Medicine & Science in Sports & Exercise:
APPLIED SCIENCES: Biodynamics
The assessment of intersegmental motion and pelvic tilt in elite oarsmen
MCGREGOR, ALISON1; ANDERTON, LISA2; GEDROYC, WADY2
1BioDynamics Group, Department of Musculoskeletal Surgery, Imperial College of Science, Technology & Medicine, London, UNITED KINGDOM and
2IMR Unit, St Mary’s Hospital, London, UNITED KINGDOM
Submitted for publication April 2001.
Accepted for publication December 2001.
McGREGOR, A., L. ANDERTON, and W. GEDROYC. The assessment of intersegmental motion and pelvic tilt in elite oarsmen. Med. Sci. Sports Exerc., Vol. 34, No. 7, pp. 1143–1149, 2002. Low back pain (LBP) is a common problem in elite oarsmen. The relevance of spinal and pelvic flexibility to good rowing technique and the incidence of LBP is unclear.
Purpose: The aim of this study was to investigate patterns of spinal and pelvic mobility in a group of elite oarsmen with and without a history of LBP.
Methods: Twenty elite oarsmen were recruited into this study, including nine with no history of spinal problems, four with a current spinal problem, and the remainder with a history of LBP. Subjects were scanned using an interventional magnetic resonance imaging (MRI) scanner. Four key stages of the rowing stroke were simulated within the scanner, and sagittal images of the lumbar spine and sacrum were obtained. From these images intersegmental motion was determined along with the angle of lordosis and position of the lumbar spine and sacrum.
Results: Different mobility trends were seen; oarsmen with no history of LBP demonstrated the greatest mobility in their lower lumbar regions (at the L5/S1 level in the catch position 7.5° ±1.3 in normals; 4.8° ±1.2 in previous LBP groups; and 2.8° ±5.5 in current LBP group) and the lowest rotation of their pelvis (level in the catch position 13.9° ±11.2 in normals; 16.1° ±6.8 in previous back pain groups; and 15.2° ±11.2 in current back pain group). In contrast, those with either current or previous LBP presented with a hypomobility of their spine which appeared to be compensated for by increased pelvic rotation.
Conclusions: Marked differences were observed in the motion characteristics of these 3 groups of oarsmen. At present it is not known if these changes are causative or effect.
In western society low back pain (LBP) has risen to epidemic figures, with epidemiological studies indicating a prevalence of between 15 and 30% (1). It is a complex problem that is subject to a range of influences and although it is most prevalent among people in their middle years of life, it is increasingly common in younger people, particularly those involved in competitive sports. Many sports have been plagued by a rise in spinal problems with incidence rates of 1.1% to 30%, depending on the sport (4). In recent years, many argue that the incidence of low back pain in rowers has risen substantially, although there is no clear evidence to support this claim.
Rowing is a motor skill that requires high levels of consistency, coherence, accuracy, and continuity, particularly at an elite level. It is a strenuous sport and as a result is frequently associated with a high injury rate among competitive participants of all standards. Recent investigations into injury patterns suggest that the spine is the most frequently injured region in rowers, accounting for 15 to 20% of injuries (9,18). Several speculations have been made regarding injuries to the spine, including the nature of the sport itself and aspects of rowing technique, the weight-training regime and changes in rowing equipment (3,11).
There are two types of rowing: sculling and sweep oar. The oarsman uses two oars during sculling and one in a sweep-oared boat. However, the basic components of the stroke remain the same in the two types of rowing, with the rowing stroke consisting of four distinct but interrelated phases; the finish, recovery, catch, and drive (Fig. 1) (13). Stallard (21) speculated that the majority of injuries in rowers were mechanical in origin and related to rowing technique. It has been observed that differences exist in terms of rowing capacity and skill at different competitive levels (20), with success in international competition being related to technical skills and high levels of fitness, although the relationship between technique and injury have not been investigated. However, at present the definition of good rowing technique is highly descriptive with technique and skill being assessed in terms of stroke length, frequency, consistency, and efficiency (8). Biomechanical and especially kinesiological investigations into the mechanical efficiency of rowers are rare, and coaches rely on the esthetic appearance of technique. As a result there is a limited understanding of the movement of the body segments, particularly the spine, during rowing. A recent study investigated ergometer-rowing technique and identified clear patterns of lumbar and lumbo-pelvic motion in elite rowers. Deviations from these patterns of good technique were seen in aberrant rowing techniques and as a result of fatigue (2). However, this study was limited to the assessment of the gross motion of the lumbar spine and was unable to investigate details of intersegmental motion and details of pelvic motion. Therefore, this study aimed to investigate patterns of intersegmental lumbar spine and pelvic motion in a group of elite oarsmen with either no, past, or a current history of low back pain.
Twenty elite rowers ranging from International, Under 23 to Senior I Open Oarsmen were recruited, primarily from the Imperial College and Queen’s Tower Boat Clubs, and written informed consent was obtained. The mean age of subjects was 22.6 ± 4.3 yr. All were sweep stroke oarsmen with 10 rowing stroke side and 12 bow side. Of these subjects, 9 reported previous low back pain that had required intervention and resulted in time off training, 4 subjects reported current low back pain preventing full training, and 7 had no history of low back pain. Low back pain was defined as pain experienced in the lumbar spine with or without radiation to the buttocks; subjects with sciatica were not included in this study. Subjects were categorized into the three groups, following a clinical examination by an experienced physiotherapist who has worked with the crews for the past two years. Ratings of severity were not recorded.
Subjects were scanned using a General Electric Signa SPIO Interventional MRI scanner (General Electric, Milwaukee, WI). This open configuration MRI scanner consists of two connected but opposing ring “doughnut” magnets, Figure 2A. The gap between these magnets is 56 cm, generating a uniform field of 0.5 tesla. A transmit receive flexible RF coil (General Electric) is secured around the subject’s waist and lumbar spine, and a multi-coil magnetic resonance tracking device (General Electric) was positioned in line with the subject’s lumbar spinous processes, Figure 2B. Subjects were scanned with a fast spoiled gradient echo (FSPGR) sequence. The parameters set were time of repetitions (TR) 14.6; time of excitations (TE) 7.3; scan time 2 s; flip angle 60°; slice thickness 10 mm; field of view (FOV) 30 cm; matrix 256 by 128; and number of excitations 1. This was performed in conjunction with the magnetic resonance (MR) tracking program (General Electric) via the Sun SPARC workstation (Sun Microsystems, Inc., Santa Clara, CA). The MR signal in a MR tracking procedure is detected by two small receive coils contained within the tracking device. The MR signal received is analyzed using a Fourier transform that identifies a sharp peak in the power spectrum. The frequency of this peak indicates the location of the coil in the scanning volume (5). As a result, the MR tracking system can be used in combination with the imaging functions of the MR scanner to locate the position of the coil and then utilize this to position the MR image. This mode of operation is frequently referred to as the “guided scan” mode of operation. This technique permits the tracking of the sagittal position of the spine with respect to the subject’s position in the scanner.
An MRI compatible wooden rowing jig was constructed which permitted the simulation of four key stages in the rowing stroke (the catch, early and late drive, and this finish) within the scanner (Fig. 2A), while maintaining the lumbar spine within the main bore of the magnet. Subjects were asked to adopt their usual position at each phase of the stroke (Fig. 2C and D), and the length of the oar was adjusted accordingly. In each position subjects were asked to pull on the oar (thus loading the spine) as they would while rowing and to remain as still as possible in this position while a sagittal image was obtained through the midline of the spinous process. Verification of these positions within the scanner was not possible due to the damage and distortions caused by the magnetic field. Future studies aim to address this by recording static postures on the rowing rig out of the scanning environment and comparing these with dynamic measurements of technique. At present it is not clear how factors such as stroke rating and fatigue influence technique, and these factors may also influence the representative nature of these images.
Images were analyzed on a conventional workstation to allow the measurement of spinal kinematics. From the sagittal images obtained in each of the simulated rowing phases, measurements of sacral inclination and lordosis were performed using the methods described by Saraste et al. (19). In addition, measurements of the angle formed between each of the lumbar intervertebral disks (L1/L2, L2/L3, etc.) and the angle of lumbar spinal inclination were obtained as described by Usabiaga et al. (22). Although these techniques were designed for the analysis of lateral x-ray views of the spine, they adapt readily to the MRI images, particularly as the nature of MRI eliminates much of the blurring generated in x-rays from imaging a three-dimensional structure in two dimensions. Previous studies using these techniques on MRI sagittal scans of the spine have found them to be repeatable to within one degree (15). The repeatability of subjects achieving the correct positions was not investigated because of financial and time restraints; however, all subjects were very experienced oarsmen.
The statistical analysis was performed using the statistical package Stata, Version 6 (Stata Corporation, College Station, TX) on a personal computer. Power statistics revealed that with a minimum number of four subjects in each group, a 2° difference could be detected at the 50% power level using a 0.05 significance level. A two-way ANOVA was used to investigate whether any differences existed between the 3 population groups for each variable in each of the four rowing positions. The statistical threshold was set at P < 0.05. Orthogonal contrasts were then employed to locate where any differences noted by the ANOVA lay.
Different patterns of spinal and pelvic positioning were observed in the three groups of oarsmen. The rowers with no history of back problems presented with greater rotation of the lumbar into flexion at the catch, returning to a neutral upright position at the finish (Fig. 3A and B). Rowers with either a current or previous history of low back pain tended to present with a stiffness in the lower lumbar spine with little angulation occurring in these segments and consequently either gained their range by compensating either at the pelvis or at the upper lumbar or lower thoracic spine, (Fig. 4A, B, C, and D). They also tended to tilt the pelvis and overextend the spine at the finish position.
Early signs of disk degeneration, including loss of disk height and signal, were observed in a small proportion of the oarsmen with either current or past low back pain. This, however, did not appear to be associated with either the age of the oarsman or the length of time spent rowing.
The Catch Position
At the catch, rowers attempted to hold their lumbar spines in an upright position relative to the sacrum, and this was reflected by the angle of the lumbar spine (Fig. 5). In all subjects the sacrum and pelvis appeared to be held in anterior tilt. This tended to be more marked in those oarsmen with either current or previous spinal problems; however, it did not reach statistical significance. In addition, rowers tended to flatten their lumbar lordosis unless they suffered a current back problem and lordosis persisted. This may be explained by the statistical finding that rowers with current low back pain exhibited a significant loss of angulation at the L5/S1 (P < 0.05) and L1/L2 (P < 0.01) intervertebral levels (Fig. 6). Those rowers with a previous history of low back pain also presented with a significant loss in angulation at the L5/S1 level.
Drive Phase 1 Position
In this position both the rowers with no back pain and those with previous back pain attempted to hold the lumbar spine in an upright vertical position, while those with current back pain started to extend their lumbar spine relative to the sacrum (Fig. 5). The sacrum and pelvis continued to be held in slight anterior tilt for most oarsmen; however, those with either current or previous spinal problems tended to hold their sacrum in a more upright position (Fig. 7), although this did not reach significance. The angle of lordosis increased in all study groups. The patterns of intersegmental motion generally demonstrated the spine straightening up from its previous slightly flexed position. However, there was no change in the angulation at the L5/S1 level in those rowers who had current or previous low back pain, and this level remained hypomobile compared to the control group (P < 0.05).
Drive Phase 2 Position
Drive Phase 2 position reflected a similar but nonsignificant pattern to that seen in Phase 1 of the drive, but in this later phase of the stroke fewer differences were observed between the groups. Nevertheless, there was a slight tendency for the rowers with back pain to start rotating their sacrum and pelvis posteriorly. This may be attributed to poor control of the pelvis and lumbar spine as a result of either weakness or inhibition in the spinal stabilizing muscles.
The Finish Position
Rowers presenting with current low back pain tended to extend their lumbar spines and to rotate their sacra and pelves posteriorly compared with the control subjects who maintained their lumbar spines in the neutral position (P < 0.05). In addition, current and previous low back pain rowers tended to present with greater angles of lumbar lordosis. In terms of intersegmental lumbar motion, both low back pain groups tended to exhibit greater degrees of extension throughout the spine (Fig. 8), particularly at the L5/S1 level where significant differences in angulation were noted (P < 0.05), while those with no history of low back pain maintained the spine in an upright neutral position.
The exact incidence of low back pain among rowers is controversial. However, there is a general consensus that back pain is one of the most frequently reported injuries among the rowing population. These injuries are frequently attributed to high pressure training techniques and schedules, and the changes in rowing technique and equipment. Hosea et al. (10) postulated that the back was at risk because it serves as a cantilever for transmitting the forces generated by the legs to the oar, while Hagerman (7) linked the injuries to the generation of maximal muscle force in a position of spinal hyperextension. Stallard (21) associated the rise in spinal injuries with changes in seat slide and foot position in modern boats, and Christiansen et al. (3) questioned the impact of changes in oar shape and dimension on the spine. However, until a satisfactory method is developed to assess the kinematics of rowing technique it is difficult to ascertain the impact of both equipment and training strategies on skill.
Hosea et al. (10) stated that trunk movement in a well-trained rower range from 30 degrees of flexion at the catch to 28 degrees of extension at the end of stroke. The more recent study of Bull et al. (2) using objective markers to track global parameters of spinal motion suggested a slightly different range of 20 degrees of flexion at the catch and 30 degrees of extension at the finish. However, the way in which the trunk achieves these two extremes of position is far from clear. From the sagittal images of the spine obtained in this study, it is clear that the rower achieves the different positions in the rowing stroke through a combination of lumbar spine angulation and pelvic rotation. This is commonly referred to as lumbopelvic rhythm. Alterations in this lumbopelvic rhythm are observed in the rowers with either a current or past history of low back pain, which is in agreement with findings among the general low back pain population (6,14). Rowers with either previous or current low back pain tended to present with a tendency not to use angulation of their lower lumbar spines to achieve the different positions required in rowing, and tended to compensate for this apparent stiffness by exhibiting greater movement at either the pelvis, or the lumbothoracic junction, or a combination of both.
Angulation of the sacrum and pelvis appears greater at the catch and during the drive phases where it is possible that the tendency to posteriorly rotate the pelvis during the drive is a reflection of a compromised trunk stabilization mechanism. Koutedakis et al. (12) postulated that low knee flexor/extensor strength ratio were related to the development of low back pain in rowers since this ratio can influence the lumbopelvic rhythm. Koutedakis felt that derotation of the pelvis during the drive phase of rowing was accomplished by the posterior pelvic muscles, predominately the gluteals and the hamstring muscle group; therefore, the presence of weak or tight hamstring muscle would influence this. However, recent studies into strength and flexibility patterns of oarsmen have found no significant differences in either quadriceps-hamstring ratios or hamstring flexibility when compared with a control study group (17). It is not possible from this work to comment on the flexibility and strength patterns in injured oarsmen, however. Jull et al. (11) holds a theory of a pelvic crossed syndrome that may provide a possible explanation of the pelvic movements observed in this study. This syndrome consists of tight iliopsoas and erector spinae muscles in combination with weak abdominals and gluteal muscles, a feature frequently observed clinically in rowers. This leads to a forward tilting of the pelvis in the upright position resisted by increased tone in the hamstring muscles, which would explain the tendency of those rowers with back pain to gain a greater degree of pelvic rotation or tilt at the catch. The phenomenon of weak abdominals may be a factor in the apparent inability to control the pelvis, observed during the drive phase of rowing. This would suggest that research into the strength and flexibility of rowers warrants further investigation, particularly with respect to hamstring flexibility and core stability strength.
A large proportion of the oarsmen investigated demonstrated early signs of disk degeneration that was not influenced by age or time spent rowing. However, data regarding the incidence of disk degeneration in younger people suggests that this is not an abnormal finding (16).
A key limitation of this work is its inability to investigate dynamic motion within the scanner and a reliance on static postures. At present it is not clear how static postures relate to the dynamic situation, thus further work is required in this area. Previous work has quantified “gross” motion of the lumbar spine during rowing (2), yet it has not to date been ascertained how or if factors such as stroke rate or fatigue or back pain influence this technique; this is an area currently under investigation. Fatigue has been shown to influence the position of the pelvis and motion of the lumbar spine (2); however, the relevance of this to back pain is not yet established. Preliminary unpublished data suggests that low back pain does lead to alterations in the position of the pelvis, in accordance with the findings of this study.
It is also unclear if the changes in lumbar spine mobility and pelvic rotation are causative or an effect of low back pain. Further serial studies of oarsmen are required to determine whether the changes observed in this study are a result of or a precursor to back pain.
The authors would like to thank the Imperial College and Queen’s Tower Boat Clubs for their support of this work. In particular we would like to thank Mr. Bill Mason for his teaching and insights into rowing technique, and Mr. Rick Fulton and Mr. Pete Holt for coordinating subject recruitment.
Address for correspondence: Dr. Alison McGregor, PhD, MSc, MCSP, Lecturer, Department of Musculoskeletal Surgery, Faculty of Medicine, Imperial College of Science, Technology & Medicine, Charing Cross Hospital, London, W6 8RF, England, UK; E-mail: email@example.com
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