Classical ballet dancers combine artistry and physical skills to perform graceful and exciting movements. Lengthy, exacting dance training potentially promotes unique adaptation of motor control to; execute these movements; maintain optimal physiological function, and provide stability to avoid injury and pain. Yet low back pain (LBP) is common in dancers. Differences in motor control are frequently observed between non-dancers with and without LBP. This often involves reduced and delayed activity of deep trunk muscles and augmented activity of superficial muscles. These changes are proposed to affect the control of movement and stiffness of the trunk. LBP is also associated with deficits in postural control, an aspect of motor control, which depends on control of the trunk. Some features of adaptation in motor control are relatively common; but there are some features that are specific to individuals or different populations. It is essential to understand how motor control is adapted in elite classical ballet dancers with LBP as less optimal motor control has potential to impair performance and limit the capacity to dance. The overall objective of this thesis was to investigate aspects of motor control in dancers with and without LBP, with specific attention to trunk muscle morphology and to postural stability. Studies I and II investigated trunk muscle size, symmetry and function, in dancers with and without LBP, at rest and during simple manoeuvres, with magnetic resonance imaging (MRI). Reduced size of the multifidus muscle was observed in dancers with LBP and dancers with both back and hip/pelvic region pain. This finding is similar to that for non-dancers. Study II provided preliminary evidence of a behavioural change in transversus abdominis (the deepest abdominal muscle); expressed as reduced length change of this muscle measured with MRI, in dancers with LBP. Thickness of transversus abdominis, obliquus internus abdominis and multifidus muscles were asymmetrical in dancers but this was not related to LBP. This may be related to repetitive performance of asymmetrical movements. Studies III and IV investigated postural control. In Study III, the trunk was perturbed in order to measure the dynamic properties of stiffness, damping and mass as an indication of control of the trunk. Dancers with LBP had less damping (control of velocity) than dancers without LBP, but this could be changed with motor imagery in the dancers with LBP. Study IV used linear and non-linear measures of centre of pressure trajectories to investigate standing balance in dancers with and without LBP and non-dancers. Balance was measured with the feet in parallel and the dance-specific turned out ‘first’ position; which increases the dependence on trunk motion for balance in the anteroposterior direction. Dancers without LBP used more movement to control balance than non-dancers. These findings suggest that “less” movement does not define optimal balance in dancers. Dancers with a history of LBP used strategies that were more similar to non-dancers than to their LBP-free counterparts. This compromised balance in dancers with LBP has potential to impact on performance. Each of these studies has identified differences in aspects of motor control between dancers with and without LBP and, in the case of balance, between non-dancers and the dancers’ groups. These changes in motor control associated with LBP are potentially modifiable and may provide a basis for the development of prevention or treatment programs to reduce the morbidity related to LBP in professional classical ballet dancers.

PurposeTrunk control is essential in ballet and may be compromised in dancers with a history of low back pain (LBP) by associated changes in motor control. This study aimed to compare trunk mechanical properties between professional ballet dancers with and without a history of LBP. As a secondary aim, we assessed whether asking dancers to use motor imagery to respond in a "fluid" manner could change the mechanical properties of the trunk and whether this was possible for both groups.MethodsTrunk mechanical properties of stiffness and damping were estimated with a linear second-order system, from trunk movement in response to perturbations, in professional ballet dancers with (n = 22) and without (n = 8) a history of LBP. The second-order model adequately described trunk movement in response to the perturbations. Trials were performed with and without motor imagery to respond in a fluid manner to the perturbation.ResultsDancers with a history of LBP had lower damping than dancers without LBP during the standard condition (P = 0.002) but had greater damping during the "fluid" condition (P < 0.001), with values similar to dancers without LBP (P = 0.226). Damping in the dancers without LBP was similar between the conditions (P > 0.99). Stiffness was not different between the dancers with and those without a history of LBP (P = 0.252) but was less during the fluid condition than the standard condition (P < 0.001).ConclusionAlthough dancers with a history of LBP have less trunk damping than those without LBP, they have the capacity to modulate the trunk's mechanical properties to match that of pain-free dancers by increasing damping with motor imagery. These observations have potential relevance for LBP recurrence and rehabilitation.

Objectives: To evaluate the morphology of transversus abdominis and obliquus internus abdominis muscles and the ability to "draw in" the abdominal wall, in professional ballet dancers without low back pain, with low back pain or both hip region and low back pain.Design: Observational study.Methods: Magnetic resonance images of 31 dancers were taken at rest and during voluntary abdominal muscle contraction. Measurements included the thickness of transversus abdominis and obliquus internus abdominis muscles, lateral slide of the anterior extent of the transversus abdominis muscles (transversus abdominis slide) and reduction in total cross sectional area of the trunk.Results: The transversus abdominis and obliquus internus abdominis muscles were thicker in male dancers and the right side was thicker than the left in both genders. There was no difference in muscle thickness as a proportion of the total thickness, between dancers with and without pain, although there was a trend for female dancers with low back pain only to have a smaller change in transversus abdominis muscle thickness with contraction than those without pain. Transversus abdominis slide was less in female dancers than in male dancers. When gender was ignored, the extent of transversus abdominis slide was less in dancers with low back pain only. Reduction in trunk cross sectional area with contraction was not different between genders or groups.Conclusions: This study provides evidence that the abdominal muscles (transversus abdominis and obliquus internus abdominis) are asymmetrical in dancers and although the abdominal muscles are not different in structure (resting thickness) in dancers with LBP, there is preliminary evidence for the behavioural change of reduced slide of transversus abdominis during the 'draw in' of the abdominal wall. (C) 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

STUDY DESIGN Cross-sectional, observational study. OBJECTIVES To investigate the cross-sectional area (CSA) of trunk muscles in professional ballet dancers with and without low back pain (LBP). BACKGROUND LBP is the most prevalent chronic injury in classical ballet dancers. Research on nondancers has found changes in trunk muscle size and symmetry to be associated with LBP. There are no studies that examine these changes in ballet dancers. METHODS Magnetic resonance imaging was performed in 14 male and 17 female dancers. The CSAs of 4 muscles (multifidus, lumbar erector spinae, psoas, and quadratus lumborum) were measured and compared among 3 groups of dancers: those without LBP or hip pain (n = 8), those with LBP only (n = 13), and those with both hip-region pain and LBP (n = 10). RESULTS Dancers with no pain had larger multifidus muscles compared to those with LBP at L3-5 (P<.024) and those with both hip-region pain and LBP at L3 and L4 on the right side (P<.027). Multifidus CSA was larger on the left side at L4 and L5 in dancers with hip-region pain and LBP compared to those with LBP only (P<.033). Changes in CSA were not related to the side of pain (all, P>.05). The CSAs of the other muscles did not differ between groups. The psoas (P<.0001) and quadratus lumborum (P<.01) muscles were larger in male dancers compared to female dancers. There was a positive correlation between the size of the psoas muscles and the number of years of professional dancing (P = .03). CONCLUSION In classical ballet dancers, LBP and hip-region pain and LBP are associated with a smaller CSA of the multifidus but not the erector spinae, psoas, or quadratus lumborum muscles.

PURPOSE:This panel-randomized intervention trial was designed to examine the effect of a motor control training program for elite Australian Football League players with and without low back pain (LBP). METHODS:The outcome measures included cross-sectional area (CSA) and symmetry of multifidus, quadratus lumborum, and psoas muscles and the change in CSA of the trunk in response to an abdominal drawing-in task. These measures of muscle size and function were performed using magnetic resonance imaging. Availability of players for competition games was used to assess the effect of the intervention on the occurrence of injuries. The motor control program involved performance of voluntary contractions of the multifidus and transversus abdominis muscles while receiving feedback from ultrasound imaging. Because all players were to receive the intervention, the trial was delivered as a stepped-wedge design with three treatment arms (a 15-wk intervention, a 8-wk intervention, and a waitlist control who received a 7-wk intervention toward the end of the playing season). Players participated in a Pilates program when they were not receiving the intervention. RESULTS:The intervention program was associated with an increase in multifidus muscle size relative to results in the control group. The program was also associated with an improved ability to draw-in the abdominal wall. Intervention was commensurate with an increase in availability for games and a high level of perceived benefit. CONCLUSIONS:The motor control program delivered to elite footballers was effective, with demonstrated changes in the size and control of the targeted muscles. In this study, footballers who received the intervention early in the season missed fewer games because of injury than those who received it late in the playing season.