A Musculoskeletal Model of the Hand and Wrist Capable of Simulating Functional Tasks

Objective: The purpose of this work was to develop an open-source musculoskeletal model of the hand and wrist and to evaluate its performance during simulations of functional tasks. Methods: The musculoskeletal model was developed by adapting and expanding upon existing musculoskeletal models. An optimal control theory framework that combines forward-dynamics simulations with a simulated-annealing optimization was used to simulate maximum grip and pinch force. Active and passive hand opening were simulated to evaluate coordinated kinematic hand movements. Results: The model's maximum grip force production matched experimental measures of grip force, force distribution amongst the digits, and displayed sensitivity to wrist flexion. Simulated lateral pinch strength fell within variability of in vivo palmar pinch strength data. Additionally, predicted activation for 7 of 8 muscles fell within variability of EMG data during palmar pinch. The active and passive hand opening simulations predicted reasonable activations and demonstrated passive motion mimicking tenodesis, respectively. Conclusion: This work advances simulation capabilities of hand and wrist models and provides a foundation for future work to build upon. Significance: This is the first open-source musculoskeletal model of the hand and wrist to be implemented during both functional kinetic and kinematic tasks. We provide a novel simulation framework to predict maximal grip and pinch force which can be used to evaluate how potential surgical and rehabilitation interventions influence these functional outcomes while requiring minimal experimental data.

Evaluation of the Quantitative Myasthenia Gravis Score and Grip Strength in Chinese Patients With Myasthenia Gravis: An Observational Study

Introduction: The quantitative myasthenia gravis score is a commonly used scale for evaluating muscle weakness associated with myasthenia gravis (MG). It has been reported that some items used in the scale have low discriminative properties. However, there has been no research investigating the applicability of the quantitative MG score (QMGS) in Chinese patients with MG. In addition, the scoring method and ranges of grip strength items in QMGS need to be further evaluated.Methods: This study included 106 Chinese patients with MG, enrolled between September 2020 and February 2021, who were evaluated using the QMGS. Each item in the QMGS was analyzed for distribution. Three methods of evaluating grip strength, grip strength decrement, maximum grip strength, and relative grip strength, were compared. The correlation between the QMG total score minus grip strength score, and three evaluating methods, was analyzed.Results: The grip strength, swallowing, speech, diplopia, ptosis, and facial muscles items showed a clustered distribution. Most patients (94%) presented their maximum grip strength in the first four grip strength measurements. The QMG total score minus the grip strength score had a weak correlation with grip strength decrement (R grip r = 0.276; L grip r = 0.353, both p < 0.05) and moderate correlations with maximum grip strength (R grip r = −0.508; L grip r = −0.507; both p < 0.001) and relative grip strength (R grip r = −0.494; L grip r = −0.497, both p < 0.001).Conclusions: This study suggested that partial items in the QMGS have low discriminative properties for Chinese populations and the maximum grip strength value is the better method to evaluate grip strength compared to the other two scoring methods. Based on the quartiles of maximum grip strength, we propose new scoring ranges for the grip strength items.

Are reaching and grasping effector-independent? Similarities and differences in reaching and grasping kinematics between the hand and foot

While reaching and grasping are highly prevalent manual actions, neuroimaging studies provide evidence that their neural representations may be shared between different body parts, i.e. effectors. If these actions are guided by effector-independent mechanisms, similar kinematics should be observed when the action is performed by the hand or by a cortically remote and less experienced effector, such as the foot. We tested this hypothesis with two characteristic components of action: the initial ballistic stage of reaching, and the preshaping of the digits during grasping based on object size. We examined if these kinematic features reflect effector-independent mechanisms by asking participants to reach toward and to grasp objects of different widths with their hand and foot. First, during both reaching and grasping, the velocity profile up to peak velocity matched between the hand and the foot, indicating a shared ballistic acceleration phase. Secondly, maximum grip aperture and time of maximum grip aperture of grasping increased with object size for both effectors, indicating encoding of object size during transport. Differences between the hand and foot were found in the deceleration phase and time of maximum grip aperture, likely due to biomechanical differences and the participants' inexperience with foot actions. These findings provide evidence for effector-independent visuomotor mechanisms of reaching and grasping that generalize across body parts.

Body muscle gain and markers of cardiovascular disease susceptibility in young adulthood: A cohort study

Background The potential benefits of gaining body muscle for cardiovascular disease (CVD) susceptibility, and how these compare with the potential harms of gaining body fat, are unknown. We compared associations of early life changes in body lean mass and handgrip strength versus body fat mass with atherogenic traits measured in young adulthood. Methods and findings Data were from 3,227 offspring of the Avon Longitudinal Study of Parents and Children (39% male; recruited in 1991–1992). Limb lean and total fat mass indices (kg/m2) were measured using dual-energy X-ray absorptiometry scans performed at age 10, 13, 18, and 25 y (across clinics occurring from 2001–2003 to 2015–2017). Handgrip strength was measured at 12 and 25 y, expressed as maximum grip (kg or lb/in2) and relative grip (maximum grip/weight in kilograms). Linear regression models were used to examine associations of change in standardised measures of these exposures across different stages of body development with 228 cardiometabolic traits measured at age 25 y including blood pressure, fasting insulin, and metabolomics-derived apolipoprotein B lipids. SD-unit gain in limb lean mass index from 10 to 25 y was positively associated with atherogenic traits including very-low-density lipoprotein (VLDL) triglycerides. This pattern was limited to lean gain in legs, whereas lean gain in arms was inversely associated with traits including VLDL triglycerides, insulin, and glycoprotein acetyls, and was also positively associated with creatinine (a muscle product and positive control). Furthermore, this pattern for arm lean mass index was specific to SD-unit gains occurring between 13 and 18 y, e.g., −0.13 SD (95% CI −0.22, −0.04) for VLDL triglycerides. Changes in maximum and relative grip from 12 to 25 y were both positively associated with creatinine, but only change in relative grip was also inversely associated with atherogenic traits, e.g., −0.12 SD (95% CI −0.18, −0.06) for VLDL triglycerides per SD-unit gain. Change in fat mass index from 10 to 25 y was more strongly associated with atherogenic traits including VLDL triglycerides, at 0.45 SD (95% CI 0.39, 0.52); these estimates were directionally consistent across sub-periods, with larger effect sizes with more recent gains. Associations of lean, grip, and fat measures with traits were more pronounced among males. Study limitations include potential residual confounding of observational estimates, including by ectopic fat within muscle, and the absence of grip measures in adolescence for estimates of grip change over sub-periods. Conclusions In this study, we found that muscle strengthening, as indicated by grip strength gain, was weakly associated with lower atherogenic trait levels in young adulthood, at a smaller magnitude than unfavourable associations of fat mass gain. Associations of muscle mass gain with such traits appear to be smaller and limited to gains occurring in adolescence. These results suggest that body muscle is less robustly associated with markers of CVD susceptibility than body fat and may therefore be a lower-priority intervention target.

Grip strength from midlife as an indicator of later-life brain health and cognition: evidence from a British birth cohort

Background Grip strength is an indicator of physical function with potential predictive value for health in ageing populations. We assessed whether trends in grip strength from midlife predicted later-life brain health and cognition. Methods 446 participants in an ongoing British birth cohort study, the National Survey of Health and Development (NSHD), had their maximum grip strength measured at ages 53, 60–64, and 69, and subsequently underwent neuroimaging as part of a neuroscience sub-study, referred to as “Insight 46”, at age 69–71. A group-based trajectory model identified latent groups of individuals in the whole NSHD cohort with below- or above-average grip strength over time, plus a reference group. Group assignment, plus standardised grip strength levels and change from midlife were each related to measures of whole-brain volume (WBV) and white matter hyperintensity volume (WMHV), plus several cognitive tests. Models were adjusted for sex, body size, head size (where appropriate), sociodemographics, and behavioural and vascular risk factors. Results Lower grip strength from midlife was associated with smaller WBV and lower matrix reasoning scores at age 69–71, with findings consistent between analysis of individual time points and analysis of trajectory groups. There was little evidence of an association between grip strength and other cognitive test scores. Although greater declines in grip strength showed a weak association with higher WMHV at age 69–71, trends in the opposite direction were seen at individual time points with higher grip strength at ages 60–64, and 69 associated with higher WMHV. Conclusions This study provides preliminary evidence that maximum grip strength may have value in predicting brain health. Future work should assess to what extent age-related declines in grip strength from midlife reflect concurrent changes in brain structure.

Modernising the Dynamometer for Grip Assessment: Comparison between GripAble and Jamar

Introduction: Maximal grip strength (MGS) is a reliable biomarker of overall health and physiological well-being. Therefore, an accurate and reliable measurement device is vital for ensuring the validity of the MGS assessment. This paper presents GripAble, a mobile handgrip device for the assessment of MGS. GripAble’s performance was evaluated using an inter-instrument reliability test against the widely used Jamar PLUS+ dynamometer. Methods: The MGS data from sixty-three participants (N = 63) measured using GripAble and Jamar PLUS+ were collected and compared. Intra-class correlation (ICC) was performed to evaluate the inter-device reliability between GripAble and Jamar PLUS+. The influence of gender and hand on MGS were also analysed. Results: GripAble demonstrates good-to-excellent inter-instrument reliability to the Jamar PLUS+ (ICC 3,1 =0.906). There were significant differences in the mean MGS between GripAble and Jamar PLUS+ (p <0.001 for both). GripAble’s measurement output is equivalent to 69% ([68-71]%) of Jamar PLUS+’s measurement output. The average difference in mean MGS between the two devices was 10.84 ± 4.18 kg ([4.77-18.54] kg), which increases with higher MGS. There were also significant differences in MGS between male and female and between right and left hands measured using GripAble and Jamar PLUS+ (p <0.001 for all comparisons). Conclusion: GripAble has good-to-excellent inter-device reliability with Jamar PLUS+, suggesting that it can be used clinically as a dynamometer whilst also providing additional functionalities, such as remote assessment, objective evaluation of compliance to standard protocol and assessing multiple facets of grip strength beyond the standard single maximum grip test. Normative MGS data using GripAble should be collected and integrated into the software for immediate comparison. Further studies, including test-retest and inter-rater reliability of using GripAble, are discussed. 1 www.gripable.co BMC Musculoskeletal Disorders-GripAble vs Jamar v1.0 15/07/2021

488 GRIP STRENGTH FROM MIDLIFE AS AN INDICATOR OF LATER-LIFE COGNITION AND BRAIN HEALTH: EVIDENCE FROM A BRITISH BIRTH COHORT

Introduction Grip strength is an objective measure of physical function with potential predictive value for health in ageing populations. We aimed to assess whether levels and changes in grip strength from midlife predicted later-life brain health and cognition. Methods 446 participants in an ongoing British birth cohort study, the MRC National Survey of Health and Development (NSHD), had their maximum grip strength measured at ages 53, 60–64, and 69, and underwent neuroimaging as part of its neuroscience sub-study, Insight 46, at 69–71. A group-based trajectory model identified latent groups of individuals in the whole NSHD cohort with below- and above-average grip strength over time, plus a reference group. Trajectory group membership, plus standardised grip strength levels and change from age 53, were each related to MRI-derived measures of whole-brain volume (WBV) and white-matter hyperintensity volume (WMHV), plus several cognitive tests. Models were adjusted for sex, body size, head size (where appropriate), sociodemographics, and behavioural and vascular risk factors. Results Consistently below-average grip strength from midlife was associated with lower WBV and non-verbal reasoning ability at age 69–71 (e.g. low group WBV vs. reference group β = −13.38 cm^3; 95% CI = (−24.12 cm^3, −2.64 cm^3); p = 0.015). There was some accompanying evidence that above-average maximum grip strength showed a positive association with WBV, which was more pronounced in female participants (high group female WBV vs. reference group β = 18.30 cm^3; 95% CI = (1.34 cm^3, 35.29 cm^3); p = 0.034). Steeper than average declines in grip strength between 53 and 69 were additionally weakly associated with an estimated 10% higher WMHV at age 69–71 (β = 1.10, 95% CI = (1.00, 1.22); p = 0.053). Conclusion This study provides preliminary evidence that tests of maximum grip strength may have value in predicting brain health. Future work should assess how these observed differences relate to later-life negative health outcomes, and whether changes in grip strength reflect concurrent changes in brain structure and connectivity.

Aging Increases Prosocial Motivation for Effort

Social cohesion relies on prosociality in increasingly aging populations. Helping other people requires effort, yet how willing people are to exert effort to benefit themselves and others, and whether such behaviors shift across the life span, is poorly understood. Using computational modeling, we tested the willingness of 95 younger adults (18–36 years old) and 92 older adults (55–84 years old) to put physical effort into self- and other-benefiting acts. Participants chose whether to work and exert force (30%–70% of maximum grip strength) for rewards (2–10 credits) accrued for themselves or, prosocially, for another. Younger adults were somewhat selfish, choosing to work more at higher effort levels for themselves, and exerted less force in prosocial work. Strikingly, compared with younger adults, older people were more willing to put in effort for others and exerted equal force for themselves and others. Increased prosociality in older people has important implications for human behavior and societal structure.

25 Sarcopenia, Long-Term Conditions, and Multimorbidity From Mid-Life to Later Life: Findings From 499,046 UK Biobank Participants

Introduction Sarcopenia, the loss of muscle strength and mass, predicts adverse outcomes and becomes common with age. There is recognition that sarcopenia may occur at younger ages in those with long-term conditions (LTCs) as well as those with multimorbidity (the presence of two or more LTCs), but their relationships have been little explored. Our aims were to describe the prevalence of sarcopenia in UK Biobank, a large sample of men and women aged 40–70 years, and to explore relationships with different categories of LTCs and multimorbidity. Methods We used data from 499,046 participants in the baseline of UK Biobank. Our main outcome was probable sarcopenia based on maximum grip strength below sex-specific cut-points. Participants’ LTCs were recorded during an interview and categorised against a hierarchy. We used logistic regression to examine the independent associations between each category of LTCs and probable sarcopenia, including adjustment for age, sex, and body mass index. We also examined the association with multimorbidity. Results Probable sarcopenia had an overall prevalence of 5.3% and increased with age. The categories with the strongest associations with probable sarcopenia were musculoskeletal/trauma (OR 2.17 [95% CI: 2.11, 2.23]), endocrine/diabetes (OR 1.49 [95% CI: 1.45, 1.55]), and neurological/psychiatric (OR 1.39 [95% CI: 1.34, 1.43]) LTCs. Almost half of the sample (44.5%) had multimorbidity and they were at nearly twice the odds of probable sarcopenia (OR 1.96 [95% CI: 1.91, 2.02]) compared to those without. Conclusions We have shown an overall prevalence of 5.3% of probable sarcopenia at ages 40–70 in UK Biobank. The risk of probable sarcopenia was higher in those with some categories of LTCs, suggesting that these groups may stand to benefit from assessment of sarcopenia, during mid-life as well as old age.