Effect Of Hand Position Research Articles

ERP evidence of attentional somatosensory processing and stimulus-response coupling under different hand and arm postures.

We investigated (1) the effects of divided and focused attention on event-related brain potentials (ERPs) elicited by somatosensory stimulation under different response modes, (2) the effects of hand position (closely-placed vs. separated hands) and arm posture (crossed vs. uncrossed forearms) on the attentional modulation of somatosensory ERPs, and (3) changes in the coupling of stimulus- and response-related processes by somatosensory attention using a single-trial analysis of P300 latency and reaction times. Electrocutaneous stimulation was presented randomly to the thumb or middle finger of the left or right hand at random interstimulus intervals (700-900 ms). Subjects attended unilaterally or bilaterally to stimuli in order to detect target stimuli by a motor response or counting. The effects of unilaterally-focused attention were also tested under different hand and arm positions. The amplitude of N140 in the divided attention condition was intermediate between unilaterally attended and unattended stimuli in the unilaterally-focused attention condition in both the mental counting and motor response tasks. Attended infrequent (target) stimuli elicited greater P300 in the unilaterally attention condition than in the divided attention condition. P300 latency was longer in the divided attention condition than in the unilaterally-focused attention condition in the motor response task, but remained unchanged in the counting task. Closely locating the hands had no impact, whereas crossing the forearms decreased the attentional enhancement in N140 amplitude. In contrast, these two manipulations uniformly decreased P300 amplitude and increased P300 latency. The correlation between single-trial P300 latency and RT was decreased by crossed forearms, but not by divided attention or closely-placed hands. Therefore, the present results indicate that focused and divided attention differently affected middle latency and late processing, and that hand position and arm posture also differently affected attentional processes and stimulus-response coupling.

The effect of hand position on chest compression quality during CPR in young children: Findings from the Videography in Pediatric Resuscitation (VIPER) collaborative

ObjectiveTo determine the effect of hand position on chest compression (CC) quality during CPR in young children. MethodsProspective observational exploratory study. Patients < 8 years receiving CC for > 2 minutes were enrolled. Data was collected from video review and CC monitor device and analyzed in ‘CC segments’ (periods of CC by individual providers). Four techniques were compared: two thumbs (2 T), hands encircling the chest; two fingers (2F) on the sternum; one hand on sternum (1H); two hands on sternum (2H). Univariate analysis of CC rate and depth between hand positions was performed through nonparametric testing, stratified by age category. Results47 patients received 824 minutes of CC. Among 270 CC segments in infants < 1 yo, 2 T was used in 27%; 2F 3%; 1H 18%; 2H 26%. Among 189 CC segments in children aged 1 to 8 yo, 1H was used in 26%; 2H 74%. Across all segments, median CC rate was 117 cpm (IQR 110–125). Median depth was 2.92 cm (IQR 2.44 – 4.04) in infants < 1 yo, 3.56 cm (IQR 2.92 – 4.14) in children 1 to 8 yo. 1H achieved greater depth than 2 T in infants (p < 0.01), and 2H achieved greater depth than 1H in children > 1 (p < 0.001). ConclusionsIn infants, 1H resulted in greater CC depth than 2 T. In children 1 to 8 yo, 2H resulted in greater depth than 1H.. These data suggest that different hand position during CPR in young children from what is currently recommended may result in better CPR quality.

Band Pull-Apart Exercise: Effects of Movement Direction and Hand Position on Shoulder Muscle Activity.

Background/PurposeThe Elastic band pull-apart exercise is commonly used in rehabilitation. It involves pulling an elastic resistance band with both hands in horizontal abduction or diagonal arm movements. The extent of muscle activation during this exercise is unknown. The purpose of this study was to measure the electromyographic (EMG) activity of shoulder-girdle muscles during the pull-apart exercise using resistance bands and to determine the effects of arm position and movement direction on shoulder-girdle muscle activity.Materials/MethodsSurface EMG activity was measured on the infraspinatus, upper trapezius, middle trapezius, lower trapezius and posterior deltoid of the dominant shoulder. After measurement of maximal voluntary contraction (MVC) for each muscle, subjects performed the band pull-apart exercise in three hand positions (palm up, neutral, palm down) and three movement directions (diagonal up, horizontal, diagonal down). Elastic band resistance was chosen to elicit moderate exertion (5/10 on the Borg CR10 scale). The order of the exercises was randomized and three repetitions of each exercise were performed. Mean peak EMG activity in each muscle across the repetitions was calculated and expressed as a percentage of MVC. Peak normalized EMG activity in each muscle was compared in two-way (hand position x direction) repeated-measures ANOVA.ResultsData were collected from 10 healthy subjects (all males, age 36±12 years). Peak muscle activity ranged from 15.3% to 72.6% of MVC across muscles and exercise conditions. There was a significant main effect of hand position for the infraspinatus and lower trapezius, where muscle activity was highest with the palm up hand position (p < 0.001), and for the upper trapezius and posterior deltoid, where muscle activity was highest with the palm down position (p-value range < 0.001-0.004). There was a significant main effect of movement direction, where the diagonal up direction demonstrated the highest muscle activity for the infraspinatus, upper trapezius, lower trapezius, and posterior deltoid (p-value range < 0.001-0.02).ConclusionAltering hand position and movement direction during performance of an elastic band pull-apart exercise can affect magnitudes of shoulder-girdle muscle activity. Clinicians may alter a patient’s hand position and movement direction while performing the band pull-apart exercise in order to increase muscle activity in target muscles or diminish muscle activity in other muscles.Level of Evidence2b

Neural coding of action in three dimensions: Task- and time-invariant reference frames for visuospatial and motor-related activity in parietal area V6A.

Goal-directed movements involve a series of neural computations that compare the sensory representations of goal location and effector position, and transform these into motor commands. Neurons in posterior parietal cortex (PPC) control several effectors (e.g., eye, hand, foot) and encode goal location in a variety of spatial coordinate systems, including those anchored to gaze direction, and to the positions of the head, shoulder, or hand. However, there is little evidence on whether reference frames depend also on the effector and/or type of motor response. We addressed this issue in macaque PPC area V6A, where previous reports using a fixate-to-reach in depth task, from different starting arm positions, indicated that most units use mixed body/hand-centered coordinates. Here, we applied singular value decomposition and gradient analyses to characterize the reference frames in V6A while the animals, instead of arm reaching, performed a nonspatial motor response (hand lift). We found that most neurons used mixed body/hand coordinates, instead of "pure" body-, or hand-centered coordinates. During the task progress the effect of hand position on activity became stronger compared to target location. Activity consistent with body-centered coding was present only in a subset of neurons active early in the task. Applying the same analyses to a population of V6A neurons recorded during the fixate-to-reach task yielded similar results. These findings suggest that V6A neurons use consistent reference frames between spatial and nonspatial motor responses, a functional property that may allow the integration of spatial awareness and movement control.

Effects of Hand Positions During Video Head-Impulse Test (vHIT) in Patients With Unilateral Vestibular Neuritis.

Background: The aim of this study is to identify the effects of hand positions (head and jaw) on the video head-impulse test (vHIT).Methods: Eighty-six healthy volunteers and sixty-seven patients with unilateral vestibular neuritis (UVN) were recruited for this study. Different hand positions (head and jaw) were used in the vHIT of horizontal semicircular canals in healthy volunteers and UVN patients. All the obtained horizontal vHIT gains were analyzed.Results: It was observed that when horizontal vHIT was performed with the head hand position, the number of head impulses that produced overhigh vestibulo-ocular reflex (VOR) gains was more than that with the jaw hand position (p < 0.01), irrespective of whether the test was performed in healthy volunteers or UVN patients. The gains obtained were lower when the jaw hand position was used than that obtained when the head hand position was used (p < 0.05). However, no significant difference existed in the mean head velocity between the two hand positions (p > 0.05). Using the head hand position has greater a chance to elicit in UVN patients normal horizontal vHIT gains with refixation saccades than using the jaw hand position (p = 0.04).Conclusion: The jaw hand position can increase the accuracy of vHIT in determining the lesion side.

T128. Modulation of exteroceptive electromyographic responses in defensive peripersonal space

Introduction The cutaneous silent period (CSP) is a spinal nociceptive inhibitory reflex, that briefly interrupts voluntary contraction of limb muscles involved in reaching and grasping movements after noxious electrical stimulation of a cutaneous nerve. It is mediated by A-delta afferents. CSPs act in conjunction with flexor withdrawal reflexes to constitute a sophisticated defensive system for protecting a limb from harmful stimuli. CSP is functionally rather than anatomically organized. I1 and I2 components are considered spinal, E2 is regarded transcortical in origin. Defending the body surface from environmental threats requires sensorimotor integration between multimodal sensory afferents and motor planning of defensive movements. Cortical areas involved in this integration are the poly-sensory zone in the precentral gyrus and the ventral intraparietal area. The defensive peri-personal space (DPPS), immediately surrounding the body, was first described in macaque monkeys. Neurophysiological studies of the human DPPS demonstrated larger somatosensory blink reflexes with the stimulated hand located near the face. We investigated the effect of hand position on CSP in DPPS vs. extrapersonal space (EPS). Methods Fifteen healthy volunteers underwent serial CSP testing with the arm resting on an elevated table, elbow flexed, and the hand held either within 5 cm from the nose (NEAR) or away from the body (FAR). Electrical stimuli were applied to either digit 2 or 5 (D2, D5). Sensory thresholds (ST) were established for each subject and digit. EMG recordings were obtained from first dorsal interosseous (FDI) muscle during 20% maximal voluntary contraction, following random stimulation of either D2 or D5 in both NEAR and FAR conditions, with 5, 10, and 15X ST intensity. CSPs were identified by a decrease in mean rectified EMG activity below 80% of prestimulus baseline. CSPs were divided into I1, E2, and I2. Results Following D2 stimulation, CSPs consisted of I1, E2, and I2. With increasing stimulus intensities, CSP duration and I2 duration increased, suppression index (SI) of CSP and I2 decreased, and E2 amplitude decreased progressively, both in DPPS and EPS. E2 amplitude was significantly larger in DPPS vs. EPS, while no other parameter differed between DPPS and EPS. Following D5 stimulation, CSP equaled I2, and there was no clear E2. With increasing stimulus intensities I2 duration increased and SI decreased, both in DPPS and EPS. No parameter differed between DPPS and EPS. Conclusion Concurring with previous literature, E2 was present in FDI only when stimulating homotopic D2 and not heterotopic D5. E2 was larger in DPPS vs. EPS, representing direct neurophysiological evidence of transcortical sensorimotor processing related to DPPS, while inhibitory CSP parameters did not differ between DPPS and EPS, concurring with a spinal organization of its circuitry.

Infant chest compression quality: A video-based comparison of two-thumb versus one-hand technique in the emergency department

AimTo use video review to compare CC quality between 2-thumb encircling (2T) and one-hand anterior (1H) hand position in infants receiving CPR. MethodsEvents where an infant received >2min of CC using a CPR monitor device while videorecorded were included. CC were measured in segments provided by a single compressor; segment duration, identity of the compressor, and hand position (2T vs 1H) was determined from video review. CC rate and depth were measured by the monitor device. ResultsSeven infants received 111min of CCs from a total of 28 providers. 12/28 providers were assessed using both 2T and 1H; 6 providers used 2T and 1H in the same patient. 80 CC segments were analyzed; the median duration of CC segments was 74s (IQR 50–95s). Median CC rate across all segments was 127/min (IQR 115–142/min); median CC depth was 3.0cm (IQR 2.4–3.4cm). 2T position was used in 33/80 (41%) of segments. There was no significant difference in CC depth between 2T and 1H position (3.0±0.8 vs 3.0±0.6cm, p=0.81). 1H position was significantly associated with faster CC rate than 2T position (134±18 vs. 118±15 CC/min, p<0.001). ConclusionsDuring CC in infants, 1H position was associated with a greater prevalence of inappropriately fast CC rate compared to 2T. There was no significant difference in depth between 2T and 1H. Future studies should evaluate the effect of hand position on clinical outcomes.

Clinical Implications of Hand Position and Lower Limb Length Measurement Method on Y-Balance Test Scores and Interpretations.

The Lower Quarter Y-Balance Test (LQ-YBT) was developed to provide an effective and efficient screen for injury risk in sports. Earlier protocol recommendations for the LQ-YBT involved the athlete placing the hands on the hips and the clinician normalizing scores to lower limb length measured from the anterior-superior iliac spine to the lateral malleolus. The updated LQ-YBT protocol recommends the athlete's hands be free moving and the clinician measure lower limb length to the medial malleolus. To investigate the effect of hand position and lower limb length measurement method on LQ-YBT scores and their interpretation. Cross-sectional study. National Sports Institute of Malaysia. A total of 46 volunteers, consisting of 23 men (age = 25.7 ± 4.6 years, height = 1.70 ± 0.05 m, mass = 69.3 ± 9.2 kg) and 23 women (age = 23.5 ± 2.5 years, height = 1.59 ± 0.07 m, mass = 55.7 ± 10.6 kg). Participants performed the LQ-YBT with hands on hips and hands free to move on both lower limbs. In a single-legged stance, participants reached with the contralateral limb in each of the anterior, posteromedial, and posterolateral directions 3 times. Maximal reach distances in each direction were normalized to lower limb length measured from the anterior-superior iliac spine to the lateral and medial malleoli. Composite scores (average of the 3 normalized reach distances) and anterior-reach differences (in raw units) were extracted and used to identify participants at risk for injury (ie, anterior-reach difference ≥4 cm or composite score ≤94%). Data were analyzed using paired t tests, Fisher exact tests, and magnitude-based inferences (effect size [ES], ±90% confidence limits [CLs]). Differences between hand positions in normalized anterior-reach distances were trivial (t91 = -2.075, P = .041; ES = 0.12, 90% CL = ±0.10). In contrast, reach distances were greater when the hands moved freely for the normalized posteromedial (t91 = -6.404, P < .001; ES = 0.42, 90% CL = ±0.11), posterolateral (t91 = -6.052, P < .001; ES = 0.58, 90% CL = ±0.16), and composite (t91 = -7.296, P < .001; ES = 0.47, 90% CL = ±0.11) scores. A similar proportion of the cohort was classified as at risk with the hands on the hips (35% [n = 16]) and the hands free to move (43% [n = 20]; P = .52). However, the participants classified as at risk with the hands on the hips were not all categorized as at risk with the hands free to move and vice versa. The lower limb length measurement method exerted trivial effects on LQ-YBT outcomes. Hand position exerted nontrivial effects on LQ-YBT outcomes and interpretation, whereas the lower limb length measurement method had trivial effects.

The effect of hand position on perceived finger orientation in left- and right-handers

In the absence of visual feedback, the perceived orientation of the fingers is systematically biased. In right-handers these biases are asymmetrical between the left and right hands in the horizontal plane and may reflect common functional postures for the two hands. Here we compared finger orientation perception in right- and left-handed participants for both hands, across various hand positions in the horizontal plane. Participants rotated a white line on a screen optically superimposed over their hand to indicate the perceived position of the finger that was rotated to one of seven orientations with the hand either aligned with the body midline, aligned with the shoulder, or displaced by twice the shoulder-to-midline distance from the midline. We replicated the asymmetric pattern of biases previously reported in right-handed participants (left hand biased towards an orientation ~30° inward, right hand ~10° inward). However, no such asymmetry was found for left-handers, suggesting left-handers may use different strategies when mapping proprioception to body or space coordinates and/or have less specialization of function between the hands. Both groups’ responses rotated further outward as distance of the hand from the body midline increased, consistent with other research showing spatial orientation estimates diverge outward in the periphery. Finally, for right-handers, precision of responses was best when the hand was aligned with the shoulder compared to the other two conditions. These results highlight the unique role of hand dominance and hand position in perception of finger orientation, and provide insight into the proprioceptive position sense of the upper limbs.

Effect of Hand Positioning on DXA Total and Regional Bone and Body Composition Parameters, Precision Error, and Least Significant Change

Dual-energy X-ray absorptiometry (DXA) body composition measurements are performed in both clinical and research settings for estimations of total and regional fat mass, lean tissue mass, and bone mineral content. Subject positioning influences precision and positioning instructions vary between manufacturers. The aim of the study was to determine the effect of hand position and scan mode on regional and total body bone and body composition parameters and determine protocol-specific body composition precision errors. Thirty-eight healthy subjects (men; mean age: 27.1 ± 12.1 yr) received 4 consecutive total body GE-Lunar iDXA (enCORE v 15.0) scans with re-positioning, and scan mode was dependent on body size. Twenty-three subjects received scans in standard mode and 15 received scans in thick scan modes. Two scans per subject were conducted with subject hands prone and 2 with hands mid-prone. The precision error (root mean squared standard deviation; percentage coefficient of variation) and least significant change for each protocol were determined using the International Society for Clinical Densitometry calculator. Hands placed in the mid-prone position increased arm bone mineral density (BMD) (standard mode: 0.185 g*cm−2, thick mode: 0.265 g*cm−2; p < 0.05), total body BMD (standard mode: 0.051 g*cm−2, thick mode: 0.069 g*cm−2; p < 0.001), and total body BMD Z-score (standard mode: 0.5. thick mode: 0.7; p < 0.001). This was due to reductions in bone area and bone mineral content. In standard mode, hands mid-prone reduced fat mass (0.05 kg, p < 0.05) and increased lean mass (0.11 kg, p < 0.05). There were no differences in body composition for thick mode scans. Hands mid-prone reduced lean mass precision error at the arms, trunk, and total body (p < 0.01). DXA clinical and research centers are advised to maintain consistency in their hand positioning and scan mode protocols, and consideration should be given to the hand positioning used for reference data. As a best practice recommendation, published DXA-based studies and reports for clinic-based total body assessments should ensure that subject positioning is fully described.

Joint specific power is not affected by changes in hand position in recreational and elite cyclists.

Cycling is a sport where the majority of the external power produced is used to overcome air resistance. Cycling with an optimized aerodynamic position has been shown to greatly improve time trial performance 1 . However, although reducing frontal area of a cyclist will reduce the air resistance which must be overcome, there is less knowledge on the effect of these changes in position on technique. Lowering the position has been shown to 0influence muscle activation and lead changes in force effectiveness 2,3 but the effect of changing hand position on joint specific power has, to the best of our knowledge, not been investigated. Additionally, elite cyclists may be more accustomed to riding in aerodynamic position compared to recreational cyclists because they likely utilize an aerodynamic position to a greater extent in their efforts to achieve optimal performance. The purpose of the present study was to investigate the effect of different hand positions on joint specific power in the hip knee and ankle joints in addition to investigate potential differences between recreationally trained and elite cyclists. Â Methods Nine elite and nine recreational cyclists completed a total of 9 cycling stages using 3 different intensities (i.e. 100W, 200W and a work rate corresponding to the predetermined lactate threshold) and 3 different handgrip positions (i.e. tops, hoods, drops). All cycling was done using a freely chosen cadences with the participants private bikes mounted on a trainer. Joint specific power was calculated using kinematic measurements from a 3D motion capture system and pedal forces recorded from clipless pedals equipped with force cells. Â Results Preliminary analyses indicate that increasing the external work rate led to increased contribution of the hip joint contribution and decreased contribution of the knee joint for both the recreational and elite cyclists (p < 0.05). No effect of external work rate was found for the ankle joint. There was no effect of hand position on the joint contribution to external power in any of the groups but the elite group had increased hip joint contribution at the hoods position at the intensity corresponding to lactate threshold (p < 0.05). Â Discussion and Conclusions The results of the present study indicates that riding on the tops, hoods or drops have little impact on joint specific power in the hip, knee and ankle joints and there are no differences between recreational and elite cyclists in the effect of hand position. Technique in the form of joint specific power is not altered by utilizing a more aerodynamic position in elite or recreational cyclists.

Effects of Hand Position with Relation to Elbow and Shoulder Position on Maximum Grip Strength

This study aimed at determining the grip strength at various angles of shoulder and elbow positions and associate them with discomfort at each point. Method: 60 right handed male subjects aged 20-35 years were taken to measure grip strength at shoulder forward flexion at 0°,45°,90°,135°,180° with elbow at 0° and 90° flexion; discomfort was measured with a VAS scale. Result: scores of grip strength: minimum at 90° elbow and 180° shoulder and maximum at 0° elbow and 180o shoulder. VAS score: the maximum at 0° elbow and 135° shoulder and minimum at 0° elbow and 0° shoulder. Conclusion: there exists a relation between grip strength and discomfort.

Boundary Extension Is Sensitive to Hand Position in Young and Older Adults.

Based on preliminary reports, we expected an age-related increase in boundary extension (BE), a phenomenon in which people falsely remember seeing more of a scene than was presented. Given recent data suggesting hand-centered attentional frames in young adults contrasted with body-centered attentional frames in older adults, we predicted hand-position effects on BE in young adults only. Participants (59 young, 60 older adults) viewed photographs of complex scenes (e.g., a market) and answered yes/no questions about each. Half answered with key presses while their hands were framing the computer monitor; half while their hands were on a lapdesk. At test, participants indicated whether photographs were the same as, or at a closer or wider angle than at study. Both age groups demonstrated BE. When study-test angles were the same, participants rated test pictures as closer than at study. When study-test angles differed, older adults showed less BE than young adults. For both same- and different-angle conditions, there was a main effect of hand position (less BE when hands framed the monitor than when on participants' laps). The data confirm older adults show BE but show no age-related increase. Surprisingly, both young and older adults showed hand-centered attention.

Mixed Body/Hand Reference Frame for Reaching in 3D Space in Macaque Parietal Area PEc.

The neural correlates of coordinate transformations from vision to action are expressed in the activity of posterior parietal cortex (PPC). It has been demonstrated that among the medial-most areas of the PPC, reaching targets are represented mainly in hand-centered coordinates in area PE, and in eye-centered, body-centered, and mixed body/hand-centered coordinates in area V6A. Here, we assessed whether neurons of area PEc, located between V6A and PE in the medial PPC, encode targets in body-centered, hand-centered, or mixed frame of reference during planning and execution of reaching. We studied 104 PEc cells in 3 Macaca fascicularis. The animals performed a reaching task toward foveated targets located at different depths and directions in darkness, starting with the hand from 2 positions located at different depths, one next to the trunk and the other far from it. We show that most PEc neurons encoded targets in a mixed body/hand-centered frame of reference. Although the effect of hand position was often rather strong, it was not as strong as reported previously in area PE. Our results suggest that area PEc represents an intermediate node in the gradual transformation from vision to action that takes place in the reaching network of the dorsomedial PPC.

Editorial: Taking a hands-on approach: current perspectives on the effect of hand position on vision.

Over the past 10 years, perception scientists have uncovered a surprising connection between people's vision and their hands. There is now compelling evidence that how people perceive, attend to, think about, and remember visual information depends on how close they have their hands to that information. With their hands near, people perform figure-ground assignment more efficiently, parse temporally adjacent events more precisely, and hold more information in visual working memory. Near their hands, people also detect sudden visual onsets more quickly, but search through arrays of items more slowly, and take longer to switch between different ways of interpreting the same perceptual content (e.g., “seeing the forest” vs. “seeing the trees”). These are but some of the ways in which visual processing changes when people's hands are in proximity of viewed information—a host of effects that we refer to here, collectively, as hand-altered vision (HAV). The first decade of research into HAV has generated a substantial amount of new knowledge, which we recently reviewed in contemporaneous papers (Tseng et al., 2012; Brockmole et al., 2013). We subsequently established this Research Topic as a bridge to the next era of HAV research, through which we aimed to gather perspectives from across the research literatures on human action and peripersonal space representation. All told, the work here consists of 12 articles from 34 researchers who represent 23 institutions worldwide. Thanks to the efforts of our contributors, our scientific understanding of HAV has progressed along several major channels.

Interacting hands: the role of attention for the joint Simon effect.

Recent research in monkeys and humans has shown that the presence of the hands near an object enhances spatial processing for objects presented near the hand. This study aimed to test the effect of hand position on the joint Simon effect. In Experiment 1, two human co-actors shared a Simon task while placing their response hands either near the objects appearing on the monitor or away from the monitor. Experiment 2 varied each co-actor’s hand position independently. Experiment 3 tested whether enhanced spatial processing for objects presented near the hand is obtained when replacing one of the two co-actors by a non-human event-producing rubber hand. Experiment 1 provided evidence for a Simon effect. Hand position significantly modulated the size of the Simon effect in the joint Simon task showing an increased Simon effect when the hands of both actors were located near the objects on the monitor, than when they were located away from the monitor. Experiment 2 replicated this finding showing an increased Simon effect when the actor’s hand was located near the objects on the monitor, but only when the co-actor also produced action events in spatial reference. A similar hand position effect was observed in Experiment 3 when a non-human rubber hand replaced the human co-actor. These findings suggest that external action events that are produced in spatial reference bias the distribution of attention to the area near the hand. This strengthens the weight of the spatial response codes (referential coding) and hence increases the joint Simon effect.

Quantifying forearm muscle activity during wrist and finger movements by means of multi-channel electromyography.

The study of hand and finger movement is an important topic with applications in prosthetics, rehabilitation, and ergonomics. Surface electromyography (sEMG) is the gold standard for the analysis of muscle activation. Previous studies investigated the optimal electrode number and positioning on the forearm to obtain information representative of muscle activation and robust to movements. However, the sEMG spatial distribution on the forearm during hand and finger movements and its changes due to different hand positions has never been quantified. The aim of this work is to quantify 1) the spatial localization of surface EMG activity of distinct forearm muscles during dynamic free movements of wrist and single fingers and 2) the effect of hand position on sEMG activity distribution. The subjects performed cyclic dynamic tasks involving the wrist and the fingers. The wrist tasks and the hand opening/closing task were performed with the hand in prone and neutral positions. A sensorized glove was used for kinematics recording. sEMG signals were acquired from the forearm muscles using a grid of 112 electrodes integrated into a stretchable textile sleeve. The areas of sEMG activity have been identified by a segmentation technique after a data dimensionality reduction step based on Non Negative Matrix Factorization applied to the EMG envelopes. The results show that 1) it is possible to identify distinct areas of sEMG activity on the forearm for different fingers; 2) hand position influences sEMG activity level and spatial distribution. This work gives new quantitative information about sEMG activity distribution on the forearm in healthy subjects and provides a basis for future works on the identification of optimal electrode configuration for sEMG based control of prostheses, exoskeletons, or orthoses. An example of use of this information for the optimization of the detection system for the estimation of joint kinematics from sEMG is reported.

Musculoskeletal loading during the round-off in female gymnastics: the effect of hand position

Chronic elbow injuries from tumbling in female gymnastics present a serious problem for performers. This research examined how the biomechanical characteristics of impact loading and elbow kinematics and kinetics change as a function of technique selection. Seven international-level female gymnasts performed 10 trials of the round-off from a hurdle step to flic-flac with ‘parallel’ and ‘T-shape’ hand positions. Synchronized kinematic (3D-automated motion analysis system; 247 Hz) and kinetic (two force plates; 1,235 Hz) data were collected for each trial. Wilcoxon non-parametric test and effect-size statistics determined differences between the hand positions examined in this study. Significant differences (p < 0.05) and large effect sizes (ES>0.8) were observed for peak vertical ground reaction force (GRF), anterior–posterior GRF, resultant GRF, loading rates of these forces and elbow joint angles, and internal moments of force in sagittal, transverse, and frontal planes. In conclusion, the T-shape hand position reduces vertical, anterior–posterior, and resultant contact forces and has a decreased loading rate indicating a safer technique for the round-off. Significant differences observed in joint elbow moments highlighted that the T-shape position may prevent overloading of the joint complex and consequently reduce the potential for elbow injury.

Quantification of Prone Thoracic Manipulation Using Inertial Sensor–Derived Accelerations

ObjectiveThe aim of this study was to determine the linear acceleration, time-to-peak acceleration, and effect of hand position comparing 2 clinicians completing a thoracic manipulation. MethodsThirteen volunteers received a right- and left-“handed” prone thoracic manipulation while accelerations were recorded by an inertial sensor. Peak thrust acceleration and time-to-peak thrust were measured. ResultsThere were differences in thrust acceleration between right- and left-handed techniques for one therapist. The mean peak thrust acceleration was different between therapists, with the more practiced therapist demonstrating greater peak thrust accelerations. Time-to-peak acceleration also revealed between therapist differences, with the more practiced therapist demonstrating shorter time-to-peak acceleration. Cavitation data suggested that manipulations with greater accelerations were more likely to result in cavitation. ConclusionThe results of this study suggest that with greater frequency of use, therapists are likely to achieve greater accelerations and shorter time-to-peak accelerations. Furthermore, this study showed that an inertial sensor can be used to quantify important variables during thoracic manipulation and are able to detect intertherapist differences in technique.

Effect of Hand Position on EMG Activity of the Posterior Shoulder Musculature During a Horizontal Abduction Exercise

The reverse fly machine is a popular exercise for strengthening the horizontal shoulder abductors including the posterior deltoid. There seems to be little consensus as to which hand position most effectively targets the posterior deltoid despite this option on most machines. This study investigated the impact of varying one's hand position, and consequently altering shoulder joint rotation, on muscle activity in various glenohumeral muscles during exercise on the reverse fly machine. Nineteen resistance-trained men (mean age = 23.2 ± 4.3 years; height = 176.9 ± 7.1 centimeters; body mass = 81.3 ± 10.5 kilograms; body mass index = 25.9 ± 2.6) were recruited from a university population to participate in the study. In a repeated measures design, subjects grasped the hand bars on the machine with either a pronated (PRO) or neutral (NEU) grip and performed dynamic horizontal abduction repetitions to muscular failure using a load equating to approximately 75% body weight. The order of performance of the hand positions was counterbalanced between participants so that approximately half of the subjects performed PRO first and the other half performed NEU first. Surface electromyography was used to record both mean and peak muscle activity of the posterior deltoid, middle deltoid, and infraspinatus. Results showed that mean electromyography activity for the posterior deltoid was significantly greater in NEU compared with PRO (p = 0.046; 95% CI = 0.1-7.4% maximal voluntary isometric contraction). Similarly, mean electromyography activity of the infraspinatus also was significantly greater in NEU compared with PRO (p = 0.002; 95% CI = 3.7-13.6% maximal voluntary isometric contraction). The results of this study show that performing exercise on the reverse fly machine with a neutral hand position significantly increases activity of the posterior deltoid and infraspinatus muscles compared with a PRO hand position.