Postural control deficits due to bilateral pyramidal tract lesions exemplified by hereditary spastic paraplegia (HSP) originate from increased feedback time delay and reduced long-term error corrections.

Pyramidal tract lesions determine the clinical syndrome of Hereditary Spastic Paraplegia (HSP). The clinical impairments of HSP are typically exemplified by their deficits in mobility, leading to falls and injuries. The first aim of this study was to identify the cause for postural abnormalities caused by pyramidal tract lesions in HSP. The second aim was to specify the effect of treadmill training for postural abnormalities. We examined nine HSP patients before and after treadmill training, as well as nine healthy control subjects during perturbed and unperturbed stance. We found that HSP was associated with larger sway amplitudes and velocities. Body excursions following platform tilts were larger, and upper body excursions showed a phase lead. Model-based analysis detected a greater time delay and a reduced long-term error correction of postural reactions in the center of mass. HSP patients performed significantly better in clinical assessments after treadmill training. In addition, treadmill training reduced sway amplitudes and body excursions, most likely by increasing positional and velocity error correction gain as a compensatory mechanism, while the time delay and long-term error correction gain remained largely unaffected. Moreover, the upper body's phase lead was reduced. We conclude that HSP leads to very specific postural impairments. While postural control generally benefits from treadmill training, the effect seems to mainly rely on compensatory mechanisms, whereas the original deficits are not affected significantly.

A new approach to characterize postural deficits in chemotherapy-induced peripheral neuropathy and to analyze postural adaptions after an exercise intervention.

BACKGROUND: Postural instability presents a common and disabling consequence of chemotherapy-induced peripheral neuropathy (CIPN). However, knowledge about postural behavior of CIPN patients is sparse. With this pilot study, we used a new approach to i) characterize postural impairments as compared to healthy subjects, ii) allocate possible abnormalities to a set of parameters describing sensorimotor function, and iii) evaluate the effects of a balance-based exercise intervention. METHODS: We analyzed spontaneous and externally perturbed postural control in eight CIPN patients before and after a balance-based exercise intervention by using a modification of an established postural control model. These findings were compared to 15 matched healthy subjects. RESULTS: Spontaneous sway amplitude and velocity were larger in CIPN patients compared to healthy subjects. CIPN patients' reactions to external perturbations were smaller compared to healthy subjects, indicating that patients favor vestibular over proprioceptive sensory information. The balance-based exercise intervention up-weighted proprioceptive information in patients. CONCLUSIONS: CIPN patients' major postural deficit may relate to underuse of proprioceptive information that results in a less accurate posture control as spontaneous sway results indicate. The balance-based exercise intervention is able to partially correct for this abnormality. Our study contributes to a better understanding of postural impairments in CIPN patients and suggests an effective treatment strategy. TRIAL REGISTRATION: German Clinical Trials Register: DRKS00004340, retrospectively registered 04 January 2013.

Abnormal trunk control determines postural abnormalities in Amyotrophic Lateral Sclerosis.

BACKGROUND: Postural instability in Amyotrophic Lateral Sclerosis (ALS) occurs at an early stage of the disease and often results in falls. As ALS is considered a multisystem neurodegenerative disorder, postural instability may result from motor, sensory and central processing deficits. OBJECTIVE AND METHODS: We analysed postural control of 12 ALS patients and 12 healthy age-matched control subjects. Postural control was characterised by spontaneous sway measures and measures of postural reactions to pseudorandom anterior-posterior platform tilts, which were then correlated with clinical test scores. RESULTS: Spontaneous sway amplitudes and velocities were significantly larger and sway frequencies higher in ALS patients than in control subjects. ALS patients' body excursions following platform tilts were smaller, with relatively higher upper body excursions. We found high correlations between abnormal postural reactions and clinical tests representing motor or balance deficits. CONCLUSIONS: We conclude that ALS patients' postural abnormalities are mainly determined by an abnormal axial control and abnormally small body excursions as a function of support surface tilts, seemingly indicating better postural stabilization than control subjects. The latter contradicts the hypothesis that muscle weakness is the main source for this deficit. Instead, we suggest an altered central control strategy.

Altered postural timing and abnormally low use of proprioception in lumbar spinal stenosis pre- and post- surgical decompression.

BACKGROUND: Lumbar spinal stenosis (LSS) is frequently associated with postural instability. Although several studies evaluated patients' functional impairments, underlying sensorimotor mechanisms are still poorly understood. We aimed to assess the specific set of postural control deficits associated with LSS during spontaneous and externally perturbed stance and evaluated post-surgical changes in postural behavior. METHODS: We analyzed postural control in eleven LSS patients (age 69 ± 8 years) pre- and post-laminectomy, correlated experimental data with functional tests and patient-reported outcomes, and compared findings to 15 matched, healthy control subjects (age 70 ± 6 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by anterior-posterior pseudorandom tilts of the body support surface. We used an established postural control model to extract specific postural control parameters. RESULTS: Spontaneous sway amplitude, velocity and frequency were abnormally large in LSS patients. Furthermore, patients' postural reactions to platform tilts, represented by GAIN and PHASE were significantly altered. Based on simple feedback model simulations, we found that patients rely less on proprioceptive cues for stance regulation than healthy subjects. Moreover, their postural reactions' timing is altered. After surgery, patients' spontaneous sway amplitude was significantly reduced and their postural timing approximated the behavior of healthy subjects. CONCLUSION: The reduction in proprioceptive input for stance control due to stenosis-caused afferent dysfunction is a functional disadvantage for LSS patients - and may be the basis of increased spontaneous sway. This disadvantage may cause the timing of postural reactions to alter, with the intent of preventing rapid changes in stance regulation for safety reasons. After surgery, patients' postural timing approximated those of healthy subjects, while the abnormally low use of proprioception remained unchanged. We suggest the post-surgery rehabilitation of proprioception, eg through balance exercises on unstable surfaces and reduced visual input.

Postural instability in adult ADHD - A pilot study.

BACKGROUND: Apart from inattention, hyperactivity and impulsivity, ADHD in childhood presents with an impairment of motor coordination and balance functions. Until now, literature is scarce about sensorimotor deficits in adult ADHD. This is a pilot study that identifies and quantifies the role of sensory, motor, and central adaptation mechanisms for adult ADHD patients' sensorimotor deficits in a systematic way, using postural control. METHODS: We analyzed spontaneous and externally perturbed stance in ten adult patients suffering from ADHD. Findings were compared to data from ten matched healthy subjects. RESULTS: Spontaneous sway amplitudes and velocities were larger in ADHD patients compared to healthy subjects. Furthermore, body excursions as a function of platform tilts were abnormally large in ADHD patients, specifically in the low frequency range. Based on simple feedback model simulations, we found that ADHD patients showed a larger time delay between platform tilts and body response, and a lower value of the integral part of the neural controller, which affects the long-term control of their posture. These postural abnormalities correlated well with the hyperactivity and impulsivity dimensions of the individual ADHD symptoms. CONCLUSION: We conclude that adult ADHD patients' major postural deficit consists of an impairment of a stable, long-term sensorimotor behavior, which fits very well to the concept of impulsivity and hyperactivity.

Virtual Balancing for Studying and Training Postural Control.

Postural control during free stance has been frequently interpreted in terms of balancing an inverted pendulum. This even holds, if subjects do not balance their own, but an external body weight. We introduce here a virtual balancing apparatus, which produces torque in the ankle joint as a function of ankle angle resembling the gravity and inertial effects of free standing. As a first aim of this study, we systematically modified gravity, damping, and inertia to examine its effect on postural control beyond the physical constraints given in the real world. As a second aim, we compared virtual balancing to free stance to test its suitability for balance training in patients who are not able to balance their full body weight due to certain medical conditions. In a feasibility study, we analyzed postural control during free stance and virtual balancing in 15 healthy subjects. Postural control was characterized by spontaneous sway measures and measures of perturbed stance. During free stance, perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. In the virtual balancing task, we systematically varied the anterior-posterior position of the foot plate where the balancing forces are zero following a similar pseudorandom stimulus profile. We found that subjects' behavior during virtual balancing resembles free stance on a tilting platform. This specifically holds for the profile of body excursions as a function of stimulus frequencies. Moreover, non-linearity between stimulus and response amplitude is similar in free and virtual balancing. The overall larger stimulus induced body excursions together with an altered phase behavior between stimulus and response could be in part explained by the limited use of vestibular and visual feedback in our experimental setting. Varying gravity or damping significantly affected postural behavior. Inertia as an isolated factor had a mild effect on the response functions. We conclude that virtual balancing may be well suited to simulate conditions which could otherwise only be realized in space experiments or during parabolic flights. Further studies are needed to examine patients' potential benefit of virtual balance training.

Balance Training Enhances Vestibular Function and Reduces Overactive Proprioceptive Feedback in Elderly.

Objectives: Postural control in elderly people is impaired by degradations of sensory, motor, and higher-level adaptive mechanisms. Here, we characterize the effects of a progressive balance training program on these postural control impairments using a brain network model based on system identification techniques. Methods and Material: We analyzed postural control of 35 healthy elderly subjects and compared findings to data from 35 healthy young volunteers. Eighteen elderly subjects performed a 10 week balance training conducted twice per week. Balance training was carried out in static and dynamic movement states, on support surfaces with different elastic compliances, under different visual conditions and motor tasks. Postural control was characterized by spontaneous sway and postural reactions to pseudorandom anterior-posterior tilts of the support surface. Data were interpreted using a parameter identification procedure based on a brain network model. Results: With balance training, the elderly subjects significantly reduced their overly large postural reactions and approximated those of younger subjects. Less significant differences between elderly and young subjects' postural control, namely larger spontaneous sway amplitudes, velocities, and frequencies, larger overall time delays and a weaker motor feedback compared to young subjects were not significantly affected by the balance training. Conclusion: Balance training reduced overactive proprioceptive feedback and restored vestibular orientation in elderly. Based on the assumption of a linear deterioration of postural control across the life span, the training effect can be extrapolated as a juvenescence of 10 years. This study points to a considerable benefit of a continuous balance training in elderly, even without any sensorimotor deficits.

Elderly Use Proprioception Rather than Visual and Vestibular Cues for Postural Motor Control.

Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.