Optimum cycle frequencies in hand-rim wheelchair propulsion. Wheelchair propulsion technique

To study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n = 6) and non-wheelchair users (NW group; n = 6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m.s-1 and a slope of 2 degrees. The NW group wheeled at 0.83, 1.11 and 1.39 m.s-1 and a 1 degree slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied. Analysis of variance showed a significant effect (p less than 0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p less than 0.05). Oxygen cost was approximately 10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinematic features of wheelchair propulsion

Three male paraplegics volunteered to push their wheelchairs on a motor driven treadmill, for a total of 80 min each, at a work rate of 60-65% of their VO2 maximum, determined on an earlier test session. At 20 min intervals 16 mm high-speed film of the subjects was taken for three consecutive push cycles. The digitized film was used to compute the angular kinematics of the shoulder and elbow joints, the variations in the position of the trunk (as measured by a marker on the neck) and hand relative to the axle of the rear wheel. There were no intrasubject variations over the 80 min testing period for any of the recorded variables. This was interpreted as implying that at that work rate, fatigue was not exhibited as variations in the kinematics of movement. There were considerable differences between the style of one subject when compared to the other two over all the trials of each subject. This variation in style was most obvious in subject number PT who had a pumping style of push and recovery whereas subjects CA and GW employed a more continuous circular motion. The differences in the amount of forward lean of each subject were related to residual muscle strength. The discussion centered on the influence of the different styles on performance.     

Prediction of applied forces in handrim wheelchair propulsion

Researchers of wheelchair propulsion have usually suggested that a wheelchair can be properly designed using anthropometrics to reduce high mechanical load and thus reduce pain and damage to joints. A model based on physiological features and biomechanical principles can be used to determine anthropometric relationships for wheelchair fitting. To improve the understanding of man-machine interaction and the mechanism through which propulsion performance been enhanced, this study develops and validates an energy model for wheelchair propulsion. Kinematic data obtained from ten able-bodied and ten wheelchair-dependent users during level propulsion at an average velocity of 1m/s were used as the input of a planar model with the criteria of increasing efficiency and reducing joint load. Results demonstrate that for both experienced and inexperienced users, predicted handrim contact forces agree with experimental data through an extensive range of the push. Significant deviations that were mostly observed in the early stage of the push phase might result from the lack of consideration of muscle dynamics and wrist joint biomechanics. The proposed model effectively verified the handrim contact force patterns during dynamic propulsion. Users do not aim to generate mechanically most effective forces to avoid high loadings on the joints.     

An elastic analysis of Listeria monocytogenes propulsion

The bacterium Listeria monocytogenes uses the energy of the actin polymerization to propel itself through infected tissues. In steady state, it continuously adds new polymerized filaments to its surface, pushing on its tail, which is made from previously cross-linked actin filaments. In this paper we introduce an elastic model to describe how the addition of actin filaments to the tail results in the propulsive force on the bacterium. Filament growth on the bacterial surface produces stresses that are relieved at the back of the bacterium as it moves forward. The model leads to a natural competition between growth from the sides and growth from the back of the bacterium, with different velocities and strengths for each. This competition can lead to the periodic motion observed in a Listeria mutant.     

Short-term adaptations in co-ordination during the initial phase of learning manual wheelchair propulsion.

The purpose of this study was to analyse adaptations in kinematics and muscle activity/co-contraction in novice able-bodied subjects during the initial phase of learning hand rim wheelchair propulsion. Nine able-bodied subjects performed three 4-min practice blocks on a wheelchair ergometer. The external power output and velocity were constant for all blocks, respectively 0.25 W x kg(-1) and 1.11 m x s(-1). Electromyography of 16 arm, shoulder, back and chest muscles and kinematics were measured. Some small changes in the segmental movement pattern were seen during the practice period. Moreover, an increase in muscle activity and co-contraction of several muscles was found over time. The hypothesis that subjects instinctively search for an optimum frequency, in which the recovery phase is related to the eigenfrequency of the arms and, therefore, the least muscle activity, could not be supported. Since co-contraction of antagonist pairs remained the same or even increased, the hypothesis that there would be a decrease in muscle co-contraction as a result of practice, was not confirmed. This study was probably too short for the novice subjects to explore this new task of wheelchair propulsion completely and reach an optimum in terms of cycle frequency and muscle activity/co-contraction.     

A comparison of static and dynamic optimization muscle force predictions during wheelchair propulsion

The primary purpose of this study was to compare static and dynamic optimization muscle force and work predictions during the push phase of wheelchair propulsion. A secondary purpose was to compare the differences in predicted shoulder and elbow kinetics and kinematics and handrim forces. The forward dynamics simulation minimized differences between simulated and experimental data (obtained from 10 manual wheelchair users) and muscle co-contraction. For direct comparison between models, the shoulder and elbow muscle moment arms and net joint moments from the dynamic optimization were used as inputs into the static optimization routine. RMS errors between model predictions were calculated to quantify model agreement. There was a wide range of individual muscle force agreement that spanned from poor (26.4% F_max error in the middle deltoid) to good (6.4% F_max error in the anterior deltoid) in the prime movers of the shoulder. The predicted muscle forces from the static optimization were sufficient to create the appropriate motion and joint moments at the shoulder for the push phase of wheelchair propulsion, but showed deviations in the elbow moment, pronation–supination motion and hand rim forces. These results suggest the static approach does not produce results similar enough to be a replacement for forward dynamics simulations, and care should be taken in choosing the appropriate method for a specific task and set of constraints. Dynamic optimization modeling approaches may be required for motions that are greatly influenced by muscle activation dynamics or that require significant co-contraction.     

The influence of altering push force effectiveness on upper extremity demand during wheelchair propulsion

Manual wheelchair propulsion has been linked to a high incidence of overuse injury and pain in the upper extremity, which may be caused by the high load requirements and low mechanical efficiency of the task. Previous studies have suggested that poor mechanical efficiency may be due to a low effective handrim force (i.e. applied force that is not directed tangential to the handrim). As a result, studies attempting to reduce upper extremity demand have used various measures of force effectiveness (e.g., fraction effective force, FEF) as a guide for modifying propulsion technique, developing rehabilitation programs and configuring wheelchairs. However, the relationship between FEF and upper extremity demand is not well understood. The purpose of this study was to use forward dynamics simulations of wheelchair propulsion to determine the influence of FEF on upper extremity demand by quantifying individual muscle stress, work and handrim force contributions at different values of FEF. Simulations maximizing and minimizing FEF resulted in higher average muscle stresses (23% and 112%) and total muscle work (28% and 71%) compared to a nominal FEF simulation. The maximal FEF simulation also shifted muscle use from muscles crossing the elbow to those at the shoulder (e.g., rotator cuff muscles), placing greater demand on shoulder muscles during propulsion. The optimal FEF value appears to represent a balance between increasing push force effectiveness to increase mechanical efficiency and minimize upper extremity demand. Thus, care should be taken in using force effectiveness as a metric to reduce upper extremity demand.     

An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes.

The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of current-voltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.     

Effect of resistance load on biomechanical characteristics of racing wheelchair propulsion over a roller system

The purpose of this study was to examine how resistance load influenced the kinematic characteristics and the activity of selected muscles (flexor and extensor carpi radialis, biceps brachii, triceps brachii, antero-middle and postero-middle deltoids, pectoralis major, and upper trapezius) during maximum effort racing wheelchair stroking using 3D videographic and surface EMG techniques. Fifteen male experienced wheelchair racers served as subjects and three consecutive stroke cycles were analyzed for two load conditions. In contrast to previous studies where variations in speed were a result of variations in pushing effort or disability classification, a reduction in stroking speed caused by increasing load did not result in a decrease in stroking frequency. Increases in load significantly influenced the push and recovery times but not the stroke time or frequency. The vertical ranges of motion and vertical velocities at initial hand contact of the upper extremity joints decreased significantly from light to heavy resistance conditions. These results suggest that the vertical motion is influenced greatly by the load. Various degrees of muscle co-contractions were observed in most phases of the stroke cycle. The activation pattern of the deltoid muscle was different from what has been previously reported, probably because of the exaggerated forward lean trunk position adopted by our subjects. Although the overall EMG activity remained the same or decreased when the resistance was increased, stroking under a heavy resistance load is likely to be more demanding physiologically because of the greater push time-recovery time (work-rest) ratio with increasing resistance.     

An on-line method for the collection and analysis of quasi-steady-state kinetic data for enzyme-catalyzed reactions.

A special mixing device for initiating enzyme-catalyzed reactions is used to rapidly achieve an unperturbed quasi-steady state. An on-line computer is employed to sample the initial conditions, the mixing time, and concentrations that change as a function of time during this quasi-steady state phase. A statistical method for estimating initial, quasi-steady state rates from the time course of the enzyme-catalyzed reaction is described. Practical considerations for using this parameter estimation system lead to the conclusion that for the enzyme-catalyzed reaction tested, the extent overall reaction should be above .2% for high initial substrate concentrations, and above 1% for initial substrate concentrations in the range of the Michaelis constant. Application of this method to a typical enzyme-catalyzed reaction suggests that objective estimates of initial rates from a given set of concentrations and corresponding times can be obtained with a standard error in the range of 2–3%, but that reproducibility is not better than about 10%. When this procedure was used to estimate initial rates for the glycerol dehydrogenase-catalyzed oxidation of glycerol by NAD, it was found that this enzyme did not behave according to the classical “Michaelis-Menten” mechanism of enzyme action.     

An active porous medium model for ciliary propulsion

The velocity profile in the cilia sublayer on dense ciliated cell surfaces is calculated by using an active porous medium model. Calculations using the beat patterns observed on Opalina and in cilia lining the airways of the lung predict maximum velocities similar to those observed in nature.     

Upper limb joint kinetics during manual wheelchair propulsion in patients with different levels of spinal cord injury

The purpose of this study was to compare the forces and moments of the whole upper limb, analyzing forces and moments at the shoulder, elbow and wrist joints simultaneously during manual wheelchair propulsion of persons with different levels of spinal cord injury (SCI) on a treadmill. Fifty-one people participated in this study and were grouped by their level of SCI: C6 tetraplegia (G1), C7 tetraplegia (G2), high paraplegia (G3), and low paraplegia (G4). An inverse dynamic model was defined to compute net joint forces and moments from segment kinematics, the forces acting on the pushrim, and subject anthropometrics. Right side, upper limb kinematic data were collected with four camcorders (Kinescan–IBV). Kinetic data were recorded by replacing the wheels with SmartWheels (Three Rivers Holdings, LLC). All participants propelled the wheelchair at 3 km/h for 1 min. The most noteworthy findings in both our tetraplegic groups in relation to paraplegic groups were increased superior joint forces in the shoulder (G1 and G2 vs G3 p<0.001; G1 and G2 vs G4 p<0.01), elbow (G1 vs G3 p<0.001; G1 vs G4 p<0.05) and wrist (G1 vs G4 p<0.001), an increased adduction moment in the shoulder (G1 vs G3 p<0.001; G1 vs G4 p<0.01; G2 vs G3 and G4 p<0.05) and the constancy of the moments of force of the wrist the fact that they reached their lowest values in the tetraplegic groups. This pattern may increase the risk of developing upper limb overuse injuries in tetraplegic subjects.     

Method for kinetic analysis of drug-induced cell cycle perturbations.

A method is described for quantitative study of the flux of cells through the cell cycle phases in in vitro systems perturbed by chemicals, such as chemotherapeutic agents. The method utilizes cell count and the flow cytometric technique of bromodeoxyuridine (BrdUrd) labeling, according to an optimized strategy. Cells are exposed to BrdUrd during the last minutes of drug treatment and fixed for analysis at 0, 1/3Ts, 2/3Ts, Ts, and Tc + TG1 recovery times, where Ts, TG1, Tc are the mean durations of phases S and G1 and of the whole cycle of control cells. As an example of application of the proposed procedure, a kinetic study of the effect of 1-(2-chloroethyl)-1-nitrosourea (CNU) on the L1210 cell cycle is described. Simple data analysis, requiring only a pocket calculator, showed that cells in phases G1 and G2M at the end of a 1 h treatment with 1 microgram/ml CNU were fully able to leave these phases but were destined to remain blocked in the following G2M phase (G1 for a minority of them). We also found that cells initially in S phase were slightly delayed in completing their S phase and that 50% of them remained temporarily blocked in the subsequent G2M phase, irrespective of their position in the S phase.     

Multi-enzyme kinetic analysis of glycolipid biosynthesis.

Gangliosides are acidic glycosphingolipids synthesized sequentially by a series of glycosyltransferases acting in parallel biosynthetic pathways. While most glycosyltransferases are highly specific, some, however, may catalyze equivalent steps in each pathway using different gangliosides as substrates (e.g. N-acetylgalactosaminyltransferase, sialyltransferase-IV). A multi-enzyme kinetic analysis was developed on the condition that serial enzymatic reactions operate below substrate saturation. A multi-enzyme kinetic analysis enabled a simultaneous calculation of the Vmax/Km value of each enzyme derived from the equilibrium concentration of the respective substrate. Substrate concentrations [S] were determined by radioactive labelling of gangliosides in intact cells with the precursor sugars [14C]galactose and [14C]glucosamine, followed by high-performance thin-layer chromatography and autoradiography of the radiolabelled glycolipids. On the basis of Michaelis-Menten kinetics, Vmax/Km values were derived from [S] by a system of linear equations. The procedure was used to analyze the development of the glycolipid composition during differentiation of rat gliomaxmurine neuroblastoma (NG108-15) cells. The Vmax/Km values calculated by multi-enzyme kinetic analysis were consistent with the kinetic data obtained with solubilized enzymes. Application of multi-enzyme kinetic analysis to published data on the correlation of enzyme activities with ganglioside levels in various cell lines and tissues indicated the validity of this method for analysis of the glycolipid biosynthesis, in particular, of its initial steps. On the basis of the kinetic analysis, it is suggested that the cell lines can be divided into two groups with respect to the substrate pools of GM3 used by sialyltransferase-II and N-acetylgalactosaminyltransferase-I. The first group encompasses the majority of the neuroblastoma cell lines and the embryonic rat brain where the two enzymes share a common pool of GM3. In the second group, the two enzymes do not compete for the same pool of GM3, indicating a different subcellular localization of CMP-NeuAc:GM3 alpha2-8-sialyltransferase and UDP-N-acetylgalactosaminyl:GM3 N-acetylgalactosaminyltransferase. In this study, the theory of a multi-enzyme kinetic analysis is discussed and its application to analysis of the glycolipid biosynthesis in neuroblastoma cells is demonstrated. A multi-enzyme kinetic analysis can be applied to other biosynthetic pathways and provides the advantage of analyzing kinetic data with intact cells or tissue samples.     

An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes

Summary The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of currentvoltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for the carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.     

Kinematic analysis of the 100-m wheelchair race

The purpose of this study was to compare the speed and selected stroke cycle characteristics during different phases of the 100-m wheelchair race for paraplegic athletes. Four male and two female wheelchair racers in T4 classification and one male and three female athletes in T3 classification served as the participants. Two S-VHS camcorders (60 fields/s) were panned horizontally to cover the first and second 50 m of the 100-m race, respectively. Average speed, stroke length and frequency, contact and recovery times during the first 10 m (initial acceleration phase, IAP), the maximum speed phase (MSP), and the last 10 m (final phase, FP) of the race were determined. For each parameter, an ANOVA with repeated measures was performed and Tukey post hoc tests were completed when appropriate (alpha=0.01). The 100-m times ranged from 16.10 to 22.18 s. Significant differences were found between IAP and MSP and between IAP and FP in stroke speed, stroke length, and push and recovery times, but not in stroke frequency. The relatively constant stroke frequency across different phases may suggest that wheelchair racers like to maintain the same stroking rhythm throughout a 100-m race. The distance and time needed to reach the maximum speed ranged from 43.9 m and 11.2 s to 82.2 m and 18.9 s, respectively. The significant correlation between 100-m time and maximum speed (p<0.001) signifies the importance of maximum speed in determining 100-m performance.     

Versatile, protective jacket for chronically instrumented dogs.

A versatile nylon jacket was designed for mixed-breed dogs to permit easy access to cardiac instrumentation and to protect the leads when not in use.     

An instrumented,dynamic test for anterior laxity of the ankle joint complex

Evaluation of anterior laxity of the ankle joint complex is a difficult clinical problem. Currently, the prime determinant for anterolateral ligament function is the subjective manual examination of anterior laxity of the ankle joint complex. An instrumented dynamic test was developed for objective measurement of anterior laxity of the ankle joint complex. The principle of the test was to apply a force-impulse to the calcaneus, within the muscle reflex time, and to measure anterior–posterior and mediolateral rotation. The test was performed on a cadaver specimen and on 15 volunteers of which five subjects suffered from chronic one-sided lateral ankle ligament instability.

In the cadaver test, anterior translation values increased from 5 to 11 mm, after cutting the anterior talofibular ligament and subsequently cutting the calcaneofibular ligament. In the 10 normal subjects, the mean anterior translation value was 6.7 mm (±1.9 mm). The relative variation of the test result within a measurement session was 2.5% (±1.6%). Between the sessions the relative laxity variation was 2.6% (±2.6%). In the ten normal subjects the mean right–left difference was not significantly different from zero. In four out of the five patients it was more than 2 mm. As in the cadaver test in all measurements, the mediolateral rotations were small (<2.5°). The volunteers complained about same pain at the heel after multiple test sessions.

In conclusion the dynamic, functional test appears to be capable of objectively measuring a value for anterior laxity of the ankle joint complex reflecting the functional status of the anterolateral ankle ligaments.