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PubMed2004

Instant of chair-rise lift-off can be predicted by foot-floor reaction forces.

OBJECTIVE: To develop a predictive model of the lift-off event during chair rise in healthy subjects, using foot-floor reaction forces. BACKGROUND: An important event during chair rise is lift-off from the seat: the transition from the inherently stable three-point contact to the unstable two-point contact. There is no consistent or generally agreed upon method for estimating the time of lift-off when an instrumented seat is unavailable. METHODS: Twenty healthy volunteers were divided into a testing set and training set. Each subject performed repeated chair rise trials at different speeds. Seat-floor and foot-floor forces, recorded with two force platforms, were used to develop a model of the lift-off event. RESULTS: The magnitude of the vertical foot-floor reaction at lift-off (F0VF) was linearly related (R2 = 0.71, P < 0.001) to the peak vertical foot-floor reaction force (FMVF). A linear model was developed for the training group, which enabled prediction of lift-off time for the testing group with an absolute average error of 6 ms (about 1 data frame at 150 Hz). The linear model derived for the entire sample was: F0VF = 28.14 + FMVF * (0.6434). CONCLUSIONS: The lift-off event for healthy subjects performing chair rise can be accurately predicted from foot-floor reaction forces, without requiring an instrumented seat.

Body Weight↗

PubMed1996

Contralateral shoe-lift: effect on oxygen cost of walking with an immobilized knee.

OBJECTIVE: Evaluate the effect of a contralateral shoe-lift on the oxygen cost of walking with an artificially immobilized knee. DESIGN: A prospective quantitative evaluation of oxygen cost of walking under varying conditions. Subjects walked (1) normally (N), (2) with one knee immobilized (1), (3) with one knee immobilized and with a one-half-inch shoe-lift applied to the contralateral shoe (I1/2"L), and (4) with one knee immobilized and with a one-inch shoe-lift (I1"L). SETTING: Exercise physiology laboratory. SUBJECTS: Ten able-bodied subjects without known cardiopolmonary or musculoskeletal problems. MAIN OUTCOME MEASURE: Breath-by-breath oxygen consumption measurements in mL/kg/m. RESULTS: Oxygen cost on average was 20% more with the knee immobilized (I) compared to normal (N) (mean difference = .0298 +/- .0245mL/kg/m, p = .002). Oxygen cost was significantly less (11% versus 20% above that of normal walking) with the half-inch shoe-lift (mean difference between I1/2" and I = .0167 +/- .0138mL/kg/m, p = .002). Similarly, oxygen cost was significantly less (12% versus 20% above that of normal walking) with the one-inch shoe-lift (mean difference between I1"L and I = .0142 +/- .0116, p = .002). CONCLUSION: This study demonstrates that a subject with an immobilized knee requires less energy to walk with a contralateral shoe-lift and provides scientific evidence for prescribing a shoe-lift in patients with an immobilized knee as a result of knee joint fusion, knee immobilization as a result of casting or orthotics, or spastic paretic stiff-legged gait associated with upper motor neuron disease.

Adult↗

PubMed2001

Metabolic cost of walking with and without a shoe lift on the contralateral foot of an immobilised extended knee.

The purpose of the present study was to determine the metabolic cost of walking with and without a shoe-lift on the contralateral foot of an immobilised extended knee. Eight male subjects were randomly allocated and participated in both the treatment (walking with a 2.5 cm shoe-lift) and control (walking without a shoe-lift) conditions. Cardiac output (Q) and related cardiovascular measurements were analysed to determine the effect of a shoe-lift on central (heart rate (HR); stroke volume (SV)) and peripheral (arteriovenous oxygen difference (a-vO2 diff)) components of oxygen consumption (VO2). A metabolic analyser was used to determine VO2 (ml x kg(-1) x min(-1)), which was converted to oxygen cost (ml x kg(-1) x m(-1)). The shoe-lift had no significant (p > 0.05) effect on VO2 or oxygen cost. There were no significant differences in Q, HR, SV, a-vO2 diff, systemic vascular resistance, carbon dioxide production, respiratory exchange ratio, expired ventilation, tidal volume and respiratory rate between the two walking conditions with and without a shoe-lift. These findings demonstrate that a shoe-lift added to the contralateral foot of an immobilised extended knee does not produce clinically important effects on oxygen cost or efficiency during walking.

Adult↗

PubMed2003

Evidence for a role of antagonistic cocontraction in controlling trunk stiffness during lifting.

Activity of the abdominal muscles during symmetric lifting has been a consistent finding in many studies. It has been hypothesized that this antagonistic coactivation increases trunk stiffness to provide stability to the spine. To test this, we investigated whether abdominal activity in lifting is increased in response to destabilizing conditions. Ten healthy male subjects lifted 35 l containers containing 15 l of water (unstable condition), or ice (stable condition). 3D-kinematics, ground reaction forces, and EMG of selected trunk muscles were recorded. Euler angles of the thorax relative to the pelvis were determined. Inverse dynamics was used to calculate moments about L5S1. Averaged normalized abdominal EMG activity was calculated to express coactivation and an EMG-driven trunk muscle model was used to estimate the flexor moment produced by these muscles and to estimate the L5S1 compression force. Abdominal coactivation was significantly higher when lifting the unstable load. This coincided with significant increases in estimated moments produced by the antagonist muscles and in estimated compression forces on the L5S1 disc, except at the instant of the peak moment about L5S1. The lifting style was not affected by load instability as evidenced by the absence of effects on moments about L5S1 and angles of the thorax relative to the pelvis. The data support the interpretation of abdominal cocontraction during lifting as subserving spinal stability. An alternative function of the increased trunk stiffness due to cocontraction might be to achieve more precise control over the trajectory of lifted weight in order to avoid sloshing of the water mass in the box and the consequent perturbations.

Abdomen↗

PubMed2003

Trunk muscle response to lifting unbalanced loads with and without knowledge of centre of mass.

OBJECTIVE: To examine the effects of lifting a bin with a variable centre of mass on muscle activity, with and without knowledge of the centre of mass. BACKGROUND: Numerous parameters related to lifting have been examined yet the effects of changing the load centre of mass in two dimensions, with or without knowledge, has not been examined. METHODS: Participants lifted a 6 kg industrial tote bin with a 7 and 11 kg mass randomly placed in each of nine compartments, into which the interior of the bin was partitioned. Participants were not restricted in lifting style other than using the handles, which were equipped with force gauges. Two series (9 lifts per series) were completed using the 7 kg load without knowledge of the load placement and one series with knowledge of the load placement. One series was completed using an 11 kg mass without knowledge of load placement. Electromyographic activity of the upper and lower erector spinae, latissimus dorsi and the external obliques were collected bilaterally. RESULTS: Left and right muscle pairs demonstrated mirror images for all muscles with lowest activity levels when the load was placed nearer the lifter in the sagittal plane. Peak electromyographic activity of the upper erector spinae and latissimus dorsi increased with the weight in the compartments nearest the body and/or the ipsilateral handle. Conversely, peak electromyographic activity of the lower erector spinae and the obliques increased when the weight was on the contralateral side. Peak upper erector electromyographic activity reached up to 41% of maximum and the lower erectors reached 50% of maximum, while the obliques and latissimus dorsi were below 5% and 7%, respectively. No electromyographic activity differences were found between the known and unknown load placements. DISCUSSION: A segmental control strategy appears to exist during lifting that works from the upper to lower torso based on peak electromyographic activity activity. When lifting a bin with a varied centre of mass, highest peak electromyographic activity for the upper and lower erector spinae occurred when the load is closest to the body, regardless of load knowledge. Based on our findings with asymmetrical loads, we conclude that the moments acting on the wrist play an important role in spinal loading and must be included in future studies. RELEVANCE: Asymmetrical loads are often encountered in daily life. Regardless of the lifter's knowledge of the balance of the load, the differential and asymmetrical loading of the muscles of the back play a role in the development of low back pain.

Abdominal Muscles↗

PubMed2002

The effect of shoe wedges and lifts on symmetry of stance and weight bearing in hemiparetic individuals.

OBJECTIVE: To determine the effect of shoe wedges and lifts on symmetry of stance and weight bearing in hemiparetic individuals. DESIGN: Weight bearing on the paretic side was measured in patients with hemiparesis during quiet standing and in conditions of compelled weight shift. SETTING: Free-standing acute inpatient rehabilitation hospital. PARTICIPANTS: Nine individuals with hemiparesis as a result of unilateral stroke who were able to stand for 3 to 5 minutes without assistance or rest, and satisfied other inclusion criteria. INTERVENTIONS: Compelled shift of the body weight was induced with different shoe wedges (5 degrees, 7.5 degrees, 12.5 degrees) or shoe lifts (0.6, 0.9, 1.2cm), which extended under the entire shoe of the unaffected limb. Weight-bearing symmetry scores were used to characterize the symmetry of stance. MAIN OUTCOME MEASURES: Weight-bearing symmetry scores. RESULTS: Without a shoe wedge or a shoe lift, weight-bearing symmetry was characterized by underloading of the paretic limb (39.90% +/-.80% of body weight). Weight shift induced by shoe wedges or shoe lifts applied to the unaffected limb promoted improved symmetry of weight bearing and stance. A shoe wedge of 5 degrees provided the most symmetrical weight distribution (51.44% +/- 1.88% of body weight). CONCLUSION: Shoe wedges and shoe lifts under the unaffected limb induced compelled weight shift toward the paretic limb, resulting in improved symmetry of stance of individuals with mild hemiparesis. We suggest that improved symmetry of bipedal standing obtained with a shoe wedge or a shoe lift applied to the unaffected limb can help overcome the learned disuse of the affected limb. We further suggest that weight distribution induced by shoe wedges or shoe lifts may help in the treatment of ambulatory hemiparetic individuals with asymmetrical stance caused by unilateral stroke.

Adult↗

PubMed2000

Prevention and correction of the "face-lifted" appearance.

In spite of the increasing demand and popularity of facial rejuvenation procedures, there has been little real change of traditional techniques over the past few decades. Face lifts continue to be lateral vector techniques, whether skin lifts, superficial musculoaponeurotic system (SMAS) lifts, or deep plane malar fat maneuvers are done. Lower eyelid procedures continue to include removal of orbital fat in most cases. Laser blepharoplasties combine transconjunctival fat removal with laser skin abrasion. Forehead lifts continue to be optional in most cases, in spite of clear indications. The unfortunate results of these traditional procedures that may occur are becoming easy to recognize. The unopposed tension of lateral vector face lifts allows the cheek tissues to descend eventually over the tightened jawline, creating a "lateral sweep" or pulled appearance of the face. A crescent-shaped mound over the malar area is the inferior orbicularis oculi muscle, not repositioned with conventional procedures. Following conventional blepharoplasty, the lower eyelid contour becomes deeper, and often an hollow appearance develops. A composite face lift combined with an arcus marginalis release can correct these typical problems. The primary vector of the face is superiomedial, which will reverse the unopposed tension of lateral vector techniques and reposition the cheek tissues to their original position. The arcus marginalis release combined with repositioning of the complete orbicularis muscle in a zygorbicular midface flap can be used to correct the most severe hollow lower eyelid. Unwanted and unattractive results are not the fault of the surgeon or the patient but are caused by the surgical technique. As a primary rejuvenative procedure, a composite rhytidectomy will deliver an impressive result that will disallow the ultimate lateral sweep and hollow eyes. In patients that have the unhappy signs of surgery this procedure can effectively correct the face-lifted appearance.

Adipose Tissue↗

PubMed1992

Biomechanical exploration on dynamic modes of lifting.

Whatever the lifting method used, dynamic factors appear to have an effect on the safe realization of movement, and NIOSH guidelines recommend smooth lifting with no sudden acceleration effects. On the other hand, inertial forces may play an important role in the process of transfer of momentum to the load. The direction by which these inertial forces may affect the loadings on body structures and processes of energy transfers cannot be determined a priori. A biomechanical experiment was performed to examine if there were differences in the execution processes between a slow-continuous lift and an accelerated-continuous lift, and also between accelerated lifts either executed continuously or interrupted with a pause. The lifts were executed from a height of 15 cm to a height of 185 cm above the head and with two different loads (6.4 and 11.6 kg). Five experienced workers in manual materials handling were used as subjects. Films and force platforms recordings supplied the data; dynamic segmental analyses were performed to calculate net muscular moments at each joint; a planar single-muscle equivalent was used to estimate compression loadings at L5/S1; total mechanical work, joint work distribution, and energy transfers were determined from a kinetic approach based on the integration of joint power as a function of time. Analyses of variance with repeated measures were applied to the three treatments. The results showed that joint muscular moments, spinal loadings, mechanical work, and muscular utilization ratios were generally increased by the presence of acceleration without inducing benefits of improved energy transfers; therefore slower lifts with reduced acceleration may be safer when handling moderately heavy loads. The maximum values of kinematic and kinetic factors were generally not affected by the pause, but the occurrence of jerks in the movement (acceleration, ground forces, and muscular moments) suggests that the pause may not be indicated when considering total exposure to muscular exertion. Full consideration should be given to the dynamics of motion when assessing risk factors in working tasks.

Acceleration↗

PubMed1992

Influence of body segment dynamics on loads at the lumbar spine during lifting.

Flexion-extension moments acting at the L5/S1 level and hip joints were calculated using three different techniques; a pure static analysis, a static analysis including the inertial force of the load, and a dynamic analysis. Ten subjects participated in the study and were asked to lift a box weighing either 50 N or 150 N, using a freestyle technique. The lifts were performed at normal and fast speed. The intra-subject lifting techniques were consistent when lifting the same loads. The moments predicted by the dynamic analysis and the static analysis were the same when holding weights in static postures. When performing the lifts, differences in the peak moments occurred between static and dynamic analyses. These differences were influenced by external load and by lifting speed. Taking the effect of the inertia of load into account in the static analysis resulted in an increase in the moment magnitude, but the predicted moment was still much less than in the dynamic analysis which yielded the largest moment magnitudes. The difference between dynamic and static analysis was greatest when lifting 50 N at fast speed; an 87% increase in L5/S1 moment and a 95% increase in hip moment was observed when replacing the pure static with a dynamic analysis.

Adult↗

PubMed1993

The influence of load knowledge on lifting technique.

The purpose of this study was to analyse the influence of load knowledge on lifting technique. Ten men lifted a box containing either no weight or weights of 150, 250 or 300 N with and without knowledge of what was inside the box. The kinetics and kinematics of the lift were analysed using a force plate, an optoelectronic motion analysis system, and a rigid body link model. At 0 N lifting, the unknown load resulted in a jerk-like motion and a significantly increased peak L5-S1 flexion-extension moment. At 150 N there was also a significant increase in the speed of trunk extension with unknown weights, but the L5-S1 moment remained unchanged. At higher load levels there were only minor differences between lifting techniques when knowing and not knowing the load. We conclude that lifts are approached assuming a certain weight, and that when the assumption is wrong and the load lighter than anticipated lifting is performed with a 'jerking' motion, creating unnecessary loads on the lower back.

Adult↗

PubMed1985

Physiological stresses in warehouse operations with special reference to lifting technique and gender: a case study.

A field study was conducted to evaluate the effects of lifting technique (free-style vs. straight-back, bent-knee) on male workers' performances and physiological responses. A secondary objective was to study physiological stresses to female order selectors using the free-style lifting technique only. Six male and six female workers performed their routine work of grocery order selection in three different warehouses while their oxygen uptake and heart rates were measured. Workers' performances were determined using the traditional work measurement techniques (time study, methods time measurement and master standard data systems) employed by the warehouses. Total cases, weight, volume, actual and allowed time for each order were also determined. Statistical analysis showed that the performance levels of the male workers (allowed time per order * 100/actual time per order) were significantly lower and oxygen uptake and heart rates were higher for the straight-back, bent-knee method as compared to the free-style lifting technique. Male workers lifted more cases, weight and volume/min with the free-style lifting technique than with the straight-back, bent-knee method. It is concluded that the traditionally recommended straight-back, bent knee method of lifting is slower and physiologically more demanding. It is practically impossible for a substantial number of workers to meet the existing time or performance standards based on traditional work measurement techniques--when using the straight-back, bent-knee method of lifting recommended by the warehouses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Prediction of maximum acceptable weight of lift in the horizontal and vertical planes using simulated job dynamic strengths.

An investigation was undertaken to determine the feasibility of predicting maximum weights of lift that are acceptable to individuals by measuring the individuals' simulated job dynamic strengths. Since almost all manual materials handling jobs are dynamic in nature, it was hypothesized that correlations between maximum weights acceptable for lifting and the dynamic strengths measured under similar conditions would be high compared to isometric strengths. If so, then a relatively simple procedure can be developed to estimate what people are willing to lift safely. With the use of a specially designed and constructed three-dimensional dynamic strength simulator, 19 males and 6 females lifted loads in two vertical and two horizontal planes. Their dynamic strengths also were measured under identical conditions. The correlations between simulated job dynamic strengths and acceptable weights of lift were much higher (0.52 to 0.67) compared to correlations between isometric strengths and acceptable weights of lift (0.29 to 0.38). This also confirmed earlier findings that dynamic strengths are more suitable predictors of the maximum weights people are willing to handle. Simple equations are presented between simulated job dynamic strengths and maximum acceptable weights of lift in the horizontal and vertical planes. These equations demonstrate that dynamic strength can be used reliably when matching jobs with individuals.

Adult↗

PubMed1994

The multiplane face lift.

The technique and experience with multiplane face lift are reviewed. The multiplane face lift can be thought of as a fourth-generation rhytidectomy, combining features of the extended SMAS and deep-plane face lifts. It is felt that this lift can more adequately address the problem of the nasolabial fold and can effect better bidirectional pull. Though difficult to quantify, it is expected that this lift will produce a longer-lasting result with no greater risk of complications than the more conventional lift. The multiplane face lift also can be used safely with ancillary procedures, such as blepharoplasty, rhinoplasty, and suction lipectomy.

Female↗

PubMed2003

Multidimensional signal exploration using multiple correspondence analysis. An example of a load lifting study.

Most empirical studies concerning rehabilitation yield numerous multidimensional signals (dozens of time variables are obtained for dozens of empirical situations). The purpose of this paper is to suggest a statistical analysis procedure based on: 1) space-time fuzzy windowing; 2) signal behavior characterization within the windows using membership value averages (MVA); and 3) MVA analysis using the multiple correspondence analysis (MCA). A load lifting study provided an example of 78 multidimensional signals including 89 time variables (forces, energy indicators, linear and angular positions, speeds, and accelerations). The main goal of MCA was to compare and contrast biomechanical signals from two lifting modes: "free" and "isokinetic." In the first mode, three loads were tested--light, medium, and heavy. In the second, three speeds were tested--slow, medium, and fast. Thirteen male individuals without disabilities participated in this study. The MCA showed that most of the free load-lifting strategies cannot be used in isokinetic lifting because the constraints of the subject and the environment are different. In addition, as the level of difficulty increases, free lifting became more economical while isokinetic lifting became less economical. These results would appear to indicate that movement strategies used for free lifting cannot be learned using an isokinetic machine during rehabilitation sessions for chronic low back pain. MCA was also suggested as a tool for comparing patients with control individuals. To achieve this aim, the notion of "supplementary data" was introduced.

Adult↗

PubMed1998

Development of a colony lift immunoassay to facilitate rapid detection and quantification of Escherichia coli O157:H7 from agar plates and filter monitor membranes.

E. coli O157:H7 is a food-borne adulterant that can cause hemorrhagic ulcerative colitis and hemolytic uremic syndrome. Faced with an increasing risk of foods contaminated with E. coli O157:H7, food safety officials are seeking improved methods to detect and isolate E. coli O157:H7 in hazard analysis and critical control point systems in meat- and poultry-processing plants. A colony lift immunoassay was developed to facilitate the positive identification and quantification of E. coli O157:H7 by incorporating a simple colony lift enzyme-linked immunosorbent assay with filter monitors and traditional culture methods. Polyvinylidene difluoride (PVDF) membranes (Millipore, Bedford, Mass.) were prewet with methanol and were used to make replicates of every bacterial colony on agar plates or filter monitor membranes that were then reincubated for 15 to 18 h at 36 +/- 1 degree C, during which the colonies not only remained viable but were reestablished. The membranes were dried, blocked with blocking buffer (Kirkegaard and Perry Laboratories [KPL], Gaithersburg, Md.), and exposed for 7 min to an affinity-purified horseradish peroxidase-labeled goat anti-E. coli O157 antibody (KPL). The membranes were washed, exposed to a 3,3',5,5'-tetramethylbenzidine membrane substrate (TMB; KPL) or aminoethyl carbazole (AEC; Sigma Chemical Co., St. Louis, Mo.), rinsed in deionized water, and air dried. Colonies of E. coli O157:H7 were identified by either a blue (via TMB) or a red (via AEC) color reaction. The colored spots on the PVDF lift membrane were then matched to their respective parent colonies on the agar plates or filter monitor membranes. The colony lift immunoassay was tested with a wide range of genera in the family Enterobacteriaceae as well as different serotypes within the E. coli genus. The colony lift immunoassay provided a simple, rapid, and accurate method for confirming the presence of E. coli O157:H7 colonies isolated on filter monitors or spread plates by traditional culture methods. An advantage of using the colony lift immunoassay is the ability to test every colony serologically on an agar plate or filter monitor membrane simultaneously for the presence of the E. coli O157 antigen. This colony lift immunoassay has recently been successfully incorporated into a rapid-detection, isolation, and quantification system for E. coli O157:H7, developed in our laboratories for retail meat sampling.

Agar↗

PubMed1998

Utilisation of substrates during tethered flight with and without lift generation in the African fruit beetle Pachnoda sinuata (Cetoniinae).

We have investigated the pattern of metabolic changes during tethered flight with and without lift generation in the African fruit beetle Pachnoda sinuata. Two distinct metabolic phases occur during lift-generating flight. The first phase is characterised by a high rate of oxygen consumption and a rapid change in proline and alanine levels in the haemolymph and flight muscles and in glycogen level in the flight muscles. Carbohydrates are released from the fat body into the haemolymph. These carbohydrates are oxidised during the second phase. Changes in proline and alanine levels in the haemolymph and flight muscles and in glycogen level in the flight muscles are minor during the second phase and the rate of oxygen consumption is reduced. During lift-generating flight, metabolic changes are rapid. Proline concentrations in the haemolymph and flight muscles fall dramatically during the first 30 s of flight, while alanine concentrations rise concomitantly. While haemolymph concentrations of proline and alanine remain virtually unchanged thereafter, further changes in the levels of these amino acids occur in the flight muscles during 5 min of flight. The initial levels of the two amino acids in the flight muscles are re-established over 1 h of rest following a 5 min flight, while this process takes longer in the haemolymph. The concentration of haemolymph carbohydrates increases during the first 30 s of flight and declines thereafter during 5 min of flight. The pre-flight levels are restored after 1 h of subsequent rest. The stores of glycogen in the flight muscles are rapidly diminished during the first 10 s of flight and decrease at a lower rate during further flight lasting up to 5 min. A subsequent 1 h of rest is sufficient almost to restore pre-flight levels. Haemolymph lipid levels are slightly but significantly increased during 11 min of flight and after 1 h of subsequent rest. During flight without lift production, the metabolic changes are considerably slower and beetles fly approximately seven times longer than during lift-generating flight. Resting basalar (BM), dorso-ventral (DVM) and dorso-longitudinal (DLM) flight muscles show no differences in levels of proline, alanine and glycogen. After different periods of flight, during which lift and wing loading were minimised, the DVM was found to have the highest level of proline after 5 min of flight. Levels of alanine in the DVM were lower than in the DLM. There was no evidence to suggest that different flight muscles are specialised for either proline or carbohydrate utilisation. Proline and carbohydrates participate equally in supplying energy to the flight muscles during lift-generating flight. The contribution to the energy supply by the flight muscles is 54 %, while that of the haemolymph is 46 %.

Animals↗

PubMed2001

The control of flight force by a flapping wing: lift and drag production.

We used a dynamically scaled mechanical model of the fruit fly Drosophila melanogaster to study how changes in wing kinematics influence the production of unsteady aerodynamic forces in insect flight. We examined 191 separate sets of kinematic patterns that differed with respect to stroke amplitude, angle of attack, flip timing, flip duration and the shape and magnitude of stroke deviation. Instantaneous aerodynamic forces were measured using a two-dimensional force sensor mounted at the base of the wing. The influence of unsteady rotational effects was assessed by comparing the time course of measured forces with that of corresponding translational quasi-steady estimates. For each pattern, we also calculated mean stroke-averaged values of the force coefficients and an estimate of profile power. The results of this analysis may be divided into four main points. (i) For a short, symmetrical wing flip, mean lift was optimized by a stroke amplitude of 180 degrees and an angle of attack of 50 degrees. At all stroke amplitudes, mean drag increased monotonically with increasing angle of attack. Translational quasi-steady predictions better matched the measured values at high stroke amplitude than at low stroke amplitude. This discrepancy was due to the increasing importance of rotational mechanisms in kinematic patterns with low stroke amplitude. (ii) For a 180 degrees stroke amplitude and a 45 degrees angle of attack, lift was maximized by short-duration flips occurring just slightly in advance of stroke reversal. Symmetrical rotations produced similarly high performance. Wing rotation that occurred after stroke reversal, however, produced very low mean lift. (iii) The production of aerodynamic forces was sensitive to changes in the magnitude of the wing's deviation from the mean stroke plane (stroke deviation) as well as to the actual shape of the wing tip trajectory. However, in all examples, stroke deviation lowered aerodynamic performance relative to the no deviation case. This attenuation was due, in part, to a trade-off between lift and a radially directed component of total aerodynamic force. Thus, while we found no evidence that stroke deviation can augment lift, it nevertheless may be used to modulate forces on the two wings. Thus, insects might use such changes in wing kinematics during steering maneuvers to generate appropriate force moments. (iv) While quasi-steady estimates failed to capture the time course of measured lift for nearly all kinematic patterns, they did predict with reasonable accuracy stroke-averaged values for the mean lift coefficient. However, quasi-steady estimates grossly underestimated the magnitude of the mean drag coefficient under all conditions. This discrepancy was due to the contribution of rotational effects that steady-state estimates do not capture. This result suggests that many prior estimates of mechanical power based on wing kinematics may have been grossly underestimated.

Animals↗

PubMedDate not supplied

Compelled weightbearing in persons with hemiparesis following stroke: the effect of a lift insert and goal-directed balance exercise.

The hypotheses have been tested that 1) symmetry of weightbearing in persons who have sustained a stroke could be improved by the addition of a lift to the shoe on the non-paretic lower limb and 2) compelled weightbearing resulting from the addition of a lift in conjunction with targeted exercise helps to overcome the learned disuse of the paretic limb. Weightbearing on the paretic side was measured in eight persons with hemiparesis during quiet standing and in conditions of compelled weight shift. Compelled weight shifts were applied with special lifts to the shoe on the non-paretic limb of the subjects. An increase in symmetrical weightbearing was recorded in conditions of compelled weight shifts: 10-mm lift provided the best symmetry of bipedal standing. We suggest that improved symmetry of bipedal standing obtained with the lift of the non-paretic limb would help in overcoming the learned disuse of the affected limb. Pre- and post-test results of a person with hemiparesis who was wearing a shoe lift on the non-paretic limb during a 6-week physical therapy program showed statistically significant improvement of walking speed, stride length, and weightbearing. Such findings support the idea of using compelled weightbearing via lifting and targeted exercise during treatment.

Aged↗