Head movement during sudden base translations as a measure of risks for falls in the elderly

Design and usability of a system for the study of head orientation

The ability to control head orientation relative to the body is a multisensory process that mainly depends on proprioceptive, vestibular, and visual sensory systems. A system to study the sensory integration of head orientation was developed and tested. A test seat with a five-point harness was assembled to provide passive postural support. A lightweight head-mounted display was designed for mounting multiaxis accelerometers and a mini-CCD camera to provide the visual input to virtual reality goggles with a 39° horizontal field of view. A digitally generated sinusoidal signal was delivered to a motor-driven computer-controlled sled on a 6-m linear railing system. A data acquisition system was designed to collect acceleration data. A pilot study was conducted to test the system. Four young, healthy subjects were seated with their trunks fixed to the seat. The subjects received a sinusoidal anterior–posterior translation with peak accelerations of 0.06g at 0.1 Hz and 0.12g at 0.2, 0.5, and 1.1 Hz. Four sets of visual conditions were randomly presented along with the translation. These conditions included eyes open, looking forward, backward, and sideways, and also eyes closed. Linear acceleration data were collected from linear accelerometers placed on the head, trunk, and seat and were processed using MATLAB. The head motion was analyzed using fast Fourier transform to derive the gain and phase of head pitch acceleration relative to seat linear acceleration. A randomization test for two independent variables tested the significance of visual and inertial effects on response gain and phase shifts. Results show that the gain was close to one, with no significant difference among visual conditions across frequencies. The phase was shown to be dependent on the head strategy each subject used.

Sensorial Afferents, Expectations, and Craniocervical Postural Relations in Adults who are Blind and Sighted

In this study, the neck and head relative to the ground were more flexed, while the head relative to the neck was more extended, in the subjects who were blind than in the sighted subjects. The introduction of external (sound) or proprioceptive (mandibular position, look ahead) inputs modified craniocervical posture and relationships (extension) in both groups.

The role of head-in-space stability on stepping reactions in young and elderly adults

This study compared head kinematic responses and step latency following an anteriorly directed postural perturbation between two groups (Young, mean age 27.39; Elderly, mean age 71.9). We further attempted to demonstrate, for the first time, a positive linear relationship between sagittal plane head angular velocities and stepping responses in both groups. It was hypothesized that the Elderly would demonstrate higher head angular velocities and greater step latencies than the Young. We also hypothesized that a positive linear relationship would show that, following a perturbation, trials where head angular velocity was low yielded quicker step responses. Each participant experienced three perturbations under five different visual conditions designed to alter visual input and head/trunk coordination. Repeated-measures ANOVA was used, with α set at 0.05. For each test condition, the Elderly consistently demonstrated longer step latencies while exhibiting higher head angular velocities. For each group, a positive linear relationship was shown between the two dependent variables (Young: r=0.86; Elderly, r=0.84). During a postural perturbation, as head angular velocity increased, stepping responses were delayed.

Inertial loading during gait evokes unique neuromuscular adaptations in old adults

This study examined the neuromuscular adaptations of young and old adults in response to a challenge to balance during gait. 12 young (22.2 +/- 2.0 yr.) and 10 old adults (78.8 +/- 6.3 yr.) performed five level walking trials with and without a challenge to balance which consisted of adding a load bilaterally to the participants' ankles and increasing gait speed (1.5 m/sec. and 1.7 m/sec.). Onset, duration, and amplitude of muscle activity in the vastus lateralis, rectus femoris, biceps femoris, and semimembranosus were calculated. Old adults responded to the added load by increasing the activation intensity of their vastus lateralis and semimembranosus disproportionately when compared with young adults. Also, old adults activated their knee flexors earlier and all muscles for a longer period of time than young adults. These findings suggest old adults alter both magnitude of activation and duration of lower extremity musculature in response to increased inertial and velocity demands, and these response characteristics differ from those of young adults.

The reaction strategy of lower extremity muscles when slips occur to individuals with trans-femoral amputation

The aim of this study is to investigate the surface electromyography (sEMG) responses of lower extremity muscles for both healthy people and individuals with trans-femoral amputation (TFA), when slip events occur during level walking. Six male individuals with unilateral TFA and five healthy subjects participated in this study. Each subject was required to walk at a self-selected comfortable pace along a 5m plastic walkway, and to perform walking trials on dry and oily conditions respectively. The sEMG signals of muscles on legs and around waist were recorded in each trial and the normalized instantaneous muscle power (IMP) values were employed to quantify the response intensity. The IMP profiles of each muscle in oily-surface walking trials were compared quantitatively with that in dry-surface trials. There are three main findings in this study. (1) Different muscle reaction strategies are employed in slip events by the healthy persons and the individuals with TFA, respectively. Moreover, when the slip event occurs on the prosthetic leg and the intact leg of the individuals with TFA respectively, the muscle reaction strategies are also different. (2) The individuals with TFA face higher risks of fall than the healthy persons no mater slips occur on the prosthetic side or the intact side. (3) The hip muscles, especially the gluteus maximus (GMA) muscles, always enormously contribute to posture adjustment and balance recovery in slip events.

Postural Control Adaptability to Floor Oscillation in the Elderly

We established a method to evaluate postural control adaptability, applying it to 341 subjects, aged 18-29 years (young subjects) and 50-79 years, in order to investigate the influences of age and gender on adaptability. Subjects stood with eyes closed on a force plate fixed to a floor oscillator, which was sinusoidally oscillated in the anteroposterior direction with 0.5 Hz frequency and 2.5 cm amplitude. Five trials of 1-minute oscillation were conducted, with a short rest between trials. The mean speed of fluctuation of the center of foot pressure (CFP), as detected by the force plate, was calculated as an index of postural steadiness. Mean CFP speed decreased significantly in all age groups with trial repetition. The adaptability capability of elderly subjects was categorized as "good," "moderate," or "poor," as evaluated against a standard value, based on the variation of the regression of mean CFP speed between the 1st and 5th trials in young subjects. Results showed that the magnitude of reduction in the mean speed, with practice, was linearly related to the initial mean speed. We found a general decline in adaptability, and increase in initial mean speed, in subjects aged 60 years and older, with no gender difference detected in any age group. The proportion of subjects exhibiting moderate and poor adaptability increased gradually with age. In conclusion, age, but not gender, appears to affect adaptation of postural sway with short-term practice, although some elderly subjects maintain postural sway velocity and adaptability capabilities similar to those of young subjects.

Acceleration patterns of the head and pelvis when walking are associated with risk of falling in community-dwelling older people

BACKGROUND

A large proportion of falls in older people occur when walking, however the mechanisms underlying impaired balance during gait are poorly understood. This study evaluated acceleration patterns of the head and pelvis when walking on a level and an unpredictably irregular surface to determine whether older people at risk of falling demonstrate an impaired ability to stabilize the body under challenging conditions.

METHODS

One hundred community-dwelling older people aged between 75 and 93 years were evaluated for their risk of falling using a range of physiological tests previously found to be accurate predictors of falling in prospective studies. Temporo-spatial gait parameters and acceleration patterns at the head and pelvis were then measured in three orthogonal planes while subjects walked on a flat corridor and an unpredictably irregular walkway. Harmonic ratios of head and pelvis accelerations in each plane were calculated to provide an indicator of stability.

RESULTS

Subjects with a high risk of falling exhibited reduced temporo-spatial gait parameters and increased step timing variability. Harmonic ratios of acceleration patterns were reduced at the head and pelvis in the vertical and antero-posterior directions. These differences were particularly evident when walking on the irregular surface.

CONCLUSION

Older people at risk of falling adopt a more conservative basic walking pattern, but this does not ensure that the movements of the head and pelvis are stable. The irregular pelvis and head accelerations evident in the high risk group suggests that these subjects may have difficulty controlling trunk motion and maintaining a stable visual field when walking, particularly on irregular terrain.