Abstract
Background:
The low back is the most common injury location in pole vaulters, and low back pain (LBP) can easily become chronic. Therefore, knowing the physical characteristics of athletes experiencing repeated LBP may be beneficial for recovery and injury prevention.
Purpose:
The purpose of this study was to describe and analyze the physical characteristics of pole vaulters with chronic LBP.
Study Design:
A cross-sectional study
Methods:
Twenty male pole vaulters participated in this study. A questionnaire was used to garner descriptive and personal data, including personal best performance in the pole vault. Additionally, the following physical characteristics were measured: 1) isokinetic muscle strength of hip and knee flexors and extensors, 2) active/passive range of motion and muscle flexibility in multiple joints and regions, 3) performance on the Functional Movement Screen™ (FMS™) and 4) spinal column alignment. Subjects were categorized using the questionnaire and divided into two groups, one with and one without chronic LBP.
Results:
The personal best performance and angle on the active straight leg raise test (SLR) were significantly lower and smaller, respectively, in the chronic LBP group than in the non-chronic LBP group. Additionally, the difference between the passive SLR angle and active SLR angle (ΔSLR) was significantly larger in the chronic LBP group than in the non-chronic LBP group. Those with chronic LBP had were more likely to have a FMS™ composite score ≤14.
Conclusion:
The active SLR angle and ΔSLR were significantly smaller and larger, respectively, in the chronic LBP group than in the non-chronic LBP group. This may be because of the poor stability of trunk or incompetence of the kinetic chain required for raising the lower limbs. The chronic LBP group had a significantly higher probability of having an FMS™ composite score of ≤14. it may be important to examine the active straight leg raise (vs. passive only), and fundamental movements as screened by the FMS ™ in pole vaulters.
Level of Evidence:
2b.
Keywords: chronic low back pain, functional movement screen, physical factors, pole vault
INTRODUCTION
Pole vaulters jump to great heights and have heavy loads applied to their bodies during this movement. Although many characteristic injuries are expected to occur, there are only a few epidemiological studies on this topic.1-5 Rebella5 reported that the lower back was the most common injury location in collegiate pole vaulters. He discussed that pole vaulters may be particularly susceptible to this injury because the plant/takeoff phases place the spine in forced hyperextension as the athlete drives forward off the ground. Additionally, Gainor et al6 analyzed the biomechanics of the spine in pole vaulters in relation to spondylolysis, and they reported that a maximum angular acceleration of 150 radians/s2 occurs in spine during takeoff. Previous authors5,6 have reported that the occurrence of low back pain (LBP) in pole vaulters is related to spine hyperextension during the takeoff phase.
In pole vault, the shoulder joint flexes and hip joint extends at takeoff. Previous authors have reported that the range of motion (ROM) of both joints is related to LBP. Narita et al7 reported that shoulder flexibility was recognized as a factor related to LBP in male elite junior divers and discussed the role of limited shoulder flexibility in causing lumbar hyperextension. In addition, Kitamura et al8 reported that the LBP group had less hip extension ROM than the control group (without LBP) in swimmers. Therefore, this study hypothesized that in the presence of limited ROM of the shoulder and hip joints, the lumbar spine causes a compensatory motion during takeoff, resulting in LBP. In addition, it is speculated that pole vaulters are likely to have chronic pain because the frequency of vaulting induces LBP.
Physical factors that can be measured in the sagittal plane have been inferred to be associated with the development of LBP. The authors of the current study postulated that the lumbar spine may perform certain compensatory movements such as hyperextension, in the presence of limited shoulder flexion and hip extension during the takeoff, and spinal flexion if there is lack of hip flexion strength or ROM during the maximum pole bending phase (Figure 1). In addition, the authors believe that the center of gravity is displaced forward from the body by approaching while carrying the pole in the run-up phase, and the resultant forward rotating force exerted on the spine may be an additional cause of lumbar stress. Consequently, it is necessary to examine spinal column alignment and flexibility of the lower back, which are reported to be risk factors for LBP in athletes.9-11
Figure 1.
Pole vault model. Run-up phase, Pole plant (PP) phase, Takeoff (TO) phase,Maximum pole bending (MPB) phase, peak height of center of gravity (HP).
However, because all basic data on physical factors (such as body mas, muscle flexibility) have not been reported in pole vaulters, the importance of physical factors related to LBP remains unclear. Stanton et al12 reported that the recurrence of LBP in general populations was found to be 33% by primary care clinicians within one year using “pain at follow-up” definition. LBP has a high risk of recurrence, and improvement of chronic LBP may be effective in the prevention of recurrence. Recurrence of LBP in pole vaulters appears to be high, therefore, it may be helpful to identify the characteristics of these athletes with chronic LBP and propose remedial measures for managing LBP.
The purpose of this study was to describe and analyze the physical characteristics of pole vaulters with chronic LBP. The second purpose of this study was to clarify the relationship between FMS™ performance with and without chronic LBP. The authors hypothesized that chronic LBP is related to limited ROM of hip extension and shoulder flexion.
METHODS
Population
This was a cross-sectional study involving 20 male collegiate pole vaulters (mean ± SD; age, 19.8 ± 1.3 years; height, 173.7 ± 7.7 cm; body mass, 67.9 ± 6.4 kg). Pole vaulters with any pain at the time of measurement and with pain or anxiety that they could not participate in practice were excluded from this study. All participants provided written informed consent, and approval for the study was obtained from the Chukyo University Human Research Ethics Committee (No. 2016-050).
Assessments and measures Questionnaire
Participants were divided into two groups (chronic LBP and non-chronic LBP) on the basis of the answers to a questionnaire provided to them. (Appendix A) Participants who answered “Yes” to the question, “Do you often feel LBP?” were assigned to the chronic LBP group. This study obtained information about the history of injury for each athlete. History of injury was defined as an event that “caused the athlete to cease participation that day or miss a subsequent practice/competition”. The takeoff-leg was also investigated using the same questionnaire and was defined as the leg used during vaulting. The opposite leg was termed the lead leg. The side of the body was described in terms of the takeoff-leg as takeoff leg side and lead leg side. In addition, \ subjects self-reported their height and personal best record of pole vault on the questionnaire.
Hip and knee: flexion and extension isokinetic strength13,14
Isokinetic strength tests were performed using an isokinetic dynamometer (Biodex System 3; Biodex, Shirley, NY, USA). The participants performed each of the tests (hip and knee flexion/extension) for three repetitions at the same angular velocity (60 deg/s). Subjects performed hip and knee strength tests on different days to exclude the effect of fatigue. Body weight was measured using a body component analyzer (Inbody470, InBody Japan, Japan), the peak torque was normalized to body weight (%).
In the hip test, the participant lay supine on the dynamometer, grasped the bars on the side of the dynamometer, and his body was stabilized with straps on the chest, pelvis, and thigh of the untested leg. To prevent pelvic movement, the participant maximally flexed his neck and contracted his trunk muscles. The knee angle was kept at 90 degrees throughout the measurement. The hip test was conducted between 0 degrees (full extension) and 115 degrees of flexion. In the knee test, the participant was seated on the dynamometer, and his body was stabilized with straps on the chest, pelvis, and thigh of the untested leg. The knee test was conducted between 0 degrees (full extension) and 90 degrees of flexion.
Active/passive ROM, muscle flexibility, and spinal column alignment
Active/passive ROM and muscle flexibility were measured with the participants lying down on a bed. All measurements were recorded using a camera (EX-F1, CASIO, Tokyo, Japan) and were analyzed using image analysis software (NIH ImageJ ver.14.4). This study subtracted active ROM from passive ROM and indicated it as Δ to show the ability to active control the motion, excluding limits of individual's muscles and joints.
The following measurements were performed as shown in Figure 2:
Passive shoulder flexion: The angle between a line connecting the two landmarks on the humerus and a line parallel to the trunk.
Passive ankle dorsiflexion: The angle between a line perpendicular to the line connecting the fibular head and the lateral malleolus and a line connecting the fifth metatarsal head and styloid process.
Passive knee extension: The angle obtained by subtracting 90 º from the angle between a line connecting the greater trochanter and the lateral epicondyle of femur and a line connecting the fibular head and the lateral malleolus.
Active/passive knee flexion: The angle between a line connecting the greater trochanter and the lateral epicondyle of femur and a line connecting the fibular head and the lateral malleolus)
Active/passive straight leg raise (SLR): The angle between a line connecting the greater trochanter and the lateral malleolus and a line parallel to the trunk.
Active/passive hip flexion: The angle between a line connecting the greater trochanter and the lateral epicondyle of femur and a line parallel to the trunk.
Active/passive hip extension: The angle was measured in the same method as hip flexion.
Figure 2.
.Measurement position of active and passive range of motion, muscle tightness in each region. (1: passive shoulde flexion, 2: passive ankle flexion, 3: passive knee extension, knee flexion, 5: straight leg raise, 6: hip flexion, 7: hip extionsion)
Spinal column alignment was measured in various postures (erect position, extended positin, and flexed position of crawling on hands and knees) using the Spinal Mouse™ system.15 The device is moved along the midline of the spine starting at the spinous process of C7 and finishing at S3. These landmarks are initially determined by palpation and marked on the skin surface with a cosmetic pencil. Two rolling wheels follow the contour of the spine and are interfaced to a personal computer. This information is then used to calculate the relative positions of the sacrum and vertebral bodies of the underlying bony spinal column using an intelligent, recursive algorithm. The Spinal Mouse™ has demonstrated relatively high accuracy in testing the sagittal plane of spinal morphology and function, making it a reliable and valid measuring instrument.16-18
Functional Movement Screen™19
The Functional Movement Screen™ (FMS™) is an objective screening tool consisting of seven movement tests (deep squat, hurdle step, in-line lunge, shoulder mobility reaching, active straight leg raise, trunk stability push up, and rotary stability) and three clearing tests (impingement, press-up, and posterior rocking). Test scores range from 0 to 3 for each test, with the highest total composite score being 21. If pain occurs during movement and clearing test, the score of the relevant test is considered to be 0. Of note, because this study included athletes with chronic LBP, lower scores could be expected. Therefore, comparison was between the composite score evaluated with and without including the 0 scores on individual tests. All pole vaulters did not have any pain during the seven screening tests, but some did on the clearing test of FMS™.
Statistical analysis
SPSS version 23 (IBM Corp., Armonk, NY, USA) was used for data analysis. The normality of all data was analyzed using the Shapiro–Wilk test. Differences in normally distributed data between the chronic and non-chronic LBP groups were analyzed using an unpaired t-test, and differences in non-normally distributed data were analyzed using the Mann–Whitney U test. Results are expressed as mean ± standard deviation (95% confidence interval). The chi square test was used for data analysis of FMS™. Contingency tables (2 × 2) were created to relate findings from the FMS™ as a diagnostic test for the development of injury and chronic LBP. The subjects were divided into composite scores at or above 14 and those below as it has been reported that injuries tend to occur at FMS™ composite score ≤ 14 in previous studies. 20 Results were considered significant at the 5% critical level (p < .05).
RESULTS
All 20 pole vaulters had a reported history of LBP, and eight pole vaulters had chronic LBP. Table 1 presents the average, standard deviation (SD), 95% confidence interval (95% CI), and statistical comparisons of each measurement by groups. There were no significant differences in age, height, or weight between the chronic and non-chronic LBP groups (p > .05). There were significant differences in the personal best record between the chronic LBP group (4.45 ± 0.56 [95% CI: 3.98-4.92] m) and the non-chronic LBP group (4.96 ± 0.34 [95% CI: 4.75-5.17] m) (p < .05).
Table 1.
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| Chronic LBP | Non-chronic LBP | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Measurements | average | SD | 95%CI | average | SD | 95%CI | p- value | |||
| Age(years) | 19.5 | 1.2 | 18.5-20.5 | 20 | 1.4 | 19.1-20.9 | 0.422 | |||
| Height(cm) | 172.4 | 9.7 | 167.1-177.7 | 174.6 | 6.3 | 170.6-178.6 | 0.544 | |||
| Weight(kg) | 65.9 | 8.0 | 59.3-72.6 | 69.2 | 5.0 | 66.0-72.4 | 0.273 | |||
| Personal best record(m) | 4.5 | 0.6 | 4.0-4.9 | 5.0 | 0.3 | 4.8-5.2 | 0.020* | |||
| Isokinetic muscle strength (%): | ||||||||||
| Takeoff-leg-side | ||||||||||
| knee | extension | 277.7 | 45.4 | 239.8-315.6 | 279.2 | 36.6 | 256.0-302.5 | 0.934 | ||
| flexion | 144.9 | 25.0 | 124.0-165.8 | 149.1 | 23.8 | 134.5-164.7 | 0.711 | |||
| hip | extension | 242.5 | 42.1 | 207.3-277.8 | 248.4 | 53.1 | 214.6-282.2 | 0.797 | ||
| flexion | 211.0 | 39.1 | 178.4-243.7 | 217.3 | 29.4 | 198.7-236.0 | 0.685 | |||
| Lead-leg-side | ||||||||||
| knee | extension | 273.0 | 52.8 | 228.9-317.2 | 269.2 | 32.5 | 248.6-289.9 | 0.843 | ||
| flexion | 143.5 | 26.2 | 113.2-173.7 | 148.5 | 24.5 | 133.0-164.1 | 0.665 | |||
| hip | extension | 284.6 | 54.7 | 170.0-739.1 | 252.6 | 54.2 | 218.2-287.0 | 0.214 | ||
| flexion | 219.9 | 40.2 | 186.3-253.5 | 217.7 | 33.8 | 196.2-239.2 | 0.895 | |||
| Range of motion (°): | ||||||||||
| Takeoff-leg-side | ||||||||||
| passive | shoulder | flexion | 138.8 | 12.5 | 128.4-149.3 | 135.5 | 10.8 | 128.6-142.3 | 0.521 | |
| passive | ankle | flexion | 9.7 | 6.4 | 4.3-15.1 | 11.9 | 8.3 | 6.6-17.1 | 0.543 | |
| passive | SLR | 75.6 | 5.5 | 71.0-80.2 | 81.0 | 11.8 | 73.5-88.5 | 0.242 | ||
| active | 57.5 | 5.9 | 52.5-62.5 | 71.5 | 12.8 | 63.4-79.6 | 0.010* | |||
| Δ | 18.1 | 6.9 | 12.3-23.9 | 9.5 | 6.1 | 5.7-13.4 | 0.009* | |||
| passive | knee | extension | 69.6 | 7.6 | 63.3-76.0 | 71.7 | 11.0 | 64.7-78.7 | 0.654 | |
| flexion | 160.9 | 4.8 | 156.9-164.9 | 157.8 | 12.2 | 150.0-165.5 | 0.678 | |||
| active | flexion | 142.7 | 5.8 | 137.9-147.5 | 144.5 | 6.2 | 140.5-148.4 | 0.522 | ||
| Δ | flexion | 18.2 | 2.1 | 16.4-20.0 | 13.3 | 13.1 | 5.0-21.6 | 0.157 | ||
| passive | hip | extension | 20.1 | 6.6 | 14.6-25.6 | 17.2 | 3.5 | 15.0-19.4 | 0.214 | |
| flexion | 127.0 | 5.7 | 122.2-131.8 | 130.6 | 8.2 | 125.4-135.8 | 0.296 | |||
| active | extension | 13.5 | 6.2 | 8.3-18.7 | 11.0 | 5.0 | 7.8-14.1 | 0.331 | ||
| flexion | 110.2 | 6.5 | 104.8-115.6 | 113.6 | 8.5 | 108.2-119.0 | 0.344 | |||
| Δ | extension | 6.6 | 3.4 | 3.8-9.4 | 6.2 | 5.3 | 2.8-9.6 | 0.858 | ||
| flexion | 16.8 | 8.3 | 9.9-23.8 | 17.0 | 8.1 | 11.8-22.1 | 0.967 | |||
| Lead-leg-side | ||||||||||
| passive | shoulder | flexion | 131.7 | 9.1 | 124.0-139.3 | 137.7 | 13.0 | 129.4-145.9 | 0.274 | |
| passive | ankle | flexion | 14.8 | 8.4 | 7.8-21.8 | 13.8 | 9.7 | 7.6-19.9 | 0.809 | |
| passive | SLR | 78.2 | 2.8 | 75.9-80.4 | 80.7 | 11.7 | 73.2-88.1 | 0.489 | ||
| active | 63.5 | 6.9 | 57.7-69.2 | 74.2 | 14.2 | 62.4-86.1 | 0.063 | |||
| Δ | 14.7 | 8.5 | 7.6-21.8 | 6.5 | 6.4 | 2.4-10.5 | 0.024* | |||
| passive | knee | extension | 157.3 | 6.7 | 151.7-162.8 | 159.7 | 11.2 | 152.2-167.1 | 0.595 | |
| flexion | 160.1 | 5.5 | 155.5-164.7 | 162.4 | 5.7 | 158.8-166.0 | 0.387 | |||
| active | flexion | 142.7 | 6.4 | 137.4-148.1 | 147.5 | 9.0 | 141.8-153.2 | 0.211 | ||
| Δ | flexion | 17.4 | 4.6 | 13.6-21.2 | 14.9 | 5.4 | 11.4-18.3 | 0.473 | ||
| passive | hip | extension | 20.1 | 5.3 | 15.7-24.6 | 18.1 | 4.6 | 15.2-21.1 | 0.391 | |
| flexion | 130.3 | 8.0 | 123.6-137.0 | 130.9 | 6.6 | 125.7-136.1 | 0.843 | |||
| active | extension | 11.7 | 6.1 | 6.6-16.9 | 10.7 | 4.6 | 7.8-13.7 | 0.683 | ||
| flexion | 117.4 | 7.4 | 111.2-123.6 | 116.9 | 8.2 | 111.7-122.1 | 0.895 | |||
| Δ | extension | 8.4 | 4.6 | 4.5-12.2 | 7.4 | 6.3 | 3.4-11.4 | 0.710 | ||
| flexion | 12.9 | 7.8 | 6.4-19.4 | 14.0 | 5.9 | 10.3-17.7 | 0.718 | |||
| Spinal column alignment(°): | ||||||||||
| thoracic kyphosis | erect position | 32.6 | 7.3 | 26.5-38.7 | 32.8 | 7.1 | 28.3-37.3 | 0.950 | ||
| extended position | 15.6 | 10.8 | 6.6-24.7 | 12.3 | 12.2 | 4.5-20.0 | 0.535 | |||
| flexed position | 46.3 | 9.9 | 37.9-54.6 | 53.4 | 9.5 | 47.4-59.4 | 0.121 | |||
| lumbar lordosis | erect position | -18.9 | 8.9 | -26.3-11.5 | -20.3 | 6.2 | -24.2-16.4 | 0.671 | ||
| extended position | -24.6 | 6.3 | -29.9-19.3 | -27.7 | 7.1 | -32.2-23.1 | 0.341 | |||
| flexed position | 25.4 | 12.1 | 15.2-35.5 | 26.8 | 9.5 | 20.7-32.8 | 0.780 | |||
LBP = low back pain; SD = standard deviation; CI = confidence interval; SL = , straight leg raise
Spinal column alignment(+):kyphosis, (-):lordosis
Δ:the value obtained by subtracting the results of the Active range of motion from Passive range of motion
*:Significant difference at p<0.05
There were no significant differences between the groups in the isokinetic peak torque of hip and knee flexion or extension (p > .05), normalized to body weight.
Active SLR angle in the chronic LBP group (57.5 ± 5.9 ° [95% CI: 52.5–62.5]) was significantly smaller than that in the non-chronic LBP group (71.5 ± 12.8 ° [95% CI: 63.4–79.6]) on the takeoff leg side (p < .05). ΔSLR (subtracted active SLR from passive SLR) in the chronic LBP group (takeoff leg side, 18.1 ± 6.9 ° [95% CI: 12.3-23.9]; lead leg side, 14.7 ± 8.5 ° [95% CI: 7.6–21.8]) was significantly larger than that in the non-chronic LBP group (takeoff leg side, 9.5 ± 6.1 ° [95% CI: 5.7-13.4]; lead leg side, 6.5 ± 6.4 ° [95% CI: 2.4–10.5]) for both legs (p < .05). No significant differences in other factors were observed between the groups (p > .05). There were no significant differences between the groups in the thoracic kyphosis angle or lumbar lordosis angle in three positions (p > .05).
The number of 0's in each group recorded during the clearing tests was four in chronic LBP group (press-up, 2; posterior rocking, 2) and four in the non-chronic LBP group (impingement, 3; posterior rocking, 1). Seven participants in the chronic LBP group had an FMS™ composite score evaluated with clearing tests of ≤14, whereas one of the participants had a score ≥15. Six participants in the chronic LBP group had an FMS™ composite score evaluated without clearing tests of ≤14, whereas two participants had scores ≥15. Two participants in the non-chronic LBP group had an FMS™ composite score evaluated with and without clearing tests of ≤14, while ten participants had scores ≥15. In the group with chronic LBP, there were significantly more participants with an FMS™ composite score ≤ 14 (Table 2). Table 3 presents the number of athletes who scored a 0, 1, 2, or 3 on each of the FMS™ screening tests. In the chronic LBP group, four of eight athletes scored a one in the shoulder mobility reaching test and in the trunk stability push-up test.
Table 2.
Difference in Functional Movement Screen™ composite score between chronic low back pain group and non-chronic low back pain group.
| FMS™ Composite Score | Chronic LBP (n = 8) | Non-chronic LBP (n = 12) | p-value | Odds ratio | |
|---|---|---|---|---|---|
| With clearing test | ≤14 | 7 | 2 | 0.005* | 26.60 |
| ≥15 | 1 | 10 | |||
| Without clearing test | ≤14 | 6 | 2 | 0.019* | 15.00 |
| ≥15 | 2 | 10 |
LBP, low back pain; FMS, Functional Movement Screen *Significant difference at p<0.05
Table 3.
The number of athletes who scored each of the FMS™ test scores.
| Score | DS | HS | ILL | |||
|---|---|---|---|---|---|---|
| chronic LBP | non-chronic LBP | chronic LBP | non-chronic LBP | chronic LBP | non-chronic LBP | |
| 3 | 3 | 8 | 0 | 7 | 2 | 6 |
| 2 | 4 | 4 | 7 | 5 | 5 | 6 |
| 1 | 1 | 0 | 1 | 0 | 1 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Score | SMR | ASLR | TSPU | RS | |||||
|---|---|---|---|---|---|---|---|---|---|
| chronic LBP | non-chronic LBP | chronic LBP | non-chronic LBP | chronic LBP | non-chronic LBP | chronic LBP | non-chronic LBP | ||
| 3 | 2 | 4 | 0 | 7 | 2 | 7 | 0 | 0 | |
| 2 | 2 | 3 | 5 | 4 | 0 | 4 | 5 | 11 | |
| 1 | 4 | 2 | 3 | 1 | 4 | 1 | 1 | 0 | |
| 0 | 0 | 3(2,2,1) | 0 | 0 | 2(3,1) | 0 | 2(2,2) | 1(1) | |
LBP = low back pain; DS = Deep Squat; HS = Hurdle Step; IL = , In-Line Lunge; SMR = Shoulder Mobility Reach; ASLR = Active Straight Leg Raise;
(scores listed) = actual scores, evaluated without clearing test
DISCUSSION
The purpose of this study was to describe and analyze the physical characteristics of pole vaulters with chronic LBP. The second purpose of this study was to clarify the relationship between FMS™ performance with and without chronic LBP. Unlike this study's hypothesis, there were no significant differences in ROM of shoulder flexion and hip extension between the groups. This study found that compared with those without chronic LBP, male collegiate pole vaulters with chronic LBP had a lower personal best record, a significantly decreased active SLR angle on the takeoff leg side and a larger ΔSLR for both legs; furthermore, the chronic LBP group had more significantly more participants with an FMS™ composite score ≤ 14.
The FMS™ is a tool that screens movement stability and mobility required for functional movement patterns during specific tasks, and it is widely used in sports. In addition, the interrater and intrarater reliabilities of this tool have been reported to be high by previous authors.21 However, the meaning of low scores in each screening test is complicated and requires careful interpretation.
There were significantly more individuals who had an FMS™ composite score of less than 14 in the chronic LBP group than in the non-chronic LBP group. The FMS™ may be used a prediction system for the occurrence of injuries and it has been reported in the literature that there is a high incidence of injuries in athletes with a composite score of ≤14.20 In this study, significantly more participants in the chronic LBP group scored 14 or less than those in the non-chronic LBP group. Therefore, this study suggest that the FMS™ should be considered in the periodic evaluation of athletes. In addition, among the eight athletes in the group with chronic LBP, four athletes scored a 1 on the trunk stability push-up and three athletes scored a 1 on the active SLR. With these findings, it may be reasonable to consider prescribing corrective strengthening exercises to rectify the low scores to improvement chronic LBP in collegiate pole vaulters.22 Wang et al23 have reported that exercises targeting deep abdominal muscles are effective for treating chronic LBP in the general population. Exercises to address anti-rotation stress to the trunk may be effective in attaining greater stability of the trunk. Furthermore, four of eight athletes in the group with chronic LBP scored a 1 on the shoulder mobility reaching test; however, no significant difference was found in shoulder joint flexion on ROM measurement. Therefore, the lack of combined shoulder joint mobility (as measured in the SM screen) might be considered to cause a score of a 1. The FMS™ is targeted for use with athletes who do not have pain, but the subjects of this study may have experienced chronic LBP and may have changed their movement at a level that they were unable to recognize. In other words, there is a possibility that the measured function is lower owing to chronic LBP, thus explaining the low scores. However, during competitions, since the sport performance continues even when athletes are in chronic pain, the FMS™ may help clarify the biomechanics dysfunction by evaluating the fundamental movements.
The active SLR angle in the chronic LBP group was smaller than that in the non-chronic LBP group on the takeoff-leg-side. SLR may be limited because of malfunction of the primary acting muscle and/or tightness of the antagonist muscle. However, there was no significant difference between the groups in passive SLR and knee extension angle, which are measures of the tightness of the lower limb. Therefore, active SLR was smaller in the group with chronic LBP. Hu et al24 reported that the ipsilateral iliacus, rectus femoris, adductor longus, psoas, and contralateral psoas are active during active SLR. In addition, Hu et al24 discussed that the psoas is active on both sides to stabilize the lumbar spine in the frontal plane. Therefore, result of this study may be related to poor stability of trunk or incompetence of the rest of the kinetic chain required when raising the lower limbs. Anatomically, the psoas major muscle attaches to costal processes and the disks of lumbar vertebrae. When working as a hip flexor, it is possible that the lower limb cannot be raised because the low back lacks stability.
To further analyze the influence of tightness of lower limbs, ΔSLR was calculated by subtracting the active SLR angle from the passive SLR angle. This study found that the group with chronic LBP had significantly larger ΔSLR for both legs. Passive SLR, a test to evaluate tightness of the posterior lower limbs, was not significantly different between the groups, while ΔSLR was larger in the chronic LBP group. Therefore, ΔSLR may be a useful indicator of the stability of the low back, as active SLR excludes the tightness of the back of the lower limb. As such, ΔSLR may more accurately capture the deficits in the kinetic chain when lifting the lower limbs.
The chronic LBP group had significantly lower personal best vaulting heights than the non-chronic LBP group, however this difference cannot be solely attributed to LBP. This result was contrary to the consideration that as the competition level increases, more injuries may occur in the low back. Athletes of lower competition levels are inexperienced at taking off and run-up. As such, it is conceivable that poor technique during take-off and increased time at the horizon lead to repeated loads being placed on the lumbar spine. Therefore, the authors considered that collegiate pole vaulters at lower levels of competition may have chronic LBP secondary to repeat vaulting. It is also possible that the competition level may not improve owing to their chronic LBP. In addition, there were no significant differences between the groups in terms of age, height, or weight. In a previous study, it was reported that body weight10,11 and BMI9,10 are risk factors for LBP, but no differences were found in this study. It was considered that weight is directly linked to performance. However, no difference was recognized in this study.
Limitations
This study has several limitations. First, this study utilized a limited sample size, and only male collegiate athletes were assessed. As a result, the training condition, training contents, and sex may have influenced the occurrence of chronic LBP. This study could not recruit female collegiate athletes and thus excluded them to avoid the effects of sex differences. Second, this study did not assess degenerative changes to the lumbar spine to make an actual diagnosis, rather, used only self-report of pain. In addition, this study investigated history of LBP using the questionnaire, so there was likely recall bias. This study also defined chronic LBP using a questionnaire. There is no common definition of chronic low back pain, and it is necessary to propose a common definition in future. Third, it is not possible to demonstrate a cause–effect relationship between physical factors and chronic LBP, in a cross-sectional study, using self-report. Therefore, it is necessary to study the relationship between physical factors and LBP longitudinally in future research.
CONCLUSION
The results of the current cross-sectional study on the relationship between chronic LBP and physical factors identified that in collegiate pole vaulters with chronic LBP, the personal best record for vault height was lower, active SLR angle on takeoff-leg-side was smaller, the ΔSLR on both legs was larger, and a composite FMS™ score ≤ 14 was more frequent, when compared to athletes without chronic LBP. Thus, it may be necessary to examine the active straight leg raise (vs. passive only), and fundamental movements as screened by the FMS ™. Stability of the trunk and throughout the kinetic chain may be important to be addressed while training.
Appendix
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