretching, and trunk stabilization exercises were performed more frequently in the intervention group. Furthermore, the control group was 3.78-fold more likely to develop LBP than the intervention group, even after adjusting for confounding factors. The participants in the intervention group who performed each exercise showed improvement in several corresponding physical function tests. Moreover, nearly 70% of those who developed LBP during the observation period attributed their pain to lumbar extension. None of those who developed LBP consulted a doctor despite the perceived poor performance during volleyball, a finding similar to that reported in previous studies.[8,30] Thus, the method used to prevent the development and severity of pain in the gymnasium rather than in the hospital is crucial.
Considering that previous studies showed that multiple movements can induce LBP, this is the first randomized controlled trial to investigate the effectiveness of self-customized exercises corresponding to physical function tests in preventing LBP in high school volleyball players.[15] Compliance and program timing have often been causes for concern in studies investigating injury prevention programs in sports. In a study on shoulder and elbow injury prevention in youth baseball players, Sakata et al[31] showed that the easiest method to increase exercise program compliance was to simplify the program. By simplifying the number of exercises and reducing the exercise time to approximately 10 minutes, the compliance rate improved from 57.4% to 73.4% after implementing the program from 1 to 2 times per week.[31,32] The present study achieved a compliance rate of 100% with a program conducted 5 to 6 times per week, which could have been attributed to the following reasons: most of the participants in the intervention group’s program consisted of 2 exercises; the exercises were simple and could be performed rapidly; the exercises addressed physical functions that the players themselves lacked; and the exercises could be performed under the supervision of a coach during club practices. A systematic review of LBP prevention suggested the efficacy of exercise in conjunction with education.[33] It is possible that the players showed more interest in the exercise and were able to perform it after receiving feedback on the results of physical function tests, as performed in this study. Another study reported that volleyball players engaged in longer practice sessions than those playing other sports,[34] and another showed that players with more years of experience were more likely to develop LBP.[8] Given the numerous chronic problems due to overuse associated with repetitive practice,[35] warming up before practice and daily care are imperative. Based on the results of previous studies, the semi-customized exercise interventions provided herein were conducted during the warm-up period before touching the volleyball. We believe that simple exercises customized for each player and performed almost daily played a role in preventing the development of LBP over a short period of 4 weeks. Lumbar spondylolysis, which can lead to missed practice sessions and quitting volleyball altogether, is not uncommon in young volleyball players.[36] Although the players in the present study did not miss the practice sessions due to pain, nearly 70% experienced pain when extending their lumbar spine. Thus, self-assessment, such as that used in this study, may be important in preventing the development of lumbar spondylolysis. However, it remains unclear how our intervention exercises affected lower back load during volleyball-specific movements, thereby warranting further research.
The present study showed that jack-knife stretching, gastrocnemius stretching, iliopsoas stretching, and trunk stabilization exercises were particularly effective in improving physical function test performance. The jack-knife stretch has been reported to be effective for tight hamstrings[37] and may help prevent LBP given that several individuals with a history of LBP have tight hamstrings.[38,39] Decreased ankle dorsiflexion ROM has been reported to be a potential risk factor for LBP.[40,41] As such, focusing on gastrocnemius stretching may have an indirect effect on preventing LBP. Volleyball players with hamstring tightness or reduced ankle dorsiflexion ROM may experience increased strain on the lower back considering their need for more hip flexion when receiving lower balls. Given that repetition of such movement can promote the development of flexion-type LBP, eliminating these factors can be considered helpful in preventing LBP. On the other hand, a questionnaire survey by Mizoguchi et al[8] found that players with LBP were strongly aware that they were catching the ball behind their shoulders during the spiking motion and that they experienced LBP during the back swing when serving, which we believe might have reflected pain during lumbar extension. Furthermore, Kujala et al[42] found that iliopsoas tightness and lumbar hyperlordosis were associated with LBP among young athletes. Most of the players in their study also developed LBP during lumbar extension. Yamazaki et al showed that tight hamstrings are one of the negative predictors of bone union in lumbar spondylolysis,[43] which may affect not only flexion-type but also extension-type LBP. Therefore, iliopsoas stretching could have prevented extension-type LBP in volleyball players. Finally, trunk stabilization exercises have been reported to be effective in preventing LBP and reducing pain in gymnasts aged 11 to 16 years.[44] We found that this exercise was effective in preventing LBP in high school volleyball players who had inferior trunk stabilization ability. The control group exhibited a significant increase in shoulder ER ROM, and the intervention group showed a slight but nonsignificant increase. Several studies[45,46] have reported that overhead athletes develop deficiencies in glenohumeral internal rotation from repetitive overhead activities accompanied by excessive shoulder ER ROM. Similarly, reports have found that volleyball players also have excessive ER ROM,[47] with the players in the present study having excessive shoulder ER ROM (approximately 120°) at the end of 4 weeks. Given that this condition can lead to shoulder pain and injury,[45,48] future researchers should consider focusing on shoulder joint care throughout the playing season.
For other items that did not improve, it is possible that the exercise was not appropriate for the test. The BB requires not only spinal flexibility but also trunk extension strength, suggesting that simple spinal flexibility exercises alone are not sufficient to improve it. We expected that Side-FFD would be enhanced by trunk rotation. However, because the trunk rotation exercise mainly involves thoracic rotation, Side-FFD, which mainly involves lateral flexion of the lumbar spine, did not improve. Shoulder and trunk ROM values did not show statistical improvement, as most of the participants showed a good ROM before the intervention. On the other hand, many of these tests are not a factor in the development of LBP in high school volleyball players,[15] hence future studies may need to narrow down the tests more. However, a few reports have shown that decreased HAB ROM of the dominant shoulder in volleyball players is associated with current LBP,[15] and that decreased shoulder elevation angle in divers is compensated by lumbar extension.[49] Therefore, when a marked decrease in these ROM is observed, it may be necessary to treat it while assessing its relationship to lumbar spine motion.
5. Limitations
Some limitations of the present study need to be acknowledged and considered when interpreting our results. First, the sample comprised high school volleyball players in Saitama, Japan. Given that volleyball practice sessions may differ in other countries, our data may not be representative for all high school volleyball players. Furthermore, despite including domestic high schools with similar practice schedules, the effectiveness of the intervention may vary depending on the number of team members and practice intensity. However, despite the difficulty of standardizing these factors, we did our best to account for such factors by performing the intervention during the warm-up period. Second, the participants in the intervention group, the coaches who monitored the exercises, and the physical therapists who provided instructions to the participants were not blinded to the group allocation. Hence, the possibility of Pygmalion and Hawthorne effects in the intervention group must be considered. To limit these effects and achieve blinding of the participants, team coaches, and physical therapists, future studies should consider introducing different exercises to the teams in the control group. Third, no imaging tests were used to monitor LBP, and we could not diagnose the type of tissue damage in participants who developed LBP. Although LBP was mildly symptomatic, the physical function tests and preventive exercises used may have helped prevent severe LBP given that they can be easily utilized for self-assessment in daily life and can be performed relatively quickly. Furthermore, as the status of the participants after the intervention period could not be determined, we are uncertain whether 1 or 2 types of exercises performed 5 to 6 times a week for 4 weeks was appropriate. Future studies should examine long-term outcomes. Finally, as this study focused on high school volleyball players at the same competitive level, the present method may not be applicable to high school volleyball players across the entire country. However, considering the numerous high schools throughout the country with the level of competition targeted in this research, we believe that our efforts in preventing LBP will be of some help to them.
6. Conclusions
This is the first prospective study to analyze whether an LBP prevention program can reduce the incidence of LBP in high school volleyball players. We found that self-customized exercises were effective in reducing the incidence of LBP. We are confident that including LBP prevention exercises would be an appropriate approach in the management of high school volleyball players. Nonetheless, further studies with larger samples are warranted, which would allow subgroup analyses examining factors for compliance, sex-specific differences, court position’s risk, and long-term effects of similar physical function tests and preventive exercises.
Acknowledgments
A part of this report was presented at the 6th Annual Meeting of the Japanese Society for Physiotherapy of Musculoskeletal, Japan, in 2018. We would like to thank the coaches and players of the high school volleyball clubs in Saitama, Japan, for their valuable cooperation.
Author contributions
Conceptualization: Hiroyuki Naka, Kiyokazu Akasaka, Naoki Shimada, Takahiro Otsudo, Yasuaki Mizoguchi.
Data curation: Takahiro Otsudo, Yasuaki Mizoguchi.
Formal analysis: Kiyokazu Akasaka, Takahiro Otsudo, Yasuaki Mizoguchi.
Investigation: Hiroyuki Naka, Naoki Shimada, Yasuaki Mizoguchi.
Methodology: Kiyokazu Akasaka, Takahiro Otsudo, Yasuaki Mizoguchi.
Project administration: Kiyokazu Akasaka, Yasuaki Mizoguchi.
Supervision: Kiyokazu Akasaka, Kiyokazu Akasaka.
Visualization: Kiyokazu Akasaka, Yasuaki Mizoguchi.
Writing – original draft: Yasuaki Mizoguchi.
Writing – review & editing: Hiroyuki Naka, Kiyokazu Akasaka, Naoki Shimada, Takahiro Otsudo.
Abbreviations:
- BB =
- backbends in a supine position
- ER =
- external rotation
- FFD =
- finger–floor distance
- HAB =
- horizontal abduction
- LBP =
- low back pain
- MTT =
- modified Thomas test
- ROM =
- range of motion
How to cite this article: Mizoguchi Y, Akasaka K, Otsudo T, Shimada N, Naka H. Efficacy of semi-customized exercises in preventing low back pain in high school volleyball players: A randomized controlled trial. Medicine 2022;101:36(e30358).
The authors have no funding and conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request. The data that support the findings of this study are available from the corresponding author upon reasonable request.
Contributor Information
Yasuaki Mizoguchi, Email: yassunnyassunn@gmail.com.
Takahiro Otsudo, Email: otsudo@saitama-med.ac.jp.
Naoki Shimada, Email: naoki.pt.1004@gmail.com.
Hiroyuki Naka, Email: h.naka.pt@gmail.com.
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