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19.4 Decreased margin of stability in response to postural perturbations in persons with low back pain
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Chapter 19. Pain and fatigue I•
Effects of a fatiguing treadmill exercise on body balance
M. Bove, A. Brunori, C. Cogo, E. Faelli, R Ruggeri. Department
of Experimental Medicine, Section of Human Physiology, University of Genoa, Italy The aim of this study was to investigate whether a fatiguing treadmill exercise might affect body sway. Six male healthy subjects, aged 26.5±2.8 years, neither aerobically trained nor involved in professional sports, were studied. Center of pressure (COP) measurements were performed at the beginning of the experiments with eyes open (EO) and closed (EC) for control. Fatigue exercise was based on a treadmill running with an increasing speed (initial velocity: 6.5km/h with steps of 1 km/h at each minute to reach the maximum speed of 14.5 km/h). Metabolic and posturographic parameters were simultaneously monitored. Postural sway was analyzed by static posturography with EO and EC during quiet stance. The fatigue exercise was followed by twenty posturography trials (spaced by at least one minute) during which the EO and EC condition was alternated. On average, during the treadmill exercise, heart rate, respiratory frequency and respiratory exchange ratio reached the peak of 180 beats/min, 35 breaths/min and 1.3, respectively. A destabilizing effect due to the physical exercise was observed in body sway path (SP). SP was significantly larger with respect to control condition for about ten minutes after the exercise in both EO and EC condition. Significant linear relationships between SP and the metabolic parameters were found. These findings suggest that body sway can be affected by a strenuous exercise, that induces an important fatigue. This method could be useful to test professional sportsmen who need to maintain a good equilibrium to initiate a motor task after a strenuous fatigue.
I•
Anticipatian of pastural instability alters body orientation in persons with recurrent low back pain
S. Brumagne, I. Paulus, S. van Deun, E Staes. Department of
Rehabilitation Sciences', Faculty of Kinesiology and Rehabilitation Sciences', K.U. Leuven, Belgium Introduction: The purpose of this study was to investigate whether persons with low back pain (LBP) have an altered internal representation of body orientation when postural instability is anticipated. Insight to the mechanisms of altered postural control in persons with recurrent LBP could lead to better interventions for LBP patients. Methods: Twenty healthy individuals and 28 persons with recurrent LBP (20 26 years) participated in this study. Body inclination was evaluated with two piezoresistive electrogoniometers placed on the sacrum $2 and thoracic vertebra T1 in upright posture for the conditions as follows: 1) quiet stance with vision and, 2) without vision; 3) prior to the third trial, vibration of the triceps surae muscles for 15 s to induce postural instability was applied, followed by three minutes of rest. The actual trial consisted of one minute quiet stance without vision in anticipation of postural instability due to muscle vibration. Results: No differences in body inclination were observed when visual information was available between the two groups (p > 0.05). However, significant more forward inclination was seen in the LBP persons when vision was occluded (+7.4%) and when vibrationinduced postural instability was anticipated (+19%) (p<0.05) compared to the healthy individuals. Discussion and Conclusion: Persons with LBP seem to have an altered internal representation of body orientation, probably due to an
inaccurate proprioceptive postural control. In addition, in anticipation of postural instability, LBP persons position their body center of mass more in the middle of the support base, however, at the expense of increased trunk muscle activity.
I
•
A
distinct clinical syndrome defining the postural patient
RM. Gagey, B. Weber, A. Scheibel, L. Bonnier. Institute of
Posturology, Paris', France The clinical and stabilometric profiles of 67 patients examined at the Institute of Posturology were described as precisely as possible after analysis of their files. They consulted mainly for chronic pain, frequently associated with dizziness. Pointed questioning ascertained that these pains mostly run along the body axis, and are accompanied by eye anomalies, particularly heterophoria, headaches and often signs of temporomandibular joint dysfunction. These patients had clinically corroborated postural asymmetries, whose tonic nature was confirmed by their variability. Some manifestations were significantly more frequent among women. Generally speaking, pain or dizziness dominated the ends of the spectrum of symptoms manifested by these 67 patients. The stabilometric parameter abnormalities [1] observed were not constant. Often underestimated, otherwise vaguely designated as 'postural deficiency syndrome' [2], this set of predominantly axial pains and tonic asymmetries deserves being examined in greater depth. French-speaking private practitioners have now reached a consensus that such an entity, frequently encompassing non-specific symptoms, indeed exists, and that for the time being it is mostly established a posteriori by the disappearance of symptoms, associated with normalization of tonic asymmetries and stabilometric parameters, obtained by the studied manipulation of the postural system inputs [3].
References [1] Normes 85, Paris, ADAR 1985. [2] Da Cunha HM. In: Actualit~s en r~ducation fonctionnelle et en r~adaptation, 4 e S~r. Paris, Masson, 1979; 27 31. [3] http ://orthoptie.net/archive_posturelist.html
I•
Decreased margin of stability in response to pastural perturbations in persons with low back pain
J.R. Hitt 1, S.M. Henry 1, S.L. Jones 1, J.Y. Bunn 2. 1Physical
Therapy Department, University of Vermont, Burlington, Vermont, 2Department of Mathematics and Statistic, Department, University of Vermont, Burlington, Vermont, USA Introduction: Low back pain (LBP) has been associated with abnormal movement strategies, likely due to differences in neuromuscular control. This study characterized postural responses in subjects with and without chronic, recurrent LBP following support surface translations. Methods: Twenty-six LBP subjects (39±13 yrs) and twentyfour non-LBP (NLBP) subjects (32±10yrs) were given support surface translations, randomly delivered in 12 different horizontal directions. Using kinematic, force plate and anthropometric data, the net center of pressure (CP), total body center of mass (CM) and joint angular displacements were derived and analyzed with a repeated measures analysis of variance design to characterize the neuromuscular responses in the two groups. Results: LBP subjects exhibited delayed onsets of the anterior/posterior CP (p<0.0001) and CM (p 0.0373). LBP subjects
Chapter 19. Pain and fatigue
S122
also displayed less anterior/posterior CP displacement (p <0.0001) while having larger CM displacement (p 0.0267) compared to NLBP subjects. Overall, the trunk angular displacement in the frontal plane was reduced for LBP subjects. D i s c u s s i o n : Subjects with LBP have altered automatic postural coordination, both in magnitude and timing of responses as reflected in the reduced CP displacement and reduced trunk angular displacement, indicating alterations in neuromuscular control. C o n c l u s i o n : These data suggest the automatic postural control of subjects with LBP is altered such that there is an overall stiffening strategy for LBP subjects. With a larger CM displacement and a smaller CP displacement, the LBP subjects are responding such that their margin of stability for balance is reduced.
I•
Persons with chronic low back pain (LBP) demonstrate less dynamic frontal plane torque responses to unexpected perturbations
S.L. Jones 1, S.M. Henry 1, C.C. Raasch 2, J.R. Hitt 1, J.Y. Bunn 1.
1Technician, Department of Physical Therapy University of Vermont, :Exponent Failure Analysis' Associates Inc., USA Individuals with chronic LBP demonstrate altered movement strategies that may result from changes in neuromuscular control. Often unexpected movement precedes a painful episode, thus it is important to quantify the automatic postural responses of this population. The purpose of this study was to compare the responses of individuals with and without LBP during a systematic task. M e t h o d s : Eleven subjects without LBP (NLBP; 38±8 years) and twelve subjects with chronic, recurrent LBP (LBP; 38±8 years) stood with feet on separate force plates mounted on a moveable platform, which was translated unexpectedly in one of 12 directions. Forces, 3-D body kinematics and anthropometric data were used to calculate frontal plane torques at the ankle, hip and trunk using inverse dynamics. Peak torque, time to peak and torque integrals were analyzed using a repeated measures analysis of variance design. Results: In response to medial-lateral perturbations, both groups responded in a proximal to distal manner with an initial peak trunk torque occurring approximately 125 ms after perturbation onset, followed by sequential hip and ankle peak torque production. The LBP group demonstrated less dynamic responses characterized by decreased torque at the ipsilateral ("unloaded) hip (p 0.01) and increased torque at the contralateral ("loaded") hip (p 0.02) relative to the NLBP group. D i s c u s s i o n a n d C o n c l u s i o n : Patients with LBP demonstrated altered neuromuscular responses to unexpected perturbations, exhibiting less dynamic control in the frontal plane. This impaired coordination in response to unexpected perturbation may result in increased susceptibility to exacerbation of symptoms or further injury. Introduction:
I•
Persons with chronic low back pain (LBP) demonstrate reduced sagittal plane joint torques in response to surface translations
S.L. Jones 1 , S.M. H e n r y 1 , C.C. R a a s c h 2, J.R. Hitt 1 , J.Y. Bunn 1.
1Department of Physical Therapy, Burlington, University of Vermont, 2Exponent Failure Analysis' Associates Inc., USA
integrals were analyzed with a repeated measures analysis of variance design. R e s u l t s : In response to anterior-posterior perturbations, both groups initiated a peak hip and trunk torque response approximately 175 ms after perturbation onset followed by sequential torque peaks at the ankle, knee, hip and trunk, which reflects some combination of the ankle and hip strategies. Despite these similarities, individuals with LBP demonstrated reduced joint torque magnitudes (p 0.001) and later peak torques (p 0.002) compared to healthy individuals. D i s c u s s i o n a n d C o n c l u s i o n s : Persons with LBP demonstrate intact hip and ankle strategies in response to surface translations despite using decreased magnitudes of torque relative to healthy individuals. A strategy of stiffening achieved by co-contraction of agonist/antagonist musculature could be a plausible explanation, which may reflect pain avoidance behaviour.
I•
Effect of fatigue on postural sway dynamics: the viscoelastic modeling approach
M. Kuczyfiski, G. Czeczkowski. Department of Gymnastics, Academy of Physical Education, Wroclaw, Poland I n t r o d u c t i o n : Muscle fatigue may cause increased postural sway and
endanger body equilibrium. However, neither there is a consensus regarding the magnitude of changes in the variability of postural sway in fatigued condition, nor the exact mechanisms underlying those changes have yet been described [1 3]. M e t h o d s : Sixteen young healthy subjects performed squats until refusal. Their center-of-pressure (COP) time series were recorded during two consecutive 20 s quiet stances on a force plate in eyes open and eyes closed condition. The CoP signals were used to compute traditional measures of sway variability and dynamics of postural corrections based on the viscoelastic modeling [4,5]. R e s u l t s : Fatigue resulted in increased variability of postural sway in the anterior-posterior plane, with associated higher postural stiffness. In the medial-lateral plane the CoP variability remained unaffected, while postural damping highly increased. D i s c u s s i o n a n d c o n c l u s i o n : Our results further elucidate the mechanisms of quiet stance explaining the role of stiffness and damping in preserving balance after fatigue. This knowledge may result in preventing falls and musculoskeletal injury.
References [1] Gribble PA, Hertel J. J Electromyography Kinesiol 2004; 14:641 646. [2] Corbeil P e t al. Gait Posture 2003; 18:92 100. [3] Yaggie JA, McGregor SJ. Arch Phys Med Rehab 2002; 83:224 228. [4] Kuczyfiski M, Ostrowska B. Gait Posture 2005 (in press). [5] Kuczyfiski M. DSc. thesis, AWF Wroclaw 2003.
I•
Gait analaysis related to the level of lumbosacral radiculopathy in patients with chronic low back pain
S.H. Lee, C.H. Ryu, H.-S. Yang, Y.O. Park. Department of Rehabilitation Medicine, Seoul Veterans Hospital, Seoul, South Korea To study gait patterns of patients with chronic lumbosacral radiculopathy, and to investigate whether gait parameters can reflect functional deficit in relation to the level of lumbosacral radiculopathy M e t h o d s : Three-dimensional gait analysis were performed on 24 patients of chronic lumbosacral radiculopathy (twelve with L5 and twelve with S1 radiculopathy), diagnosed by electrophysiologic study and magnetic resonance imaging study, and 12 healthy control subjects. Temporospatial, kinematic and kinetic parameters were obtained. R e s u l t s : In patients with lumbosacral radiculopathy, walking velocity, stride length, ratio of single support time and range of pelvic obliquity were less than control group. Increased double support Introduction:
Unexpected movement often precedes initiation of a painful episode for individuals with LBP, thus it is important to characterize the automatic postural responses of this population. The purpose of this study was to compare the neuromuscular responses of individuals with and without LBP elicited by a systematic task. M e t h o d s : Eleven subjects without LBP (NLBP; 38±8 years) and twelve subjects with chronic, recurrent LBP (LBP; 38±8 years) were instructed to stand with feet on separate force plates mounted on a moveable platform that was translated unexpectedly in one of 12 directions. Forces, 3-D body kinematics and anthropometric data were used to calculate net sagittal plane torques at the ankle, knee, hip and trunk using inverse dynamics. Peak torque, time to peak and torque Introduction:
Chapter 19. Pain and fatigue I•
Effects of a fatiguing treadmill exercise on body balance
M. Bove, A. Brunori, C. Cogo, E. Faelli, R Ruggeri. Department
of Experimental Medicine, Section of Human Physiology, University of Genoa, Italy The aim of this study was to investigate whether a fatiguing treadmill exercise might affect body sway. Six male healthy subjects, aged 26.5±2.8 years, neither aerobically trained nor involved in professional sports, were studied. Center of pressure (COP) measurements were performed at the beginning of the experiments with eyes open (EO) and closed (EC) for control. Fatigue exercise was based on a treadmill running with an increasing speed (initial velocity: 6.5km/h with steps of 1 km/h at each minute to reach the maximum speed of 14.5 km/h). Metabolic and posturographic parameters were simultaneously monitored. Postural sway was analyzed by static posturography with EO and EC during quiet stance. The fatigue exercise was followed by twenty posturography trials (spaced by at least one minute) during which the EO and EC condition was alternated. On average, during the treadmill exercise, heart rate, respiratory frequency and respiratory exchange ratio reached the peak of 180 beats/min, 35 breaths/min and 1.3, respectively. A destabilizing effect due to the physical exercise was observed in body sway path (SP). SP was significantly larger with respect to control condition for about ten minutes after the exercise in both EO and EC condition. Significant linear relationships between SP and the metabolic parameters were found. These findings suggest that body sway can be affected by a strenuous exercise, that induces an important fatigue. This method could be useful to test professional sportsmen who need to maintain a good equilibrium to initiate a motor task after a strenuous fatigue.
I•
Anticipatian of pastural instability alters body orientation in persons with recurrent low back pain
S. Brumagne, I. Paulus, S. van Deun, E Staes. Department of
Rehabilitation Sciences', Faculty of Kinesiology and Rehabilitation Sciences', K.U. Leuven, Belgium Introduction: The purpose of this study was to investigate whether persons with low back pain (LBP) have an altered internal representation of body orientation when postural instability is anticipated. Insight to the mechanisms of altered postural control in persons with recurrent LBP could lead to better interventions for LBP patients. Methods: Twenty healthy individuals and 28 persons with recurrent LBP (20 26 years) participated in this study. Body inclination was evaluated with two piezoresistive electrogoniometers placed on the sacrum $2 and thoracic vertebra T1 in upright posture for the conditions as follows: 1) quiet stance with vision and, 2) without vision; 3) prior to the third trial, vibration of the triceps surae muscles for 15 s to induce postural instability was applied, followed by three minutes of rest. The actual trial consisted of one minute quiet stance without vision in anticipation of postural instability due to muscle vibration. Results: No differences in body inclination were observed when visual information was available between the two groups (p > 0.05). However, significant more forward inclination was seen in the LBP persons when vision was occluded (+7.4%) and when vibrationinduced postural instability was anticipated (+19%) (p<0.05) compared to the healthy individuals. Discussion and Conclusion: Persons with LBP seem to have an altered internal representation of body orientation, probably due to an
inaccurate proprioceptive postural control. In addition, in anticipation of postural instability, LBP persons position their body center of mass more in the middle of the support base, however, at the expense of increased trunk muscle activity.
I
•
A
distinct clinical syndrome defining the postural patient
RM. Gagey, B. Weber, A. Scheibel, L. Bonnier. Institute of
Posturology, Paris', France The clinical and stabilometric profiles of 67 patients examined at the Institute of Posturology were described as precisely as possible after analysis of their files. They consulted mainly for chronic pain, frequently associated with dizziness. Pointed questioning ascertained that these pains mostly run along the body axis, and are accompanied by eye anomalies, particularly heterophoria, headaches and often signs of temporomandibular joint dysfunction. These patients had clinically corroborated postural asymmetries, whose tonic nature was confirmed by their variability. Some manifestations were significantly more frequent among women. Generally speaking, pain or dizziness dominated the ends of the spectrum of symptoms manifested by these 67 patients. The stabilometric parameter abnormalities [1] observed were not constant. Often underestimated, otherwise vaguely designated as 'postural deficiency syndrome' [2], this set of predominantly axial pains and tonic asymmetries deserves being examined in greater depth. French-speaking private practitioners have now reached a consensus that such an entity, frequently encompassing non-specific symptoms, indeed exists, and that for the time being it is mostly established a posteriori by the disappearance of symptoms, associated with normalization of tonic asymmetries and stabilometric parameters, obtained by the studied manipulation of the postural system inputs [3].
References [1] Normes 85, Paris, ADAR 1985. [2] Da Cunha HM. In: Actualit~s en r~ducation fonctionnelle et en r~adaptation, 4 e S~r. Paris, Masson, 1979; 27 31. [3] http ://orthoptie.net/archive_posturelist.html
I•
Decreased margin of stability in response to pastural perturbations in persons with low back pain
J.R. Hitt 1, S.M. Henry 1, S.L. Jones 1, J.Y. Bunn 2. 1Physical
Therapy Department, University of Vermont, Burlington, Vermont, 2Department of Mathematics and Statistic, Department, University of Vermont, Burlington, Vermont, USA Introduction: Low back pain (LBP) has been associated with abnormal movement strategies, likely due to differences in neuromuscular control. This study characterized postural responses in subjects with and without chronic, recurrent LBP following support surface translations. Methods: Twenty-six LBP subjects (39±13 yrs) and twentyfour non-LBP (NLBP) subjects (32±10yrs) were given support surface translations, randomly delivered in 12 different horizontal directions. Using kinematic, force plate and anthropometric data, the net center of pressure (CP), total body center of mass (CM) and joint angular displacements were derived and analyzed with a repeated measures analysis of variance design to characterize the neuromuscular responses in the two groups. Results: LBP subjects exhibited delayed onsets of the anterior/posterior CP (p<0.0001) and CM (p 0.0373). LBP subjects
Chapter 19. Pain and fatigue
S122
also displayed less anterior/posterior CP displacement (p <0.0001) while having larger CM displacement (p 0.0267) compared to NLBP subjects. Overall, the trunk angular displacement in the frontal plane was reduced for LBP subjects. D i s c u s s i o n : Subjects with LBP have altered automatic postural coordination, both in magnitude and timing of responses as reflected in the reduced CP displacement and reduced trunk angular displacement, indicating alterations in neuromuscular control. C o n c l u s i o n : These data suggest the automatic postural control of subjects with LBP is altered such that there is an overall stiffening strategy for LBP subjects. With a larger CM displacement and a smaller CP displacement, the LBP subjects are responding such that their margin of stability for balance is reduced.
I•
Persons with chronic low back pain (LBP) demonstrate less dynamic frontal plane torque responses to unexpected perturbations
S.L. Jones 1, S.M. Henry 1, C.C. Raasch 2, J.R. Hitt 1, J.Y. Bunn 1.
1Technician, Department of Physical Therapy University of Vermont, :Exponent Failure Analysis' Associates Inc., USA Individuals with chronic LBP demonstrate altered movement strategies that may result from changes in neuromuscular control. Often unexpected movement precedes a painful episode, thus it is important to quantify the automatic postural responses of this population. The purpose of this study was to compare the responses of individuals with and without LBP during a systematic task. M e t h o d s : Eleven subjects without LBP (NLBP; 38±8 years) and twelve subjects with chronic, recurrent LBP (LBP; 38±8 years) stood with feet on separate force plates mounted on a moveable platform, which was translated unexpectedly in one of 12 directions. Forces, 3-D body kinematics and anthropometric data were used to calculate frontal plane torques at the ankle, hip and trunk using inverse dynamics. Peak torque, time to peak and torque integrals were analyzed using a repeated measures analysis of variance design. Results: In response to medial-lateral perturbations, both groups responded in a proximal to distal manner with an initial peak trunk torque occurring approximately 125 ms after perturbation onset, followed by sequential hip and ankle peak torque production. The LBP group demonstrated less dynamic responses characterized by decreased torque at the ipsilateral ("unloaded) hip (p 0.01) and increased torque at the contralateral ("loaded") hip (p 0.02) relative to the NLBP group. D i s c u s s i o n a n d C o n c l u s i o n : Patients with LBP demonstrated altered neuromuscular responses to unexpected perturbations, exhibiting less dynamic control in the frontal plane. This impaired coordination in response to unexpected perturbation may result in increased susceptibility to exacerbation of symptoms or further injury. Introduction:
I•
Persons with chronic low back pain (LBP) demonstrate reduced sagittal plane joint torques in response to surface translations
S.L. Jones 1 , S.M. H e n r y 1 , C.C. R a a s c h 2, J.R. Hitt 1 , J.Y. Bunn 1.
1Department of Physical Therapy, Burlington, University of Vermont, 2Exponent Failure Analysis' Associates Inc., USA
integrals were analyzed with a repeated measures analysis of variance design. R e s u l t s : In response to anterior-posterior perturbations, both groups initiated a peak hip and trunk torque response approximately 175 ms after perturbation onset followed by sequential torque peaks at the ankle, knee, hip and trunk, which reflects some combination of the ankle and hip strategies. Despite these similarities, individuals with LBP demonstrated reduced joint torque magnitudes (p 0.001) and later peak torques (p 0.002) compared to healthy individuals. D i s c u s s i o n a n d C o n c l u s i o n s : Persons with LBP demonstrate intact hip and ankle strategies in response to surface translations despite using decreased magnitudes of torque relative to healthy individuals. A strategy of stiffening achieved by co-contraction of agonist/antagonist musculature could be a plausible explanation, which may reflect pain avoidance behaviour.
I•
Effect of fatigue on postural sway dynamics: the viscoelastic modeling approach
M. Kuczyfiski, G. Czeczkowski. Department of Gymnastics, Academy of Physical Education, Wroclaw, Poland I n t r o d u c t i o n : Muscle fatigue may cause increased postural sway and
endanger body equilibrium. However, neither there is a consensus regarding the magnitude of changes in the variability of postural sway in fatigued condition, nor the exact mechanisms underlying those changes have yet been described [1 3]. M e t h o d s : Sixteen young healthy subjects performed squats until refusal. Their center-of-pressure (COP) time series were recorded during two consecutive 20 s quiet stances on a force plate in eyes open and eyes closed condition. The CoP signals were used to compute traditional measures of sway variability and dynamics of postural corrections based on the viscoelastic modeling [4,5]. R e s u l t s : Fatigue resulted in increased variability of postural sway in the anterior-posterior plane, with associated higher postural stiffness. In the medial-lateral plane the CoP variability remained unaffected, while postural damping highly increased. D i s c u s s i o n a n d c o n c l u s i o n : Our results further elucidate the mechanisms of quiet stance explaining the role of stiffness and damping in preserving balance after fatigue. This knowledge may result in preventing falls and musculoskeletal injury.
References [1] Gribble PA, Hertel J. J Electromyography Kinesiol 2004; 14:641 646. [2] Corbeil P e t al. Gait Posture 2003; 18:92 100. [3] Yaggie JA, McGregor SJ. Arch Phys Med Rehab 2002; 83:224 228. [4] Kuczyfiski M, Ostrowska B. Gait Posture 2005 (in press). [5] Kuczyfiski M. DSc. thesis, AWF Wroclaw 2003.
I•
Gait analaysis related to the level of lumbosacral radiculopathy in patients with chronic low back pain
S.H. Lee, C.H. Ryu, H.-S. Yang, Y.O. Park. Department of Rehabilitation Medicine, Seoul Veterans Hospital, Seoul, South Korea To study gait patterns of patients with chronic lumbosacral radiculopathy, and to investigate whether gait parameters can reflect functional deficit in relation to the level of lumbosacral radiculopathy M e t h o d s : Three-dimensional gait analysis were performed on 24 patients of chronic lumbosacral radiculopathy (twelve with L5 and twelve with S1 radiculopathy), diagnosed by electrophysiologic study and magnetic resonance imaging study, and 12 healthy control subjects. Temporospatial, kinematic and kinetic parameters were obtained. R e s u l t s : In patients with lumbosacral radiculopathy, walking velocity, stride length, ratio of single support time and range of pelvic obliquity were less than control group. Increased double support Introduction:
Unexpected movement often precedes initiation of a painful episode for individuals with LBP, thus it is important to characterize the automatic postural responses of this population. The purpose of this study was to compare the neuromuscular responses of individuals with and without LBP elicited by a systematic task. M e t h o d s : Eleven subjects without LBP (NLBP; 38±8 years) and twelve subjects with chronic, recurrent LBP (LBP; 38±8 years) were instructed to stand with feet on separate force plates mounted on a moveable platform that was translated unexpectedly in one of 12 directions. Forces, 3-D body kinematics and anthropometric data were used to calculate net sagittal plane torques at the ankle, knee, hip and trunk using inverse dynamics. Peak torque, time to peak and torque Introduction: