Radial force distribution changes associated with tangential force production in cylindrical grasping, and the importance of anatomical registration

Radial force (F(r)) distributions describe grip force coordination about a cylindrical object. Recent studies have employed only explicit F(r) tasks, and have not normalized for anatomical variance when considering F(r) distributions. The goals of the present study were (i) to explore F(r) during tangential force production tasks, and (ii) to examine the extent to which anatomical registration (i.e. spatial normalization of anatomically analogous structures) could improve signal detectability in F(r) data. Twelve subjects grasped a vertically oriented cylindrical handle (diameter=6 cm) and matched target upward tangential forces of 10, 20, and 30 N. F(r) data were measured using a flexible pressure mat with an angular resolution of 4.8°, and were registered using piecewise-linear interpolation between five manually identified points-of-interest. Results indicate that F(r) was primarily limited to three contact regions: the distal thumb, the distal fingers, and the fingers' metatacarpal heads, and that, while increases in tangential force caused significant increases in F(r) for these regions, they did not significantly affect the F(r) distribution across the hand. Registration was found to substantially reduce between-subject variability, as indicated by both accentuated F(r) trends, and amplification of the test statistic. These results imply that, while subjects focus F(r) primarily on three anatomical regions during cylindrical grasp, inter-subject anatomical differences introduce a variability that, if not corrected for via registration, may compromise one's ability to draw anatomically relevant conclusions from grasping force data.     

Statistical decision theory and trade-offs in the control of motor response

We present a novel approach to the modeling of motor responses based on statistical decision theory. We begin with the hypothesis that subjects are ideal motion planners who choose movement trajectories to minimize expected loss. We derive predictions of the hypothesis for movement in environments where contact with specified regions carries rewards or penalties. The model predicts shifts in a subject's aiming point in response to changes in the reward and penalty structure of the environment and with changes in the subject's uncertainty in carrying out planned movements. We tested some of these predictions in an experiment where subjects were rewarded if they succeeded in touching a target region on a computer screen within a specified time limit. Near the target was a penalty region which, if touched, resulted in a penalty. We varied distance between the penalty region and the target and the cost of hitting the penalty region. Subjects shift their mean points of contact with the computer screen in response to changes in penalties and location of the penalty region relative to the target region in qualitative agreement with the predictions of the hypothesis. Thus, movement planning takes into account extrinsic costs and the subject's own motor uncertainty.     

Light distributions on the retina: relevance to macular pigment photoprotection

Light exposure has been implicated in age-related macular degeneration (AMD). This study was designed to measure cumulative light distribution on the retina to determine whether it peaked in the macula. An eye-tracker recorded the subject's field of view and pupil size, and superimposed the gaze position. Fifteen na?ve subjects formed a test group; 5 formed a control group. In phase 1, all subjects viewed a sequence of photographic images. In phase 2, the na?ve subjects observed a video; in phase 3, they performed computer tasks; in phase 4, the subjects walked around freely. In phase 1, control subjects were instructed to gaze at bright features in the field of view and, in a second test, at dark features. Test group subjects were allowed to gaze freely for all phases. Using the subject's gaze coordinates, we calculated the cumulative light distribution on the retina. As expected for control subjects, cumulative retinal light distributions peaked and dipped in the fovea when they gazed at bright or dark features respectively in the field of view. The light distribution maps obtained from the test group showed a consistent tendency to peak in the macula in phase 3, a variable tendency in phase 4, but little tendency in phases 1 and 2. We conclude that a tendency for light to peak in the macula is a characteristic of some individuals and of certain tasks. In these situations, risk of AMD could be increased but, at the same time, mitigated by the presence of macular carotenoids.     

The strength-dexterity test as a measure of dynamic pinch performance

We have developed a method to quantify the dynamic interaction between fingertip force magnitude (strength) and directional control (dexterity) during pinch with a novel strength-dexterity (S-D) test based on the principle of buckling of compression springs. The test consists of asking participants to use key and opposition pinch to attempt to fully compress springs, in random order, with a wide range of combinations of strength and dexterity requirements. The minimum force required to fully compress the spring and the propensity of the spring to buckle define the strength and dexterity requirements, respectively. The S-D score for each pinch style was the sum of the strength values of all springs successfully compressed fully. We tested 3 participant groups: 18 unimpaired young adults (40yr), and 14 adults diagnosed with carpo-metacarpal osteoarthritis (CMC OA) (>or = 36yr). We investigated the repeatability of the S-D test with 74 springs by testing 14 young adults twice on different days. The per-spring repeatability across subjects was >or = 94%. A minimum performance score for young adults was found as they all could compress a subset of 39 springs. Using this subset of springs, we compared the ability of the S-D score vs. maximal pinch force values to distinguish unimpaired hands from those with CMC OA of the thumb. The score for this 39-spring S-D test distinguished between CMC OA and asymptomatic older adults, whereas pinch meter readings did not (p<0.05). We conclude that the S-D test is repeatable and applicable to clinical research. We propose including the S-D test in studies aiming to quantify impairment and compare treatment outcomes in orthopaedic and neurological afflictions that degrade dynamic manipulation.     

Influence of the relative difference in chair seat height according to different lower thigh length on floor reaction force and lower-limb strength during sit-to-stand movement

Chair-seat height affects the burden on the lower-limbs during sit-to-stand (STS) movement. Previous studies used the same height chair, attaching importance to practicability, but the difference in each subject's lower thigh length may relate to the burden on the lower-limbs. This study aimed to examine the influence of different lower thigh lengths on floor reaction force and lower-limb strength during an STS movement. Thirty young-adult male subjects participated in this study (age: 22.7+/-2.6 yr, height: 172.8+/-4.8 cm, body-mass: 66.3+/-5.2 kg). The subjects were divided into three groups (G1>42 cm, 42 cm > or =G2 > or =38 cm, 38 cm >G3) based on lower thigh length (G1: 44.1+/-2.5 cm, G2: 39.8+/-1.3 cm, G3: 34.3+/-2.1 cm). Namely, G1 was characterized by lower thigh length longer than 105% of 40 cm, G2 by 95-105% of lower thigh length and G3 by lower thigh length less than 95% of 40 cm, respectively. Subjects performed an STS movement twice from chairs at 40 cm-height and height adjusted by the lower thigh length of each subject. Vertical floor reaction force and electromyogram (EMG) on the rectus femoris and tibialis anterior muscles during an STS movement were measured to evaluate the force of knocking over and the burden on the lower-limbs. Fifteen parameters regarding floor reaction force (10) and EMG (5) were selected for analyses. Significant differences were found in floor reaction force at hip-syneresis (F1) and the impulse between hip-syneresis and appearance of the peak floor reaction force (F2). G1 was greater than G2 for the former, and G3 for the latter. Significant differences were found in active muscle mass of the tibialis anterior from the beginning of an STS movement to hip-syneresis (TE1) and peak active muscle level of the tibialis anterior (TE6). G1 was greater than G2 for the former, and G2 and G3 for the latter. It was suggested that when an STS movement is performed using a chair with the same height for each subject, the load imposed on the subject's leg at the time of an STS movement and the STS movement achievement strategy differed since chair seat height changes relatively by the difference in lower thigh length. Moreover, it is thought that the difference in these load conditions and movement strategies occurs when the chair seat height of a subject's lower thigh length is longer than 110%. When conducting the ability to achieve STS movement rating test, chair seat height considering each subject's lower thigh length may be needed.     

Impaired mirror-image imitation in Asperger and high-functioning autistic subjects

Imitation is crucial for proper development of social and communicative skills. Here, we argue that, based on an error analysis of a behavioral imitation task, adult Asperger and high-functioning autistic subjects suffer from an intriguing deficit of imitation: they lack the natural preference for imitation in a mirror-image fashion. The imitation task consisted of a simple movement sequence of putting a pen with the left or right hand into a green or a blue cup using one of two possible grips. The subjects were asked to imitate the experimenter's hand movements either using the crossed hand (e.g., the subject's right hand corresponding to the experimenter's right hand) for imitation or to imitate as if looking in a mirror (e.g., the subject's left hand corresponding to the experimenter's right hand). When people normally view other persons face-to-face, they prefer to imitate as in a mirror, and observation of mirror-image-like movements speeds up performance in nonimitative tasks. However, our autistic subjects, defective in social cognition, did not profit from mirror-image movements of others. These results provide a new insight into the difficulties that autistic subjects face in viewing and understanding actions of others.     

Isometric Arm Strength and Subjective Rating of Upper Limb Fatigue in Two-Handed Carrying Tasks

Sustained carrying could result in muscular fatigue of the upper limb. Ten male and ten female subjects were recruited for measurements of isometric arm strength before and during carrying a load for a period of 4 minutes. Two levels of load of carrying were tested for each of the male and female subjects. Exponential function based predictive equations for the isometric arm strength were established. The mean absolute deviations of these models in predicting the isometric arm strength were in the range of 3.24 to 17.34 N. Regression analyses between the subjective ratings of upper limb fatigue and force change index (FCI) for the carrying were also performed. The results indicated that the subjective rating of muscular fatigue may be estimated by multiplying the FCI with a constant. The FCI may, therefore, be adopted as an index to assess muscular fatigue for two-handed carrying tasks.     

Normalizing upper trapezius EMG amplitude: Comparison of ramp and constant force procedures

The present study compared three procedures for normalization of upper trapezius surface electromyographic (EMG) amplitudes: (a) a ramp procedure (providing data in per cent of maximal voluntary contraction, MVC); (b) a constant force procedure based on two reference contractions (two-force procedure) (%MVC) and (c) a procedure expressing muscle activation in per cent of a reference voluntary electrical activity (%RVE). The study also evaluated the repeatability of the ramp and the RVE procedures and estimated the force exertion (%MVC) corresponding to the RVE. To illustrate the ergonomic effect of different normalization procedures, trapezius EMG during two work tasks was compared after normalization by the two-force and the RVE procedures. Fifteen subjects participated in the whole study. We found that force estimates obtained by the ramp procedure equation could be translated to force estimates obtained by the two-force procedure by the equation: %MVC_2force = − 0.6 + 0.9*%MVC_ramp, although with a considerable imprecision due to large inter-individual differences. In the ramp procedure, the intra-individual test-retest coefficient of variation (CV) depended on the force level; it was 45% at 5% MVC and 10% at 30% MVC. The CV of the RVE was 15%. The reference contraction used in the RVE procedure corresponded from 13–79% MVC (median 33%MVC). The load reducing effect of an ergonomic intervention was less obvious with the RVE procedure than with the two-force procedure due to a larger inter-individual variation. The advantages and disadvantages of the different procedures are discussed.     

Reliability of segmental accelerations measured using a new wireless gait analysis system

The purpose of this study was to determine the inter- and intra-examiner reliability, and stride-to-stride reliability, of an accelerometer-based gait analysis system which measured 3D accelerations of the upper and lower body during self-selected slow, preferred and fast walking speeds. Eight subjects attended two testing sessions in which accelerometers were attached to the head, neck, lower trunk, and right shank. In the initial testing session, two different examiners attached the accelerometers and performed the same testing procedures. A single examiner repeated the procedure in a subsequent testing session. All data were collected using a new wireless gait analysis system, which features near real-time data transmission via a Bluetooth network. Reliability for each testing condition (4 locations, 3 directions, 3 speeds) was quantified using a waveform similarity statistic known as the coefficient of multiple determination (CMD). CMD's ranged from 0.60 to 0.98 across all test conditions and were not significantly different for inter-examiner (0.86), intra-examiner (0.87), and stride-to-stride reliability (0.86). The highest repeatability for the effect of location, direction and walking speed were for the shank segment (0.94), the vertical direction (0.91) and the fast walking speed (0.91), respectively. Overall, these results indicate that a high degree of waveform repeatability was obtained using a new gait system under test-retest conditions involving single and dual examiners. Furthermore, differences in acceleration waveform repeatability associated with the reapplication of accelerometers were small in relation to normal motor variability.     

Spatio-temporal evaluation of neck muscle activation during postural perturbations in healthy subjects.

The purpose of this study was to examine the spatio-temporal activation of the sternocleidomastoid (SCM) and cervical extensor (CE) muscles with respect to the deltoid muscle onset during rapid voluntary upper limb movement in healthy volunteers. The repeatability and reliability of the spatio-temporal aspects of the myoelectric signals were also examined. Ten subjects performed bilateral and unilateral rapid upper limb flexion, abduction and extension in response to a visual stimulus. EMG onsets and normalised root mean square (nRMS) values were calculated for the SCM and CE muscles. Subjects attended three testing sessions over non-consecutive days allowing the repeatability and reliability of these measures to be assessed. The SCM and CE muscles demonstrated feed-forward activation (activation within 50 ms of deltoid onset) during rapid arm movements in all directions. The sequence and magnitude of neck muscle activation displayed directional specificity, however, the neck flexor and extensor muscles displayed co-activation during all perturbations. EMG onsets demonstrated high repeatability in terms of repeated measure precision (nSEM in the range 1.9-5.7%). This was less evident for the repeatability of nRMS values. The results of this study provide a greater understanding of cervical neuromotor control strategies. During bilateral and unilateral upper limb perturbations, the SCM and CE muscles demonstrate feed-forward co-activation. It seems apparent that feed-forward activation of neck muscles is a mechanism necessary to achieve stability for the visual and vestibular systems, whilst ensuring stabilisation and protection of the cervical spine.     

One Digit Interruption: The Altered Force Patterns during Functionally Cylindrical Grasping Tasks in Patients with Trigger Digits

Most trigger digit (TD) patients complain that they have problems using their hand in daily or occupational tasks due to single or multiple digits being affected. Unfortunately, clinicians do not know much about how this disease affects the subtle force coordination among digits during manipulation. Thus, this study examined the differences in force patterns during cylindrical grasp between TD and healthy subjects. Forty-two TD patients with single digit involvement were included and sorted into four groups based on the involved digits, including thumb, index, middle and ring fingers. Twelve healthy subjects volunteered as healthy controls. Two testing tasks, holding and drinking, were performed by natural grasping with minimal forces. The relations between the force of the thumb and each finger were examined by Pearson correlation coefficients. The force amount and contribution of each digit were compared between healthy controls and each TD group by the independent t test. The results showed all TD groups demonstrated altered correlation patterns of the thumb relative to each finger. Larger forces and higher contributions of the index finger were found during holding by patients with index finger involved, and also during drinking by patients with affected thumb and with affected middle finger. Although no triggering symptom occurred during grasping, the patients showed altered force patterns which may be related to the role of the affected digit in natural grasping function. In conclusion, even if only one digit was affected, the subtle force coordination of all the digits was altered during simple tasks among the TD patients. This study provides the information for the future studies to further comprehend the possible injuries secondary to the altered finger coordination and also to adopt suitable treatment strategies.     

Effects of stimulation frequencies and patterns on performance of repetitive, nonisometric tasks.

The purpose of this paper was to determine the effects of stimulation pattern and frequency on repetitive human knee movements. Quadriceps femoris muscles were stimulated against a load equal to 10% of each subject's maximum voluntary isometric force. The main variable of interest was the number of repetitions in which the leg reached a target angle of 40 degrees of knee extension. Sixteen different trains were tested, including 1) six constant-frequency trains with frequencies ranging from 9 to 100 Hz, 2) five variable-frequency trains with an initial 5-ms triplet and mean frequencies ranging from 11 to 35 Hz, and 3) five doublet-frequency trains, which used doublets (2 pulses with a 5-ms interpulse interval) to replace single pulses, with mean frequencies of 17-57 Hz. Testing was stopped when the subject failed to reach the target angle for three consecutive activations. Results showed that no single pattern was best for all subjects. The 33- and 100-Hz constant-frequency trains, 35-Hz variable-frequency trains, and 27- and 36-Hz doublet frequency trains each met the target the most times for some subjects. The results showed that, under our testing conditions, higher frequency trains were better suited for producing repetitive knee movements than lower frequency trains.     

Matching unrelated stimuli with same discriminative functions: training order effects

Previous research has shown that after training simple discriminations (A1+/A2−, B1+/B2−), bringing these tasks under conditional control (J1–A1, J2–A2) leads to transfer of discriminative control (J1+/J2−) and to generalized matching on the basis of same discriminative functions (e.g. J1–B1, J2–B2). The same occurs when conditional discriminations are trained (D1–E1, D2–E2; F1–G1, F2–G2). When the subjects are then trained to demonstrate correct relations (D1–E1, D2–E2) when given X1 and to demonstrate incorrect relations when given X2 (XD–E), transfer of discriminative control (X1+/X2−) and generalized matching on the basis of same discriminative functions emerges (e.g. X1F1–G1, X2F1–G2). The present study investigated if these performances are dependent on the training and/or testing order. In Experiment 1, the lower-order contingency tasks were trained before the higher-order contingency tasks (A1+/A2−, B1+/B2− before J–A, and D–E, F–G before XD–E). Half the subjects received the J–B test before the more complex XF–G test (Condition A), while for the other subjects, this testing order was reversed (Condition B). Finally, all subjects received additional tests in which they were given the opportunity to demonstrate the discriminative properties of the J and X stimuli (J1+/J2−, X1+/X2−), and to match the A, J, and X stimuli with newly introduced stimuli of same discriminative properties (e.g. J1-POLITE, J2-RUDE). Experiment 2 was the same except that the training order was reversed (J–A before A1+/A2−, B1+/B2−, and XD–E before D–E, F–G). The results were affected by the training order but not by the testing order. Transfer of discriminative functions and generalized matching on the basis of same functions only occurred reliably when the lower-order contingency tasks were trained first. A stimulus-control account of the data is offered.     

Normalization of surface EMG amplitude from the upper trapezius muscle in ergonomic studies — A review

Surface electromyographic (EMG) amplitude from the upper trapezius muscle is widely used as a measure of shoulder-neck load in ergonomic studies. A variety of methods for normalizing EMG amplitude from the upper trapezius (EMGamp_ut) have been presented in the literature. This impedes meta-analyses of, for instance, upper trapezius load in relation to development of shoulder-neck disorders. The review offers a thorough discussion of different normalization procedures for EMGamp_ut. The following main issues are focused: output variable, location of electrodes, posture and attempted movement during normalization, load and duration of reference contractions, signal processing and test-retest repeatability. It is concluded that translations of EMGamp_ut into biomechanical variables, for example relative force development in the shoulder or in the upper trapezius itself, suffer from low validity, especially if used in work tasks involving large and/ or fast arm movements. The review proposes a standard terminology relating to normalization of EMGamp_ut and concludes in a concrete suggestion for a normalization procedure generating bioelectrical variables which reflect upper trapezius activation.     

The influence of providing feedback on force production and within-participant reproducibility during maximal voluntary exertions for the anterior deltoid,middle deltoid,and infraspinatus

The normalization of electromyographic signals to a maximum voluntary reference contraction is common practice within the ergonomics research paradigm. However, there is a lack of support for a common protocol for obtaining maximum repeatable exertions. Specifically, there is minimal evidence to support the use of providing force magnitude feedback during the production of voluntary maximum exertions (MVE) in terms of both signal amplitude and repeatability. Therefore, the purpose of this study was to determine (1) if an MVE force magnitude feedback protocol increased both the force exerted and corresponding muscle activity, (2) if force magnitude feedback improved the within-participant reproducibility of the force or activity observed, and (3) if the surface electromyography (sEMG) signal processing method affected the repeatability of determining peak muscle activity.Seventeen participants completed a series of MVEs; first without feedback of the forces they produced, then with feedback of the forces they were producing, and again without feedback to determine if providing force feedback influenced their ability to produce a maximum force. Hand force and sEMG from the anterior deltoid, middle deltoid, and infraspinatus were measured during each exertion. The results showed that the highest forces and muscle activities were achieved when force feedback was provided. Force magnitude feedback resulted in a 7–22% increase in magnitude (for force and activity) and a decrease of 11–46% in the coefficient of variation specifying an improvement in the within-participant reproducibility. Signal processing techniques also affected within-participant reproducibility, however to a much lesser extent. The peak value from a 500-ms moving window average of the linear enveloped or root mean squared sEMG was the most reproducible technique tested.     

Contralateral activity in a homologous hand muscle during voluntary contractions is greater in old adults.

This study compared the amount of contralateral activity produced in a homologous muscle by young (18-32 yr) and old (66-80 yr) adults when they performed unilateral isometric and anisometric contractions with a hand muscle. The subjects were not aware that the focus of the study was the contralateral activity. The tasks involved the performance of brief isometric contractions to six target forces, slowly lifting and lowering six inertial loads, and completing a set of 10 repetitions with a heavy load. The unintended force exerted by the contralateral muscle during the isometric contractions increased with target force, but the average force was greater for the old adults (means +/- SD; 12.6 +/- 15.3%) compared with the young adults (6.91 +/- 11.1%). The contralateral activity also increased with load during the anisometric contractions, and the average contralateral force was greater for the old subjects (5.28 +/- 6.29%) compared with the young subjects (2.10 +/- 3.19%). Furthermore, the average contralateral force for both groups of subjects was greater during the eccentric contractions (4.17 +/- 5.24%) compared with the concentric contractions (3.20 +/- 5.20%). The rate of change in contralateral activity during the fatigue task also differed between the two groups of subjects. The results indicate that old subjects have a reduced ability to suppress unintended contralateral activity during the performance of goal-directed, unilateral tasks.     

Age-related changes in finger coordination in static prehension tasks.

We studied age-related changes in the performance of maximal and accurate submaximal force and moment production tasks. Elderly and young subjects pressed on six dimensional force sensors affixed to a handle with a T-shaped attachment. The weight of the whole system was counterbalanced with another load. During tasks that required the production of maximal force or maximal moment by all of the digits, young subjects were stronger than elderly. A greater age-related deficit was seen in the maximal moment production tests. During maximal force production tests, elderly subjects showed larger relative involvement of the index and middle fingers; they moved the point of thumb force application upward (toward the index and middle fingers), whereas the young subjects rolled the thumb downward. During accurate force/moment production trials, elderly persons were less accurate in the production of both total moment and total force. They produced higher antagonistic moments, i.e., moment by fingers that acted against the required direction of the total moment. Both young and elderly subjects showed negative covariation of finger forces across repetitions of a ramp force production task. In accurate moment production tasks, both groups showed negative covariation of two components of the total moment: those produced by the normal forces and those produced by the tangential forces. However, elderly persons showed lower values of the indexes of both finger force covariation and moment covariation. We conclude that age is associated with an impaired ability to produce both high moments and accurate time profiles of moments. This impairment goes beyond the well-documented deficits in finger and hand force production by elderly persons. It involves worse coordination of individual digit forces and of components of the total moment. Some atypical characteristics of finger forces may be viewed as adaptive to the increased variability in the force production with age.     

Time-integrated position error accounts for sensorimotor behavior in time-constrained tasks

Several studies have shown that human motor behavior can be successfully described using optimal control theory, which describes behavior by optimizing the trade-off between the subject's effort and performance. This approach predicts that subjects reach the goal exactly at the final time. However, another strategy might be that subjects try to reach the target position well before the final time to avoid the risk of missing the target. To test this, we have investigated whether minimizing the control effort and maximizing the performance is sufficient to describe human motor behavior in time-constrained motor tasks. In addition to the standard model, we postulate a new model which includes an additional cost criterion which penalizes deviations between the position of the effector and the target throughout the trial, forcing arrival on target before the final time. To investigate which model gives the best fit to the data and to see whether that model is generic, we tested both models in two different tasks where subjects used a joystick to steer a ball on a screen to hit a target (first task) or one of two targets (second task) before a final time. Noise of different amplitudes was superimposed on the ball position to investigate the ability of the models to predict motor behavior for different levels of uncertainty. The results show that a cost function representing only a trade-off between effort and accuracy at the end time is insufficient to describe the observed behavior. The new model correctly predicts that subjects steer the ball to the target position well before the final time is reached, which is in agreement with the observed behavior. This result is consistent for all noise amplitudes and for both tasks.     

Reading hidden intentions in the human brain

When humans are engaged in goal-related processing, activity in prefrontal cortex is increased. However, it has remained unclear whether this prefrontal activity encodes a subject's current intention. Instead, increased levels of activity could reflect preparation of motor responses, holding in mind a set of potential choices, tracking the memory of previous responses, or general processes related to establishing a new task set. Here we study subjects who freely decided which of two tasks to perform and covertly held onto an intention during a variable delay. Only after this delay did they perform the chosen task and indicate which task they had prepared. We demonstrate that during the delay, it is possible to decode from activity in medial and lateral regions of prefrontal cortex which of two tasks the subjects were covertly intending to perform. This suggests that covert goals can be represented by distributed patterns of activity in the prefrontal cortex, thereby providing a potential neural substrate for prospective memory. During task execution, most information could be decoded from a more posterior region of prefrontal cortex, suggesting that different brain regions encode goals during task preparation and task execution. Decoding of intentions was most robust from the medial prefrontal cortex, which is consistent with a specific role of this region when subjects reflect on their own mental states.     

Effects of age and gender on finger coordination in MVC and submaximal force-matching tasks.

The objective of the study is to examine the effects of age and gender on finger coordination. Twelve young (24 +/- 8 yr; 6 men and 6 women) and 12 elderly (75 +/- 5 yr; 6 men and 6 women) subjects performed single-finger maximal contraction [maximal voluntary contraction (MVC)], four-finger MVC, and four-finger ramp force production tasks by pressing on individual force transducers. A drop in the force of individual fingers during four-finger MVC tasks compared with single-finger MVC tasks (force deficit) was larger, whereas unintended force production by other fingers during single-finger MVC tasks (enslaving) was smaller, in elderly than in young subjects and in women than in men. Force deficit was smaller and enslaving was larger in subjects with higher peak force. During the ramp task, the difference between the variance of total force and the sum of variances of individual forces showed a logarithmic relation to the level of total force, across all subject groups. These findings suggest that indexes of finger coordination scale with force-generating capabilities across gender and age groups.