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Background: Orthostatic hypotension (OH) is common in older adults with hypertension. Antihypertensive treatment (AHT) prevents cardio- and cerebrovascular events. However, physicians are concerned to cause OH, making them hesitant to initiate or augment AHT in older adults with hypertension., Methods: We systematically researched electronic databases for trials with older participants (≥65 years) with hypertension and OH assessment after initiating, discontinuing, or augmenting AHT. Study quality was assessed using the ROBINS-I tool. Meta-analyses on OH prevalence and postural blood pressure (BP) drop were performed., Results: Twenty-five studies (26,695 participants) met inclusion criteria, of which fifteen could be included in the meta-analyses. OH prevalence decreased after AHT initiation or augmentation (risk ratio 0.39 (95 % CI = 0.21-0.72; I 2  = 47 %; p < 0.01), n = 6 studies), but also after AHT discontinuation (risk ratio 0.39 (95 % CI = 0.28-0.55; I 2  = 0 %; p < 0.01), n = 2 studies). Postural BP drop did not change after initiation or augmentation of AHT (mean difference 1.07 (95 % CI = -0.49-2.64; I 2  = 92 %; p = 0.18), n = 11 studies). The main reason for ten studies not to be included in the meta-analyses was absence of baseline OH data. Most of these studies reported OH incidences between 0 and 2 %. Studies were heterogeneous in OH assessment methods (postural change, timing of BP measurements, and OH definition). Risk of bias was moderate to serious in twenty studies., Conclusion: Results suggest that AHT initiation or augmentation decreases OH prevalence, implying that the risk of inducing OH may be overestimated in current AHT decision-making in older adults. However, the overall low level of evidence and the finding that AHT discontinuation reduces OH prevalence limit firm conclusions at present and highlight an important research gap. Future AHT trials in older adults should measure OH in a standardized protocol, adhering to consensus guidelines to overcome these limitations., Competing Interests: Declaration of competing interest None., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Physical inactivity in hospitalized older adults is highly prevalent and associated with detrimental health outcomes. Understanding its determinants is important for prognosis and tailoring interventions in geriatric rehabilitation inpatients., Methods: Within the REStORing health of acutely unwell adulTs (RESORT) observational, longitudinal cohort, geriatric rehabilitation inpatients wore an inertial sensor (ActivPAL4) for one week to objectively assess instrumented sedentary behavior (i-SB) and physical activity (i-PA). Determinants were grouped in five geriatric domains: morbidity, cognition/psychology, physical performance, functional performance, and nutritional status. Their association with i-SB (mean sitting, lying, non-upright time) and i-PA (mean number of steps, sit-to-stand transitions and upright time) quintiles were examined using multivariate ordinal logistic regression analyses with Bonferroni correction (p < 0.006)., Results: A total of 145 inpatients were included (mean age 83.0, SD 7.7 years; 55.9% females). More comorbidities were associated with a lower daily number of steps (OR:0.91, 95%CI: 0.86-0.96) and lower upright time (OR:0.93, 95%CI: 0.88-0.98). Depressive symptoms (higher Hospital Anxiety and Depression Scale score) were associated with higher non-upright time (OR: 1.12, 95%CI: 1.03-1.21) and lower upright time (OR: 0.89, 95%CI: 0.83-0.96). Better physical performance (higher Functional Ambulation Classification, gait speed, and Short Physical Performance Battery score) was associated with lower i-SB measures (OR range: 0.07-0.78, p < 0.0005) and higher i-PA measures (OR range: 1.35-19.50, p < 0.0005). Higher functional performance (Katz index of Activities of Daily Living score) was associated with lower i-SB measures (OR range: 0.61-0.69, p ≤ 0.003) and higher i-PA measures (OR range: 1.60-3.64, p < 0.0005). Being malnourished was associated with lower i-PA measures (OR range: 0.29-0.32, p ≤ 0.004)., Conclusions: Worse morbidity, depressive symptoms, worse physical and functional performance, and worse nutritional status were associated with higher i-SB and lower i-PA. These determinants should be taken into account while designing and promoting multidisciplinary physical activity interventions., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Engaging in physical activity (PA) and avoiding sedentary behavior (SB) are important for healthy ageing with benefits including the mitigation of disability and mortality. Whether benefits extend to key determinants of disability and mortality, namely muscle strength and muscle power, is unclear., Aims: This systematic review aimed to describe the association of objective measures of PA and SB with measures of skeletal muscle strength and muscle power in community-dwelling older adults., Methods: Six databases were searched from their inception to June 21 st , 2020 for articles reporting associations between objectively measured PA and SB and upper body or lower body muscle strength or muscle power in community dwelling adults aged 60 years and older. An overview of associations was visualized by effect direction heat maps, standardized effect sizes were estimated with albatross plots and summarized in box plots. Articles reporting adjusted standardized regression coefficients (β) were included in meta-analyses., Results: A total of 112 articles were included representing 43,796 individuals (range: 21 to 3726 per article) with a mean or median age from 61.0 to 88.0 years (mean 56.4 % female). Higher PA measures and lower SB were associated with better upper body muscle strength (hand grip strength), upper body muscle power (arm curl), lower body muscle strength, and lower body muscle power (chair stand test). Median standardized effect sizes were consistently larger for measures of PA and SB with lower compared to upper body muscle strength and muscle power. The meta-analyses of adjusted β coefficients confirmed the associations between total PA (TPA), moderate-to-vigorous PA (MVPA) and light PA (LPA) with hand grip strength (β = 0.041, β = 0.057, and β = 0.070, respectively, all p ≤ 0.001), and TPA and MVPA with chair stand test (β = 0.199 and β = 0.211, respectively, all p ≤ 0.001)., Conclusions: Higher PA and lower SB are associated with greater skeletal muscle strength and muscle power, particularly with the chair stand test., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

To individualize nutritional interventions for the prevention and treatment of malnutrition and sarcopenia, it is required to understand the nutritional needs of older adults. This study explores the nutritional needs of geriatric outpatients. We hypothesized that inadequate energy and protein intake is common in geriatric outpatients. Data were retrieved from 2 cohort studies encompassing community-dwelling older adults referred to geriatric outpatient mobility clinics in Amsterdam, The Netherlands and Melbourne, Australia. Indirect calorimetry and a food diary, respectively, were used to assess resting metabolic rate (RMR) and energy and protein intake. Total energy expenditure (TEE) was calculated by the RMR multiplied by an activity factor of 1.4. An energy deficit was defined as a relative difference >10% between TEE and energy intake. A protein deficit was defined as protein intake <1.2 g/kg body weight per day. Bland-Altman analysis assessed the agreement between energy and protein requirements versus intake at an individual level. Seventy-four outpatients were included (25 males, median age 78.9 [IQR: 72.8-86.1] years). The mean difference between TEE and energy intake was 292 (SD 481) kcal/d. An energy deficit was present in 46 outpatients. The median protein intake was 1.00 (IQR: 0.87-1.19) g/kg body weight per day and a protein deficit was present in 57 outpatients. There was a low agreement between energy and protein requirements versus intake at an individual level. In conclusion, over half of the outpatients had energy and/or protein deficits. Integrating dietetic services at geriatric outpatient mobility clinics could potentially improve nutrition- and muscle-related outcomes in a multidisciplinary approach., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Sedentary behaviour (SB) and physical activity (PA) can be objectively assessed with inertial sensors to describe bodily movement. Higher SB and lower PA is associated with higher chronological age and negative health outcomes. This study aimed to quantify the association between instrumented measures of SB (i-SB) and PA (i-PA) and mortality in community-dwelling older adults, to subsequently compare the quantitative effect sizes and to determine the dose-response relationships., Methods: An electronic search in six databases from inception to 27th of June 2019 was conducted. All articles reporting on i-SB or i-PA and mortality in community-dwelling older adults aged 60 years or older were considered eligible. A meta-analysis was conducted for the association between i-SB and i-PA and mortality expressed in Hazard Ratios (HR) and 95% Confidence Intervals (95% CI). A meta-regression analysis was performed to determine the dose-response relationship between i-SB and steps per day and mortality., Results: Twelve prospective articles representing eleven cohorts, reporting data of 38,141 participants were included. In total 2502 (6.4%) participants died during follow-up (2.0 to 9.8 years). Comparing the most sedentary with the least sedentary groups of participants resulted in a pooled HR of 2.44 (95% CI 1.82-3.25). Comparing the least active with the most active groups of participants resulted in a pooled HR of 1.93 (95% CI 1.39-2.69); 2.66 (95% CI 2.11-3.35); 3.43 (95% CI 2.61-4.52), and 3.09 (95% CI 2.33-4.11) for light, moderate-to-vigorous-, total PA and steps per day, respectively. Meta-regression analyses showed clear dose-response relationships between i-SB and steps per day and mortality risk., Conclusion: Both i-SB and i-PA are significantly associated with mortality in community-dwelling older adults, showing the largest effect size for total physical activity. Dose-response relationships could be observed for i-SB and steps per day., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Objectives: Changes of vasoconstriction may be measured non-invasively using pulse transit time. This study assessed the sensitivity, test-retest reliability and validity of pulse transit time during vasoconstriction provocation and active standing, and the predictive value of pulse transit time for blood pressure drop., Methods: Fifty-five younger (age < 65 years) and 31 older adults (age > 70 years) underwent electrocardiography, wrist and finger photoplethysmography and continuous blood pressure and total peripheral resistance measurements during vasoconstriction provocation using a cold pressor test (21 younger adults), or active stand tests (all other participants). Pulse transit time was defined as the time lag between the electrocardiography R-peak and the peak in the photoplethysmography first derivative; sensitivity as a significant decrease relative to baseline; test-retest reliability as the intra class correlation between different repeats of the same test; validity as the association between peripheral resistance and pulse transit time; predictive value as the association between supine resting pulse transit time and mean arterial pressure drop during active standing., Results: Finger pulse transit time was sensitive and reliable (ICC 0.2-0.8) during vasoconstriction provocation, but wrist pulse transit time was poorly reliable (ICC 0-0.5); only finger pulse transit time was sensitive to and reliable (ICC 0.4-0.8) during active standing in both younger and older adults. Finger pulse transit time was not associated with total peripheral resistance. Supine resting pulse transit time had predictive value for blood pressure drop during active standing in older adults (β -0.16; p 0.025)., Conclusions: Pulse transit time was sensitive to and reliable during vasoconstriction provocation and active standing, but did not significantly differ between younger and older adults. Pulse transit time could not be demonstrated to particularly reflect vasoconstriction, but it had predictive value for blood pressure drop during active standing., Competing Interests: Declaration of competing interest None., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Orthostatic hypotension (OH) may negatively affect physical functioning and aggravate morbidities, but existing evidence is contradictory., Methods: MEDLINE (from 1946), PubMed (from 1966) and EMBASE databases (from 1947) were systematically searched for studies on the association of OH and physical functioning in older adults, categorized as: balance, gait characteristics, walking speed, Timed Up and Go time, handgrip strength (HGS), physical frailty, exercise tolerance, physical activity, activities of daily living (ADL), and performance on the Hoehn and Yahr scale (HY) and Unified Parkinson's Disease Rating Scale (UPDRS). Study quality was assessed using the Newcastle Ottawa Scale., Results: Forty-two studies were included in the systematic review (29,421 individuals) and 29 studies in the meta-analyses (23,879 individuals). Sixteen out of 42 studies reported a significant association of OH with worse physical functioning. Meta-analysis showed a significant association of OH with impaired balance, ADL performance and HY/UPDRS III performance, but not with gait characteristics, mobility, walking speed, TUG, HGS, physical frailty, exercise tolerance, physical activity and UPDRS II performance., Conclusions: OH was associated with impaired balance, ADL performance and HY/UPDRS III performance, but not with other physical functioning categories. The results suggest that OH interventions could potentially improve some aspects of physical functioning., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The dynamic behavior of the wrist joint is governed by nonlinear properties, yet applied mathematical models, used to describe the measured input-output (perturbation-response) relationship, are commonly linear. Consequently, the linearly estimated model parameters will depend on properties of the applied perturbation properties (such perturbation amplitude and velocity). We aimed to systematically address the effects of perturbation velocity on linearly estimated neuromechanical parameters. Using a single axis manipulator ramp and hold perturbations were applied to the wrist joint. Effects of perturbation velocity (0.5, 1 and 3 rad/s) were investigated at multiple background torque levels (0, 0.5 and 1 N·m). With increasing perturbation velocity, estimated joint stiffness remained constant, while damping and reflex gain decreased. This variation in model parameters is dependent on background torque levels, i.e. muscle contraction. These observations support the future development of nonlinear models that are capable of describing wrist joint behavior over a larger range of loading conditions, exceeding the restricted range of operation that is required for linearization., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Hospitalization may induce a decrease of muscle strength and muscle mass in older patients due to physical inactivity, malnutrition and diseases, negatively affecting health outcome. We aimed to examine the literature on change in muscle strength and muscle mass in older patients during hospitalization. A literature search was performed in major electronic databases from inception to March 2016. Studies including hospitalized patients with a mean age≥65years, describing change of hand grip strength and/or muscle mass were found eligible. Extracted data were divided in hand grip strength or muscle mass and stratified by elective or acute admission. Meta-analysis was conducted using Comprehensive Meta-analysis. Twenty-five studies were included, describing a total of 1789 patients with a mean age range of 65 to 85.8years and an overall median length of stay of 14.7days. Pooled hand grip strength and muscle mass were found to significantly decrease in electively admitted older patients during hospitalization (standardized mean difference (95% confidence interval): -0.42 (-0.66, -0.17) and -0.44 (-0.61, -0.27)), but not in acutely admitted older patients (standardized mean difference (95% confidence interval): 0.18 (-0.02, 0.37) and -0.25 (-0.58, 0.09)). In conclusion, decrease in muscle strength and muscle mass in older patients is dependent on the type of admission., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: About half of all chronic stroke patients experience loss of arm function coinciding with increased stiffness, reduced range of motion and a flexed wrist due to a change in neural and/or structural tissue properties. Quantitative assessment of these changes is of clinical importance, yet not trivial. The goal of this study was to quantify the neural and structural properties contributing to wrist joint stiffness and to compare these properties between healthy subjects and stroke patients., Methods: Stroke patients (n=32) and healthy volunteers (n=14) were measured using ramp-and-hold rotations applied to the wrist joint by a haptic manipulator. Neural (reflexive torque) and structural (connective tissue stiffness and slack lengths and (contractile) optimal muscle lengths) parameters were estimated using an electromyography driven antagonistic wrist model. Kruskal-Wallis analysis with multiple comparisons was used to compare results between healthy subjects, stroke patients with modified Ashworth score of zero and stroke patients with modified Ashworth score of one or more., Findings: Stroke patients with modified Ashworth score of one or more differed from healthy controls (P<0.05) by increased tissue stiffness, increased reflexive torque, decreased optimal muscle length and decreased slack length of connective tissue of the flexor muscles., Interpretation: Non-invasive quantitative analysis, including estimation of optimal muscle lengths, enables to identify neural and non-neural changes in chronic stroke patients. Monitoring these changes in time is important to understand the recovery process and to optimize treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Upper motor neuron diseases (UMND), such as stroke and spinal cord injury (SCI), are assumed to produce alterations in muscle tissue in association with neural damage. Distinguishing between these two factors is of clinical importance in choosing appropriate therapy. We studied the effect of changes in the gain of the Ia reflex pathway and tissue viscoelasticity on the emergence, frequency, and persistence of ankle clonus: a clinically significant, involuntary oscillatory movement disorder. Monte Carlo simulations were performed to explain our experimental observations in patients with stroke (n = 3) and SCI (n = 4) using a nonlinear antagonistic muscle model of the human ankle joint. Ia reflex gain was varied by changing motor unit pool threshold and gain, and passive tissue viscosity and elasticity were varied by changing optimal muscle length. Tissue viscoelasticity appeared to have a strong effect on the emergence and persistence of clonus. Observed frequencies of ankle movement, prior to and after the experimental intervention of a sudden damper, was predicted by the model. The simulations revealed that reflex gains were largest in patients with the largest tissue viscoelasticity. We conclude that ankle clonus in stroke and SCI is the result of a combination of, and suggests a relation between, (i) a decrease in threshold and an increase in gain of the motor unit pool and (ii) a decrease in optimal muscle length., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Rehabilitation of patients with joint affecting diseases makes an appeal to available compensating motions. Objective information about compensatory motions is required for clinical decision-making. Our objective was to quantify resulting shoulder and arm motions from limited elbow mobility during activities of daily living in healthy controls and patients., Methods: Ten hemophilia patients with reduced elbow motion and ten controls volunteered in a kinematic motion analysis of thorax, shoulder, arm and wrist during 5 experimental activities of daily living. In controls, the elbow range of motion was limited by an elbow brace with variable flexion and extension stops. The elbow angle of patients was not intervened. Outcome variables were minimal required elbow range of motion for successful activity of daily living completion and concurring compensatory motions., Findings: An elbow flexion and extension domain was identified separated by a 97° to 110° interval in which none of the observed tasks could be fulfilled. A minimal average elbow flexion angle of 86° and an additional range of motion of 36° were required to finish all tasks successfully. Predominant significant compensatory motion was found in the glenohumeral joint and wrist., Interpretation: Two functional elbow flexion domains exist, separated by a transition domain of 36°. Treatment should be focussed to bridge both domains. Limiting treatments, e.g. arthrodesis of the elbow joint within this transition range, especially in a cosmetic 90°, leads to severe disability. Limited joint range of motion requires increased compensatory motions in other joints., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Muscles behave as elastic springs during the initial strain phase, indicated as short range stiffness (SRS). Beyond a certain amount of strain the muscle demonstrates a more viscous behavior. The strain at which the muscle transits from elastic- to viscous-like behavior is called the elastic limit and is believed to be the result of breakage of cross-bridges between the contractile filaments. The aim of this study was to test whether the elastic limit, measured in vivo at the wrist joint, depended on the speed of lengthening. Brief extension rotations were imposed to the wrist joint (n=8) at four different speeds and at three different levels of voluntary torque using a servo controlled electrical motor. Using a recently published identification scheme, we quantified the elastic limit from measured joint angle and torque. The results showed that the elastic limit significantly increased with speed in a linear way, indicating to a constant time of approximately 30 ms before cross-bridges break. The implications for movement control of the joint are discussed., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: There is growing recognition of the serious consequences of sarcopenia on the functionality and autonomy in old age. Recently, the age-related changes in several inflammatory mediators have been implicated in the pathogenesis of sarcopenia. The purposes of this systematic review were two-fold: (1) to describe the patterns of muscle strength loss with age in the general population, and (2) to quantify the loss of muscle strength in rheumatoid arthritis as representative for an underlying inflammatory state. Handgrip strength was used as a proxy for overall muscle strength., Results: Results from 114 studies (involving 90,520 subjects) and 71 studies (involving 10,529 subjects) were combined in a meta-analysis for the general and rheumatoid arthritis population respectively and standardized at an equal sex distribution. For the general population we showed that between the ages of 25 years and 95 years mean handgrip strength declined from 45.5 kg to 23.2 kg for males and from 27.1 kg to 12.8 kg for females. We noted a steeper handgrip strength decline after 50 years of age (rate of 0.37 kg/year). In the rheumatoid arthritis population handgrip strength was not associated with chronological age between the ages of 35 years and 65 years and was as low as 20.2 kg in male and 15.1 in female. Rheumatoid arthritis disease duration was inversely associated with handgrip strength., Conclusions: This meta-analysis shows distinct patterns of age-related decrease of handgrip strength in the general population. Handgrip strength is strongly associated with the presence and duration of an inflammatory state as rheumatoid arthritis. The putative link between age-related inflammation and sarcopenia mandates further study as it represents a potential target for intervention to maintain functional independence in old age., (Copyright © 2010 Elsevier B.V. All rights reserved.)

In patients with rotator cuff tears lost elevation moments are compensated for by increased deltoid activation. Concomitant proximal directed destabilizing forces at the glenohumeral joint are suggested to be compensated for by 'out-of-phase' adductor activation, preserving glenohumeral stability. Aim of this study was to demonstrate causality between moment compensating deltoid activation and stability compensating 'out-of-phase' adductor muscle activation. A differential arm loading with the same magnitude of forces applied at small and large moment arms relative to the glenohumeral joint was employed to excite deltoid activation, without externally affecting the force balance. Musculoskeletal modeling was applied to analyze the protocol in terms of muscle forces and glenohumeral (in)stability. The protocol was applied experimentally using electromyography (EMG) to assess muscle activation of healthy controls and cuff tear patients. Both modeling and experiments demonstrated increased deltoid activation with increased moment loading, which was higher in patients compared to controls. Model simulation of cuff tears demonstrated glenohumeral instability and related 'out-of-phase' adductor muscle activation which was also found experimentally in patients when compared to controls. Through differential moment loading, the assumed causal relation between increased deltoid activation and compensatory adductor muscle activation in cuff tear patients could be demonstrated. 'Out-of-phase' adductor activation in patients was attributed to glenohumeral instability. The moment loading protocol discerned patients with cuff tears from controls based on muscle activation., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Background: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an adequate salvage procedure. Analysis of muscle function to find biomechanical ground of such success is scarce., Methods: We compared pre- and postoperative clinical outcome of TMj transfer, i.e. Range of Motion, pain, Constant Shoulder scores and arm force. TMj activation was evaluated in 14 patients suffering massive cuff tears using activation ratios to describe the desired 'in-phase' and undesired 'out-of-phase' contribution to the external arm moment. Additionally, we analyzed activation of the latissimus dorsi (LD) and the medial part of the deltoids (DE). The activation ratios were compared to controls and TMj activation ratios were related to clinical outcome., Findings: TMj tendon transfer improved arm function. Pre-operatively, we observed 'out-of-phase'abduction activation of TMj and LD. After transfer patients activated TMj according to its new anatomical position. 'Out-of-phase' LD abduction activation persisted. The clinical improvements coincided with changes in activation ratio of TMj., Interpretation: 'Out-of-phase' TMj adductor activation is associated with compromised arm function in patients with irreparable cuff tears. After transfer, TMj is activated in correspondence with its new anatomical function, which was supportive for the improved arm function.

Non-invasive dynamical measurements of 3D scapular motion can be performed easily by attachment of a 6 DOF electromagnetic receiver onto the skin above the acromion. To quantify the introduction of possible errors due to skin displacement, we assessed 3D scapular positions on n=8 subjects by both tripod and skin-fixed method. Error analysis included the variables method (tripod, skin-fixed simultaneously with tripod, separate skin-fixed at 0 and 0.25Hz of elevation speed), plane of elevation (0 degrees and 90 degrees ) and observation (receiver replacement: n=3). Inter-individual 'group' differences depended on elevation plane and showed an average underestimation of scapular rotation of 6.5 degrees (worst case 13 degrees ) using the skin-fixed method. Only the group RMSE, not the individual RMSE, could be successfully lowered using linear regression (to about 2 degrees ). Inter-trial reliability (RMSE <3.24 degrees , ICC>0.94) and RMSE between 0 and 0.25Hz recordings (about 2.5 degrees ) were satisfactory. Intra-observer RMSE after replacement of the skin-fixed receiver was 5 degrees . The skin-fixed method is suitable for dynamic recordings of scapular rotations; however, measurements are precise only when the acromion receiver is not replaced. Combined with a relatively low accuracy, we conclude that the skin-fixed method should be used only in combination with tripod 'calibration'.

Objective: To assess the reliability of force direction dependent EMG parameters in shoulder muscles for future clinical research., Design: EMG measurements of shoulder muscles including the rotator cuff were performed during isometrical external loading in various directions covering 360 degrees in a plane perpendicular to the humeral axis., Background: Relating EMG to force direction bypasses problems associated with the unknown position and velocity dependence of the EMG signal. For clinical application, information on the reliability of force direction dependent parameters is required., Methods: The EMG of shoulder muscles of healthy subjects was related to force direction. The activation patterns obtained where parameterised after least squares function fitting, returning three force direction dependent parameters, i.e. two on- and offset directions of the activity peak and the direction of highest EMG activity also called principal action. Within-trial, inter-trial, inter-day and inter-subject variabilities were estimated., Results: With a group size of n = 10, the 95% confidence interval for inter-day measurements was found to be about +/-5 degrees on a scale of 360 degrees for the principal action and just below +/-10 degrees for the intercepts., Conclusion: The method allows for intra-individual measurements on different days with sufficient accuracy so that shoulder muscle co-ordination of patients before and after interventions like surgery or physical therapy can be evaluated., Relevance: Quantitative data on shoulder muscle function in vivo are required to assess the effectiveness of interventions on the shoulder.

Objective: To present an isometric method for validation of a shoulder model simulation by means of experimentally obtained electromyography and addressing all muscles active around the shoulder joints., Background: Analysis of muscle force distribution in the shoulder by means of electromyography during motion tasks is hampered by artificial and non-linear amplitude modulation and is often limited to downward directed external forces. This application of EMG is therefore inadequate and insufficient for the validation of shoulder model simulations. We suggest an isometric method including multi-directional forces to overcome these problems., Methods: A force with constant magnitude is actively rotated stepwise in 20 directions perpendicular around the arm while kept in one position. The isometric muscle activation (EMG) is a function of the clockwise-rotated force angle, characterized by baseline activation, and a section of increased muscle activation characterized by baseline interception and direction and magnitude of maximum muscle activation. Comparison of the parameterized muscle activation with predicted muscle forces from model simulation illustrates the applicability for musculo-skeletal model validation., Results: All recorded shoulder muscles were active over a section of force angles of at least 180 degrees. Some muscles demonstrated two activation sections. The estimated model sensitivity for the baseline interception was SD=5 degrees -10 degrees. The Principal Action was the most reliable parameter (SD=4 degrees ). A correlation of 0.778 was observed between model simulations and EMG recordings., Conclusions: The methodology addresses all shoulder muscles over a substantial section of planar force directions. This enables the comparison of experimentally determined direction of activation on- and offset and direction of maximum activation with equivalent muscle forces, predicted from model simulation.

Objective: To quantify the size of the supraspinatus outlet as it is dictated by both the three-dimensional geometry of the shoulder and the relative orientation of the humerus with respect to the scapula during motions of the arm., Design: Previously obtained data of shoulder kinematics were brought into a geometrical model of the shoulder, derived from a cadaver study., Background: Knowledge of the parameters dictating the size of the supraspinatus outlet is essential for a better understanding of the impingement syndrome of the shoulder., Methods: A geometrical model, based on fitting spheres to various anatomical items of the shoulder was derived from three-dimensional position data of the gleno-humeral joint and coraco-acromial arch of 32 cadaver shoulders. Kinematical data were collected from 10 healthy volunteers. The geometrical and kinematical data were combined to study the supraspinatus outlet during elevation of the humerus in the frontal and sagittal plane., Results: No single geometry parameter correlated significantly with the initial size of the outlet. During arm elevation, the greater tuberosity was moved away from the coraco-acromial arch quite effectively resulting in narrowing of the outlet during elevation in the frontal plane from 60 degrees to 120 degrees only. Deviations from the average were quite substantial. This was caused by kinematical and especially geometrical variability., Conclusion: The size of the outlet is dictated by both the geometry and kinematics of the gleno-humeral joint. Assessment of the individual susceptibility to impingement requires three-dimensional viewing techniques including three-dimensional movements of both the scapula and humerus., Relevance: Little is known about etiology and pathogenesis of various shoulder disorders such as the impingement syndrome. The supraspinatus outlet plays probably a key role. More knowledge on the architecture of the outlet is required for a better understanding.