Biomedical subjects

V M Zatsiorsky

Publications and source records attributed to V M Zatsiorsky.

At least 19 recordsLinked to original sources

PubMed2002

Prehension synergies: effects of object geometry and prescribed torques.

We studied the coordination of forces and moments exerted by individual digits in static tasks that required balancing an external load and torque. Subjects ( n=10) stabilized a handle with an attachment that allowed for change of external torque. Thumb position and handle width systematically varied among the trials. Each subject performed 63 tasks (7 torque values x 3 thumb locations x 3 widths). Forces and moments exerted by the digit tips on the object were recorded. Although direction and magnitude of finger forces varied among subjects, each subject used a similar multidigit synergy: a single eigenvalue accounted for 95.2-98.5% of the total variance. When task parameters were varied, regular conjoint digital force changes (prehension synergies) were observed. Synergies represent preferential solutions used by the subjects to satisfy mechanical requirements of the tasks. In particular, chain effects in force adjustments to changes in the handle geometry were documented. An increased handle width induced the following effects: (a). tangential forces remained unchanged, (b). the same tangential forces produced a larger moment T (t), (c). the increased T (t) was compensated by a smaller moment of the normal forces T(n), and (d). normal finger forces were rearranged to generate a smaller moment. Torque control is a core component of prehension synergies. Observed prehension synergies are only mechanically necessitated in part. The data support a theory of hierarchical organization of prehension synergies.

Adult↗

PubMed2001

Bilateral deficit and symmetry in finger force production during two-hand multifinger tasks.

A comprehensive study of patterns of finger forces during one-hand and two-hand multifinger maximal force production trials was performed with particular emphasis on differences between tasks involving symmetrical and asymmetrical finger groups (symmetrical and asymmetrical tasks). Twelve healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations. Force deficit (FD) for a finger group within a hand was defined as a drop in peak force in a multifinger task as compared to the sum of individual finger peak forces in single-finger tasks. FD showed a dependence on both the number of fingers within the hand and the number of fingers in the other hand. An additional drop in peak finger forces was seen in two-hand tests (bilateral deficit, BD). BD summed over two hands was independent of the number of fingers involved in the two-hand tasks, but dependent on the distribution of fingers between the two hands. BD for a hand was larger for tasks involving fewer fingers within the hand and more fingers in the other hand. It was higher for asymmetrical tasks than for symmetrical tasks. The difference between asymmetrical and symmetrical tasks was due to the different behavior of asymmetrically involved fingers. FD was larger for asymmetrical master (explicitly involved) fingers, while forces produced involuntarily by asymmetrical slave (explicitly non-involved) fingers were larger. These differences brought down the total moment produced by both hands in the frontal plane. FD and BD are phenomena of different origin whose effects sum up. The observations have led to further development of a previously proposed double-representation, mirror-image (DoReMi) hypothesis and refinement of the neural network underlying the two-hand finger interaction.

Adult↗

PubMed2001

A method to study lumbar spine response to axial compression during magnetic resonance imaging: technical note.

STUDY DESIGN: A magnetic resonance imaging (MRI)-compatible device was developed to apply calibrated compression loads to the lumbar spine during imaging. Experiments were performed to establish a protocol to measure lumbar load-response and estimate muscle-force contribution to spinal load. OBJECTIVE: To develop experimental methodology for direct study of lumbar spine response to compression load. SUMMARY OF BACKGROUND DATA: Most lumbar MRI scans require subjects to lie relaxed and supine, but spinal stenosis has been demonstrated to increase during moderate compressive loading. Several devices have been used to load the spine during MRI, but they could not maintain and/or change calibrated loads during MRI experiments. Furthermore, artifact from viscoelastic creep during imaging was not considered. METHODS: An MRI-compatible spine compression unit with pneumatic load elements was developed to produce calibrated compression loads. Young healthy men were loaded with 140% body weight for up to 10 minutes to establish an appropriate test protocol. Muscle force contribution to spinal load was estimated from electromyography experiments. RESULTS: The spine compression unit produced specified loads +/- 29 N (standard deviation). Spine viscoelastic creep reached steady state by 6.5 minutes, leaving 3.5 minutes for image acquisition. The subjects could support 1.0 body weight for the requisite 10 minutes. Muscle compressive force estimates were only 135 N during application of 1.4 x body weight external compression load; thus, internal muscle forces during supine spine compression could be neglected. CONCLUSIONS: The lumbar load/image protocol fits within the time constraints of creep deformation and subject endurance. These methods allow acute lumbar mechanical response measurements during loading.

Adult↗

PubMed2001

The effect of a fatiguing exercise by the index finger on single- and multi-finger force production tasks.

We studied the effects of fatigue, induced by a 60-s maximal isometric force production with the index finger, on multi-finger coordination and force production by the other fingers of the hand. Finger forces were measured during single- and multi-finger maximal voluntary force production (MVC) at two sites, the middle of the distal or the middle of the proximal phalanges. Two fatiguing exercises involving force production by the index finger were used, one at the distal phalanx and the other at the proximal phalanx. The MVC of the index finger dropped by about 33% when it was produced at the site involved in the fatiguing exercise. In addition, large transfer effects of fatigue were observed across sites of force application and across fingers. Force deficit increased under fatigue, especially due to a drop in the recruitment of the index finger. Under fatigue, the index finger was less enslaved during force production by other fingers. During multi-finger tasks, the percentage of total force produced by the index finger was significantly reduced after the fatiguing exercise. The principle of minimization of secondary moments was violated under fatigue. We suggest that the most impaired (fatigued) finger shows less interaction with other fingers or, in other words, is being progressively removed from the multi-finger synergy. Some of the observed changes in finger coordination suggest effects of fatigue at a central (neural) level.

Adult↗

PubMed2001

Bilateral multifinger deficits in symmetric key-pressing tasks.

Maximal voluntary force during simultaneous bilateral and multifinger exertion has been shown to be smaller than the sum of unilateral or single-finger exertions. The goal of this study was to study the force deficit associated with bilateral multifinger tasks. Eight normal college students performed four types of maximal isometric key-pressing tasks: (1) unilateral single-finger, (2) bilateral single-finger, (3) unilateral multifinger, and (4) bilateral multifinger. Forces produced by the index (I), middle (M), ring (R), and little (L) fingers and surface electromyography (EMG) of extrinsic finger flexors were recorded. Multifinger deficit (MFD) was defined as the percentage difference between the force (or EMG) produced by a set of fingers and the sum of the forces (or EMGs) produced by the individual fingers in their unilateral single-finger tasks. Bilateral deficit (BLD) was defined as the percentage difference between the force (or EMG) produced by a set of fingers and the sum of the forces (or EMGs) produced by the finger subsets of the left and right hands. Significant BLD and MFD in force and EMG were found for all bilateral multifinger tasks and some of the bilateral single-finger tasks. Both BLD and MFD were dependent on the number of fingers involved. BLD ranged from 3% to 22.7% for force and from 8.9% to 31.0% for EMG, including bilateral single-finger and bilateral multifinger tasks. MFDs in force during bilateral I-, IM-, IMR-, and IMRL-finger tasks were 13.2%, 37.8%, 53.2%, 52.3%, respectively; and the corresponding MFDs in EMG were 11.7%, 51.3%, 67.6%, and 71.0%, respectively. BLD and MFD in EMG were found to vary in parallel with the corresponding force deficits. It was suggested that the neural ceiling effect remains the most plausible mechanism underlying the observed deficits. The central nervous system is unable to activate maximally a large number of muscle groups at the same time during tasks involving multiple body parts. During bilateral multifinger tasks, the ceiling effect may be organized hierarchically: (1) a certain limited neural drive is shared bilaterally, leading to a BLD; (2) at each hand, a certain limited neural drive is shared by multiple fingers, leading to MFD within a hand; (3) the deficits at bilateral and unilateral multifinger levels are cumulative during bilateral multifinger tasks, leading to a higher deficit associated with the tasks.

Adult↗

PubMed2001

The effect of finger extensor mechanism on the flexor force during isometric tasks.

The role of the intrinsic finger flexor muscles was investigated during finger flexion tasks. A suspension system was used to measure isometric finger forces when the point of force application varied along fingers in a distal-proximal direction. Two biomechanical models, with consideration of extensor mechanism Extensor Mechanism Model (EMM) and without consideration of extensor mechanism Flexor Model (FM), were used to calculate forces of extrinsic and intrinsic finger flexors. When the point of force application was at the distal phalanx, the extrinsic flexor muscles flexor digitorum profundus, FDP, and flexor digitorum superficialis, FDS, accounted for over 80% of the summed force of all flexors, and therefore were the major contributors to the joint flexion at the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joints. When the point of force application was at the DIP joint, the FDS accounted for more than 70% of the total force of all flexors, and was the major contributor to the PIP and MCP joint flexion. When the force of application was at the PIP joint, the intrinsic muscle group was the major contributor for MCP flexion, accounting for more than 70% of the combined force of all flexors. The results suggest that the effects of the extensor mechanism on the flexors are relatively small when the location of force application is distal to the PIP joint. When the external force is applied proximally to the PIP joint, the extensor mechanism has large influence on force production of all flexors. The current study provides an experimental protocol and biomechanical models that allow estimation of the effects of extensor mechanism on both the extrinsic and intrinsic flexors in various loading conditions, as well as differentiating the contribution of the intrinsic and extrinsic finger flexors during isometric flexion.

Biomechanical Phenomena↗

PubMed2000

On the fractal properties of natural human standing.

We analyzed the temporal evolution of the displacement of the center of pressure (COP) during prolonged unconstrained standing (30 min) in non-impaired human subjects. The COP represents the collective outcome of the postural control system and the force of gravity and is the main parameter used in studies on postural control. Our analysis showed that the COP displacement during human standing displays fractal properties that were quantified by the Hurst exponent obtained from the classical rescaled adjusted range analysis. The average fractal or Hurst exponent (H) was 0.35+/-0.06. The presence of long-range correlations from a few seconds to several minutes due to the fractal characteristics of the postural control system has several important implications for the analysis of human balance.

Adult↗

PubMed2000

The effect of fatigue on multifinger co-ordination in force production tasks in humans.

1. This study investigated the effects of fatigue, induced by production of maximal isometric force for 60 s with four fingers, upon indices of multifinger co-ordination. 2. Measurements of individual finger forces were performed during single- and multifinger maximal force production (maximal voluntary contraction, MVC) for two sites of force application, the middle of the distal or the middle of the proximal phalanxes. Two fatiguing exercises were used, involving force production at the distal phalanxes and at the proximal phalanxes. Fourteen subjects were tested. 3. The total force in four-finger tasks dropped by about 43 % when it was produced at the site involved in the fatiguing exercise. During force production at the other site, MVC dropped by 23 %. During single-finger MVC tests, force drop with fatigue was similar across all four fingers (about -25 % of their corresponding MVCs). 4. Force production by one finger was accompanied by involuntary force production by other fingers (enslaving). Enslaving remained unchanged by fatigue when measured during force generation at the site involved in the fatiguing exercise, but increased during force production at the other site. 5. The total MVC of four fingers acting in parallel was smaller than the sum of the MVCs of these fingers in single-finger tasks (force deficit). The force deficit increased with fatigue. Force-sharing patterns during four-finger tasks showed only minor changes under fatigue. 6. These results indicate that the effects of fatigue were not limited to changes in the force-generating capabilities of the muscles. In particular, fatigue could lead to a reorganisation at a neural level that defines commands to individual fingers.

Adult↗

PubMed2000

Enslaving effects in multi-finger force production.

When a person produces isometric force with one, two, or three fingers, the other fingers of the hand also produce a certain force. Enslaving is the involuntary force production by fingers not explicitly involved in a force-production task. This study explored the enslaving effects (EE) in multi-finger tasks in which the contributions of the flexor digitorum profundus (FDP), flexor digitorum superficialis (FDS), and intrinsic muscles (INT) were manipulated. A new experimental technique was developed that allows the redistribution of the muscle activity between the FDP, FDS, and INT muscles. In the experiment, ten subjects were instructed to perform maximal voluntary contractions with all possible one-, two-, three-, and four-finger combinations. The point of force application was changed in parallel for the index, middle, ring, and little fingers from the middle of the distal phalanx, to the distal interphalangeal joint, and then to the proximal interphalangeal joint. It was found that: (1) the EE of similar amplitude were present in various experimental conditions that involved different muscle groups for force production; (2) the EE were large on average--the slave fingers could produce forces reaching 67.5% of the maximal forces produced by themselves in a single-finger task; (3) the EE were larger for neighboring fingers; and (4) the EE were non-additive--in most cases, the EE from two or three fingers were smaller than the EE from at least one finger. EE among different muscles suggest a widespread neural interaction among the structures controlling flexor muscles in the hand as the main mechanism of finger enslaving.

Adult↗

PubMed2000

Contribution of the extrinsic and intrinsic hand muscles to the moments in finger joints.

OBJECTIVE: The purpose of this current work is to develop a method of estimating force produced by the extrinsic and intrinsic hand muscles, and to estimate the contribution of these muscles to the finger joint moments. DESIGN: Experimental methods and a biomechanical model were developed for the estimation of (a) moments produced at finger joints, and (b) contribution of the intrinsic and extrinsic muscles to the moments, (c) forces of the extrinsic and intrinsic muscles within individual fingers. BACKGROUND: Because of the differential insertions of the extrinsic flexors, it is possible to isolate their mechanical effect at finger joints. METHODS: During the experiment, the location of force application was varied in parallel along individual fingers. The points of force application were on the distal phalanx, at the distal interphalangeal joint, or at the proximal interphalangeal joint. RESULTS: When the point of force application was varied in the proximal direction from the distal phalanx to the proximal interphalangeal joint the moment at a given joint decreased. The intrinsic and extrinsic muscle forces were dependent on the experimental conditions. The extrinsic muscles were the major contributors in counterbalancing finger joint moments when the point of force application was distal beyond the proximal interphalangeal joint. CONCLUSION: This current work provides both an experimental protocol and a biomechanical model that allows estimation of the contribution of the intrinsic and extrinsic muscles to finger joint moments. RELEVANCE: This study suggests ways of identifying the source of functional deficiency in the hand.

Adult↗

PubMed2000

Influence of compression hosiery on physiological responses to standing fatigue in women.

PURPOSE: The purpose of this investigation was to examine the influence of various designs of commercial hosiery, which use graduated compression, on the physiological and performance responses to standing fatigue. METHODS: Twelve healthy women (age = 23.0+/-2.1 yr, height = 165.7+/-5.0 cm, percent body fat = 22.6+/-4.2%, body mass = 60.0+/-8.9 kg) volunteered to participate in this investigation. All subjects completed four identical standing fatigue protocols with different garment conditions each separated by 7 d. The standing fatigue protocol involved a total of 8 h of standing on hard floors during which subjects participated in various tasks and experimental testing procedures. In addition, all activity and dietary profiles of the subjects were carefully controlled 48 h before each experimental session. Before the standing fatigue protocol, subjects completed a battery of tests to establish morning baseline values. Experimental tests included determination of lower leg venous cross-sectional area, blood pressure, heart rate, perceived discomfort ratings, circumferences measurements, total body water, variation in center of pressure during "quiet" standing, vertical jump performance, and specific regional patterns of foot pressures. RESULTS: This investigation demonstrated that commercial hosiery with various forms of graduated compression and construction were effective in mediating a reduction in edema in the ankles and legs while reducing the amount of venous pooling and discomfort in the lower body. Different constructions of garments may mediate these overall effects via different physiological mechanisms related to fluid shifts and muscle tissue damage. CONCLUSION: Wearing various types of graduated compression hose during the day as it relates to women in standing professions may minimize edema and muscle tissue disruption, thereby increasing comfort in the legs.

Adult↗

PubMed2000

Rambling and trembling in quiet standing.

The goal of this study was to explore the rambling-trembling decomposition in quiet standing. The center of pressure (COP) and the horizontal ground reaction force (F(hor)) were registered in healthy subjects standing in an upright bipedal posture on a force platform. The COP positions at the instants when F(hor) = 0 were identified (instant equilibrium points, IEP) for the anterior-posterior direction, then the COP time series, were partitioned into its components using 2 different techniques, rambling-trembling decomposition and gravity line decomposition. The two decomposition techniques provided very similar results. An unexpectedly large correlation between the trembling trajectory and the difference between COP and gravity line was found, r = 0.91 (range, 0.83 < r < 0.98). The correlation implies that the GL moves from an IEP to the subsequent IEP along a smooth trajectory that can be predicted by the spline approximation. A substantial negative cross-correlation at a zero time lag was observed between the trembling and the F(hor), -0.90 < r < -0.75. For the rambling trajectory, the coefficients of correlation with F(hor) were low, -0.33 < r < -0.05. The data support the hypothesis that during quiet standing the body sways for two reasons: the migration of the reference point (rambling) and the deviation away from that point (trembling).

Adult↗

PubMed1999

Reconstruction of equilibrium trajectories during whole-body movements.

The framework of the equilibrium-point hypothesis was used to reconstruct equilibrium trajectories (ETs) of the ankle, hip and body center of mass during quick voluntary hip flexions ('Japanese courtesy bow') by standing subjects. Different spring loads applied to the subject's back were used to introduce smooth perturbations that are necessary to reconstruct ETs based on a series of trials at the same task. Time patterns of muscle torques were calculated using inverse dynamics techniques. A second-order linear model was employed to calculate the instantaneous position of the spring-like joint or center of mass characteristic at different times during the movement. ETs of the joints and of the center of mass had significantly different shapes from the actual trajectories. Integral measures of electromyographic bursts of activity in postural muscles demonstrated a relation to muscle length corresponding to the equilibrium-point hypothesis.

Adult↗

PubMed1999

Patterns of center of presure migration during prolonged unconstrained standing.

Prolonged (>30 min) unconstrained standing (PUS) was studied in 10 young healthy subjects. The usual methods of stabilographic analysis assume a random center of pressure (COP) migration. This study was based on the opposite idea and showed that during PUS, specific and consistent patterns of the COP migration can be recognized by a computer algorithm. Three COP migration patterns were found: (a) shifting, a fast displacement of the average position of COP from one region to another; (b) fidgeting, a fast and large displacement and returning of COP to approximately the same position; and (c) drifting, a slow continuous displacement of the average position of COP. A software code was written and default parameter values were chosen for recognizing COP migration patterns. For 30-min PUS the following patterns were identified: Shifting was generally observed every 316 +/- 292 sec in the anterior-posterior (a-p) direction with an average shift amplitude of 17 +/- 15 mm, and every 199 +/- 148 sec in the medial-lateral (m-l) direction with an average shift amplitude of 22 +/- 38 mm. Corresponding time intervals for fidgeting were 59 +/- 15 sec in the a-p direction and 49 +/- 16 sec in the m-l direction. The average drift-to-drift interval was 319 +/- 173 sec in the a-p direction and 529 +/- 333 sec in the m-l direction.

Adult↗

PubMed1999

Instant equilibrium point and its migration in standing tasks: rambling and trembling components of the stabilogram.

A method of decomposing stabilograms into two components, termed rambling, was developed. The rambling component reveals the motion of a moving reference point with respect to which the body's equilibrium is instantly maintained. The trembling component reflects body oscillation around the reference point trajectory. The concepts of instant equilibrium point (IEP) and discrete IEP trajectory are introduced. The rambling trajectory was computed by interpolating the discrete IEP trajectory with cubic spline functions. The trembling trajectory is found as a difference between the approximated rambling trajectory and the COP trajectory. Instant values of the horizontal ground reaction force at a zero time lag. It suggests that trembling is strongly influenced by a restoring force proportional to the magnitude of COP deviation from the rambling trajectory and acts without a time delay. An increment in relative COP position per unit of the restoring force in mm/N, was on average 1.4 +/- 0.4. The contribution of rambling and trembling components in the stabilogram was ascertained. The rambling variability is approximately three times larger than the trembling variability.

Adult↗

PubMed1998

Force sharing among fingers as a model of the redundancy problem.

The aim of this study was to test Bernstein's idea that motor synergies provide solutions to the motor redundancy problem. Forces produced by individual fingers of one hand were recorded in one-, two-, three-, and four-finger tasks. The subjects (n=10) were asked to produce maximal total force (maximal voluntary contraction, MVC) and to match a ramp total force profile using different combinations of fingers. We found that individual finger forces were smaller in multifinger MVC tasks than in single-finger tasks. The deficit increased with the number of fingers involved. A saturation effect was observed: when several effectors were involved, adding a new effector did not significantly change the total force output. The data confirmed the idea that the central neural drive arriving at the level of synergies has a certain limit, a ceiling, that cannot be exceeded. The central nervous system cannot maximally activate the muscles serving all the fingers at the same time. Secondly, during the course of ramp trials, forces produced by individual fingers were linearly related to each other. Hence, a force sharing pattern was established at the beginning of the trial and did not change during the ramp period. A hypothesis is suggested that force distribution among fingers may be organized so as to minimize unnecessary rotational moment with respect to the functional longitudinal axis of the hand. Finally, in the four-finger trials, variance of the total maximal force output in ten consecutive attempts was smaller than the sum of variances of the maximal individual finger forces. The finding suggests that the control system of the motor tasks studied involves at least two levels, a central neural drive level and a synergy level. At the synergy level, an intercompensation in individual finger force production is observed.

Adult↗

PubMed1998

Motor redundancy during maximal voluntary contraction in four-finger tasks.

The goal of the study was to investigate force-sharing patterns in multi-finger tasks. Maximal normal force (MNF) as well as the force-time curves produced by individual fingers were measured in 10 young male subjects in three tasks: (1) holding an instrumented handle in a pad opposition with the thumb at seven different locations, from opposing the index finger (L0) to opposing the little finger (L6); (2) holding the handle in a pad opposition with the thumb at an individually selected comfortable location; and (3) pressing with the four fingers against the same handle fixed to the external support. We found that: (1) The moment due to the normal finger forces changed systematically when the thumb position varied from L0 to L5/ L6, and it was equal to zero at a certain middle position of the thumb, the neutral position. At this position, the shear force produced by the fingers was zero. (2) The total MNF changed in an ascending-descending manner when the thumb position varied from L0 to L5/L6. The highest value of the maximal total normal force was produced at a position of the thumb that was preferred as the most comfortable position in the grip task. (3) In the press task, the neutral line - the line with respect to which the moment generated by the four fingers equals zero - was at the same location as the preferred thumb position in the grip tasks. (4) Larger total normal force corresponded to smaller total shear forces. (5) In grip tasks, with the thumb in a comfortable position, the force-force relationships among fingers were approximately linear. Hence, in these thumb positions, the force-sharing pattern was established at the beginning of the trial. At the extreme positions of the thumb, irregular patterns of the force-force relationships were observed. (6) In trials with different thumb locations, a significant correlation was found between the maximal force produced by the index and small fingers. (7) Peak force exerted by individual fingers in the multi-finger tasks was much smaller than the maximal force displayed by the same fingers in the single-finger tasks. The peak force depended on the thumb position and varied from 11.3% to 65.2% of the maximal force exerted by the same finger in the single-finger task. With the thumb in the comfortable position, the relative peak force for all fingers was approximately at the same level, 50-55%. The data are in agreement with the hypothesis that the total force is shared among individual fingers, minimizing the moment with respect to the functional hand axis.

Fingers↗

PubMed1998

A principle of error compensation studied within a task of force production by a redundant set of fingers.

Based on previous studies, we formulated a principle of error compensation as a major principle of synergy organization during motor tasks performed by a redundant set of effectors. Within the present study, we tested the principle by an investigation of the performance of individual fingers during isometric force production when another task was performed simultaneously. Subjects were asked to press at about 30% of the maximal contraction force with three fingers (index, middle, and ring) acting in parallel. Then, they were required to perform a series of taps at 2 Hz with one of the fingers. In all the tasks, nontapping fingers changed their force production without a time delay with the changes in the force by the tapping finger. During tapping with the index and with the middle finger, both nontapping fingers showed changes in their force negatively correlated with changes in force of the tapping finger. During tapping with the ring finger, two types of behavior could be seen in different subjects with the force of the middle finger going out of phase (group 1) or in phase (group 2) with the force of the ring finger. In both cases, the force of the index finger was out of phase with the force of the ring finger. These changes, on average, induced a compensation for the expected drop in finger force during tapping, ranging in different conditions from 94% to 102%. The ratio of forces produced by the nontapping fingers did not change during the tapping in all the cases except group 2 during ring-finger tapping, when the index finger started to generate significantly higher force as compared to the middle finger. We interpret the data as results of the action of a feed-forward central mechanism leading to parallel changes in forces produced by fingers united into a structural unit.

Adult↗