Head-trunk Coordination Research Articles

Modifications to head-trunk coordination dynamics during running and sidestepping

ABSTRACT The purpose of this study was to determine how the intrinsic head-trunk coordination dynamics that exist during forward running are modified during a dynamic sidestepping task. Fourteen athletes performed both forward running and sidestepping tasks. Head-trunk coordination and range of motion were assessed during the flight and stance phases in the transverse and sagittal planes. The sidestepping task resulted in greater in-phase head-trunk coordination during stance in the transverse plane (p < .001, ES = −1.71) and in reduced anti-phase coordination between head and trunk in the sagittal plane (p < .001, ES = 1.52). Statistical non-parametric mapping revealed that during sidestepping the sagittal plane coupling angle shifted away from anti-phase earlier during midstance. The sidestepping task resulted in greater transverse and sagittal plane head and trunk range of motion and greater vertical trunk centre of mass displacement. Sidestepping modified the intrinsic coordination dynamics that are present during forward running, with greater transverse plane head contributions and reductions in compensatory sagittal plane head motion, which may occur during the transition from weight acceptance to propulsion during the stance phase. These changes in the intrinsic coordination dynamics of the upper body during sidestepping tasks may impact visual perception and readiness compared to forward running during complex sports tasks.

Head control and head-trunk coordination as a function of anticipation in sidestepping

ABSTRACT Head reorientation precedes body reorientation during direction change to facilitate gaze realignment, thus enhancing perceptual awareness. Whole body kinematics are dependent on the available planning time. The purpose of this study was to assess the role of anticipation on head control and head-trunk coordination during sidestepping tasks. Fourteen male collegiate athletes performed anticipated and unanticipated sidestepping tasks. Transverse plane head, trunk and heading direction, as well as head-trunk coordination were assessed. During change of direction tasks, we observed greater head orientation towards the new travel direction, followed by heading direction and then trunk direction during both anticipated and unanticipated tasks. With reduced planning time, heading in the preparatory phase and trunk rotation in the preparatory and stance phases were significantly less oriented towards the new travel direction, with no differences in head rotation. During anticipated sidestepping, significantly greater in-phase coordination was observed during the preparatory phase compared to unanticipated sidestepping. Head reorientation facilitates gaze realignment and may be prioritized irrespective of planning time during sidestepping tasks. During anticipated trials, the head and trunk move more synchronously compared to unanticipated sidestepping, highlighting the potential benefits of aligning the degrees of freedom earlier in the change of direction stride and optimizing perceptual awareness.

Early Blindness Limits the Head-Trunk Coordination Development for Horizontal Reorientation

During locomotion, goal-directed orientation movements in the horizontal plane require a high degree of head-trunk coordination. This coordination is acquired during childhood. Since early visual loss is linked to motor control deficits, we hypothesize that it may also affect the development of head-trunk coordination for horizontal rotations. However, no direct evidence exists about such a deficit. To assess this hypothesis, we tested early blind and sighted individuals on dynamic sound alignment through a head-pointing task with sounds delivered in acoustic virtual reality. Participants could perform the head-pointing with no constraints, or they were asked to immobilize their trunk voluntarily. Kinematics of head and trunk were assessed individually and with respect to each other, together with spatial task performance. Results indicated a head-trunk coordination deficit in the early blind group; yet, they could dampen their trunk movements so as not to let their coordination deficit affect spatial performance. This result highlights the role of vision in the development of head-trunk coordination for goal-directed horizontal rotations. It also calls for clarification on the impact of the blindness-related head-trunk coordination deficit on the performance of more complex tasks akin to daily life activities such as steering during locomotion or reaching to targets placed sideways.

Eye–Head–Trunk Coordination While Walking and Turning in a Simulated Grocery Shopping Task

Previous studies argued that body turns are executed in an ordered sequence: the eyes turn first, followed by the head and then by the trunk. The purpose of this study was to find out whether this sequence holds even if body turns are not explicitly instructed, but nevertheless are necessary to reach an instructed distal goal. We asked participants to shop for grocery products in a simulated supermarket. To retrieve each product, they had to walk down and aisle, and then turn left or right into a corridor that led towards the target shelf. The need to make a turn was never mentioned by the experimenter, but it nevertheless was required in order to approach the target shelf. Main variables of interest were the delay between eye and head turns towards the target shelf, as well as the delay between head and trunk turns towards the target shelf. We found that both delays were consistently positive, and that their magnitude was near the top of the range reported in literature. We conclude that the ordered sequence of eye – then head – then trunk turns can be observed not only with a proximal, but also with a distal goal.

Changes in coordination and variability during running as a function of head stability demands.

The purpose of this study was to identify changes in segment/joint coordination and coordination variability in running with increasing head stability requirements. Fifteen strides from twelve recreational runners while running on a treadmill at their preferred speed were collected. Head stability demands were manipulated through real-time visual feedback that required head-gaze orientation to be contained within boxes of different sizes, ranging from 21 to 3 degrees of visual angle in 3-degree decrements. Coordination patterns and coordination variability were assessed between head and trunk segments, hip and knee joints, and knee and ankle joints in the three cardinal planes, respectively. Mean coupling angles and the standard deviation of the coupling angles at each individual point of the stance phase were calculated using a modified vector coding technique and circular statistics. As head stability demands increased, transverse plane head-trunk coordination was more anti-phase and showed increased head‑leading and decreased trunk‑leading patterns; for the lower extremity, there was increased in-phase and decreased anti-phase sagittal plane coordination. Increased head stability demands also resulted in an increase in coordination variability for both upper body and lower extremity couplings during the second half of the stance phase. Overall, the results provide evidence that coordinative adaptations to increasing head stability demands occur throughout the entire body: 1) through more independent control of the head relative to the trunk; 2) by increasing in-phase coordination between lower extremity joints, and 3) through increased coordination variability in the second half of stance in both upper body segmental and lower extremity joint couplings. These adaptations likely contribute to the reduction of the range of motion of the trunk in vertical direction.

Changes In Coordination And Variability During Running As A Function Of Head Stability Demands

Stabilization of the head in space is important during running, but less is known about how individuals accomplish the head-in-space equilibrium through segmental and joint coordinative adaptations. PURPOSE: To identify changes in segment/joint coordination and its variability in running with increasing head stability requirements. METHODS: Fifteen strides from twelve recreational runners (29.67 ± 4.4 years; 1.73 ± 0.08 m; 72.1 ± 13.9 kg) while running on a treadmill at their preferred speed were collected. Head stability demands were manipulated through real-time visual feedback that required head-gaze orientation to maintain within boxes of different sizes, ranging from 21 to 3 degrees of visual angle with 3-degree decrements. Coordination patterns and variability were assessed between head and trunk segments, hip and knee joints, and knee and ankle joints in three cardinal planes, respectively. Mean phase angles and the standard deviation of the phase angles at each individual point of the stance phase were calculated using vector coding and circular statistics. A statistical analysis was performed to detect differences in coordination pattern frequency and waveform of coordination pattern and variability between visual conditions. RESULTS: As head stability demands increased, transverse plane head-trunk coordination was more anti-phase (i.e., segments rotating the opposite direction; 3.3%, p=0.028), and showed increased head-leading (1.7%, p=0.001) and decreased trunk-leading patterns (10.3%, p=0.015); for the lower extremity, there was increased in-phase (hip-knee: 5%, p=0.015; knee-ankle: 6.4%, p=0.010) and decreased anti-phase (hip-knee: 16.7%, p=0.003; knee-ankle: 10.8%, p=0.001) sagittal plane coordination during the second half of the stance phase. An increase in coordination variability was also observed for lower extremity couplings between the hip and knee and knee and ankle joints. CONCLUSION: Overall, the results provide evidence that coordinative adaptations to increasing head stability demands occur throughout the entire body (1) through more independent control of the head relative to the trunk, and (2) by increasing in-phase coordination and variability between lower extremity joints, contributing to the reduction of range of motion in vertical direction.

Can a simple clinical test demonstrate head-trunk coordination impairment in neck pain?

BackgroundSensorimotor impairment in neck pain sufferers is well established. Recent research has identified impairment in head and trunk co-ordination in this population. Presently, no clinically appropriate testing exists to quantify such impairment. ObjectiveTo determine if a simple and clinically relevant test of head-trunk co-ordination can identify dysfunction in neck pain subjects when compared to healthy controls. Study designCross-sectional observational study. MethodsThirty-one neck pain and 29 healthy control subjects were assessed using head- and chest-mounted lasers with a target positioned 90 cm away. Subjects were required to rotate the trunk at least 45° with the head laser to be kept as accurately as possible in the centre of the target while sitting and standing. Maximal deviation of the head to the left and right of the target's centre with each trunk movement was measured. ResultsThe neck pain group demonstrated significantly greater head deviation from the centre in all but one test direction (p= <0.03). Head deviation to the same side as trunk rotation was larger in the neck pain group for both sitting and standing (p= <0.01). No significant differences existed between testing in sitting and standing. ConclusionDifferences in trunk-head control exist in persons suffering from neck pain compared to healthy individuals, which can be demonstrated using simple equipment suggesting clinical utility of the measure. Performing the task in standing would seem most suitable as it can avoid influence by reduced thoracic mobility. Further research is required to establish the clinical suitability of this test.

Reduced Purposeful Head Movements During Community Ambulation Following Unilateral Vestibular Loss

Background. Individuals with unilateral vestibular hypofunction (UVH) alter their movement and reduce mobility to try to stabilize their gaze and avoid symptoms of dizziness and vertigo. Objective. To determine if individuals with UVH 6 weeks after surgery demonstrate altered head and trunk kinematics during community ambulation. Methods. A total of 15 vestibular schwannoma patients with documented postoperative unilateral vestibular loss and 9 healthy controls with symmetrical vestibulo-ocular reflexes participated in this cross-sectional study. Head kinematics (head turn frequency, amplitude, and velocity) and head-trunk coordination during community ambulation were obtained from inertial measurement units for all head movements and within specific amplitudes of head movement. Results. Individuals with UVH made smaller (mean 26° [SD = 3°] vs 32° [SD = 6°]), fewer (mean 133 [SD = 59] vs 221 [SD = 64]), and slower (mean 75°/s [SD = 8°/s] vs 103°/s [SD = 23°/s]) head turns than healthy individuals (P < .05) but did not demonstrate significantly increased head-trunk coupling (mean 38% [SD = 18%] vs 31% [SD = 11%], P = .22). When small (≤45°) and large (>45°) head turns were considered separately, individuals with UVH demonstrated increased head-trunk coupling compared with healthy individuals for large head turns (mean 54% [SD = 23%] vs 33% [SD = 10%], P = .005). Conclusions. This study demonstrated that although walking at an adequate speed, individuals with UVH made fewer, smaller, and slower head movements symmetrically in both directions compared with healthy individuals and did not decouple their head movement relative to their trunk when required to make larger purposeful head turns during community ambulation.

Characterization of Head-Trunk Coordination Deficits After Unilateral Vestibular Hypofunction Using Wearable Sensors

Individuals with vestibular hypofunction acutely restrict head motion to reduce symptoms of dizziness and nausea. This restriction results in abnormal decoupling of head motion from trunk motion, but the character, magnitude, and persistence of these deficits are unclear. To use wearable inertial sensors to quantify the extent of head and trunk kinematic abnormalities in the subacute stage after resection of vestibular schwannoma (VS) and the particular areas of deficit in head-trunk motion. This cross-sectional observational study included a convenience sample of 20 healthy adults without vestibular impairment and a referred sample of 14 adults 4 to 8 weeks after resection of a unilateral VS at a university and a university hospital outpatient clinic. Data were collected from November 12, 2015, through November 17, 2016. Functional gait activities requiring angular head movements, including items from the Functional Gait Assessment (FGA; range, 1-30, with higher scores indicating better performance), the Timed Up & Go test (TUG; measured in seconds), and a 2-minute walk test (2MWT; measured in meters). Primary outcomes included peak head rotation amplitude (in degrees), peak head rotation velocity (in degrees per second), and percentage of head-trunk coupling. Secondary outcomes were activity and participation measures including gait speed, FGA score, TUG time, 2MWT distance, and the Dizziness Handicap Inventory score (range, 0-100, with higher scores indicating worse performance). A total of 34 participants (14 men and 20 women; mean [SD] age, 39.3 [13.6] years) were included. Compared with the 20 healthy participants, the 14 individuals with vestibular hypofunction demonstrated mean (SD) reduced head turn amplitude (84.1° [15.5°] vs 113.2° [24.4°] for FGA-3), reduced head turn velocities (195.0°/s [75.9°/s] vs 358.9°/s [112.5°/s] for FGA-3), and increased head-trunk coupling (15.1% [6.5%] vs 5.9% [5.8%] for FGA-3) during gait tasks requiring angular head movements. Secondary outcomes were also worse in individuals after VS resection compared with healthy individuals, including gait speed (1.09 [0.27] m/s vs 1.47 [0.22] m/s), FGA score (20.5 [3.6] vs 30.0 [0.2]), TUG time (10.9 [1.7] s vs 7.1 [0.8] s), 2MWT (164.8 [37.6] m vs 222.6 [26.8] m), and Dizziness Handicap Inventory score (35.4 [20.7] vs 0.1 [0.4]). With use of wearable sensors, deficits in head-trunk kinematics were characterized along with a spectrum of disability in individuals in the subacute stage after VS surgery compared with healthy individuals. Future research is needed to fully understand how patterns of exposure to head-on-trunk movements influence the trajectory of recovery of head-trunk coordination during community mobility.

Feasibility and Validity of Discriminating Yaw Plane Head-on-Trunk Motion Using Inertial Wearable Sensors.

A consequence of vestibular loss is increased coupling of head-on-trunk motion, particularly in the yaw plane, which adversely affects community mobility in these patients. Inertial sensors may provide a means of better understanding normal decoupling behaviors in community environments, but demonstration of their validity and responsiveness is needed. This paper examined the validity and measurement sensitivity of inertial sensors in quantifying yaw plane head-trunk decoupling during unrestricted and restricted cervical motion conditions in healthy adults. Peak head turn amplitude and velocity, head-trunk coupling, and trunk turn lag were simultaneously measured using wearable inertial sensors and a motion capture system. Agreement between motion capture and the inertial sensors was excellent (intraclass correlation coefficients(2,1) >.75) for all measured outcomes during a static head turn task and for peak head turn velocity and trunk turn lag during a walking task. Cervical collar use significantly reduced head turn amplitude and velocity, and increased coupling of head-on-trunk motion (p<.02). Measurement of head and trunk coordination during gait activities using inertial sensors is valid and feasible. Amplitude and velocity outcomes were most reliable and responsive to experimental alterations in head motion. Using inertial sensors to quantify abnormal kinematics following vestibular loss may provide insights into recovery of head-trunk coordination in these individuals.

Head Stability and Head-Trunk Coordination in Horseback Riders: The Contribution of Visual Information According to Expertise.

Maintaining equilibrium while riding a horse is a challenging task that involves complex sensorimotor processes. We evaluated the relative contribution of visual information (static or dynamic) to horseback riders' postural stability (measured from the variability of segment position in space) and the coordination modes they adopted to regulate balance according to their level of expertise. Riders' perceptual typologies and their possible relation to postural stability were also assessed. Our main assumption was that the contribution of visual information to postural control would be reduced among expert riders in favor of vestibular and somesthetic reliance. Twelve Professional riders and 13 Club riders rode an equestrian simulator at a gallop under four visual conditions: (1) with the projection of a simulated scene reproducing what a rider sees in the real context of a ride in an outdoor arena, (2) under stroboscopic illumination, preventing access to dynamic visual cues, (3) in normal lighting but without the projected scene (i.e., without the visual consequences of displacement) and (4) with no visual cues. The variability of the position of the head, upper trunk and lower trunk was measured along the anteroposterior (AP), mediolateral (ML), and vertical (V) axes. We computed discrete relative phase to assess the coordination between pairs of segments in the anteroposterior axis. Visual field dependence-independence was evaluated using the Rod and Frame Test (RFT). The results showed that the Professional riders exhibited greater overall postural stability than the Club riders, revealed mainly in the AP axis. In particular, head variability was lower in the Professional riders than in the Club riders in visually altered conditions, suggesting a greater ability to use vestibular and somesthetic information according to task constraints with expertise. In accordance with this result, RFT perceptual scores revealed that the Professional riders were less dependent on the visual field than were the Club riders. Finally, the Professional riders exhibited specific coordination modes that, unlike the Club riders, departed from pure in-phase and anti-phase patterns and depended on visual conditions. The present findings provide evidence of major differences in the sensorimotor processes contributing to postural control with expertise in horseback riding.

Understanding the effects of spaceflight on head–trunk coordination during walking and obstacle avoidance

Prolonged exposure to spaceflight conditions results in a battery of physiological changes, some of which contribute to sensorimotor and neurovestibular deficits. Upon return to Earth, functional performance changes are tested using the Functional Task Test (FTT), which includes an obstacle course to observe post-flight balance and postural stability, specifically during turning. The goal of this study was to quantify changes in movement strategies during turning events by observing the latency between head-and-trunk coordinated movements. It was hypothesized that subjects experiencing neurovestibular adaptations would exhibit head-to-trunk locking (‘en bloc’ movement) during turning, exhibited by a decrease in latency between head and trunk movement. FTT data samples were collected from 13 ISS astronauts and 26 male 70-day head down tilt bed rest subjects, including bed rest controls (10 BRC) and bed rest exercisers (16 BRE). Samples were analyzed three times pre-exposure, immediately post-exposure (0 or 1-day post) and 2–3 times during recovery from the unloading environment. Two 3D inertial measurements units (XSens MTx) were attached to subjects, one on the head and one on the upper back. This study focused primarily on the yaw movements about the subject׳s center of rotation. Time differences (latency) between head and trunk movement were averaged across a slalom obstacle portion, consisting of three turns (approximately three 60° turns). All participants were grouped as ‘decreaser’ or ‘increaser’, relating to their change in head-to-trunk movement latency between pre- and post-environmental adaptation measures. Spaceflight unloading (ISS) showed a bimodal response between the ‘increaser’ and ‘decreaser’ group, while both bed rest control (BRC) and bed rest exercise (BRE) populations showed increased preference towards a ‘decreaser’ categorization, displaying greater head–trunk locking. It is clear that changes in movement strategies are adopted during exposure to an unloading environment. These results further the understanding of vestibular–somatosensory convergence and support the use of bed rest as an exclusionary model to better understand sensorimotor changes in spaceflight.

The role of head stabilization in locomotion in children with cerebral palsy

The objective of the present study was to highlight the role of head stabilization and to analyze multisegment head-trunk coordination during gait in children with cerebral palsy (CP). Postural control was measured and compared in a group of 16 CP subjects and a control group of 16 healthy subjects. The subjects had to walk along an out-and-back course at their freely chosen gait speed. For each gait cycle, motion analysis techniques were used to calculate the amplitude of the head angle (relative to the trunk) in the sagittal and frontal planes. Kinematic analysis revealed a number of significant intergroup differences, with a more pronounced variation in the head angle (relative to the trunk) in the CP group than in the control group. There were no significant intergroup differences in terms of the angular amplitude of the head in the sagittal plane. The greater variability of the head angle in the frontal plane in the CP subjects might reflect the presence of greater head roll as a compensatory strategy. These finding suggest that the clinical evaluation of posture during gait in children with CP should be reconsidered.

Head, arm and trunk coordination during reaching in children

During postural and locomotor tasks, the orientation of the head with respect to space is maintained in order to serve as an egocentric reference value for maintaining balance. In young children during locomotor tasks, task difficulty determines the coordination of movements between head-trunk segments: the more difficult the task, the more the child limits the head on trunk movement ("en bloc") rather than letting the head move freely in space. For reaching tasks, however, there are no data about the development and maturation of coordination between the head and trunk movements and when the pattern of coordination is considered mature. The goal of this study was to characterize the development of head-trunk coordination during reaching from a sitting position in typically developing children. Forty-four typically-developing (TD) children aged from 2.8 to 11.8 years and six healthy adults participated. Children were divided into five groups (G1-G5) according to their age: 2-3, 4-5, 6-7, 8-9 and 10-11 years old. The task involved reaching towards and grasping a piece of food in the younger group or a wooden block in the older children and adults with the dominant hand, adequate to the grip size of each participant, and returning it to the mouth area to simulate self-feeding. The object was placed in line with the midline of the body at three different distances from the trunk according to the participant's arm length (two within and one beyond arm's length). Rotational movements of the head and trunk in three planes; yaw, roll and pitch, were recorded using three-dimensional tracking systems (Optotrak, Northern Digital, Model 3010 or Ariel Performance Analysis System). The variables analysed were relative head and trunk angle, absolute head and trunk angle, the anchoring index (AI) and initial direction of head and trunk rotation (direction index: DI). Patterns of head-trunk coupling were different along different axes of rotation and across groups. For the AI, a head-stabilized-on-trunk (HST) or "en bloc" pattern was observed with approximately the same frequency as a head-stabilized-in-space (HSS) pattern in the youngest children in the yaw plane for reaches within arm's length. In all other planes and for reaches of all distances, a HSS pattern was evident in the youngest children and remained consistent across the groups of children. Compared to the children, adult reaching was characterised by fixed head-trunk coordination (HST) in the roll plane at all reach distances, and greater decoupling in yaw plane motion for the two closest distances. There were no age-related differences in the pitch plane strategy which was mainly HSS. The DI patterns matured by 2-3 or 4-5 years of age, except for reaches to T1 in the pitch plane. In addition, in the roll plane, there was evidence of a two-step maturation that was not complete until adulthood. Maturation of strategies used to stabilize the head and trunk relative to each other and to the reaching arm differ across movement planes for a seated reaching task. Our data suggest that different aspects of head and trunk coordination during reaching movement mature at different rates, like for locomotor tasks previously described, and that the maturation follows a non-chronological and protracted course. These results can serve as a comparative database with which to contrast head and trunk coordination in children with movement disorders. However, in terms of typical development, these data should be considered specific for the task studied and may not reflect general principles of motor development.

Locomotor Skills and Balance Strategies in Adolescents Idiopathic Scoliosis

Locomotor balance control assessment was performed to study the effect of idiopathic scoliosis on head-trunk coordination in 17 patients with adolescent idiopathic scoliosis (AIS) and 16 control subjects. The aim of this study was to explore the functional effects of structural spinal deformations like idiopathic scoliosis on the balance strategies used during locomotion. Up to now, the repercussion of the idiopathic scoliosis on head-trunk coordination and balance strategies during locomotion is relatively unknown. Seventeen patients with AIS (mean age 14 years 3 months, 10 degrees < Cobb angle > 30 degrees) and 16 control subjects (mean age 14 years 1 month) were tested during various locomotor tasks: walking on the ground, walking on a line, and walking on a beam. Balance control was examined in terms of rotation about the vertical axis (yaw) and on a frontal plane (roll). Kinematics of foot, pelvis, trunk, shoulder, and head rotations were measured with an automatic optical TV image processor in order to calculate angular dispersions and segmental stabilizations. Decreasing the walking speed is the main adaptive strategy used in response to balance problems in control subjects as well as patients with AIS. However, patients with AIS performed walking tasks more slowly than normal subjects (around 15%). Moreover, the pelvic stabilization is preserved, despite the structural changes affecting the spine. Lastly, the biomechanical defect resulting from idiopathic scoliosis mainly affects the yaw head stabilization during locomotion. Patients with AIS show substantial similarities with control subjects in adaptive strategies relative to locomotor velocity as well as balance control based on segmental stabilization. In contrast, the loss of the yaw head stabilization strategies, mainly based on the use of vestibular information, probably reflects the presence of vestibular deficits in the patients with AIS.

Development of Training Programs to Mitigate Post Space Flight Gait Dysfunction

Following their return to Earth, astronauts experience disturbances in their ability to walk and maintain postural stability due to neural adaptation to the microgravity conditions of space flight. We have previously shown that astronauts returning from space flight show disturbances in locomotor control manifested by changes in various sub-systems including head-trunk coordination, dynamic visual acuity, lower limb muscle activation patterning and kinematics (Glasauer, etal., 1995; Bloomberg, et al., 1997; McDonald, et al., 1996; 1997; Layne, et al., 1997; 1998, 2001; Newman, et al., 1997; Bloomberg and Mulavara, 2003). These postflight changes in locomotor performance affect the ability of long-duration crewmembers to egress their vehicle soon after landing on Earth or following a landing on the surface of Mars. At present, no operational training intervention is available to mitigate postflight locomotor disturbances. The goal of our present research is to develop an inflight balance and gait training program that will facilitate recovery of locomotor function after long-duration space flight. The training regimen we are developing is based on the concept of variable practice. During this type of training the subject gains experience producing the appropriate adaptive motor behavior under a variety of sensory conditions and response constraints. Astronauts will conduct their nominal inflight treadmill exercise while being exposed to variations in visual flow patterns, body load and speed. These variations will challenge the locomotor system repeatedly, thereby promoting adaptive reorganization in locomotor behavior. As a result of this training a subject learns to solve a class of motor problems, rather than a specific motor solution to one problem; i.e., the subject learns response generalizability or the ability to “learn to learn” under a variety of environmental constraints. We anticipate that this training will accelerate recovery of locomotor function during readaptation to gravitational environments following spaceflight, thus facilitating neural adaptation to unit (Earth) and partial (Mars) gravity after long-duration spaceflight. To date, we have collected pre and postflight locomotion data from International Space Station Expeditions 5–9 (n =12) who will serve as part of the control group for this study. Preliminary results show that recovery of postflight locomotor function may occur through adaptive mechanisms that lead to either restitution or substitution of function. Understanding the modes of postflight readaptation has implications for development and testing of inflight training regimens.

Development of Training Programs to Mitigate Post Space Flight Gait Dysfunction

Following their return to Earth, astronauts experience disturbances in their ability to walk and maintain postural stability due to neural adaptation to the microgravity conditions of space flight. We have previously shown that astronauts returning from space flight show disturbances in locomotor control manifested by changes in various sub-systems including head-trunk coordination, dynamic visual acuity, lower limb muscle activation patterning and kinematics (Glasauer, etal., 1995; Bloomberg, et al., 1997; McDonald, et al., 1996; 1997; Layne, et al., 1997; 1998, 2001; Newman, et al., 1997; Bloomberg and Mulavara, 2003). These postflight changes in locomotor performance affect the ability of long-duration crewmembers to egress their vehicle soon after landing on Earth or following a landing on the surface of Mars. At present, no operational training intervention is available to mitigate postflight locomotor disturbances. The goal of our present research is to develop an inflight balance and gait training program that will facilitate recovery of locomotor function after long-duration space flight. The training regimen we are developing is based on the concept of variable practice. During this type of training the subject gains experience producing the appropriate adaptive motor behavior under a variety of sensory conditions and response constraints. Astronauts will conduct their nominal inflight treadmill exercise while being exposed to variations in visual flow patterns, body load and speed. These variations will challenge the locomotor system repeatedly, thereby promoting adaptive reorganization in locomotor behavior. As a result of this training a subject learns to solve a class of motor problems, rather than a specific motor solution to one problem; i.e., the subject learns response generalizability or the ability to “learn to learn” under a variety of environmental constraints. We anticipate that this training will accelerate recovery of locomotor function during readaptation to gravitational environments following spaceflight, thus facilitating neural adaptation to unit (Earth) and partial (Mars) gravity after long-duration spaceflight. To date, we have collected pre and postflight locomotion data from International Space Station Expeditions 5–9 (n =12) who will serve as part of the control group for this study. Preliminary results show that recovery of postflight locomotor function may occur through adaptive mechanisms that lead to either restitution or substitution of function. Understanding the modes of postflight readaptation has implications for development and testing of inflight training regimens.

Head-trunk coordination in elderly subjects during linear anterior-posterior translations.

This study examined whether the head of elderly subjects was less stable in space when the trunk was free to move than when the trunk was fixed to a linearly moving platform. Fourteen healthy elderly subjects were seated on a linear sled with their trunk either fixed to the seat or free to move. Subjects received 10 cm, 445 cm/s2 anterior-posterior ramps and 0.35-4.05 Hz sum-of-sines translations while performing a mental distraction task in the dark. Kinematics of the head and trunk were derived from an Optotrak motion analysis system and a linear accelerometer placed on the head. Electromyographic (EMG) signals were collected for neck and paraspinal muscles. Data were tested for significance with paired t-tests corrected for multiple testing and compared (Mann-Whitney U-test) with previously published data from 12 healthy young adults (Keshner 2003). Linear acceleration trajectories of the head corresponded to the direction of sled linear acceleration when the trunk was fixed and countered the direction of the sled when the trunk was free. Angular head accelerations countered the sled or the trunk when the trunk was fixed or free, respectively. Peak amplitudes of head angular acceleration in space were greater with a fixed trunk. With the trunk free, amplitudes of head linear peak acceleration, angular accelerations, and response gains exceeded those of the young adults. Muscle EMG response latencies did not vary with the timing of head acceleration onset but the neck muscles were activated more frequently in a direction consistent with a vestibulocollic or cervicocollic reflex. Differences in angular motion of the head could be explained by the biomechanical constraints of the two tasks having one freely moving mass (head) with the trunk fixed and two freely moving masses (head and trunk) with the trunk free. These data suggest that elderly subjects rely upon active trunk mechanics in order to coordinate their head and trunk motion; however, a contribution by vestibular and ascending segmental inputs cannot be completely ruled out. A less flexible trunk in the elderly could explain why they were not as successful as young adults in stabilizing their heads in space when the trunk was free to move.

Head-trunk coordination during linear anterior-posterior translations.

The purpose of this study was to evaluate the relative contributions of inputs from the vestibular system and the trunk to head-trunk coordination. Twelve healthy adults and 6 adults with diminished bilateral labyrinthine input (LD) were seated with their trunk either fixed to the seat or free to move. Subjects received 10-cm, 445-cm/s(2) anterior-posterior ramps and 0.35- to 4.05-Hz sum-of-sines translations while performing a mental distraction task in the dark. Kinematics of the head and trunk were derived from an Optotrak motion analysis system and a linear accelerometer placed on the head. EMG signals were collected from neck and paraspinal muscles. Data were tested for significance with multivariate ANOVA (MANOVA) and Bonferroni post hoc analyses. Initial linear and angular head acceleration directions differed in healthy subjects when the trunk was fixed or free, but did not differ in LD subjects. Peak head angular accelerations were significantly greater with the trunk fixed than when free, and were greater in LD than in control subjects. EMG response latencies did not differ when the trunk was fixed or free. Low-frequency phase responses in the healthy subjects were close to 90 degrees and had a delayed descent as frequency increased, suggesting some neural compensation that was absent in the LD subjects. Results of this study revealed a strong initial reliance on system mechanics and on signals from segmental receptors. The vestibular system may act to damp later response components and to monitor the position of the head in space secondary to feedback from segmental proprioceptors rather than to generate the postural reactions.

Changes in walking strategies after spaceflight.

Over the last several years, our laboratory has investigated postflight astronaut locomotion with the aim of better understanding how adaptive changes in underlying sensorimotor mechanisms contribute to postflight gait dysfunction. One of the first questions we asked focused on the effects of spaceflight on head movement control during postflight locomotion. We hypothesized that adaptive modification in multiple sensorimotor systems caused by exposure to the microgravity conditions of spaceflight would lead to disruption in head-trunk coordination during postflight walking. These changes in head-trunk coordination strategies would then disrupt gaze control and alter the organization of terrestrial locomotor control strategies. The data presented indicate that some behavior observed after spaceflight may represent an adaptive reorganization of motor responses targeted at restoring functional mobility but in a novel way that is not observed or required during preflight walking. This observation has implications for the interpretation of all tests of postflight sensorimotor function.