Background/Aim During competitive diving, divers jump up from 1 to 3 m springboards or 5 to 10 m platforms and dive into the water. The impact forces are very large in the water entry phase, and, as such, microtraumatic injuries are common due to the tremendous physical stress placed on the diver. Low-back pain (LBP) is the most frequently reported symptom in divers. This study aimed to extract possible risk factors related to LBP from physical and technical characteristics in Japanese elite junior divers.
Methods Eighty-three elite junior divers (42 men and 41 women) in Japan were included in this study. LBP was assessed by a questionnaire, interview and physical examination during a national training camp. Morphological data, physical fitness and diving skills were also evaluated. The factors related to LBP were extracted by using logistic-regression analysis and the forward-selection method (likelihood ratio).
Results A total of 37.3% (31 reports) of back pain occurred in the lumbar region. Shoulder flexibility (OR 0.919; 95% CI 0.851 to 0.992) and age (OR 0.441; 95% CI 0.239 to 0.814) were recognised as factors related to LBP in male-elite junior divers, whereas only age (OR 0.536; 95% CI 0.335 to 0.856) was a factor in female-elite junior divers.
Conclusions Our results suggest that shoulder flexibility is important for preventing LBP in elite-male junior divers, since they require full shoulder flexion during the water entry phase. Limited shoulder flexibility could cause lumbar hyperextension when adjusting for the angle of water entry.
- Back injuries
- Shoulder injuries
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Competitive diving involves jumping off a 10 m platform or a 1 or 3 m springboard and doing somersaults and twists in the air before entering the water. Divers jumping from a 10 m platform reach a velocity of 51 km/h before entering the water, and decelerate to 33 km/h, amounting to approximately 400 kg N of force upon impact with the water.1 Microtraumatic injuries are common in the sport2 ,3 due to the tremendous physical stress placed on the diver. Researchers have found that low back pain (LBP) is the most frequently reported symptom in divers,2–7 which we corroborated, in which the incidence of LBP in junior divers aged 13–17 was very high (38.4%). However, these divers could continue the practices with LBP.2 Based on these findings we report the necessity for an effective injury prevention plan.2
Baranto et al8 reported that a diver's first back pain episode occurs during the growth spurt period, supporting the notion that this is a very vulnerable period; thus, prevention of back pain in this period is very important. Based on scientific evidence, van Mechelen et al9 proposed a four-step practical model to formulate an effective injury prevention plan. First, investigations for the injuries are implemented to understand the rate of incidence and the severity of trauma. Second, the cause, mechanism and the risk factors for the injuries are determined. Third, a prevention plan is introduced to counteract the risk factors. Finally, a postimplementation investigation is conducted to assess the effectiveness of the prevention plan. Meeuwisse10 suggested that there are potential intrinsic and extrinsic-risk factors for sports-related injuries; age, sex, physical characteristics, aptitude, psychological characteristics, health status and history of injury are all considered as intrinsic factors. However, Steffen and Engebretsen11 acknowledged that few studies have been conducted regarding the risks for sports-related injuries, and that there is a need to elucidate the risk factors, mechanisms and prevention methods for high-level athletes. This is also true for competitive diving, since relatively few reports exist regarding the risks for injury. Understanding the athlete's intrinsic-risk factors for injury incidence is necessary to establish a prevention plan. Therefore, this study aimed to investigate the intrinsic factors that correlate with the risk factors for LBP in competitive divers.
Eighty-three divers (42 men and 41 women) who were invited to the national training camp by the Japan Swimming Federation between 2003 and 2011 (except 2006) were included in this study. Data from the divers in their first year at training camp were used for analysis (data from the same participants in subsequent years were not included in the analysis). Table 1 summarises the physical characteristics of the participants.
Assessment of LBP
LBP was investigated by interviewing and performing a physical examination conducted by a physiotherapist to determine whether LBP was present, chronic and perceived by the diver. We defined LBP as continuous pain of more than 12 weeks’ duration. The divers confirmed the presence of LBP during movement (lumbar, flexion and extension).
Investigation of physical fitness
Body measurements (the following measurements were taken in the morning)
Height (in cm) and weight (in kg): An automated digital height/weight scale (WB-510; Tanita Corporation, Itabashi-City, Tokyo, Japan) was used. The participants’ weight was measured without footwear, and height was measured while the participants stood straight with their heels together.13
Core muscle strength and endurance
Back-muscle strength (in kg): Participants stood with their feet 15 cm apart on a back-dynamometer (TKK5002; Takei Scientific Instruments Co, Nigata-City, Nigata, Japan). Measurements were made with the participants’ torso bent forward at a 30° angle, while keeping their knees extended. The participants were instructed to attempt to straighten the upper part of their body, pulling up on the handle gradually without bending their knees, until they reached a maximum effort. The value displayed on the indicator in kilograms of force was recorded.13 ,14
Thirty-second sit-ups (number of repetitions): From the supine position, participants were asked to bend their knees at a 90° angle, with their arms folded over their chest. The number of complete sit-ups (where both elbows touched the thighs) in a 30 s period was recorded.13
Sitting trunk flexion (in cm): Participants were seated with their hip joint at a 90° angle (knees extended). The anteflexion instrument (TKK5112; Takei Scientific Instruments Co) was used to measure the distance participants were able to bend their torso forward.13
Trunk extension (in cm): From a prone position, participants joined their hands behind their back and extended their torso upwards. The distance from their chin to the floor was measured and recorded.13
Standing long jump (in cm): Participants stood with their feet 10–20 cm apart and jumped forward with maximum strength. The distance between the start line and the closest point of contact to the start line was measured.13
Vertical jump (in cm): The vertical distance reached by exerting maximum strength was measured by a marker at the fingertips.13
Shoulder rotation width (distance between hands; in cm): The minimum distance between the hands was measured as an index of shoulder rotational flexibility. Participants stood with their feet shoulder-width apart, holding a rod with their arms extended at shoulder height. From that position, participants were asked to rotate their arms backwards over their head without bending their elbows. The minimum distance between their hands at which this movement was possible was measured (figure 1).
Handstand posture (points) and handstand duration (in seconds): Men's competitive diving includes a handstand component; therefore, we measured handstand posture and duration on a flat surface. The duration was measured from the time both feet left the ground to when a part of the body other than the hands touched the ground. We set an upper limit of 1 min, and those exceeding 1 min were stopped at that point. Handstand posture grading was done at the same time, and was assessed by three official diving judges of the Japan Swimming Federation. Following the grading procedures for competitive diving, handstand posture was graded from A to D, with the following corresponding numerical scores: A: 9 points, A−: 8 points, B+: 7 points, B: 6 points, B−: 5 points, C+: 4 points, C: 3 points, C−: 2 points, D: 1 point.
The average score from the three judges was used as the final score (figure 2).
All measurements were taken twice, and the better of the two was used in the analysis. Participants received an explanation of the measurement methods orally or through informational material prior to taking the measurement, with their full understanding and consent.
We divided the male and female divers into two groups based on LBP status: the pain group and the no-pain group. A comparison of the two groups based on physical fitness criteria was done by using an independent t test. To extrapolate the factors related to LBP, we analysed the data by using logistic regression and the forward selection method (likelihood ratio). We set the fitness characteristics of the participants as the independent variable and the presence of LBP as the dependent variable. Our significance level was set at 5% in all cases. A correlation coefficient was determined for factors that made a significant contribution to LBP; in addition, we calculated the OR for those factors. A regression equation estimating the rate of LBP incidence was also calculated from the data and assessment by the Hosmer-Lemeshow goodness-of-fit test (Dr SPSS II; SPSS Japan Inc, Shibuya-City, Tokyo, Japan) for Windows was used for the analysis.
The current study was conducted with consent from the divers and coaches, and was approved by the Health Science University Research Ethics Committee (Approval Number 19).
Low back pain
Thirty-one of the 83 participants (37.3%; 18 men and 13 women) reported LBP during the training camp. Twenty-six of the 31 (83.9%) experienced the pain during movement; of the 26, 15 (57.7%) experienced pain during extension, 9 during both extension and flexion (34.6%) and 2 during flexion (7.7%).
Comparison of the LBP and no-LBP groups
Table 3 shows the physical and fitness characteristics of both groups. Eighteen of 42 male divers reported of LBP. The following characteristics showed a significant difference between the LBP and no-LBP groups: age, weight, body mass index, back muscle strength, body anteflexion, body retroflexion, vertical jump, standing long jump, shoulder rotation width and handstand posture.
Thirteen of 41 female divers reported of LBP. The following characteristics showed a significant difference between the LBP and no-LBP groups: age, weight back muscle strength and body anteflexion.
Factors associated with LBP
According to logistic-regression analysis, LBP correlated significantly with age (p=0.009; OR 0.441; 95% CI 0.239 to 0.814) and shoulder rotation width (p=0.031; OR 0.919; 95% CI 0.851 to 0.992) in male divers (table 4). The following regression equation estimating the rate of incidence was derived from the factors above:
The regression model was a good fit at p = 0.961, as assessed by the Hosmer-Lemeshow test, with a discriminant accuracy of 81.1%.
For female divers, the only characteristic that showed a significant correlation with LBP was age (p = 0.009; OR, 0.536; 95% CI 0.335 to 0.856; table 5). The regression equation estimating the rate of incidence was:
Results of the Hosmer-Lemeshow test showed a goodness-of-fit of p=0.666, with a discriminant accuracy of 75%.
Low back pain
A total of 37.3% of participants reported LBP, which was perceived by the divers themselves during a national training camp. A similar investigation during the 2009 FINA World Championship revealed that 21% of divers reported LBP during the event.15 We were able to confirm the high rate of LBP in divers.
In dive forward and inward, there is a forward somersault component, which puts compressive stress on the anterior segments (vertebral body, vertebral-end plate and intervertebral disc) during take-off, in the air, and during the water entry phase. On the other hand, in dive backward and reverse with a reverse somersault component, compressive stress occurs on the posterior elements (facet joint, pars interarticularis) during take-off. Furthermore, if the angle of entry into the water is less than 90° (short) for dive backward and reverse, or greater than 90° for dive forward and inward, the dorsal side of the lumbar vertebrae experiences stress.3 ,5 ,7 Repeated dives can lead to injuries in the lumbar region, causing LBP. One of the reasons that our study revealed a greater percentage of divers suffering from LBP, compared with the FINA study (2009), is that our study included chronic cases of LBP. Moreover, we found that a greater proportion of divers experienced pain during extension of the lumbar vertebrae. Forced extension of the area is known to cause LBP,2 ,7 which can lead to facet synovitis and exhaustion/fracture of the pars interarticularis.6 Our results support these reports since competitive divers repeatedly hyperextend the lumbar vertebrae.
Risk factors for LBP
Logistic-regression analysis found that there was a significant association between LBP and shoulder rotation width and age in male divers. Shoulder rotation width for the pain group was 57.2 (SD 11.9) and 48.5 (SD 14.9) cm for the no-pain group, suggesting a lack of flexibility in the pain group. It has been reported that competitive tennis athletes whose dominant arm's rotational range of motion of the shoulder joint is less than 10°, compared with the non-dominant arm, have a higher risk for LBP.16 Our results also suggest that shoulder joint flexibility is important in competitive divers, and is a risk factor for LBP. O'Brien17 reported that, for manoeuvres that include a reverse somersault, the diver must stretch the shoulder joint backwards and arch the body more. Divers who are not as flexible in the shoulder joint compensate and correct their water entry posture by increasing the angle of extension or by moving the ribcage/thorax. It has been reported previously that the main mechanism of LBP incidence in divers is hyperextension of the lumbar vertebrae during entry into the water2 ,7; additionally, Eric18 suggested that improper alignment during water entry causes LBP. Furthermore, O'Brien17 suggested that the body loses rigidity against the impact of entering the water, when the ribcage is moved to extend the torso backwards. Taken together, divers with decreased flexibility in the shoulder joint experience stress in the lumbar vertebrae during impact with the water, which can lead to LBP. We suggest that preventing hyperextension of the lumbar region during the water entry phase and maintaining flexibility in the shoulder joint are two ways of preventing the onset of LBP. This finding could be relevant not only for diving, but also across throwing sports, swimming (ie, the streamline position) and gymnastics. Nevertheless, handstand posture points with a score of 7.1 for the LBP group and 5.1 for the no-LBP group. The handstand skill does not demand as much lumbar and shoulder extension range compared with a reverse dive, and therefore it is likely that the relationship cannot be seen in this particular test. Moreover, female shoulder rotation width was not extracted from LBP risk because women have greater shoulder flexibility.
In order to confirm our results, it will be necessary to perform motion analysis and to elucidate the relationship between range of motion of the shoulder joint and alignment during water entry. Motion analysis during diving has been performed primarily on the starting position, which defines the rest of the motion.19–21 Only Sanders and Gibson22 have analysed the motion during entry into the water; however, the analysis was carried out on the angle between the body and the water. It will be interesting to perform a similar motion analysis on the angle of the shoulder joint.
Age was a factor in both men and women, according to the logistic-regression analysis. Lumbar vertebrae during adolescence are especially vulnerable to injury and trauma.4 ,8 ,23 Furthermore, studies suggest that the period when divers first experience LBP coincides with adolescence.8 In our study, we found that the average age in the pain group was 15.6 (SD 1.4) years for men and 15.5 (SD 1.6) years for women, compared with 13.8 (SD 1.3) years for men and 13.8 (SD 1.7) for women in the no-pain group. We infer, based on the ages, that the patients in the pain group were experiencing growth related to adolescence. In other competitive sports, the number of years of experience is correlated with injury6; however, our results showing age as a greater risk factor can be explained by the fact that the participants’ age range (12–17 years) coincided with adolescence, which influenced the risk factors. Given this information, physical stress on the body experienced during adolescence can increase the risk for LBP; for this reason, we suggest that the frequency of practice for divers during adolescence be reduced to mitigate the incidence of LBP.
Limitations of the study
Ideally, a study should include at least 200 participants, with 20–50 cases of injury, to determine whether a strong correlation exists between certain risk factors and sports-related injuries.24 Therefore, one limitation of our study is the small population size (the entire population of diving athletes in Japan is approximately 450). It will be necessary for future studies to include a greater population than the one studied here.
Furthermore, our investigation included only a cross-sectional analysis, and we did not perform a follow-up survey regarding the incidence of injury. It will be important to establish a system to follow trends and to perform a cohort study.
What are the new findings?
Shoulder flexibility and age of male-junior divers are risk factors of low back pain (LBP).
Among female divers, age is the only risk factor found to be associated with LBP.
Among the male-junior divers, there was a significant difference between the LBP and no-LBP groups with regard to age, weight, body mass index, back muscle strength, body anteflexion, body retroflexion, vertical jump, standing long jump, shoulder rotation width and handstand posture.
Among the female-junior divers, there was a significant difference between the LBP and no-LBP groups with regard to age, weight back muscle strength and body anteflexion.
How might it impact on clinical practice in the near future?
LBP of elite divers may be reduced.
Shoulder joint flexibility as a factor influencing LBP may be applicable to other overhead sports.
This study will aid in understanding the preferred body characteristics associated with particular sport injuries among adolescents.
We would like to thank the coaches and divers of the Diving Committee for their cooperation during the study.
Contributors T N was involved in conceiving the research, data acquisition, data analysis, data interpretation and drafting the manuscript; K K was involved in data interpretation and supervising the conduct of the study; M T was involved in data interpretation and supervising the conduct of the study; Y S was involved in data acquisition; T N was involved in data acquisition and data interpretation; S M was involved in data interpretation and supervising the conduct of the study.
Funding This study was supported by a Grant-in-Aid for Scientific Research (B, 22300224) from the Japan Society for the Promotion of Science, and by a Health Science University Grant.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the Health Science University Research Ethics Committee.
Provenance and peer review Not commissioned; internally peer reviewed.
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