Effect of computer keyboard slope and height on wrist extension angle.

The goal of this study was to determine the systematic effect that varying the slope angle of a computer keyboard along with varying keyboard height (relative to elbow height) have on wrist extension angle while typing. Thirty participants typed on a keyboard whose slope was adjusted to +15 degrees, +7.5 degrees, 0 degrees, -7.5 degrees, and -15 degrees. The height of the keyboard was set up such that participants' wrists were at the same height as their elbows, above their elbows, and four cm below their elbows. Results showed that as keyboard slope angle moved downward from +15 degrees to -15 degrees, mean wrist extension decreased approximately 13 degrees (22 degrees at +15 degrees slope to 9 degrees at -15 degrees slope). Keyboard height had a similar effect with mean wrist extension decreasing from 21.8 degrees when the keyboard was lower than elbow height, to 7.3 degrees when the keyboard was higher than elbow height. Potential application of this research includes the downward sloping of computer keyboards, which could possibly be beneficial in the prevention of musculoskeletal disorders affecting the wrist.

Walker-assisted gait in rehabilitation: a study of biomechanics and instrumentation.

While walkers are commonly prescribed to improve patient stability and ambulatory ability, quantitative study of the biomechanical and functional requirements for effective walker use is limited. To date no one has addressed the changes in upper extremity kinetics that occur with the use of a standard walker, which was the objective of this study. A strain gauge-based walker instrumentation system was developed for the six degree-of-freedom measurement of resultant subject hand loads. The walker dynamometer was integrated with an upper extremity biomechanical model. Preliminary system data were collected for seven healthy, right-handed young adults following informed consent. Bilateral upper extremity kinematic data were acquired with a six camera Vicon motion analysis system using a Micro-VAX workstation. Internal joint moments at the wrist, elbow, and shoulder were determined in the three clinical planes using the inverse dynamics method. The walker dynamometer system allowed characterization of upper extremity loading demands. Significantly differing upper extremity loading patterns were identified for three walker usage methods. Complete description of upper extremity kinetics and kinematics during walker-assisted gait may provide insight into walker design parameters and rehabilitative strategies.

Foot and ankle sensory neuropathy, proprioception, and postural stability.

Foot and ankle sensory neuropathy may result from a variety of pathologic conditions, especially diabetes mellitus. Decreased sensation, particularly on the plantar surface of the feet, leads to obvious risks of cutaneous injury. Less obvious are the risks of fall-related injury associated with changes in other sensory systems of the foot and ankle, such as the receptors involved in joint movement and position perception. The results of a number of studies demonstrate that the neuropathic process affects these receptors in individuals with diabetes mellitus. Associated with the decreased sensory function of the foot and ankle is decreased performance on tests of static and dynamic postural stability. Subjective feelings of instability and an increased incidence of fall-related injuries have also been reported. The reduced postural stability in persons with diabetic neuropathy cannot be attributed exclusively to loss of plantar cutaneous sensation; it appears to be the result of a general loss of peripheral sensory receptor function in the lower legs, including that of the muscle spindles. During the evaluation of an individual with foot and ankle sensory neuropathy, the possibility of balance deficits should be given proper attention. Assessment of balance deficits could be particularly important when planning the course of rehabilitation for individuals with foot and ankle neuropathy who use modified footwear or have an amputation of a section of the foot or lower extremity.

Wrist and forearm posture from typing on split and vertically inclined computer keyboards.

A study was conducted on 90 experienced office workers to determine how commercially available alternative computer keyboards affected wrist and forearm posture. The alternative keyboards tested had the QWERTY layout of keys and were of three designs: split fixed angle, split adjustable angle, and vertically inclined (tilted or tented). When set up correctly, commercially available split keyboards reduced mean ulnar deviation of the right and left wrists from 12 degrees to within 5 degrees of a neutral position compared with a conventional keyboard. The finding that split keyboards place the wrist closer to a neutral posture in the radial/ulnar plane substantially reduces one occupational risk factor of work-related musculoskeletal disorders (WMSDs): ulnar deviation of the wrist. Applications of this research include commercially available computer keyboard designs that typists can use and ergonomists can recommend to their clients in order to minimize wrist ulnar deviation from typing.

Wrist and forearm postures of users of conventional computer keyboards.

The aim of this study was to perform a comprehensive investigation to document wrist and forearm postures of users of conventional computer keyboards. We instrumented 90 healthy, experienced clerical workers with electromechanical goniometers to measure wrist and forearm position and range of motion for both upper extremities while typing. For an alphabetic typing task, the left wrist showed significantly greater (p < .01) mean ulnar deviation (15.0 degrees +/- 7.7 degrees) and extension (21.2 degrees +/- 8.8 degrees) than the right wrist (10.1 degrees +/- 7.2 degrees and 17.0 degrees +/- 7.4 degrees for ulnar deviation and extension, respectively). Conversely, the right forearm had greater mean pronation (65.6 degrees +/- 8.3 degrees) than the left forearm (62.2 degrees +/- 10.6 degrees). We noted minimal functional differences in the postures of the wrists and forearms between alphabetic and alphanumeric typing tasks. Ergonomists should consider the statistically significant and probable practical difference in wrist and forearm posture between the left and right hand in ergonomic interventions in the office and in the design of computer keyboards. Actual or potential applications of this research include guiding the design of new computer keyboards.

Influence of hip position and gender on active hip internal and external rotation.

A general lack of descriptive details exists for measurements of hip rotation range of motion. This study was designed to establish the influence of gender and hip flexion position on active range of motion of the hip in external and internal rotation. Sixty (39 females and 21 males) healthy college-age (21.8 +/- 1.7 years) subjects were studied. Hip rotation of the dominant leg of each subject was measured in the prone (hip near 0 degree of flexion) and seated (hip near 90 degrees of flexion) positions using a standard goniometer. Data were analyzed using an analysis of variance model. Pearson's r statistics were used to determine the degree of association between measurements of hip rotation made seated vs. prone. A statistically significant difference (p < 0.05) was found between mean hip external rotation (ER) measured seated (36 +/- 7 degrees) and mean hip ER measured prone (45 +/- 10 degrees). Conversely, mean hip internal rotation (IR) measured seated (33 +/- 7 degrees) was not statistically different than mean hip IR measured prone (36 +/- 9 degrees). Females had statistically more active hip internal and external rotation than males (p < 0.05). A moderate degree of association existed between measurements of hip ER taken in the prone vs. seated position (r = 0.57, p < 0.05). For IR, the degree of association between the two measurement positions was slightly higher (r = 0.72, p < 0.05). Unlike the amount of active hip internal rotation which showed little difference between measurements made prone vs. seated, our data indicate that measurement position had a significant effect on the amount of active range of motion of the hip in ER. These findings are clinically significant for they stress the importance of documenting measurement position. They also stress the need for representative norms to be established for each hip position and gender.

Changes in ankle joint proprioception resulting from strips of athletic tape applied over the skin.

OBJECTIVE: In part, the believed effectiveness of taping in preventing injuries may be in the increased proprioception that it provides through stimulation of cutaneous mechanoreceptors. The objective of this study was to examine the effectiveness of strips of athletic tape applied over the skin of the ankle in improving ankle joint movement and position perception. DESIGN AND SETTING: The study consisted of a single-group, repeated-measures design, where all subjects were tested under all conditions presented in a fully randomized order. Testing was performed in the biomechanics laboratory at Marquette University. SUBJECTS: Twenty healthy males (mean age = 20.3 +/- 1.5 yr) participated in this study. MEASUREMENTS: Ankle joint movement and position perception for plantar flexion and dorsiflexion were tested using a specially designed apparatus. Each individual was tested with and without two 12.7-cm (5-inch) strips of tape applied in a distal-proximal direction directly to the skin in front of and behind the subject's talocrural joint. RESULTS: Data were analyzed with repeated-measures analyses of variance (ANOVA) models. Our results indicate that under the nonweightbearing condition, taping significantly improved (p < .05) the ability of the subjects to perceive ankle joint position, especially for a 10 degrees plantar-flexed position. In the weightbearing condition, the use of tape did not significantly alter (p > .05) the ability of the subjects to perceive ankle position. Similarly, taping did not alter ankle movement perception in either the weightbearing or nonweightbearing condition (p > .05). CONCLUSIONS: We concluded that increased cutaneous sensory feedback provided by strips of athletic tape applied across the ankle joint of healthy individuals can help improve ankle joint position perception in nonweightbearing, especially for a midrange plantar-flexed ankle position.

Diabetic sensory neuropathy effect on ankle joint movement perception.

OBJECTIVE: To determine if diabetic subjects with lower extremity cutaneous sensory neuropathy also have a loss of ankle joint movement perception. The strength of association between measurements of ankle joint movement perception and measures of cutaneous sensory function was also investigated. DESIGN: Diabetic subjects with and without sensory neuropathy and individuals without diabetes participated in this study. SETTING: All subjects were community-living individuals. PARTICIPANTS: Fifty-one subjects, ages 40 to 68. Seventeen of the 34 subjects with diabetes had significant distal sensory neuropathy as determined by cutaneous perception of mechanical vibration. All individuals without diabetes were volunteers from the community. Most subjects with diabetes were recruited through direct referral from their physicians. INTERVENTIONS: Ankle joint movement perception threshold (JMPT) was assessed using a device designed for this study. Cutaneous sensory function under both halluces was measured for vibration perception using a vibrometer and for touch-pressure perception using Semmes-Weinstein monofilaments. MAIN OUTCOME MEASURES: Ankle JMPTs (degrees) were compared to measurements of cutaneous vibration perception (volts) and touch-pressure perception (monofilaments force ratings). RESULTS: Diabetic subjects with cutaneous sensory neuropathy demonstrated a significant loss of ankle movement perception (p < .01). Correlation between JMPT and cutaneous sensory tests ranged from Spearman's rank r = .43 to .67. CONCLUSIONS: Although individuals with cutaneous sensory loss secondary to diabetic neuropathy also demonstrated loss of movement perception at the ankle, the relatively low explained variance between the two types of assessment (18% to 45%) indicates that the severity of ankle joint movement perception deficits cannot be directly implied from cutaneous sensory tests.

The lennie test for measuring scapular position in healthy young adult females: a reliability and validity study.

Normal scapular rest position is neither adequately described nor agreed upon by authorities. The purpose of this study was to devise and describe a reliable and valid test (the Lennie Test) to measure scapular position, including normal scapular rest position. Fifteen healthy females (age 19-21 years) participated in the study. Horizontal and vertical scapular position in the frontal plane was quantified by three different investigators using a scoliometer and caliper. Same-day radiographs were used to validate scapular position surface measurements. The medial borders of the scapulae were found to be parallel to the thoracic midline. The scapulae were on average 17.19 +/- 1.85 cm apart (at the level of the root of the scapulae) with the dominant arm scapula being on average 0.49 +/- 0.74 cm lower than the nondominant scapula. This difference in height between scapulae was not statistically significant (p > .01). Correlation coefficients between skin surface and radiograph measurements of scapular position ranged from .43 to .82. Intertester intraclass correlation coefficients for surface measurements of scapular position ranged from .64 to .86. The Lennie Test was found to have moderate to high intertester reliability and to provide an accurate measurement of the anatomical location of the scapulae based on X-ray verification. Surface landmark measurements for scapular position were on average within 0.56 cm and within 1.7 degrees of the measurements made from X-rays for linear and angular position, respectively. We propose the use of the Lennie Test in populations, healthy or otherwise, where scapular position needs to be objectively measured.

Postural instability in patients with diabetic sensory neuropathy.

OBJECTIVE: Recent survey evidence suggests that sensory ataxia due to diabetic neuropathy may be a more frequent and serious problem than is commonly recognized. This view is further supported by research that confirms the major contribution of the somatosensory system to the control of posture. We therefore sought to determine the effects of significant diabetic distal symmetrical polyneuropathy on the control of posture. RESEARCH DESIGN AND METHODS: Fifty-one subjects, divided into three groups, participated in this study. Seventeen had diabetes and significant sensory neuropathy, 17 had diabetes and no neuropathy, and 17 had neither diabetes nor neuropathy. The subjects were matched across groups, and stringent exclusion criteria were applied. Postural stability during quiet standing was measured using a force platform. In addition to electrophysiological and quantitative sensory tests of neuropathy, a number of physical and functional characteristics were measured for all subjects. RESULTS: Postural instability was found to be significantly associated with sensory neuropathy, but not with diabetes per se. Patients with sensory neuropathy demonstrated between 66 and 117% more instability than did control subjects (depending on the testing condition). Based on multiple linear regression analyses, the most significant correlates of instability were the quantitative sensory measures of neuropathy and age. CONCLUSIONS: The loss of sensory perception secondary to diabetic distal symmetrical sensory neuropathy has a markedly detrimental effect on postural stability. The deficit is greatest when visual or vestibular cues are absent or degraded. Patients with neuropathy need to be informed of the postural consequences of this condition to limit the potential morbidity caused by falls.

Ulceration, unsteadiness, and uncertainty: the biomechanical consequences of diabetes mellitus.

Diabetes mellitus, which results from a failure of the endocrine system to control blood glucose levels within normal limits, affects approximately 15% of the population over the age of 65 in developed countries. Between 20-50% of people with diabetes for more than 10 years will experience symmetrical distal sensory neuropathy resulting in a progressive, distal to proximal, loss of sensation in the lower extremities. The most common consequence is plantar ulceration that too often results in partial or total amputation of the foot. While neuropathy is a major permissive factor, plantar ulcers occur at locations of high plantar pressures. The measurement of pressure using tools developed and refined in the field of biomechanics has been shown to be a valuable asset to the management of the foot at risk for ulceration. In particular, the use of in-shoe measuring techniques has the potential to revolutionize the prescription of therapeutic footwear. Biomechanical techniques have also helped to evaluate other consequences of diabetic neuropathy on the foot such as callus formation, foot deformity, limited joint mobility and bony abnormalities. The reduction of afferent information from the lower extremities implies a lack of active feedback thought to be necessary for the control of human movements such as posture and gait. Our results show that diabetic neuropathy results in a significant increase in sway during standing that is not compensated for by other sensory systems. The study of the sagittal plane movements of the same individuals walking on a treadmill showed little effect on the kinematic control of gait when compared to age matched nonneuropathic control groups. This may indicate the dominance of efferent input over afferent feedback during gait. We believe that the study of the biomechanical consequences of diabetes can act as a model for many other diseases that have yet to come under the scrutiny of a multidisciplinary team.

The effects of visual factors and head orientation on postural steadiness in women 55 to 70 years of age.

This study was designed to establish reference data for the effects of head position and visual conditions on the standing posture of healthy women ages 55 to 70. Center of pressure (CoP) data were analyzed using ANOVA models. Total CoP displacement was 45% greater (significant, p less than .05) when the subjects stood with their heads back and their eyes closed, as compared to standing looking straight ahead. Visual surrounds consisting of vertical visual cues resulted in less postural sway (PS) than surrounds made of horizontal visual cues (significant, p less than .05 for anteroposterior CoP range). Experimentally reduced visual acuity resulted in greater PS, while changes in ambient lighting and spatial frequency of visual cues affected PS minimally. These results suggest that a reduction in the height of shelving, and the provision of high-contrast visual cues and vertical geometric patterns are potential intervention strategies to optimize vestibular sensory input and visual orientational cues for the maintenance of stability during stance.

The influence of visual factors on fall-related kinematic variables during stair descent by older women.

Despite the documented health hazards associated with stair descent, the mechanisms of falling on stairs remain relatively unexamined. The objectives of this study were to define kinematic variables that could be used to describe foot-stair spatial relationships during the mid-stair phase of stair descent, and to investigate the effects of various visual and environmental conditions on those variables in a group of 36 healthy women between the ages of 55 and 70. Foot clearance and foot placement were measured through high-speed film analysis. Clearance between the foot and the stair during swing phase was small under all visual conditions. Degraded visual acuity had a significant effect on cadence, foot placement, and foot clearance, but visual surround conditions did not. The kinematic variables used in this experiment may be helpful in future studies to assess the results of interventions aimed at reducing the frequency of falls on stairs.