Estimation of geometric properties of cortical bone in spinal cord injury.

OBJECTIVE: To evaluate structural and geometrical properties of the tibia shaft in subjects with spinal cord injury (SCI) and subjects without SCI and to estimate the potential usefulness of a multimodal approach to diagnosing osteoporosis in SCI. DESIGN: A cross-sectional study of randomly selected SCI and non-SCI subjects. METHODS: Measurements of bone geometric indices by computed tomography, and calculated bending stiffness with a biomechanical testing method. SETTING: An SCI center hospital. SUBJECTS: Ten men without known orthopedic or neurologic impairments (controls), 10 men with SCI who had a history of lower extremity pathologic fracture since SCI, and 10 men with SCI who had never had lower extremity pathologic fracture. RESULTS: Analysis of geometric and structural indices of subjects' tibias found a significant difference in all geometric indices between controls and the SCI subjects with pathologic fracture history. Between the controls and the SCI subjects with no fracture history, however, differences were found only in cross-sectional area and calculated bending stiffness. CONCLUSION: Structural analysis of leg bone, combined with measurement of bone density, may improve the ability to assess fracture risk in patients with SCI.

Reliability of phase-velocity measurements of tibial bone.

BACKGROUND AND PURPOSE: The Bone Stiffness Measurement Device-Swing is capable of measuring the propagation velocity of flexural waves in human tibial bone, which relates to bending stiffness. If the interrater and intrarater reliability of measurements obtained with the device are established, it can be used with confidence in assessing changes in bone. The purposes of this study were to detect potential sources of measurement error and to establish the interrater and intrarater reliability of measurements taken with the device. SUBJECTS AND METHODS: In the first part of the study, a random-effects design was used to obtain phase-velocity measurements in subjects without known orthopedic or neurological impairments. The second part of the study consisted of possible applications of the device with mixed designs on subjects with spinal cord injuries. By means of generalizability theory, multiple sources of error (eg, occasion, clinician, repetition) were estimated. For the clinical trial, 17 persons with spinal cord injuries not older than 5 weeks were tested. RESULTS: The standard error of measurement (SEM) for intrarater reliability measurements ranged from 7.3 to 9.8 m x s(-1) . The SEMs for interrater reliability measurements ranged from 5.7 to 9.5 m x s(-1). The SEMs for measurements obtained by a single clinician in a clinical population ranged from 11.9 to 39.7 m x s(-1). CONCLUSION AND DISCUSSION: The reproducibility of measurements obtained with the device is suitably high for the device to be used for evaluation in clinical and research settings.

Parameters for modeling the upper extremity.

The purpose of this paper was to provide parameters for the development of a musculoskeletal model of the upper extremity. Five upper extremity specimens were obtained from four fresh cadavers. Anthropometric measures were obtained for each cadaver. Segment inertial parameters were estimated for each specimen from anthropometric measures of the cadaver from which the specimen was obtained. The three-dimensional kinematics of the humerus, ulna, and radius in different movements of the glenohumeral, humeroulnar and ulnoradial joints were measured for each specimen using of the 3Space tracking system (Isotrack, Polhemus). The instantaneous rotation center of the glenohumeral joint and the instantaneous rotation axes of elbow flexion and forearm pronation were determined for each specimen from the kinematic data. The specimens were dissected and the muscle origins and insertions and bony structures needed in upper extremity modeling were digitized using the 3Space system. The shapes of muscle origins and insertions were estimated. Muscle length, volume and pennation angle were measured for the estimation of physiological cross-sectional areas of each muscle. The results, which are given for one specimen, showed that the rotation center of the glenohumeral joint was very close to the geometric center of the joint with a mean distance of 4 mm. The mean angle between the flexion-extension and pro-supination axes of the elbow joint was 94 degrees. The minimum distance between these two axes was about 4 mm.

Physical strain and mechanical efficiency in hubcrank and handrim wheelchair propulsion.

The physical strain and mechanical efficiency of manual wheelchair propulsion using handrim and hubcrank propelled racing wheelchairs were studied during a submaximal wheelchair exercise test on a stationary roller ergometer. Ten healthy male able-bodied subjects conducted two exercise tests in a random order and measurements of phyical strain (oxygen uptake, minute ventilation, respiratory exchange ratio, heart rate) and gross mechanical efficiency were obtained. During the experiment torque data, speed and power output were determined at a sample frequency of 0.1 Hz. Analysis of variance for repeated measures (p < 0.05) was used to establish differences. The hubcrank propulsion mechanism showed a significantly lower physical strain and higher gross mechanical efficiency in comparison with the handrim propulsion mechanism. The lower strain and higher efficiency in propelling the hubcrank partly seems to be due to the continuous biphasic cyclic propulsion movement, which allows both push and pull forces to be exerted. This involves flexor and extensor muscles around elbow and shoulder, leading to a reduced tendency to fatigue in individual muscles in the upper extremity. The more natural and neutral wrist-hand orientation also seems to diminish finger flexor activity and wrist-stabilizing muscle activity, and will thus reduce physical strain both with respect to the cardiorespiratory and musculoskeletal systems. The latter may influence the tendency to develop carpal tunnel problems positively. The reduced strain of the hubcrank propulsion mechanism clearly has a number of advantages over handrims for the human engine in the short and long run. However, technical innovation should address current practical problems of steering and braking. Clearly, hubcranks can be used in low-seated wheelchairs (i.e. racing wheelchairs) only, and in subjects with a sufficiently large range of motion in the upper extremity. Moreover, the increased width is a drawback of hubcranks. Care should be taken while negotiating door posts.

Pregnant women and working surface height and working surface areas for standing manual work.

Physically loading aspects of work may have adverse effects on the health of both the pregnant woman and the unborn child. Improving the fit between the pregnant woman and the workplace layout contributes to minimizing the load associated with given tasks. The aim of this paper is to evaluate two layout aspects for standing manual work, namely working surface height and working surface areas, for the condition of pregnancy. Two approaches were used. (1) The effects of changed body dimensions were evaluated with regard to (a) fit problems while working at a workplace in accordance with common guidelines and (b) the validity of assumptions of these guidelines. (2) The appreciation of relevant aspects of workplace layout at a specific manual task was assessed. Twenty-seven women were examined in pregnant and non-pregnant conditions. The first approach showed that fit problems are likely: guideline working surface height is just (2-7 cm) under the most protruding abdominal point, and areas based on non-pregnant abdominal depth are relatively large in pregnant condition. Further, existing methods to assess working surface areas have various assumptions that are not valid in pregnant condition. The second approach showed that at a specific manual task, women in late pregnancy preferred a considerably lower table height than the common guideline heights. Possibly, abdominal height becomes a relevant design factor with regard to working surface height during pregnancy. The task position on the working surface at which effort started became closer to the table edge due to pregnancy. Both approaches show that common guideline working surface heights for manual work, and working surface areas assessed in non-pregnant condition seem not suitable in pregnant condition.

Relationship between physical strain during standardised ADL tasks and physical capacity in men with spinal cord injuries.

To describe physical strain during activities of daily living (ADL), 44 men with spinal cord injuries (C4-L5) performed a set of standardised tasks. The physical strain was defined as the highest heart rate response expressed as a percentage of the individual heart rate reserve (%HRR). The physical strain averaged over the subjects who performed all tasks (n = 24) was (mean +/- SD): 20.2 +/- 7.2 %HRR (washing hands), 20.4 +/- 7.3 %HRR (passing a side-hung door), 28.8 +/- 10.8 %HRR (transfer to a toilet), 31.2 +/- 13.1 %HRR (ascending an 8 cm curb). 33.9 +/- 12.0 %HRR (transfer to a shower seat), 35.1 +/- 10.5 %HRR (transfer to bed), 36.4 +/- 13.3 %HRR (preparing lunch), 37.1 +/- 12.0 %HRR (washing up), 38.7 +/- 14.9 %HRR (ascending a ramp), 39.8 +/- 15.6 %HRR (transfer to a shower wheelchair), 41.4 +/- 12.1 %HRR (changing sheets), and 45.9 +/- 10.4 %HRR (entering a car). Physical strain could be notably high, but large variations among subjects were present. During all tasks, subjects with tetraplegia had significantly higher levels of strain than subjects with low (T6-L5) lesions. Physical strain was inversely related to parameters of physical capacity: isometric strength (r: -0.34 to -0.72), sprint power (r: -0.34 to -0.69), peak oxygen uptake (r: -0.41 to -0.81) and maximal power output (r: -0.52 to -0.82). Parameters of physical capacity were better predictors of physical strain than was the lesion level, and explained 37-71% of the variance in strain during ADL. It was also concluded that the method used in this study provides a quantitative and objective estimation of physical strain and may therefore be a useful tool to identify task difficulty during rehabilitation and to evaluate the results of task and physical training on the physical strain during ADL.

Physiological evaluation of a newly designed lever mechanism for wheelchairs.

Lever-propelled wheelchairs have been described as more efficient and less physically demanding than hand-rim-propelled wheelchairs. To evaluate a newly designed lever mechanism (MARC) in both one- and two-arm use, a series of wheelchair exercise tests were performed on a motor-driven treadmill. Eight able-bodied male subjects performed a standard exercise test in the prototype MARC, both in an asynchronic and a synchronic bimanual propelling mode and in an unilateral (left-sided) mode. Subsequently the subjects performed additional exercise tests in a conventional crank-to-rod lever mechanism with unilateral and bimanual propulsion and in a conventional hand rim wheelchair. Analysis of variance was used to study the effect of the different work modes upon power output and cardiorespiratory parameters statistically (p < 0.05). The MARC stood out well in comparison with the conventional lever design. The additional design features which are to be implemented (variable gearing, reverse gear) will make the MARC a useful wheelchair. One-arm wheelchair propulsion is a very strenuous form of locomotion, requiring careful consideration in terms of provision. Mechanical and ergonomic improvements are quite feasible in lever propulsion and may to a certain extent reduce this problem. To improve overall mobility of wheelchair-dependent subjects further, ergonomic and mechanical design improvements are very necessary in lever as well as hand-rim wheelchairs. A combined biomechanical and physiological research approach will help in the definition of design criteria and fitting guidelines.

Orientation of the scapula in a simulated wheelchair push.

For a systematic study of the efficiency of manual wheelchair propulsion, biomechanical and functional analysis of the wheelchair push is necessary. Recently a three-dimensional (simulation) model of the shoulder mechanism has been developed. For a complete analysis with this model, information on force and kinematics is needed. To determine the three-dimensional orientations of the scapula during wheelchair propulsion static measurements in different phases of the push (-15, 0, 15, 30, and 60) relative to the vertical through the wheel axis) and against different loads (0, 10, 20, 30 and 40% of the maximal torque) have been performed. Scapular rotations were generally small and correlated poorly with net torque on the glenohumeral joint. On the basis of the measurements of thoracal and humeral orientation and net torque, equations have been formulated which can be used to describe the scapular orientation during actual wheelchair propulsion. Its consequences and applicability are discussed.

Geometry parameters for musculoskeletal modelling of the shoulder system.

A dynamical finite-element model of the shoulder mechanism consisting of thorax, clavicula, scapula and humerus is outlined. The parameters needed for the model are obtained in a cadaver experiment consisting of both shoulders of seven cadavers. In this paper, in particular, the derivation of geometry parameters from the measurement data is described. The results for one cadaver are presented as a typical example. Morphological structures are modelled as geometrical forms. Parameters describing this form are estimated from 3-D position coordinates of a large number of datapoints on the morphological structure, using a least-squares criterion. Muscle and ligament attachments are represented as a plane or as a (curved) line. Muscle paths are determined by a geometrical form of the bony contour around which the muscle is wrapped. Muscle architecture is determined by the distribution of muscle bundles over the attachment area, mapping the distribution of the origin to the insertion. Joint rotation centers are derived from articular surfaces. Hence, muscle moment arms can be calculated. The result of this study is a set of parameters for each cadaver, describing very precisely the geometry of the shoulder mechanism. This set allows positioning of muscle force vectors a posteriori, and recalculation of position coordinates and moment arms for any position of the shoulder.

Effect of handrim velocity on mechanical efficiency in wheelchair propulsion.

To study the effect of tangential speed of the handrims independent of external power output on gross mechanical efficiency (ME), nine able-bodied subjects performed wheelchair exercise tests on a stationary ergometer. The ergometer allowed for measurement of torque and three-dimensional forces on the rims and tangential velocity of the rear wheels. The experiment comprised two series of submaximal tests against constant external power outputs (0.25 and 0.50 W.kg-1) and four wheelchair speeds (0.83, 1.11, 1.39, and 1.67 m.s-1), which simulated a wheelchair speed of 1.67 m.s-1 and mechanical advantages of 0.43-0.87. ME stayed below 10.5% and changed inversely with speed of movement of the handrims. Peak torques on the right handrim stayed even with speed, leading to a significant increase in peak power output. Energy losses owing to braking torques at the beginning and end of the push phase increased with handrim speed but hardly exceeded 5 W. The effective force component applied to the handrims was below 71% of the magnitude of the total force vector and dropped up to 13% with increasing handrim speed. It is suggested that an ineffective direction of forces on the rims might (partly) be responsible for the low ME and for a decrease in ME in relation to tangential handrim velocity. This suggestion is discussed from a number of theoretical perspectives. It is concluded that the use of handrims with a lower mechanical advantage will increase wheelchair propulsion efficiency.

A computerized wheelchair ergometer. Results of a comparison study.

To determine the validity of propulsion simulation on a stationary wheelchair ergometer, nine male able-bodied subjects performed submaximal exercise tests on the ergometer and on a motor driven treadmill (MDT). Oxygen uptake, ventilation and stroke parameters were equal for both devices, but heart rate was lower and trunk movement was less for the ergometer test. Analysis of forces and power output on the ergometer indicated that power output was equal for both wheels. The ratio between applied forces and the effectively directed force component was approximately 80%. Also a small torque was applied by the hand onto the handrim surface which contributed to the total propulsion torque around the axle. It is concluded that the ergometer is capable of simulation of wheelchair propulsion, although the different trunk motion may necessitate sufficient wheelchair propulsion experience. Force analysis results are discussed.

Unilateral immobilization affects contralateral rat gastrocnemius muscle architecture.

In order to study the effects of unilateral short length immobilization on the contralateral gastrocnemius muscle (GM), length measurements were conducted on photographs taken in the active condition (tetanic plateau). Comparison of geometry of experimental and control muscles was made at optimum muscle length. The results show that a process occurred in the muscle which can be ascribed predominantly in terms of atrophy. This atrophy did not reach a maximum after 4 weeks but gradually increased in time. The altered conditions imposed on the muscle changed its architecture. It was shown that variables of the contralateral GM muscle are not representative of those of normally used muscles and should therefore not be used as control muscles for the determination of immobilization effects.

Within-cycle characteristics of the wheelchair push in sprinting on a wheelchair ergometer.

To investigate power output and torque production in wheelchair sprinting, six able-bodied subjects performed nine 20-s sprint tests on a stationary wheelchair ergometer (load 0-8 kg). Ergometer data were analyzed and combined with kinematic data and surface electromyography. Of all power and torque parameters investigated, only maximal power output was independent of load (mean peak value 375 W, one-sided). Mean power output is suggested to be a useful indicator for anaerobic power production, but test conditions concerned speed in relation to handrim diameter should be specified. The relevance of the "mechanical constraint principle" for handrim propulsion is discussed. Within one cycle, power and torque curves showed a negative deflection at the beginning and a valley approximately halfway through the push phase. The relation of these phenomena to kinematic parameters and muscle activity is discussed.

Inertia and muscle contraction parameters for musculoskeletal modelling of the shoulder mechanism.

To develop a musculoskeletal model of the shoulder mechanism, both shoulders of seven cadavers were measured to obtain a complete set of parameters. Using antropometric measurements, the mass and rotational inertia of segments were estimated, followed by three-dimensional measurements of all morphological structures relevant for modelling, i.e. muscle origins and insertions, muscle bundle directions, ligament attachments and articular surfaces; all in relation to selected bony landmarks. Subsequently, muscle contraction parameters as muscle mass and physiological cross-sectional area were measured. The method of data collection and the results for inertia and muscle contraction parameters as prerequisities for modelling are described.

Load on the upper extremity in manual wheelchair propulsion.

To study joint contributions in manual wheelchair propulsion, we developed a three-dimensional model of the upper extremity. The model was applied to data collected in an experiment on a wheelchair ergometer in which mechanical advantage (MA) was manipulated. Five male able-bodied subjects performed two wheelchair exercise tests (external power output P(ext) = 0.25-0.50 W · kg(-1)) against increasing speeds (1.11-1.39-1.67 m.s(-1)), which simulated MA of 0.58-0.87. Results indicated a decrease in mechanical efficiency (ME) with increasing MA that could not be related to applied forces or joint torques. Increase in P(ext) was related to increases in joint torques. On the average, the highest torques were noted in shoulder flexion and adduction (35.6 and 24.6 N · m at MA = 0.58 and P(ext)= 0.50 W · kg(-1)). Peak elbow extension and flexion torques were -10.6 and 8.5 N · m. Based on the combination of torques and electromyographic (EMG) records of upper extremity muscles, anterior deltoid and pectoralis muscles are considered the prime movers in manual wheelchair propulsion. Coordinative aspects of manual wheelchair propulsion concerning the function of (biarticular) muscles in directing the propulsive forces and the redistribution of joint torques in a closed chain are discussed. We found no conclusive evidence for the role of elbow extensors in direction of propulsive forces.

Seat height in handrim wheelchair propulsion.

To study the effect of seat height on the cardiorespiratory system and kinematics in handrim wheelchair ambulation, nine non-wheelchair users participated in a wheelchair exercise experiment on a motor-driven treadmill. The subjects conducted five progressive exercise tests. After an initial try-out test, four tests were performed at different standardized seat heights of 100, 120, 140, and 160 degrees elbow extension (subject sitting erect, hands on the rim in top-dead-center = 12.00 hrs; full extension = 180 degrees). Each test consisted of four 3-minute exercise blocks at speeds of respectively 0.55, 0.83, 1.11, and 1.39 m.s-1 (2-5 km.hr-1). Analysis of variance revealed significant effects of seat height (P less than 0.05) on gross mechanical efficiency (ME), oxygen cost, push range, and push duration, and on the ranges of motion in the different arm segments and trunk. Mean ME appeared higher at the lower seat heights of 100 and 120 degrees elbow extension. This is reflected in an enhanced oxygen consumption at seat heights of 140 and 160 degrees elbow extension. Simultaneously, the push range showed a 15 to 20 degree decrease with increasing seat height, which is reflected in a decreased push duration. In the push phase, decreases in retroflexion and abduction/adduction of the upper arm were seen. The trunk shifted further forward, and the motion range in the elbow joint shifted to extension with increasing seat height. No shifts in minimum and maximum angular velocities were seen with increasing seat height. The results showed an interrelationship between wheelchair seat height and both cardiorespiratory and kinematic parameters. With respect to the cardiorespiratory system, the optimization of the wheelchair geometry, based on functional characteristics of the user, appears beneficial.

Wheelchair propulsion technique at different speeds.

To study wheelchair propulsion technique at different speeds, five well-trained subjects propelled a wheelchair on a treadmill. Measurements were made at four belt speeds of 0.56-1.39 m/s and against slopes of 2 and 3 degrees. Cardiorespiratory data were collected. Three consecutive strokes were filmed. Using markers on subject, wheelchair and treadmill frame a kinematic analysis was performed. Considerable inter-individual differences in propulsion style were found, but also general changes relative to speed occurred in the group as a whole. Cycle time decreased with speed, predominantly as the result of a shorter push time while push angle remained constant and the movement ranges of trunk and arms shifted with speed. It is concluded that despite different propulsion styles, general and continuous adaptations to speed changes occurred, mainly by flexion of the trunk and arms.

Growth of medial gastrocnemius muscle and Achilles tendon in Wistar rats.

Dimensions, architecture, material properties and functional characteristics of medial gastrocnemius muscles and Achilles tendons of young and old Wistar rats were compared. Dimensions associated with length of the leg segment grow isometric with it. Muscle belly transsectional dimensions, volume of muscle tissue and associated functional indices increase out of proportion either with the dimensions of the limb segment or the weight of the animal. As the properties of the contractile tissue remain the same and relative proportions of tissue components alter, changes in architecture result. These are not reflected in transsection of the tendon. Functional characteristics of the muscle tendon complex can be explained by architectural or dimensional-peculiarities emerging in the complex by growth processes of which the main is that the muscle belly of this pennated muscle grows in length mainly by increments in girth of the muscle fibers proper.

Propulsion technique in hand rim wheelchair ambulation.

Six male subjects took part in a pilot study on a stationary wheelchair ergometer. They propelled the ergometer at a speed of 0.55, 0.83, 1.11 and 1.39 m/s. The speed increased every 3 min. Inertia and friction force were adjusted proportional to body weight. Every third minute 750 samples of the torque and velocity signals were digitized at a sampling rate of 100 Hz. From the signals mean external power output (Pmean), peak power (Ppeak), mean torque (Mmean) and peak torque (Mpeak), work/cycle, 'time-to-peak torque' (TTP), cycle duration (CT), push time (PT) and recovery time (RT) were determined in relation to mean velocity (speed). For the mean velocity range studied, analysis of variance (P less than 0.05) revealed significant increments in Ppeak, Mpeak, Pmean, Mmean and work/cycle with increasing mean velocity, whereas CT and PT showed a significant decrease. TTP showed a decrease with speed which, however, was not statistically significant. The RT showed no significant variation as well. Our previous research into propulsion techniques mainly focused on movement frequency and timing and was conducted during wheelchair ambulation on a motor driven treadmill. Despite considerable interindividual variation in terms of movement pattern, current and previous studies showed similar trends in the timing pattern (cycle, push, recovery duration) with respect to speed. Theoretical considerations regarding variations in peak torque and work/cycle with respect to velocity are supported by the current results. Both torque and work/cycle are important technique parameters and of relevance in speed regulation. The data also suggest that wheelchair ambulation can be validly simulated and studied with the special purpose wheelchair ergometer.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of rear wheel camber in manual wheelchair propulsion.

Eight nonimpaired subjects participated in a wheelchair exercise test using a motor-driven treadmill in order to study the effect of rear wheel camber on wheelchair ambulation. The test consisted of four runs with rear wheels in 0, 3, 6, and 9 degrees camber at four speed steps of 2, 3, 4, and 5 km/hr. There were no significant effects upon oxygen cost, heart rate, and mechanical efficiency. The kinematic parameters of push time, push angle, and abduction showed differences between 3 and 6 degrees camber. The relationship between the findings, using surface EMG results for six shoulder muscles, is discussed. For one subject, data were extended to study the angular velocities of shoulder and elbow.