Postural Recovery Research Articles

AB1441-HPR Poorer postural control of patients with low back pain compared to a control group

BackgroundChanges in postural control is an important alteration found in Patients With Low Back Pain (LBP). The compromised motor control of the trunk and the alteration of muscle recruitment lead...

A cane improves postural recovery from an unpracticed slip during walking in people with Parkinson disease.

Little is known about the effects of use of a cane on balance during perturbed gait or whether people with Parkinson disease (PD) benefit from using a cane. The purpose of this study was to evaluate the effects of cane use on postural recovery from a slip due to repeated surface perturbations in individuals with PD compared with age- and sex-matched individuals who were healthy. This was a prospective study with 2 groups of participants. Fourteen individuals with PD (PD group) and 11 individuals without PD (control group) walked across a platform that translated 15 cm rightward at 30 cm/s during the single-limb support phase of the right foot. Data from 15 trials in 2 conditions (ie, with and without an instrumented cane in the right hand) were collected in random order. Outcome measures included lateral displacement of body center of mass (COM) due to the slip and compensatory step width and length after the perturbation. Cane use improved postural recovery from the first untrained slip, characterized by smaller lateral COM displacement, in the PD group but not in the control group. The beneficial effect of cane use, however, occurred only during the first perturbation, and those individuals in the PD group who demonstrated the largest COM displacement without a cane benefited the most from use of a cane. Both PD and control groups gradually decreased lateral COM displacement across slip exposures, but a slower learning rate was evident in the PD group participants, who required 6, rather than 3, trials for adapting balance recovery. Future studies are needed to examine the long-term effects of repeated slip training in people with PD. Use of a cane improved postural recovery from an unpracticed slip in individuals with PD. Balance in people with PD can be improved by training with repeated exposures to perturbations.

Biomechanical characteristics of stepping in older Tai Chi practitioners

This study compared the biomechanical characteristics of stepping in 10 older (aged 55+ years) Tai Chi (TC) practitioners and 10 age-matched non-TC (NTC) controls. Subjects were asked to take a step on an auditory cue as fast as possible, in the forward and backward directions, and with and without mental distractions, respectively. Stepping characteristics included step initiation time, preparation time for foot off, foot contact time, and step length and width. The results showed that both groups had similar step initiation time, step length and forward step width (p>0.466). Although mental distraction significantly delayed step initiation time and foot contact time, and shortened step length in both groups (p<0.003), TC practitioners had significantly shorter preparation and foot contact time, and wider backward step width than controls regardless of mental distraction (p<0.024). These group differences are in favor of TC practitioners in situations of postural recovery from potential falls, even with mental distractions, and may explain the positive effect of TC practice on fall reduction in older adults.

The Frog Vestibular System as a Model for Lesion-Induced Plasticity: Basic Neural Principles and Implications for Posture Control

Studies of behavioral consequences after unilateral labyrinthectomy have a long tradition in the quest of determining rules and limitations of the central nervous system (CNS) to exert plastic changes that assist the recuperation from the loss of sensory inputs. Frogs were among the first animal models to illustrate general principles of regenerative capacity and reorganizational neural flexibility after a vestibular lesion. The continuous successful use of the latter animals is in part based on the easy access and identifiability of nerve branches to inner ear organs for surgical intervention, the possibility to employ whole brain preparations for in vitro studies and the limited degree of freedom of postural reflexes for quantification of behavioral impairments and subsequent improvements. Major discoveries that increased the knowledge of post-lesional reactive mechanisms in the CNS include alterations in vestibular commissural signal processing and activation of cooperative changes in excitatory and inhibitory inputs to disfacilitated neurons. Moreover, the observed increase of synaptic efficacy in propriospinal circuits illustrates the importance of limb proprioceptive inputs for postural recovery. Accumulated evidence suggests that the lesion-induced neural plasticity is not a goal-directed process that aims toward a meaningful restoration of vestibular reflexes but rather attempts a survival of those neurons that have lost their excitatory inputs. Accordingly, the reaction mechanism causes an improvement of some components but also a deterioration of other aspects as seen by spatio-temporally inappropriate vestibulo-motor responses, similar to the consequences of plasticity processes in various sensory systems and species. The generality of the findings indicate that frogs continue to form a highly amenable vertebrate model system for exploring molecular and physiological events during cellular and network reorganization after a loss of vestibular function.

Postural recovery following voluntary arm movement is impaired in people with chronic low back pain

Study designRecovery of postural equilibrium following bilateral voluntary arm movement was evaluated using a case-control study, with 13 subjects with chronic LBP and 13 age- and gendermatched control subjects. ObjectivesTo evaluate control of the centre-of-pressure (COP), as a marker of the quality of control of postural equilibrium associated with voluntary arm movements, in people with and without LBP. Summary of background data. When healthy individuals perform rapid voluntary arm movements, small spinal movements (preparatory movement) opposite to the direction of the reactive moments precede voluntary arm movements. Evaluation of trunk movement in people with LBP suggests that this strategy is used infrequently in this population and is associated with an increased spinal displacement following arm flexion. As the preparatory spinal movement was also thought to be an anticipatory mechanism limiting postural perturbation caused by arm movements, we hypothesized that LBP subjects would have compromised control of postural equilibrium following arm flexion. MethodsSubjects performed bilateral voluntary rapid arm flexion while standing on support surface of different dimensions with eyes opened or closed. ResultsResults indicated that people with LBP consistently took longer to recover postural equilibrium and made more postural adjustments in different stance conditions. However, there was no increase in the excursion of the COP during the recovery period in the LBP group. ConclusionThese data suggest that while COP is tightly controlled during postural recovery, the finetuning of the control of postural equilibrium is compromised in people with LBP. Postural control dysfunctions should be considered in the management of chronic low back pain.

Postural control under visual and proprioceptive perturbations during double and single limb stances: Insights for balance training

Single Limb Stance under visual and proprioceptive disturbances is largely used in clinical settings in order to improve balance in a wide range of functional disabilities. However, the proper role of vision and proprioception in SLS is not completely understood. The objectives of this study were to test the hypotheses that when ankle proprioception is perturbed, the role of vision in postural control increases according to the difficulty of the standing task. And to test the effect of vision during postural adaptation after withdrawal of the somesthetic perturbation during double and single limb stance Eleven males were submitted to double (DLS) and single limb (SLS) stances under conditions of normal or reduced vision, both with normal and perturbed proprioception. Center of pressure parameters were analyzed across conditions. Vision had a main effect in SLS, whereas proprioception perturbation showed effects only during DLS. Baseline stability was promptly achieved independently of visual input after proprioception reintegration. In conclusion, the role of vision increases in SLS. After proprioception reintegration, vision does not affect postural recovery. Balance training programs must take that into account.

Postural muscle recovery under lowered oxygen concentration after prolonged disuse

Postural muscle recovery under lowered oxygen concentration after prolonged disuse

Changes in Lumbar Movement in People With Low Back Pain Are Related to Compromised Balance

Comparing people with and without low back pain (LBP). This study aimed to investigate lumbar spine movement and the quality of postural recovery in response to unexpected postural perturbation in people with LBP. People with chronic LBP tend to use lumbar spine motion less frequently for postural control than pain-free individuals, and after voluntary arm movement, they need more time and a greater number of postural adjustments to regain postural equilibrium. We hypothesize that motion of the lumbar spine is altered in people with chronic LBP, and this would be associated with compromised control of postural stability in response to unexpected perturbation. The response to a sudden load imposed by a weight dropped into a box held in the hands was studied in 11 individuals with chronic LBP and matched controls. Lumbopelvic motion was recorded with an electromagnetic motion analysis system. Time to recover balance was calculated from ground reaction forces. People with LBP had a delayed initiation of lumbar spine flexion (angular displacement) (Control = 44.9 [25.1] ms, LBP = 90.2 [42.3] ms, P < 0.001) and took longer to regain postural stability (Control = 460.4 [123.4] ms, LBP = 761.0 [194.2] ms, P < 0.001) after the perturbation. These data provide further evidence that the quality of balance control is compromised in LBP patients and that this is associated with poor use of spinal motion as a component of the postural strategy.

Influence of galvanic vestibular stimulation on postural recovery during sudden falls

To assess vestibular influences on recovery of balance during sudden falls, we measured the postural responses of five healthy subjects to a hold and release perturbation coupled with galvanic vestibular stimulation (GVS). Two electrode pairs were located with the anterior electrode of each pair over the mastoid process and the posterior electrode over the trapezius muscle on the same side. Bilateral unipolar GVS was generated 60 ms after a holding force against the sternum was released by individually driving left and right electrode pairs as cathode or anode at 1 mA for 12 s or 2 mA for 6 s. We computed the frequency and damping parameters of a multi-link inverted pendulum model of the body which best fit the transient postural oscillations after release for each subject. These parameters did not differ significantly across conditions indicating the GVS did not modify the preset overall strategy of postural recovery. The intensity and polarity of GVS significantly biased both the postural lean during the oscillatory period and the resting postural stance achieved during stimulation, deviating them forward for cathodal stimulation and backward for anodal. The residuals of the multi-link fit, the frequency spectra of the actual body sway ripples about the modeled sway, were different across conditions. Because GVS affected postural bias but not dynamics, it is likely that it provided erroneous velocity signals leading to vestibulospinal compensations in segmental stiffness and damping mechanisms. Our findings are consistent with theoretical analyses of the influence of GVS on the semicircular canals and otolith organs of the inner ear.

Human postural control against external force perturbation applied to the high-back

Many studies have reported postural control against support surface translation. However, postural control mechanism against external force perturbation is not clear. Therefore, in this study we investigated the postural recovery against external force (1∼4Kg) applied to the high-back in health young male subjects (24±4 years). Kinematic data and center of pressure of the reaction to an unexpected perturbation were analyzed. Experimental results showed that the hill-lifting strategy with ankle plantarflexion and knee hyperextension was used in all subjects, regardless of the force magnitude. Specifically, maximum ankle plantarflexion and hip flexion increased with the perturbation force magnitude, the heel vertical excursion and anterior COP excursion. The results of this study show that the postural control strategy for the external force perturbation is quite different from that for surface translation and needs further investigation.

Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints

Investigations of postural recovery following controlled external perturbations have provided models for healthy and pathological balance behavior. Less work, however, has investigated postural responses related to internal perturbations of the balance system. In this study, lower extremity joint (knee, or ankle) and overall fatigue of the dominant leg provided the internal perturbations to the balance system. Postural sway was examined during unilateral dominant leg standing before and immediately following fatiguing exercise, as well as at 10, 20, and 30 min post-fatigue activity. Sway was measured in both firm and sway-referenced support surface (external perturbation) conditions. Both joint-localized fatigue and overall fatigue were found to induce impairments in postural control, which were further exacerbated by external postural perturbations. Follow-up pairwise comparisons indicated that these impairments persisted at 10 and 30 min post-fatigue. No differences in postural sway were found between fatigue locations or across any interactions between sway and fatigue location. The results indicated that muscular fatigue imposed a prolonged internal perturbation to postural control, regardless of any individual or combined joint fatigue localization. This global effect, combined with the prolonged impairment in postural response, provides support for critical contributions from a central mechanism to postural deficits due to fatigue.

Balance control in the elderly: do Masters athletes show more efficient balance responses than healthy older adults?

Older adults can improve several components of their balance such as timed stance ability by participating in a short specific exercise program. However, it is not clear whether participation in more frequent and intense training can result in improved reactive balance performance in older adults. Optimal reactive responses are required to prevent falls. This study begins to evaluate this issue by comparing the reactive balance ability of elite older adults (Masters athletes) to that of healthy older adults. Kinetic and electromyography data were collected from elite older athletes and healthy older adults during backward linear underfoot perturbations at high and low speeds. Behavioral outcomes of postural recovery strategy, timing and levels of muscular activation, and time to stabilize the displaced center of pressure were measured and compared between groups. The elite older athletes were able to more frequently regain balance without stepping, stabilized their center of pressure faster than did healthy older adults and activated their tibialis anterior with a greater magnitude when perturbed at the higher speed. There were no differences between groups in these measures at the lower perturbation speed and no differences in onset latencies at either speed. Older athletes undertaking longterm high intensity training demonstrate better and more rapid stabilization of posture following perturbation than healthy older adults under challenging conditions. Further studies are advocated to determine the relative contribution of processes such as neuromotor adaptation, strength, motivation and arousal to this finding.

Intermittent postural recovery during 14 days of hindlimb unloading (HU) is not sufficient to restore cardiac autonomic imbalance in rats

Previous data indicate that 14 days of continuous HU in rats produces cardiac autonomic imbalance. We hypothesized that a daily period of normal posture may resolve these effects. Male, Sprague‐Dawley rats were randomly assigned to control (CC; n=3), continuous HU (HUC; n=4) or intermittent HU (HUI; n= 5) groups. Control rats were maintained in the normal posture. HUC rats underwent continuous elevation of the hindlimbs for 14‐days while HUI rats were returned to the normal posture for 30 minutes each day during the HU procedure. On the 14th day, mean arterial pressure (MAP) and heart rate (HR) were measured followed by selective cardiac autonomic blockade administered via i.v. injection of methylatropine and propranolol. Both HU groups exhibited significant resting tachycardia compared to CC rats, but HR was lower in HUI vs. the HUC group (CC: 366±3.9; HUC 474±7.5; HUI: 434±1.6 bpm). However, both HU groups had significantly less parasympathetic (CC: 60±7.7; HUC: 25±10.9; HUI: 15±5.2 Δbpm) and greater sympathetic cardiac tone (CC: 16±7.9; HUC: 91±10.9; HUI: 77±9.2 Δbpm) than CC rats, with no difference between HU groups with respect to either autonomic parameter. Baseline MAP was not different among any of the groups. Data indicate that while daily recovery from HU may partially restore resting HR, it is not a sufficient stimulus to reverse the autonomic imbalance produced by HU‐induced deconditioning. (Supp. by: NIH HL14388 &amp; DK 066086).

A model of cerebellum stabilized and scheduled hybrid long-loop control of upright balance.

A recurrent integrator proportional integral derivative (PID) model that has been used to account for cerebrocerebellar stabilization and scaling of transcortical proprioceptive feedback in the control of horizontal planar arm movements has been augmented with long-loop force feedback and gainscheduling to describe the control of human upright balance. The cerebellar component of the controller is represented by two sets of gains that each provide linear scaling of same-joint and interjoint long-loop stretch responses between ankle, knee, and hip. The cerebral component of the model includes a single set of same-joint linear force feedback gains. Responses to platform translations of a three-segment body model operating under this hybrid proprioception and force-based long-loop control were simulated. With low-velocity platform disturbances, "ankle-strategy"-type postural recovery kinematics and electromyogram (EMG) patterns were generated using the first set of cerebeller control gains. With faster disturbances, balance was maintained by including the second set of gains cerebellar control gains that yielded "mixed ankle-hip strategy"-type kinematics and EMG patterns. The addition of small amounts of simulated muscular coactivation improved the fit to certain human datasets. It is proposed that the cerebellum switches control gainsets as a function of sensed body kinematic state. Reduction of cerebellar gains with a compensatory increase in muscular stiffness yielded posture recovery with abnormal motions consistent with those found in cerebellar disease. The model demonstrates that stabilized hybrid long-loop feedback with scheduling of linear gains may afford realistic balance control in the absence of explicit internal dynamics models and suggests that the cerebellum and cerebral cortex may contribute to balance control by such a mechanism.

Outcomes in vestibular ablative procedures.

To assess dizziness handicap and postural recovery in 17 patients undergoing a vestibular ablative procedure. Outcomes were compared between nine patients who underwent selective vestibular neurectomy and eight patients who underwent a transmastoid labyrinthectomy. Patients underwent ablative procedures at a tertiary care facility. Patients were tested with posturography (sensory organization test [SOT]) and the Dizziness Handicap Inventory (DHI) before and 4 to 5 weeks after their procedure. The mean change scores for each of the DHI subscales and the total DHI score showed significant improvement for the labyrinthectomy group. For the neurectomy group, only the emotional DHI subscale change score showed significant improvement. No difference was noted between preprocedure and postprocedure SOT scores for either group. The results indicated that the largest proportion of significant correlations existed between DHI and the somatosensory and vestibular subtests of platform posturography. In regression analyses, a model with age (p = 0.04) and vestibular score (p = 0.001) fitted the data well and explained 52.9% of the variance. Persons who were less than 69 years old were three times more likely to report persistent episodes of dizziness after the ablative procedure, and those who had neurectomies were 2.3 times more likely to report episodes of dizziness than those who underwent transmastoid labyrinthectomy. Dizziness handicap after an ablative procedure is influenced by the type of procedure (labyrinthectomy versus neurectomy), age, and preoperative vestibular score on the SOT. Preoperative vestibular SOT score is highly associated with the emotional, physical, and functional domains of perceived handicap and quality of life after the surgery.

The influence of a concurrent cognitive task on the compensatory stepping response to a perturbation in balance-impaired and healthy elders.

This study investigated the influence of a concurrent cognitive task on the compensatory stepping response in balance-impaired elders and the attentional demand of the stepping response. Kinetic, kinematic and neuromuscular measures of a forward recovery step were investigated in 15 young adults, 15 healthy elders and 13 balance-impaired elders in a single task (postural recovery only) and dual task (postural recovery and vocal reaction time task) situation. Results revealed that reaction times were longer in all subjects when performed concurrently with a compensatory step, they were longer for a step than an in-place response and longer for balance-impaired older adults compared with young adults. An interesting finding was that the latter group difference may be related to prioritization between the two tasks rather than attentional demand, as the older adults completed the step before the reaction time, whereas the young adults could perform both concurrently. Few differences in step characteristics were found between tasks, with the most notable being a delayed latency and reduced magnitude of the early automatic postural response in healthy and balance-impaired elders with a concurrent task.

How do non-muscular torques contribute to the kinetics of postural recovery following a support surface translation?

The common platform translation paradigm used in balance control studies employs a disturbance event that applies non-muscular forces to the body for the duration of the disturbance. Previous research has explored the process of constructing the balance recovery by considering these perturbations to be trigger events, not events with an ongoing force application timeline. The purpose of this study was to quantify the effect of muscular and non-muscular torques on post-perturbation balance with particular interest in the role of the external perturbation in balance recovery. Five young adult males experienced backward translations of the support surface at three different speeds. Integration intervals were defined for each segment and angular impulses were calculated for a period of increasing angular momentum (destabilization), and a period of decreasing angular momentum (restabilization). Destabilization of distal segments was primarily due to impulse generated by the motion of the support surface. For the trunk, however, muscle and motion-dependent sources contributed most to increasing momentum. Restabilization of distal segments was achieved by muscle and platform impulses while trunk restabilization was achieved by muscle and motion-dependent terms in opposition to gravity. Increased platform speed resulted in increased muscular contribution only in the control of the trunk, while demand on distal musculature decreased with change in platform speed as the platform contribution to restabilization increased in these segments. Therefore, impulses from non-muscular sources, including the perturbation itself, are significant modifiers of the response to balance disturbances and must be accounted for in balance research.

Dissociations between behavioural recovery and restoration of vestibular activity in the unilabyrinthectomized guinea-pig.

1. In the guinea-pig, a unilateral labyrinthectomy induces postural disturbances and an ocular nystagmus which abate or disappear over time. These behavioural changes are accompanied by an initial collapse and a subsequent restoration of the spontaneous activity in the neurones of the ipsilateral vestibular nuclei. Recently, it has been shown that the vestibular neuronal activity remained collapsed over at least 10 h whereas its restoration was complete 1 week after the lesion. The aims of this study were to determine when restoration of spontaneous activity in the partially deafferented vestibular neurones started and to compare the time courses of the behavioural and neuronal recoveries in guinea-pigs that had undergone a unilateral labyrinthectomy. 2. Neuronal discharge measurements were made using chronic extracellular recording of single unit activity. After a left labyrinthectomy, electrodes, were placed on the site of the destroyed labyrinth to enable stimulation of the left vestibular nerve. Behavioural measurements included chronic recording of eye movements by the scleral search coli technique. After a left labyrinthectomy, lateral deviation of the head, twisting of the head, and eye velocity of the slow phases of the nystagmus were measured. 3. The neuronal activity of the rostral part of the vestibular nuclear complex on the lesioned side was recorded in alert guinea-pigs over 4 h recording sessions between 12 and 72 h after the lesion. 4. The criterion used to select vestibular neurones for analysis was their recruitment by an electric shock on the vestibular nerve. In addition, in order to explore a uniform population, we focused on neurones recruited at monosynaptic latencies (0.85-1.15 ms). 5. For each recording period, the mean resting rate was calculated animal by animal and the grand mean of these individual resting rate means was calculated. Previously, a decline in the grand mean resting rate from 35.8 +/- 6.0 spikes s-1 (control state) to 7.1 +/- 4.2 spikes s-1 during the first 4 h after labyrinthectomy has been shown. In the present study, the first sign of recovery was observed during the 12-16 h recording period when the resting rate grand mean increased to 16.3 +/- 3.9 spikes s-1. This grand mean activity did not change significantly during the following 12 h. Thereafter, restoration of neuronal activity improved and was complete 1 week after the lesion. 6. Although the abatement of the vestibular symptoms roughly paralleled the restoration of neuronal activity in the vestibular nuclei, some discrepancies between the time courses of both phenomena emerged. An important step in postural recovery (the animals managed to stand up) and a major part of the abatement of the nystagmus occurred before the recovery of vestibular neuronal activity. In addition, lateral deviation of the head disappeared while restoration of the neuronal activity was incomplete, but significant head twisting was still evident when vestibular resting rates had recovered completely. 7. We conclude that restoration of neuronal activity in the ipsilateral vestibular nuclei starts 12 h after the lesion and that restoration of neuronal activity in the ipsilateral vestibular nuclei is not the only mechanism underlying behavioural vestibular compensation.

Spinal plasticity after hemilabyrinthectomy and its relation to postural recovery in the frog

1. Brachial dorsal root-evoked ventral root responses were studied in the isolated brain/spinal cord preparation of frogs. One group of frogs (n = 20) had survived a hemilabyrinthectomy (HL) between 7 and 70 days. In another group of frogs (n = 30), a nerve branch to an individual labyrinthine organ was sectioned uni- or bilaterally 15 days before the recording session. In a third group of frogs (n = 5), a weight had been mounted eccentrically on the head for 15 days. A fourth group of intact frogs (n = 8) served as a control. 2. In chronic HL frogs (> or = 60 days postoperatively) the amplitudes of short- and long-latency ventral root potentials recorded on the operated side were consistently increased with respect to control values in response to all converging inputs tested. On the intact side most of these potentials were consistently increased as well, except for crossed long-latency responses after stimulation of the dorsal root on the operated side. 3. Practically identical responses were recorded in these preparations before and after the disconnection of the spinal cord from the brain stem at the level of the obex. Before this disconnection, ventral root potentials were recorded in response to electric stimulation of either one of the VIIIth nerves on the intact or on the operated side. Ventral root potentials recorded on the operated but not on the intact side were slightly increased in chronic HL frogs. 4. The time course of these changes was studied at intervals between 7 and 70 days after the lesion. The amplitudes of short-latency dorsal root-evoked ventral root potentials were increased relatively early (7-15 days) or relatively late (> or = 30 days) after HL. Ventral root potentials evoked by stimulation of either one of the N.VIII were significantly reduced in amplitude seven days after HL but normalized again or increased above control values after longer survival periods. These differences in the time courses suggest the presence of multiple, not singular mechanisms for intraspinal changes. 5. Changes in dorsal root-evoked ventral root potentials similar to those after HL were seen 15 days after a selective unilateral section of the utricular, but not after a unilateral section of the horizontal canal or saccular nerve branch. Therefore these changes were initiated either by asymmetric utricular afferent inputs or by asymmetric proprioceptive inputs resulting from lesion-induced postural deficits. 6. These two possibilities were investigated in two different sets of experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Alpha-Difluoromethylornithine delays behavioral recovery and induces decompensation after unilateral labyrinthectomy.

Biochemical and pharmacologic studies suggest a role for the ornithine decarboxylase-polyamine system as a modulator of behavioral changes during vestibular compensation. alpha-Difluoromethylornithine specifically blocks the rate-limiting step of polyamine biosynthesis. To assess the effects of alpha-difluoromethylornithine on the acute phase of postural compensation, guinea pigs were divided into groups subjected to either unilateral labyrinthectomy only (n = 7), alpha-difluoromethylornithine (500 mg/kg/day) for 4 days before labyrinthectomy (n = 10), equivalent volumes of saline for 4 days before labyrinthectomy (n = 8), and sham operations (n = 5). Yaw head tilt and roll head tilt, trunk curvature, and air-righting reflex were measured at baseline and at regular intervals up to 4 weeks. alpha-Difluoromethylornithine significantly delayed recovery of normal air-righting but had no effect on yaw head tilt, roll head tilt, and trunk curvature. We also evaluated effects of alpha-difluoromethylornithine in compensated guinea pigs. Fully compensated animals from phase 1 were randomly assigned to receive alpha-difluoromethylornithine (500 mg/kg/day) or saline once daily for 4 days. Only 33% of alpha-difluoromethylornithine animals maintained air-righting, compared with 100% of saline-treated animals (p = 0.003). Maximum trunk curvature was greater in the alpha-difluoromethylornithine group (p = 0.02). Thus alpha-difluoromethylornithine not only delayed the time course for postural recovery after unilateral labyrinthectomy, it also transiently disrupted the maintenance of the compensated state.