Differences in end range lumbar flexion during slumped sitting and forward bending between low back pain subgroups and genders
From: Man Ther. 2012 Jan 17. [Epub ahead of print]
Low back pain may be related to patterns of lumbar postures and movements used to perform different tasks, but it is unclear which patterns with which tasks contribute to low back pain. For example, increases in both lumbar flexion and extension have been linked to low back pain. Some studies have reported increased lumbar flexion in people with low back pain during activities involving flexion, such as golfing and cycling. Other studies have reported that increased lumbar extension is associated with low back pain during sitting. Inconsistent findings regarding the direction of increased lumbar movement or the presence of flexed versus extended postural alignment potentially associated with low back pain may be due to the inclusion of subjects with widely varying movement patterns in a single low back pain group. Several researchers have proposed that there are subgroups of people with low back pain whose symptoms are associated with different direction related postures or movement patterns (e.g., flexion or extension related).
If multiple low back pain subgroups are studied as a single population, differences between subgroups demonstrating patterns in opposite directions could average out to suggest no difference in motion between people with and without low back pain. When subgrouping was not included in the study design, several studies found no differences in lumbar postural alignment and motion between people with and without low back pain. Still other studies found that decreased lumbar motion is associated with low back pain. Lumbar postural alignment and motion characteristics associated with low back pain may be more clearly identified when people with low back pain are subgrouped based on lumbar patterns associated with symptoms.
Systems of subgrouping people with low back pain have allowed researchers to identify consistent differences in lumbar posture and motion between people with flexion or extension related low back pain symptoms and people without low back pain. Studies that subgrouped people with low back pain using O’Sullivan’s system reported that during typical sitting men with flexion related low back pain sat closer to their end range of available lumbar flexion compared to men without low back pain and that people in a flexion related subgroup sat in more lumbar flexion than people without low back pain and people in an extension related subgroup. Additionally, during slumped sitting, investigators found that people with extension related low back pain demonstrated less end range lumbar flexion than people with flexion related low back pain and people without low back pain. Finally, these investigators also found that people with extension related low back pain demonstrated less end range lumbar flexion during forward bending than people with flexion related low back pain. Investigators using the Movement System Impairment model for low back pain (Sahrmann SA. Diagnosis and treatment of movement impairment syndromes. St. Louis: Mosby, Inc; 2002) found that while there were no differences in standing lumbar alignment between people with and without low back pain, when subgrouped, people with low back pain in an extension related subgroup stood in more lumbar extension than people with low back pain in a flexion related subgroup and people without low back pain. Differences in end range lumbar flexion during flexion related tasks between subgroups based on the Movement System Impairment model have not been studied.
Low back pain may also be related to certain tasks. Some tasks, such as prolonged sitting and frequent forward bending, increase the risk of developing low back pain. However, the growing understanding of subgrouping suggests that the risk of low back pain may be influenced not only by what task is performed, but how high risk tasks are performed. The current study examines end range lumbar flexion during two common high risk tasks: slumped sitting and standing forward bending. End range lumbar flexion, as opposed to total lumbar flexion range of motion, was selected because the authors were only interested in the final position of the lumbar spine. Greater absolute amounts of lumbar flexion, regardless of an individual’s starting position, may indicate greater lumbar tissue laxity and a reduced ability of the passive structures of the lumbar spine to provide stability, particularly in resisting flexion. These tissue characteristics may place people at greater risk for tissue injury and pain. The specific tasks examined in the current study were chosen because they are both common flexion related tasks, but differ in the static versus dynamic nature of the task. The authors assessed the consistency of flexion related patterns across these tasks for two low back pain subgroups classified based on the Movement System Impairment model.
Differences in lumbar posture and motion between low back pain subgroups could be influenced by gender differences. Previous studies of differences in lumbar flexion between low back pain subgroups included more males in flexion related groups and more females in extension related groups. One study comparing people with flexion related low back pain to people without low back pain included only male subjects. The imbalance in gender distributions in past studies may have influenced the subgroup findings. In the back healthy population, it has been reported that men tend to adopt sitting postures and perform movements, such as forward bending, with greater lumbar flexion than women. Additionally, men tend to stand in more lumbar flexion and women in more lumbar extension. These findings suggest that, when there are uneven distributions of males and females, differences in posture and movement patterns between genders could influence differences found between low back pain subgroups. The current research will assess whether subgroup differences are independent of potential gender differences by incorporating comparable distributions of males and females within each subgroup.
The purpose of this study was to examine the effects of low back pain subgroup, classified based on the Movement System Impairment model, on lumbar end range flexion and symptom behaviour with a flexed posture (slumped sitting) and a flexion related movement (forward bending). The study included the two most prevalent of five low back pain subgroups studied to date: rotation and rotation with extension. The rotation subgroup demonstrates patterns of posture and motion and low back pain symptoms during tests associated with lumbar rotation, flexion, and extension. The rotation with extension subgroup demonstrates patterns of posture and motion and low back pain during tests associated with lumbar rotation, and extension, but not flexion. The authors predicted that the rotation subgroup would display greater end range lumbar flexion with slumped sitting and forward bending compared to the rotation with extension subgroup, and that the rotation subgroup would be more likely to report increased symptoms with both tasks than the rotation with extension subgroup. A secondary purpose was to examine differences in end range lumbar flexion between males and females and the effect of such differences on low back pain subgroup results. The authors predicted that males would show greater end range lumbar flexion than females, regardless of low back pain subgroup, and that gender effects would not be specific to either low back pain subgroup.
In this study, two low back pain subgroups, classified according to the Movement System Impairment model, demonstrated predictable differences in end range lumbar flexion across two flexion related tasks. Subjects in the rotation subgroup displayed significantly greater end range lumbar flexion during slumped sitting and a trend towards greater end range lumbar flexion during forward bending than subjects in the rotation with extension subgroup. Despite no differences between subgroups in current pain on the day of testing, the rotation subgroup was also more likely to report increased symptoms with both tasks than the rotation with extension subgroup. During both slumped sitting and forward bending, males displayed greater end range lumbar flexion than females; however, the subgroup differences identified were not the result of gender differences in end range lumbar flexion. Comparable distributions of males and females in each subgroup were used and no interactions between subgroup and gender on end range lumbar flexion were present. These findings support recommendations of subgrouping people with low back pain by demonstrating that subgroups of people with low back pain differ in amounts of end range lumbar flexion during tests of posture and potentially during movement.
The findings of the current study are consistent with previous research on slumped sitting and typical sitting. A prior study demonstrated that during slumped sitting, subjects in a flexion related low back pain subgroup sat in more end range lumbar flexion compared to an extension related low back pain subgroup. Prior studies also demonstrated that during typical sitting, subjects in a flexion related low back pain subgroup sat in more lumbar flexion compared to an extension related low back pain subgroup. The results of the current study are also consistent with others’ observations of end range lumbar flexion during forward bending in people with low back pain. Subjects in a flexion related low back pain subgroup had greater end range lumbar flexion with forward bending compared to subjects in an extension related low back pain subgroup.
The current study also indicates that gender is a factor in end range lumbar flexion during flexion related tasks. The findings are consistent with research on back healthy subjects showing males adopt greater lumbar flexion than females during prolonged sitting and that males have greater lumbar flexion and less hip flexion compared to females during forward bending and a reaching task involving forward bending. In the current study, a similar relationship between lumbar flexion exhibited by men and women during slumped sitting and forward bending was also evident in people with low back pain.
One possible reason for differences in end range lumbar flexion between genders and subgroups could be differences in hip movement. During forward bending, reduced hip flexion might contribute to greater end range lumbar flexion. This could explain differences between males and females observed in this study, where greater lumbar flexion corresponded to reduced hip flexion for males compared to females. It is logical that decreased hamstring flexibility could limit hip flexion motion during forward bending, thereby encouraging greater lumbar flexion to compensate. Studies of healthy individuals have demonstrated that males have reduced hamstring flexibility compared to females. Although there is some evidence to suggest a relationship between reduced hamstring flexibility and decreased pelvic or hip flexion during forward bending in healthy individuals and in people with low back pain, the evidence regarding the relationship between hamstring flexibility and lumbar flexion is equivocal and the studies are limited methodologically. On the other hand, the amount of hip flexion may not influence differences in end range lumbar flexion between subgroups. There were differences in end range lumbar flexion between subgroups, but not in end range hip flexion during forward bending. This may suggest that hip flexibility affecting lumbar motion is not the main issue differentiating subgroups, but rather the issue may be related to the consistent demonstration of lumbar flexion across tasks.
The finding of differences in end range lumbar flexion between genders and subgroups across two different flexion related tasks provides some support to the proposal that people adopt directional, stereotypic patterns of posture and movement. The frequent use of a limited repertoire of stereotypic posture and movement patterns used across many daily activities could lead to microtrauma to lumbar region tissues. It has been proposed that a cycle of spinal ligament subfailure leading to changes in neuromuscular control and subsequent tissue injury plays a role in low back pain. Repeated use of end range flexion across many tasks could potentially result in tissue changes that reduce spinal stability and put people at risk for tissue damage, injury, and pain. For flexion related low back pain subgroups, during postures maintained for long periods of time (e.g., slumped sitting), passive structures could lose their ability to support the spine. During movements that take the lumbar spine into a great amount of lumbar flexion (e.g., forward bending), the combination of stereotypic movement patterns involving exaggerated end range flexion and tissue laxity from prior exposure to flexion postures could promote greater repeated use of certain tissues and further injury to the lumbar spine.
The current study lends support to the proposal that repeated adoption of end range lumbar flexion during many tasks may put people at greater risk for pain during flexion. The rotation subgroup, which showed a pattern of greater lumbar flexion during slumped sitting and forward bending than the rotation with extension subgroup, were more likely to report symptoms during both tests. However, males, who showed greater lumbar flexion during slumped sitting and forward bending than females, were not more likely to report symptoms during either test. Differences in symptoms during both slumped sitting and forward bending found between subgroups, but not between genders, suggest that increased end range flexion values alone do not directly correspond to an increased likelihood of low back pain symptoms. The authors would propose that the interaction of increased end range motion, paired with decreased movement variability across activities and an increased likelihood of performing repeated end range motions, is what sets a person up to develop pain. For the rotation subgroup, avoiding lumbar flexion, particularly end range lumbar flexion, may be an important component of treatment.
The results of this study add further evidence suggesting a link between low back pain and lumbar posture and movement patterns. A greater understanding of the mechanisms that contribute to low back pain development, persistence, and recurrence can provide information to guide preventative and rehabilitative treatments for low back pain. Subgrouping people with low back pain may allow for treatments that target the posture and movement patterns most related to symptoms. Treatments emphasizing modifying lumbar movement patterns based on low back pain subgrouping are showing promise. Additional research on low back pain subgroups can provide further insight into the posture and movement patterns that contribute to low back pain and how this information can be used to improve the care of people with low back pain.
People in the rotation subgroup displayed more end range lumbar flexion during slumped sitting and forward bending than people in the rotation with extension subgroup. Men displayed greater end range lumbar flexion than women during both slumped sitting and forward bending. Differences found between subgroups, however, were not related to gender differences. These results support the proposal that people with low back pain display stereotypic patterns of posture and movement. They also support the need for subgrouping people with low back pain based upon patterns of posture and movement and symptoms consistently displayed across tasks. An increased understanding of differences between subgroups of people with low back pain is necessary to understand what contributes to low back pain problems and to guide preventative and rehabilitative treatment strategies.
