Lower Grip Force Research Articles

Efficacy of interactive manual dexterity training after stroke: a pilot single-blinded randomized controlled trial

ObjectiveTo compare the efficacy of Dextrain Manipulandum™ training of dexterity components such as force control and independent finger movements, to dose-matched conventional therapy (CT) post-stroke.MethodsA prospective, single-blind, pilot randomized clinical trial was conducted. Chronic-phase post-stroke patients with mild-to-moderate dexterity impairment (Box and Block Test (BBT) > 1) received 12 sessions of Dextrain or CT. Blinded measures were obtained before and after training and at 3-months follow-up. Primary outcome was BBT-change (after–before training). Secondary outcomes included changes in motor impairments, activity limitations and dexterity components. Corticospinal excitability and short intracortical inhibition (SICI) were measured using transcranial magnetic stimulation.ResultsBBT-change after training did not differ between the Dextrain (N = 21) vs CT group (N = 21) (median [IQR] = 5[2–7] vs 4[2–7], respectively; P = 0.36). Gains in BBT were maintained at the 3-month post-training follow-up, with a non-significant trend for enhanced BBT-change in the Dextrain group (median [IQR] = 3[− 1–7.0], P = 0.06). Several secondary outcomes showed significantly larger changes in the Dextrain group: finger tracking precision (mean ± SD = 0.3 ± 0.3N vs − 0.1 ± 0.33N; P < 0.0018), independent finger movements (34.7 ± 25.1 ms vs 7.7 ± 18.5 ms, P = 0.02) and maximal finger tapping speed (8.4 ± 7.1 vs 4.5 ± 4.9, P = 0.045). At follow-up, Dextrain group showed significantly greater improvement in Motor Activity Log (median/IQR = 0.7/0.2–0.8 vs 0.2/0.1–0.6, P = 0.05). Across both groups SICI increased in patients with greater BBT-change (Rho = 0.80, P = 0.006). Comparing Dextrain subgroups with maximal grip force higher/lower than median (61.2%), BBT-change was significantly larger in patients with low vs high grip force (7.5 ± 5.6 vs 2.9 ± 2.8; respectively, P = 0.015).ConclusionsAlthough immediate improvements in gross dexterity post-stroke did not significantly differ between Dextrain training and CT, our findings suggest that Dextrain enhances recovery of several dexterity components and reported hand-use, particularly when motor impairment is moderate (low initial grip force). Findings need to be confirmed in a larger trial.Trial registration ClinicalTrials.gov NCT03934073 (retrospectively registered)

Measuring Hand Sensory Function and Force Control in Older Adults: Are Current Hand Assessment Tools Enough?

The ability to grasp and manipulate objects is essential for performing activities of daily living. However, there is limited information regarding age-related behavioral differences in hand sensorimotor function due, in part, to the lack of assessment tools capable of measuring subtle but important differences in hand function. The purpose of this study was to demonstrate performance differences in submaximal force control and tactile pattern recognition in healthy older adults using 2 custom-designed sensorimotor assessment tools. Sensorimotor function was assessed in 13 healthy older adults (mean age 72.2 ± 5.5 years, range: 65-84 years) and 13 young adults (mean age 20 ± 1.4 years, range: 19-23 years). Clinical assessments included the Montreal Cognitive Assessment (MoCA), monofilament testing, maximum voluntary contraction (MVC), and Grooved Pegboard Test. Sensorimotor assessments included submaximal (5, 20% MVC) grip force step-tracking and tactile pattern recognition tasks. Clinical assessments revealed no or minimal group differences in MVC, monofilament thresholds, and MoCA. However, sensorimotor assessments showed that older adults took longer to discriminate tactile patterns and had poorer accuracy than young adults. Older adults also produced submaximal forces less smoothly than young adults at the 20% force level while greater variability in force maintenance was seen at 5% but not 20% MVC. These results demonstrate the ability to integrate higher-order tactile information and control low grip forces is impaired in older adults despite no differences in grip strength or cognition. These findings underscore the need for more sensitive evaluation methods that focus on sensorimotor ability reflective of daily activities.

Pattern recognition of EMG signals for low level grip force classification

Grasping of the objects is the most frequent activity performed by the human upper limb. The amputations of the upper limb results in the need for prosthetic devices. The myoelectric prosthetic devices use muscle signals and apply control techniques for identification of different levels of hand gesture and force levels. In this study; a different level force contraction experiment was performed in which Electromyography (EMGs) signals and fingertip force signals were acquired. Using this experimental data; a two-step feature selection process is applied for the designing of a pattern recognition algorithm for the classification of different force levels. The two step feature selection process consist of generalized feature ranking using ReliefF, followed by personalized feature selection using Neighborhood Component Analysis (NCA) from the shortlisted features by earlier technique. The classification algorithms applied in this study were Support Vector Machines (SVM) and Random Forest (RF). Besides feature selection; optimization of the number of muscles during classification of force levels was also performed using designed algorithm. Based on this algorithm; the maximum classification accuracy using SVM classifier and two muscle set was achieved as high as 99%. The optimal feature set consisted features such as Auto Regressive coefficients, Willison Amplitude and Slope Sign Change. The mean classification accuracy for different subjects, achieved using SVM and RF was 94.5% and 91.7% respectively.

Reported disability in relation to observed activity limitation, grip strength and physical function in women and men with rheumatoid arthritis

BackgroundThe self-reported Health Assessment Questionnaire (HAQ) is specifically designed to assess disability in arthritic patients. In many studies women report higher functional disability than men. The reasons for this difference are suggested to be multifactorial. We therefore evaluated functional disability assessed by HAQ in women and men with rheumatoid arthritis (RA) in relation to observed disability, grip force and physical function.MethodsPatients with RA, 51 women and 49 men, completed the HAQ on three occasions, some weeks apart. Between HAQ1 and HAQ2, all patients performed 17 of the 20 activities (7 domains) included in the HAQ under observation in a specially designed environment, the observed HAQ. During the same day, grip force, measured by GRIPPIT and physical function assessed by the SOFI (Signals of Functional Impairment) index were evaluated. Differences between groups were studied by the chi-square test, Mann-Whitney U test and Wilcoxon Sign Rank test. Correlations were analysed by Spearman rank correlation. Comparisons between repeated measures were performed using Friedman’s test.ResultsMedian (IQR) total HAQ1 score was 0.50 (0.88) for women and 0.25 (0.84) for men, p = 0.038, and the observed HAQ score (7 domains) 0.57 (0.9) for women and 0.43 (0.96) for men, p = 0.292. The correlations between reported HAQ1 score (7 domains) and observed HAQ score were strong, r = 0.860, p < 0.001 in women, and r = 0.820, p < 0.001 in men. For some activities the patients, both women and men, reported lower difficulty than that observed. Women had lower grip force than men, median (IQR), right and left 126 (84) Newton, versus 238 (146), p < 0.001, and there was a negative correlation between grip force and most of the separate activities in HAQ in both genders. SOFI index was similar in women and men, median (IQR) 0 (3.0) versus 0 (2.0), p = 0.277, with a moderate correlation to HAQ.ConclusionsThe results indicate that in well-treated patients with RA the correlations between reported and observed HAQ scores were strong, similarly in women and men. We found no evidence that the patient’s opinion was dependent on unawareness of her/his own ability.

Dynamic Manugraphy as a Promising Tool to Assess the Outcome of Limited Aponeurectomy in Patients With Dupuytren's Contracture.

Background: Dupuytren's contractures interfere with physiological gripping. While limited aponeurectomy is an accepted treatment modality to restore finger mobility, methods to objectify functional outcome beyond determination of the range of motion are scarce.Methods: Patients with Dupuytren's contracture being scheduled for unilateral limited aponeurectomy were invited to participate. Clinical data were gathered prospectively by chart review and interview. The DASH-score and flexion contracture for fingers were registered prior to surgery, 3 and 6 months afterwards. At the same time, dynamic manugraphy for simultaneous recording of the grip pattern and forces generated by the affected hand and anatomic areas (i.e., thumb, index finger, middle finger, ring finger, little finger and palm) were performed. All findings obtained during the follow-up period were compared to the situation at baseline. Comparison between paired samples was done using Wilcoxon rank test. All p-values are two-sided and p < 0.05 was considered to be significant.Results: Out of 23 consecutively enrolled patients, 19 (15 men, 4 women) completed follow-up examinations. Manugraphy confirmed the impairment of physiological gripping with concomitant pathological load distribution at base line. Limited aponeurectomy significantly reduced flexion contractures. However, the DASH-score remained at an excellent level in one patient, indicated improvement in 11 and worsening in seven patients. Six patients had lower grip force at t6 compared to the preoperative condition, although the preoperative flexion contracture (≥110°) was considerably improved in all of them. In four of those, the DASH-score improved while it turned worse in two of them. The force of surgically treated fingers remained unchanged in three patients while it was improved and worsened in half of the remaining patients, respectively. Manugraphy revealed physiological gripping by enlargement of contact area and higher force transmission by the fingertips in 10 of 12 patients with constant or even improved DASH-score and in three of seven patients with a worsened DASH-score.Conclusions: Assessing the reduction of flexion contracture and grip force alone is not sufficient to comprehensively reflect the functional outcome of aponeurectomy for Dupuytren's disease. Visualizing physiological grip pattern provides an additional tool to objectify the success of surgical treatment.

Measuring Hand Function in Older Adults: The Need for Better Assessment Tools

Aging is associated with a decline in hand muscle strength, dexterity, and tactile perception, leading to difficulties in activities of daily living and reduced independence (Millan-Calenti et al., 2010). However, current assessments do not adequately capture sensorimotor skills that underlie everyday activities such as dressing and food preparation. This study examined the ability of two novel assessment devices to detect age-related changes in hand force control and tactile pattern discrimination. Sensorimotor function was assessed in 13 healthy older adults (mean age 72.2 +/- 5.5y) and 13 young adults (mean age 20 +/- 1.4y). Maximum grip force (MVC), tactile sensation, and hand dexterity were measured using standard clinical techniques. Novel assessments consisted of submaximal (5-20% MVC) grip force tracking and computer-controlled tactile pattern recognition. Monofilament testing of tactile sensation was normal in the older group. In contrast, both the accuracy and speed associated with identifying tactile patterns was significantly worse in older (p<0.001) compared to young adults for both hands. While maximum grip force was similar in both groups, the ability to smoothly produce (p<0.05) and maintain (p<0.02) low grip force levels was compromised in older adults. Manual dexterity (Grooved Pegboard test) was significantly reduced in the older group (p<0.001) regardless of hand. These results indicate that the ability to extract meaningful information from tactile feedback and control low levels of force - aspects of fine hand control associated with activities of daily living – are impaired in older adults and underscore the need for more sensitive measures of hand function.

Examination Of The Time Course Effect Of Creatine Supplementation On Acute Doxorubicin-induced Skeletal Muscle Dysfunction

Chemotherapy drugs such as doxorubicin (Dox) may cause skeletal muscle dysfunction, and supplementing the diet with creatine (Cr) could counteract skeletal muscle dysfunction. Very little has been done, however, exploring the time course effects of Cr on Dox-induced skeletal muscle dysfunction. PURPOSE: To examine the effects of Cr on skeletal muscle function 1, 3, and 5 days following Dox treatment. METHODS: Male rats were randomly assigned to the control group (Con), the doxorubicin group (Dox), the standard Cr diet (2% Cr for 4 weeks) and doxorubicin group (Cr1+Dox), or the Cr loading diet (4% Cr for 1 week followed by 2% Cr 3 weeks) and doxorubicin group (Cr2+Dox). After 4 weeks of feeding, Dox groups received 15 mg/kg Dox and Con received saline. At 1, 3, and 5 days post-injection, grip force and extensor digitorum longus (EDL) forces during a 100 s ex vivo fatigue protocol were measured. RESULTS: No between group differences in grip force were observed 1 day post injection, but at 3 days, a between group difference in grip force was observed (p=0.03) with Dox and Cr1+Dox having lower grip forces than Con (-9.8% and -10.5%, respectively, p<0.05), but this difference was not observed in Cr2+Dox. A between group difference in grip force was also observed at the 5 day time point (p<0.0001) with Dox, Cr1+Dox, and Cr2+Dox having lower grip force than Con (-19.9%, -37.2%, and -19.5%, respectively, p<0.05). With ex vivo EDL function, no between group differences were observed 1 day post injection, but at day 3, EDLs from Dox generated less force than Con at the 10 s through 40 s and the 70 s through 100 s time points (p<0.05), but these differences were not observed in Cr1+Dox and Cr2+Dox. At day 5, Cr1+Dox EDLs generated significantly less force than Con at every time point during the 100 s fatigue protocol (p<0.05), and Cr2+Dox EDLs generated significantly less force than Con at the 10 s through 40 s time points (p<0.05). CONCLUSIONS: Cr supplementation provided protection against Dox-induced muscle dysfunction 3 days post injection, and this protection was more evident with the Cr loading diet (Cr2). This myoprotection, however, was not observed 5 days post Dox injection suggesting that Cr’s benefit may be limited to protecting against the early phases of acute Dox myotoxicity.

The Relation Between Disease Activity, Patient-Reported Outcomes, and Grip Force Over Time in Early Rheumatoid Arthritis.

ObjectiveThe objective of this study is to identify early predictors of future reduced grip force in patients with rheumatoid arthritis (RA) and to identify early predictors of grip force over time.MethodsIn a structured follow‐up of an inception cohort of patients with early RA, average grip force values of the dominant hand were evaluated and compared with the expected based on age‐ and sex‐specific reference values. Potential predictors of reduced grip force (less than 50% of expected) at 5 years were examined using logistic regression. Differences in percentage of expected grip force values over the study period and differences in change over time, by baseline disease parameters, were estimated using mixed linear‐effects models.ResultsAmong 200 patients with early RA, 44% had reduced grip force 5 years after diagnosis. Baseline characteristics that predicted reduced grip force at 5 years included high scores for the Health Assessment Questionnaire Disability Index (odds ratio 1.54 per SD; 95% confidence interval 1.13‐2.11), high scores for pain and patient global assessment, and low grip force. C‐reactive protein levels, the erythrocyte sedimentation rate, the 28‐joint Disease Activity Score (DAS28), rheumatoid factor, anti–cyclic citrullinated peptide antibodies, joint counts, and synovitis of individual joints in the dominant upper extremity did not predict reduced grip force. Patients with baseline synovitis of the wrist or metacarpophalangeal joints or patients with a high DAS28 had lower estimated grip force at inclusion but also greater improvement of grip force over time.ConclusionPatient‐reported outcomes predicted reduced grip strength 5 years after diagnosis. This underlines the prognostic importance of disability in early RA. Joint counts and synovitis in individual joints may change rapidly in early RA and appear to be less predictive of long‐term hand function.

Validation of the Geriatric Check in acohort of hospitalized neurological patients

The Geriatrie-Check was developed as ascreening tool for the identification of older patients with geriatric treatment requirements in hospitals. It was recommended by the Baden-Wuerttemberg Hospitals Association for routine use in hospitals in 2014 although no published validation studies are available. The test takes 3-5 min. Validation of the Geriatrie-Check in aprospective cohort of hospitalized neurological patients with and without geriatric characteristics. In this prospective cross-sectional observational study at the University Hospital Tübingen, Germany the Geriatrie-Check was compared with acomprehensive geriatric assessment in 107 neurological inpatients aged 70years and older (41% women, mean age 76.7years). The Geriatrie-Check classified 61patients (57%) as geriatric patients. These patients with apositive result in the Geriatrie-Check had ahigher percentage of frailty (according to Fried etal.), higher values in the Gérontopôle frailty screening tool, higher values in the geriatric screening according to Lachs et el., slower gait speed, lower grip force, needed longer for the timed up-and-go test, had agreater fear of falling in the Falls Efficacy Scale - International, lower scores in the Mini Mental State Examination, needed more time to perform the Trail Making TestA and B, had higher values in the Beck's Depressions InventarII and lower values in the visual analogue scale of the EQ-5D. Ahigher percentage of patients took more than five different drugs. The Geriatrie-Check has been shown to be auseful and valid tool for the identification of geriatric inpatients in neurological wards due to the good agreement with the results of the geriatric assessment.

Upper limb function in children with attention-deficit/hyperactivity disorder (ADHD)

Upper limb function was investigated in children with ADHD using objective methods. We hypothesised that children with ADHD exhibit abnormal dexterity, force application during manipulation of a novel object, and movement rhythmicity. Two groups of age- and gender-matched children were investigated: 35 typically developing children (controls, 10.5±0.4years, 32M-3F) and 29 children (11.5±0.5years, 27M-2F) with formally diagnosed ADHD according to DSM-IV-TR criteria. Participants underwent a series of screening tests and tests of upper limb function while "off" medication. Objective quantification of upper limb function involved measurement of force during a grip and lift task, maximal finger tapping task, and maximal pinch grip. Acceleration at the index finger was also measured during rest, flexion and extension, and a postural task to quantify tremor. The Movement Assessment Battery for Children-2 (MABC-2) was also administered. Significant between-group differences were observed in movement rhythmicity, manipulation of a novel object, and performance of the MABC-2 dexterity and aiming and catching components. Children with ADHD lifted a novel object using a lower grip force (P=0.036), and held the object with a more variable grip force (P=0.003), than controls. Rhythmicity of finger tapping (P=0.008) and performance on the dexterity (P=0.007) and aiming and catching (P=0.042) components of the MABC-2 were also significantly poorer in the ADHD group than controls. Movement speed, maximum pinch grip strength, and tremor were unaffected. The results of the study show for the first time that ADHD is associated with deficits in multiple, but not all domains of upper limb function.

Force related hemodynamic responses during execution and imagery of a hand grip task: A functional near infrared spectroscopy study

We examined force related hemodynamic changes during the performance of a motor execution (ME) and motor imagery (MI) task by means of multichannel functional near infrared spectroscopy (fNIRS). The hemodynamic responses of fourteen healthy participants were measured while they performed a hand grip execution or imagery task with low and high grip forces. We found an overall higher increase of [oxy-Hb] concentration changes during ME for both grip forces but with a delayed peak maximum for the lower grip force. During the MI task with lower grip force, the [oxy-Hb] level increases are stronger compared to the MI with higher grip force. The facilitation in performing MI with higher grip strength might thus indicate less inhibition of the actual motor act which could also explain the later increase onset of [oxy-Hb] in the ME task with the lower grip force. Our results suggest that execution and imagery of a hand grip task with high and low grip forces, leads to different cortical activation patterns. Since impaired control of grip forces during object manipulation in particular is one aspect of fine motor control deficits after stroke, our study will contribute to future rehabilitation programs enhancing patient's grip force control.

Single-trial decoding of imagined grip force parameters involving the right or left hand based on movement-related cortical potentials

Time–domain feature representation for imagined grip force movement-related cortical potentials (MRCP) of the right or left hand and the decoding of imagined grip force parameters based on electroencephalogram (EEG) activity recorded during a single trial were here investigated. EEG signals were acquired from eleven healthy subjects during four different imagined tasks performed with the right or left hand. Subjects were instructed to execute imagined grip movement at two different levels of force. Each task was executed 60 times in random order. The imagined grip force MRCP of the right or left hand was analyzed by superposition and averaging technology, a single-trial extraction method, analysis of variance (ANOVA), and multiple comparisons. Significantly different features were observed among different imagined grip force tasks. These differences were used to decode imagined grip force parameters using Fisher linear discrimination analysis based on kernel function (k-FLDA) and support vector machine (SVM). Under the proposed experimental paradigm, the study showed that MRCP may characterize the dynamic processing that takes place in the brain during the planning, execution, and precision of a given imagined grip force task. This means that features related to MRCP can be used to decode imagined grip force parameters based on EEG. ANOVA and multiple comparisons of time–domain features for MRCP showed that movement-monitoring potentials (MMP) and specific interval (0–150 ms) average potentials to be significantly different among 4 different imagined grip force tasks. The minimum peak negativity differed significantly between high and low amplitude grip force. Identification of the 4 different imagined grip force tasks based on MMP was performed using k-FLDA and SVM, and the average misclassification rates of 27 % ± 5 % and 24 % ± 4 % across 11 subjects were achieved respectively. The minimum misclassification rate was 15 %, and the average minimum misclassification rate across 11 subjects was 24 % ± 4.5 %. This investigation indicates that imagined grip force MRCP may encode imagined grip force parameters. Single-trial decoding of imagined grip force parameters based on MRCP may be feasible. The study may provide some additional and fine control instructions for brain–computer interfaces.

SAT0580-HPR Women and Men with Polymyositis and Dermatomyositis have Reduced Grip Force and Health Related Quality of Life at Time of Diagnosis: a Registry Study

BackgroundPolymyositis (PM) and dermatomyositis (DM) have proximal muscle weakness. Reduced grip force has previously been shown in a cross sectional study.ObjectivesTo (I) compare women and men with PM/DM to reference...

SAT0576-HPR Hand Pains and General Pain in Women and Men in Early RA, a One Year Follow Up after Diagnosis in the Tira-2 Cohort

BackgroundPain in Rheumatoid arthritis (RA) is more prevalent in women than men. Hand involvement in RA is associated with hand pain, low grip force and reduced grip ability. Hand pain...

Functional Corticospinal Projections from Human Supplementary Motor Area Revealed by Corticomuscular Coherence during Precise Grip Force Control

The purpose of the present study was to investigate whether corticospinal projections from human supplementary motor area (SMA) are functional during precise force control with the precision grip (thumb-index opposition). Since beta band corticomuscular coherence (CMC) is well-accepted to reflect efferent corticospinal transmission, we analyzed the beta band CMC obtained with simultaneous recording of electroencephalographic (EEG) and electromyographic (EMG) signals. Subjects performed a bimanual precise visuomotor force tracking task by applying isometric low grip forces with their right hand precision grip on a custom device with strain gauges. Concurrently, they held the device with their left hand precision grip, producing similar grip forces but without any precision constraints, to relieve the right hand. Some subjects also participated in a unimanual control condition in which they performed the task with only the right hand precision grip while the device was held by a mechanical grip. We analyzed whole scalp topographies of beta band CMC between 64 EEG channels and 4 EMG intrinsic hand muscles, 2 for each hand. To compare the different topographies, we performed non-parametric statistical tests based on spatio-spectral clustering. For the right hand, we obtained significant beta band CMC over the contralateral M1 region as well as over the SMA region during static force contraction periods. For the left hand, however, beta band CMC was only found over the contralateral M1. By comparing unimanual and bimanual conditions for right hand muscles, no significant difference was found on beta band CMC over M1 and SMA. We conclude that the beta band CMC found over SMA for right hand muscles results from the precision constraints and not from the bimanual aspect of the task. The result of the present study strongly suggests that the corticospinal projections from human SMA become functional when high precision force control is required.

Intra-session and inter-day reliability of forearm surface EMG during varying hand grip forces

Surface electromyography (EMG) is widely used to evaluate forearm muscle function and predict hand grip forces; however, there is a lack of literature on its intra-session and inter-day reliability. The aim of this study was to determine reliability of surface EMG of finger and wrist flexor muscles across varying grip forces. Surface EMG was measured from six forearm flexor muscles of 23 healthy adults. Eleven of these subjects undertook inter-day test–retest. Six repetitions of five randomized isometric grip forces between 0% and 80% of maximum force (MVC) were recorded and normalized to MVC. Intra- and inter-day reliability were calculated through the intraclass correlation coefficient (ICC) and standard error of measurement (SEM).Normalized EMG produced excellent intra-session ICC of 0.90 when repeated measurements were averaged. Intra-session SEM was low at low grip forces, however, corresponding normalized SEM was high (23–45%) due to the small magnitude of EMG signals. This may limit the ability to evaluate finer forearm muscle function and hand grip forces in daily tasks. Combining EMG of functionally related muscles improved intra-session SEM, improving within-subject reliability without taking multiple measurements. Removing and replacing electrodes inter-day produced poor ICC (ICC<0.50) but did not substantially affect SEM.

Disease activity and disability in women and men with early rheumatoid arthritis (RA): An 8‐year followup of a Swedish early RA project

To compare women and men regarding the course of disease activity and disability over 8 years from diagnosis of recent-onset rheumatoid arthritis (RA). A total of 149 patients were followed in the Swedish TIRA study (Early Intervention in RA) for 8 years from RA diagnosis (1996-1998) regarding 28-joint count Disease Activity Score (DAS28), pain (visual analog scale), grip force, Grip Ability Test (GAT), Signals of Functional Impairment (SOFI; hand, upper/lower extremity), walking speed, activity limitation (Health Assessment Questionnaire [HAQ]), and prescribed disease-modifying antirheumatic drugs (DMARDs). Disease activity pattern over time was similar in women and men, showing improvement during the first year and a stable situation during 6 years thereafter. However, at the 7- and 8-year followup times, deterioration was seen with a less favorable course in women. HAQ score did not differ between sexes at diagnosis, but at all followup times women had significantly higher scores than men. Women also had lower grip force and lower walking speed, but higher upper extremity mobility. DMARD prescription was similar for both sexes. Over 8 years, disease duration, sex, biologic agents, grip force, SOFI hand, and pain intensity together explained 43% of the variation in DAS28, whereas grip force, SOFI lower extremity, GAT, and pain intensity could together explain 55% of variations in HAQ score. Disease activity was fairly well managed, but disability gradually worsened. Despite similar medication, women had more disability than men. The discrepancy between disease activity and disability indicates unmet needs for multiprofessional interventions to prevent progressing disability, and patients at risk for disability need to be identified early in the process.

HAND GRIP FORCE AND FOREARM SURFACE EMG, THE RELATIONSHIP AND RELIABILITY

Surface electromyography (EMG) is widely used to evaluate forearm muscle function and predict hand grip forces; however, there is a lack of literature on its intra-session and inter-day reliability. The aim of this study was to determine reliability of surface EMG of finger and wrist flexor muscles across varying grip forces. Surface EMG was measured from six forearm flexor muscles of 23 healthy adults. Eleven of these subjects undertook inter-day test–retest. Six repetitions of five randomized isometric grip forces between 0% and 80% of maximum force (MVC) were recorded and normalized to MVC. Intra- and inter-day reliability were calculated through the intraclass correlation coefficient (ICC) and standard error of measurement (SEM).Normalized EMG produced excellent intra-session ICC of 0.90 when repeated measurements were averaged. Intra-session SEM was low at low grip forces, however, corresponding normalized SEM was high (23–45%) due to the small magnitude of EMG signals. This may limit the ability to evaluate finer forearm muscle function and hand grip forces in daily tasks. Combining EMG of functionally related muscles improved intra-session SEM, improving within-subject reliability without taking multiple measurements. Removing and replacing electrodes inter-day produced poor ICC (ICC < 0.50) but did not substantially affect SEM.

Differential representation of dynamic and static power grip force in the sensorimotor network

Previous studies investigating the blood oxygen level-dependent (BOLD) signal in the human sensorimotor cortex during static force (maintained for a few seconds) and dynamic force (repetitive force pulses) resulted in contradictory findings. Therefore, we conducted a whole-brain functional magnetic resonance imaging study during a visuomotor task requiring the production of either dynamic or static power grip force. Thereby we aimed at clarifying whether the BOLD signal behaves differently with dynamic and static force in the primary motor cortex, and whether it behaves in the same way in all areas and regions involved in force production. In the static condition, participants applied visually guided, isometric grip force on a dynamometer of 20% maximal voluntary contraction (MVC) and held this force for 21 s. In the dynamic condition, self-paced force pulses of 20% MVC were produced at a rate of 0.5 Hz. Static and dynamic force production activated an overlapping network of sensorimotor cortical and subcortical regions. However, the production of a significantly higher mean static force compared with the dynamic force resulted in a significantly smaller BOLD signal in the contralateral motor cortex, confirming observations of an earlier investigation. In addition, we found that the ipsilateral anterior cerebellum behaved similar to the motor cortex, whereas in all other activated regions the activation during static and dynamic force did not significantly differ. These findings demonstrate that various regions of the sensorimotor network participate differentially in the production and control of low static and dynamic grip force, and raise important questions concerning the interpretation of the BOLD signal with respect to mechanisms of neurovascular coupling.

Precision in isometric precision grip force is reduced in middle-aged adults

We investigated age related changes in the control of precision grip in 29 healthy adults spanning early adulthood to middle age (21-67 years). Subjects performed a visually guided, isometric precision grip ramp-and-hold force-tracking task. Target force levels were 3, 6, and 9 N. Precision and performance of force regulation was quantified. Larger errors were made during the ramp than during the hold phase. Age correlated positively with the amount of error at the lowest (3 N) force level in both phases. Force onsets were systematically earlier in middle-aged subjects and the average slope of the force during the ramp decreased with increasing age. The results show that precision during low grip force control decreases already during middle age and those subjects may modify their force generation strategies to compensate for early and subtle degenerative changes in the motor system before decline in grip strength is apparent.