Grip pattern and finger coordination differences between pianists and non-pianists

The aim of this study was to assess differences of grip pattern and finger coordination in pianists and non-pianists, using hand tasks that were unrelated to pianistic practice. Eleven pianists with more than 10 years of intensive practice were compared to 14 non-pianists. Both groups performed four tasks with their right hand: (1) gross grip at fast velocity; (2) gross grip at slow velocity; (3) hook grip at fast velocity; and (4) hook grip at slow velocity. The three-dimensional coordinates were reconstructed using a kinematic analysis system, and the flexion and extension angles of the metacarpophalangeal joints were calculated. The phase diagrams were qualitatively and quantitatively appraised in order to identify differences between the groups. Principal component analysis was used to assess differences between pianists and non-pianists in terms of the reproducibility and regularity of palmar grip cycles. Coefficients of correlation between the joint angles were used to analyze finger coordination during the tasks. The pianists showed better reproducibility and regularity in the palmar grip pattern, as well as finger movements that were more coordinated when performing different hand tasks.     

A method for estimating three-dimensional human arm movement with two electromagnetic sensors

Measurement of upper-limb movements is important in various domains. In this article, an upper-limb three-dimensional movement recording technique is proposed based on only two electromagnetic sensors. Two joints are considered with a total of seven degrees of freedom (DoF; three translations and four rotations). The chosen sequence of joint rotations is compliant with ISB recommendations: the shoulder is modelled with a ball and socket joint with three DoF and the elbow with a one DoF revolute joint. This article is focused on the procedure used to calibrate and sense the upper-limb movements from the raw data coming from the flock of birds sensors. The principle of the method is to define the centre of the wrist, elbow and shoulder joints in the frame of the adequate sensor. This operation is done by performing calibration gestures. Results are proposed and commented.     

A method for estimating three-dimensional human arm movement with two electromagnetic sensors

Measurement of upper-limb movements is important in various domains. In this article, an upper-limb three-dimensional movement recording technique is proposed based on only two electromagnetic sensors. Two joints are considered with a total of seven degrees of freedom (DoF; three translations and four rotations). The chosen sequence of joint rotations is compliant with ISB recommendations: the shoulder is modelled with a ball and socket joint with three DoF and the elbow with a one DoF revolute joint. This article is focused on the procedure used to calibrate and sense the upper-limb movements from the raw data coming from the flock of birds sensors. The principle of the method is to define the centre of the wrist, elbow and shoulder joints in the frame of the adequate sensor. This operation is done by performing calibration gestures. Results are proposed and commented.     

The relationship between consistency of propulsive cycles and maximum angular velocity during wheelchair racing

The purposes of this study were to examine the consistency of wheelchair athletes' upper-limb kinematics in consecutive propulsive cycles and to investigate the relationship between the maximum angular velocities of the upper arm and forearm and the consistency of the upper-limb kinematical pattern. Eleven elite international wheelchair racers propelled their own chairs on a roller while performing maximum speeds during wheelchair propulsion. A Qualisys motion analysis system was used to film the wheelchair propulsive cycles. Six reflective markers placed on the right shoulder, elbow, wrist joints, metacarpal, wheel axis, and wheel were automatically digitized. The deviations in cycle time, upper-arm and forearm angles, and angular velocities among these propulsive cycles were analyzed. The results demonstrated that in the consecutive cycles of wheelchair propulsion the increased maximum angular velocity may lead to increased variability in the upper-limb angular kinematics. It is speculated that this increased variability may be important for the distribution of load on different upper-extremity muscles to avoid the fatigue during wheelchair racing.     

Light Accelerates Morphogenesis and Acquisition of Interlimb Stepping in Chick Embryos

Chicks are bipedal precocious vertebrates that achieve adaptive locomotor skill within hours after hatching. Development of limb movement has been extensively studied in the chicken embryo, but few studies have focused on the preparations leading to precocious locomotor skill. Chicks typically hatch after 21 days of incubation, and recent studies provided evidence that the neural circuits for intralimb control of stepping are established between embryonic days (E) 18–20. It has also been shown that variations in light exposure during embryogenesis can accelerate or delay the onset of hatching and walking by 1 to 2 days. Our earlier work revealed that despite these differences in time to hatch, chicks incubated in different light conditions achieved similar locomotor skill on the day of hatching. Results suggested to us that light exposure during incubation may have accelerated development of locomotor circuits in register with earlier hatching. Thus, in this study, embryos were incubated in 1 of 3 light conditions to determine if development of interlimb coordination at a common time point, 19 days of incubation, varied with light exposure during embryogenesis. Leg muscle activity was recorded bilaterally and burst analyses were performed for sequences of spontaneous locomotor-related activity in one or more ankle muscles to quantify the extent of interlimb coordination in ovo. We report findings indicating that the extent of interlimb coordination varied with light exposure, and left-right alternating steps were a more reliable attribute of interlimb coordination for embryos incubated in constant bright light. We provide evidence that morphological development of the leg varied with light exposure. Based on these findings, we propose that light can accelerate the development of interlimb coordination in register with earlier hatching. Our results lead us to further propose that alternating left-right stepping is the default pattern of interlimb coordination produced by locomotor circuits during embryogenesis.     

Age-related differences in corticospinal control during functional isometric contractions in left and right hands.

The purpose of the study was to examine age-related differences in electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) during functional isometric contractions in left and right hands. EMG responses were recorded from the first dorsal interosseus muscle following TMS in 10 young (26.6 +/- 1.3 yr) and 10 old (67.6 +/- 2.3 yr) right-handed subjects. Muscle evoked potentials (MEPs) and silent-period durations were obtained in the left and right hands during index finger abduction, a precision grip, a power grip, and a scissor grip, while EMG was held constant at 5% of maximum. For all tasks, MEP area was 30% (P < 0.001) lower in the left hand of old compared with young subjects, whereas there was no age difference in the right hand. The duration of the EMG silent period was 14% (P < 0.001) shorter in old (150.3 +/- 2.9 ms) compared with young (173.9 +/- 3.0 ms) subjects, and the age differences were accentuated in the left hand (19% shorter, P < 0.001). For all subjects, the largest MEP area (10-12% larger) and longest EMG silent period (8-19 ms longer) were observed for the scissor grip compared with the other three tasks, and the largest task-dependent change in these variables was observed in the right hand of older adults. These differences in corticospinal control in the left and right hands of older adults may reflect neural adaptations that occur throughout a lifetime of preferential hand use for skilled (dominant) and unskilled (nondominant) motor tasks.     

Excitability of the motor cortex ipsilateral to the moving body side depends on spatio-temporal task complexity and hemispheric specialization

Unilateral movements are mainly controlled by the contralateral hemisphere, even though the primary motor cortex ipsilateral (M1(ipsi)) to the moving body side can undergo task-related changes of activity as well. Here we used transcranial magnetic stimulation (TMS) to investigate whether representations of the wrist flexor (FCR) and extensor (ECR) in M1(ipsi) would be modulated when unilateral rhythmical wrist movements were executed in isolation or in the context of a simple or difficult hand-foot coordination pattern, and whether this modulation would differ for the left versus right hemisphere. We found that M1(ipsi) facilitation of the resting ECR and FCR mirrored the activation of the moving wrist such that facilitation was higher when the homologous muscle was activated during the cyclical movement. We showed that this ipsilateral facilitation increased significantly when the wrist movements were performed in the context of demanding hand-foot coordination tasks whereas foot movements alone influenced the hand representation of M1(ipsi) only slightly. Our data revealed a clear hemispheric asymmetry such that MEP responses were significantly larger when elicited in the left M1(ipsi) than in the right. In experiment 2, we tested whether the modulations of M1(ipsi) facilitation, caused by performing different coordination tasks with the left versus right body sides, could be explained by changes in short intracortical inhibition (SICI). We found that SICI was increasingly reduced for a complex coordination pattern as compared to rest, but only in the right M1(ipsi). We argue that our results might reflect the stronger involvement of the left versus right hemisphere in performing demanding motor tasks.     

Internal desynchronization of circadian rhythms and tolerance of shift work

Fifteen male subjects including 12 shift workers (oil refinery operators) volunteered to document circadian rhythms in sleep-wake, grip strength of both hands, peak expiratory flow, heart rate, self-rated drowsiness, fatigue and attention. Each of these variables was measured 4 to 6 times/day for 2 to 3 weeks. In addition, both axillary temperature (with a shielded probe) and wrist activity were almost continuously recorded at 15 min intervals during the same time span. Individual time series were analyzed according to several statistical methods (power spectrum, cosinor, chi 2, etc.), in order to estimate the prominent circadian period tau and to evaluate both individual and subgroup differences with regard to tolerance of shift work, age, duration of shift work. The present study confirms for continuously recorded temperature and wrist activity, grip strength of both hands, heart rate and peak expiratory flow that intolerance of shift work is frequently associated with an internal desynchronization. However, this conclusion cannot be extended to circadian rhythms in self-rated drowsiness, fatigue and attention. The internal desynchronization among several circadian rhythms supports the hypothesis that these latter are driven by several oscillators, with presumable differences between right and left hemispheres as suggested by unequal values of tau in rhythms of both hand grip strength. Since an internal desynchronization can be observed in tolerant shift workers having no complaint, it is likely that symptoms of intolerance are related to the subject's sensitivity to internal desynchronization rather than to the desynchronization itself.     

The effects of ball impact location and grip tightness on the arm, racquet and ball for one-handed tennis backhand groundstrokes

A torque-driven, 3D computer simulation model of an arm-racquet system was used to investigate the effects of ball impact location and grip tightness on the arm, racquet and ball during one-handed tennis backhand groundstrokes. The stringbed was represented by nine point masses connected to each other and the racquet frame with elastic springs and three torsional spring-dampers between the hand and the racquet were used to represent grip tightness. For each perturbation of nine impact locations and grip tightness, simulations were run for a 50 ms period starting with ball-racquet impact. Simulations showed that during off-centre impacts below the longitudinal axis of the racquet, the wrist was forced to flex up to 16° more with up to six times more wrist extension torque when compared to a centre impact simulation. Perturbing grip tightness had no substantial effect on centre impact simulations. However, for off-centre impacts (below the longitudinal axis of the racquet) a tight grip condition resulted in a substantial decrease in racquet rotation within the hand (less than 2°) and an increase of 6° in wrist flexion angle when compared to the equivalent simulation with a normal grip. In addition there was approximately 20% more wrist extension torque when compared with equivalent off-centre impact simulation with a normal grip. Consequently off-centre impacts below the longitudinal axis of the racquet may be a substantial contributing factor for tennis elbow injuries with a tight grip aggravating the effect due to high eccentric wrist extension torques and forced wrist flexion.     

Interlimb coordination,gait, and neural control of quadrupedalism in chimpanzees

Interlimb coordination is directly relevant to the understanding of the neural control of locomotion, but few studies addressing this topic for nonhuman primates are available, and no data exist for any hominoid other than humans. As a follow-up to Jungers and Anapol's ([1985] Am. J. Phys. Anthropol. 67:89–97) analysis on a lemur and talapoin monkey, we describe here the patterns of interlimb coordination in two chimpanzees as revealed by electromyography. Like the lemur and talapoin monkey, ipsilateral limb coupling in chimpanzees is characterized by variability about preferred modes within individual gaits. During symmetrical gaits, limb coupling patterns in the chimpanzee are also influenced by kinematic differences in hindlimb placement (“overstriding”). These observations reflect the neurological constraints placed on locomotion but also emphasize the overall flexibility of locomotor neural mechanisms. Interlimb coordination patterns are also species-specific, exhibiting significant differences among primate taxa and between primates and cats. Interspecific differences may be suggestive of phylogenetic divergence in the basic mechanisms for neural control of locomotion, but do not preclude morphological explanations for observed differences in interlimb coordination across species. Am J Phys Anthropol 102:177–186, 1997 © 1997 Wiley-Liss, Inc.     

Self-Sustained Motor Activity Triggered by Interlimb Reflexes in Chronic Spinal Cord Injury,Evidence of Functional Ascending Propriospinal Pathways

The loss or reduction of supraspinal inputs after spinal cord injury provides a unique opportunity to examine the plasticity of neural pathways within the spinal cord. In a series of nine experiments on a patient, quadriplegic due to spinal cord injury, we investigated interlimb reflexes and self-sustained activity in completely paralyzed and paretic muscles due to a disinhibited propriospinal pathway. Electrical stimuli were delivered over the left common peroneal nerve at the fibular head as single stimuli or in trains at 2–100 Hz lasting 1 s. Single stimuli produced a robust interlimb reflex twitch in the contralateral thumb at a mean latency 69 ms, but no activity in other muscles. With stimulus trains the thumb twitch occurred at variable subharmonics of the stimulus rate, and strong self-sustained activity developed in the contralateral wrist extensors, outlasting both the stimuli and the thumb reflex by up to 20 s. Similar behavior was recorded in the ipsilateral wrist extensors and quadriceps femoris of both legs, but not in the contralateral thenar or peroneal muscles. The patient could not terminate the self-sustained activity voluntarily, but it was abolished on the left by attempted contractions of the paralyzed thumb muscles of the right hand. These responses depend on the functional integrity of an ascending propriospinal pathway, and highlight the plasticity of spinal circuitry following spinal cord injury. They emphasize the potential for pathways below the level of injury to generate movement, and the role of self-sustained reflex activity in the sequelae of spinal cord injury.     

Elbow and wrist joint contact forces during occupational pick and place activities

A three-dimensional, mathematical model of the elbow and wrist joints, including 15 muscle units, 3 ligaments and 4 joint forces, has been developed. A new strain gauge transducer has been developed to measure functional grip forces. The device measures radial forces divided into six components and forces of up to 250N per segment can be measured with an accuracy of +/-1%. Ten normal volunteers were asked to complete four tasks representing occupational activities, during which time their grip force was monitored. Together with kinematic information from the six-camera Vicon data, the moment effect of these loads at the joints was calculated. These external moments are assumed to be balanced by the internal moments, generated by the muscles, passive soft tissue and bone contact. The effectiveness of the body's internal structures in generating joint moments was assessed by studying the geometry of a simplified model of the structures, where information about the lines of action and moment arms of muscles, tendons and ligaments is contained. The assumption of equilibrium between these external and internal joint moments allows formulation of a set of equations from which muscle and joint forces can be calculated. A two stage, linear optimisation routine minimising the overall muscle stress and the sum of the joint forces has been used to overcome the force-sharing problem. Humero-ulnar forces of up to 1600N, humero-radial forces of up to 800N and wrist joint forces of up to 2800N were found for moderate level activity. The model was validated by comparison with other studies.     

Prognostic value of early features in rheumatoid disease.

Extensive data on 102 patients who presented with rheumatoid disease within a year of onset were gathered by a prospective study to assess the prognostic value of early features. Outcome was evaluated at a mean 4-5 years from onset on the basis of functional grade, extent of joint disease, early morning stiffness, and grip strength. Twenty-six patients improved, 14 pursued a mild steady course, and 62 had a persistently severe or deteriorating condition. The features recorded at the first visit were correlated with outcome. Those indicating a poor prognosis were: older age at onset, being underweight, poor grip strength, many affected joints, involvement of wrist or metatarsophalangeal joints, poor functional status, fulfilment of many of the American Rheumatism Association criteria for rheumatoid disease, raised erythrocyte sedimentation rate, seropositivity on sheep cell agglutination or latex tests, low haemoglobin level, raised blood urea level, and early erosions on x-ray films.     

Wrist splint effects on muscle activity and force during a handgrip task

Wrist splints are commonly prescribed to limit wrist motion and provide support at night and during inactive periods but are often used in the workplace. In theory, splinting the wrist should reduce wrist extensor muscle activity by stabilizing the joint and reducing the need for co-contraction to maintain posture. Ten healthy volunteers underwent a series of 24 10-s gripping trials with surface electromyography on 6 forearm muscles. Trials were randomized between splinted and nonsplinted conditions with three wrist postures (30 degrees flexion, neutral, and 30 degrees extension) and four grip efforts. Custom-made Plexiglas splints were taped to the dorsum of the hand and wrist. It was found that when simply holding the dynamometer, use of a splint led to a small (<1% MVE) but significant reduction in activity for all flexor muscles and extensor carpi radialis (all activity <4% maximum). At maximal grip, extensor muscle activity was significantly increased with the splints by 7.9-23.9% MVE. These data indicate that splinting at low-to-moderate grip forces may act to support the wrist against external loading, but appears counterproductive when exerting maximal forces. Wrist bracing should be limited to periods of no to light activity and avoided during tasks that require heavy efforts.     

Kinematic accuracy of three surface registration methods in a three-dimensional wrist bone study

The use of registration techniques to determine motion transformations noninvasively has become more widespread with the increased availability of the necessary software. In this study, three surface registration techniques were used to generate carpal bone kinematic results from a single cadaveric wrist specimen. Surface contours were extracted from specimen computed tomography volume images of the forearm, carpal, and metacarpal bones in four arbitrary positions. Kinematic results from each of three registration techniques were compared with results derived from multiple spherical markers fixed to the specimen. Kinematic accuracy was found to depend on the registration method and bone size and shape. In general, rotation errors of the capitate and scaphoid were less than 0.5 deg for all three techniques. Rotation errors for the other bones were generally less than 2 deg, although error for the trapezoid was greater than 2 deg in one technique. Translation errors of the bones were generally less than 1 mm, although errors of the trapezoid and trapezium were greater than 1 mm for two techniques. Tradeoffs existed in each registration method between image processing time and overall kinematic accuracy. Markerless bone registration (MBR) can provide accurate measurements of carpal kinematics and can be used to study the noninvasive, three-dimensional in vivo kinematics of the wrist and other skeletal joints.     

Phase-entrainment dynamics of visually coupled rhythmic movements

Do interlimb rhythmic coordinations between individuals exhibit the same relations among the same observable quantities as interlimb rhythmic coordination within an individual? The 1∶1 frequency locking between the limbs of two people was investigated using a paradigm in which each person oscillated a hand-held pendulum, achieving and maintaining the mutual entrainment through vision. The intended coordination was antiphase, φ=π, and the difference between the uncoupled eigenfrequencies, Δω, was manipulated through differences in the lengths of the two pendulums. The mean phase relation and its variance for visually coupled coordinations differing in Δω were predicted by an order parameter equation developed by Haken et al. (1985) and Schöner et al. (1986) for the relative phase of correlated movements of limb segments. Specifically, the experiment revealed that: (1) the deviation of φ from π increased with increasing deviation of Δω from 0; and (2) fluctuations in φ increased with increasing deviation of Δω from 0. With deviations of Δω from 0, new peaks were added at higher harmonics in φ's power spectrum. These results were in agreement with previous research on the stable states of interlimb coordination within a person, mediated by mechanoreceptive rather than photoreceptive mechanisms. Additionally, they were in agreement with previous research on phase transitions in interlimb coordination which have been shown to conform to the same order parameter dynamics whether the coupling be mechanoreceptively or photoreceptively based. It was suggested that phase entrainment in biological movement systems may abide by dynamical principles that are indifferent to the details of the coupling.     

A new manual power grip

A manual power grip for holding a cylindrical object using a relaxed index finger is described and analysed. In a group of 21 young adult students it provided greater grip strength than the conventional oblique power grip. It allowed a significant increase in the range of adduction-abduction at the wrist. In recent years it appears to have been empirically used by a number of top class racquet players and is the basis of the modern assault rifle grip. A new design of strain gauge dynamometer, in the shape of a cylinder, which permits the testing of a number of grip types and wrist positions is described. Standard grip testing protocol is used with this device which also allows the concomitant use of a goniometer for the assessment of wrist mobility.     

Neuromechanical control of the forearm muscles during gripping with sudden flexion and extension wrist perturbations

The purpose of this study was to investigate how gripping modulates forearm muscle co-contraction prior to and during sudden wrist perturbations. Ten males performed a sub-maximal gripping task (no grip, 5% and 10% of maximum) while a perturbation forced wrist flexion or extension. Wrist joint angles and activity from 11 muscles were used to determine forearm co-contraction and muscle contributions to wrist joint stiffness. Co-contraction increased in all pairs as grip force increased (from no grip to 10% grip), corresponding to a 36% increase in overall wrist joint stiffness. Inclusion of individual muscle contributions to wrist joint stiffness enhanced the understanding of forearm co-contraction. The extensor carpi radialis longus (ECRL) and brevis had the largest stiffness contributions (34.5 ± 1.3% and 20.5 ± 2.3%, respectively), yet muscle pairs including ECRL produced the lowest co-contraction. The muscles contributing most to wrist stiffness were consistent across conditions (ECRL for extensors; Flexor Digitorum Superficialis for flexors), suggesting enhanced contributions rather than muscular redistribution. This work provides investigation of the neuromuscular response to wrist perturbations and gripping demands by considering both co-contraction and muscle contributions to joint stiffness. Individual muscle stiffness contributions can be used to enhance the understanding of forearm muscle control during complex tasks.     

Interlimb Reflexes Induced by Electrical Stimulation of Cutaneous Nerves after Spinal Cord Injury

Whether interlimb reflexes emerge only after a severe insult to the human spinal cord is controversial. Here the aim was to examine interlimb reflexes at rest in participants with chronic (>1 year) spinal cord injury (SCI, n = 17) and able-bodied control participants (n = 5). Cutaneous reflexes were evoked by delivering up to 30 trains of stimuli to either the superficial peroneal nerve on the dorsum of the foot or the radial nerve at the wrist (5 pulses, 300 Hz, approximately every 30 s). Participants were instructed to relax the test muscles prior to the delivery of the stimuli. Electromyographic activity was recorded bilaterally in proximal and distal arm and leg muscles. Superficial peroneal nerve stimulation evoked interlimb reflexes in ipsilateral and contralateral arm and contralateral leg muscles of SCI and control participants. Radial nerve stimulation evoked interlimb reflexes in the ipsilateral leg and contralateral arm muscles of control and SCI participants but only contralateral leg muscles of control participants. Interlimb reflexes evoked by superficial peroneal nerve stimulation were longer in latency and duration, and larger in magnitude in SCI participants. Interlimb reflex properties were similar for both SCI and control groups for radial nerve stimulation. Ascending interlimb reflexes tended to occur with a higher incidence in participants with SCI, while descending interlimb reflexes occurred with a higher incidence in able-bodied participants. However, the overall incidence of interlimb reflexes in SCI and neurologically intact participants was similar which suggests that the neural circuitry underlying these reflexes does not necessarily develop after central nervous system injury.