Gynaecological and obstetrical bleeding in women with factor XI deficiency - a systematic review.

INTRODUCTION: Menstrual bleeding, pregnancy and delivery present an intrinsic haemostatic challenge to women with bleeding disorders such as factor XI (FXI) deficiency. AIM: To provide a systematic overview of studies on gynaecological and obstetrical bleeding problems in women with FXI deficiency. METHODS: We searched MEDLINE, EMBASE and the Cochrane library for studies that present original data on the incidence of and treatment options for gynaecological and obstetrical bleeding in FXI-deficient women. RESULTS: We identified 27 studies, including a total of 372 women with FXI deficiency. All studies were observational, no interventional treatment studies were found. Most patients had a mild deficiency (FXI ≥ 20 IU dL-1 ). Heavy menstrual bleeding (HMB) was reported in 7-67%. In 7/19 (37%) women who underwent gynaecological procedures, a bleeding complication occurred, including in 2/7 hysterectomies (29%). About 3-20% of reported pregnancies ended in a miscarriage; of these miscarriages 0-25% (4/23 miscarriages) were complicated by bleeding. Terminations of pregnancies (TOP) were complicated by bleeding in 4 out of 11 cases (36%). In 90 out of 498 (18%) deliveries a postpartum haemorrhage (PPH) was reported, ranging from 0 to 50% in individual studies. In 21% (66/321) of deliveries, prophylaxis was given. This was associated with 9% (6/66) PPH, compared to 19% in deliveries without prophylaxis (84/432). Epidural analgesia was performed without complications in 44 patients. CONCLUSION: Women with FXI deficiency have a clearly increased risk of HMB, and of bleeding complications after miscarriage, TOP and delivery. No high quality data are available regarding prophylactic treatment.

Bone turnover markers predict hip bone loss in elderly European men: results of the European Male Ageing Study (EMAS).

SUMMARY: The aim of this study was to determine whether bone turnover markers (BTMs) predict changes in areal bone mineral density (aBMD) in middle-aged and elderly European men. Older men with high bone turnover are at a higher risk of accelerated hip bone loss, but the clinical utility of BTMs in individuals is limited. INTRODUCTION: Prospective studies on the value of BTMs to predict changes in aBMD in men are few and conflicting. The aim of this study was to determine whether BTMs predict changes in aBMD in middle-aged and elderly European men. METHODS: In 487 men aged 40-79 years from the European Male Ageing Study (EMAS), BTMs were assessed at baseline and dual-energy X-ray absorptiometry (DXA) at the lumbar spine (LS), femoral neck (FN) and total hip (TH) was performed at baseline and after a mean follow-up of 4.3 years. RESULTS: The mean aBMD decreased by 0.32%/year at FN and 0.22%/year at TH and increased by 0.32%/year at LS. Higher baseline levels of ß C-terminal cross-linked telopeptide (ß-CTX) and N-terminal propeptide of type I procollagen (PINP) were significantly associated with higher loss of hip aBMD in the whole cohort and men aged 60-79 years. These associations remained significant after adjustment for age, centre and body mass index (BMI). Men aged 60-79 years with ß-CTX in the upper quintile were more likely of being in the upper quintile of annual percentage (%) aBMD loss at FN (OR=4.27; 95% CI=2.09-8.73) and TH (OR=3.73; 95% CI=1.84-7.57). The positive predictive value (PPV) was 46% at both hip sites. CONCLUSION: Older men with high bone turnover have a higher risk of accelerated hip bone loss, but the PPV is low. BTMs are therefore unlikely to be of clinical utility in predicting accelerated hip bone loss in individual subjects.

The effects of a sleeve knee brace during stair negotiation in patients with symptomatic patellofemoral osteoarthritis.

BACKGROUND: The patellofemoral joint is an important source of pain in knee osteoarthritis. Most biomechanical research in knee osteoarthritis has focused on the tibiofemoral joint during level walking. It is unknown what happens during stair negotiation in patients with patellofemoral joint osteoarthritis, a task commonly increasing pain. Conservative therapy for patellofemoral joint osteoarthritis includes the use of a sleeve knee brace. We aimed to examine the effect of a sleeve knee brace on knee biomechanics during stair negotiation in patellofemoral joint osteoarthritis patients. METHODS: 30 patellofemoral joint osteoarthritis patients (40-70 years) ascended and descended an instrumented staircase with force plates under two conditions - wearing a Lycra flexible knee support (Bioskin Patellar Tracking Q Brace) and no brace (control condition). Knee joint kinematics (VICON) and kinetics were recorded. FINDINGS: During stair ascent, at the knee, the brace significantly reduced the maximal flexion angle (2.70, P = 0.002), maximal adduction angle (2.00, P = 0.044), total sagittal range of motion (2.00, P = 0.008), total frontal range of motion (1.70, P = 0.023) and sagittal peak extension moment (0.05 Nm/kg, P = 0.043) compared to control. During stair descent, at the knee, the brace significantly reduced the maximal flexion angle (1.80, P = 0.039) and total sagittal range of motion (1.50, P = 0.045) compared to control. INTERPRETATION: The small changes in knee joint biomechanics during stair negotiation observed in our study need to be investigated further to help explain mechanisms behind the potential benefits of a sleeve knee brace for painful patellofemoral joint osteoarthritis.

Sarcopenia and its relationship with bone mineral density in middle-aged and elderly European men.

UNLABELLED: The aim of this study was to determine the relationship between reduced muscle mass (sarcopenia) and areal bone mineral density (BMD(a)) in middle-aged and elderly community-dwelling European men. Men with sarcopenia had significantly lower BMD(a) and were more likely to have osteoporosis compared with men without sarcopenia. INTRODUCTION: In men, the relationship between reduced muscle mass (sarcopenia) and BMD(a) is unclear. This study aimed to determine this relationship in middle-aged and elderly community-dwelling men. METHODS: Men aged 40-79 years from the Manchester (UK) and Leuven (Belgium) cohorts of the European Male Ageing Study were invited to attend for assessment including dual-energy X-ray absorptiometry, from which appendicular lean mass (aLM), fat mass (FM) and whole-body, spine and hip BMD(a) were determined. Relative appendicular skeletal muscle mass (RASM) was calculated as aLM/height². Muscle strength was assessed in subjects from Leuven. Sarcopenia was defined by RASM at <7.26 kg/m² and by the recent definition of the European Working Group on Sarcopenia in Older People (RASM at <7.26 kg/m(2) plus low muscle function). Linear regression was used to determine the associations between aLM, FM, muscle strength and BMD(a) and logistic regression to determine the association between sarcopenia and osteoporosis. RESULTS: Six hundred seventy-nine men with a mean age of 59.6 (SD = 10.7), contributed data to the analysis; 11.9 % were sarcopenic by the conventional definition. After adjustment for age and centre, aLM, RASM and FM were positively associated with BMD(a). Men with RASM at <7.26 kg/m² had significantly lower BMD(a) compared with those with RASM at ≥7.26 kg/m(2). In a multivariable model, aLM was most consistently associated with BMD(a). Men with sarcopenia were more likely to have osteoporosis compared with those with normal RASM (odds ratio = 3.0; 95 % CI = 1.6-5.8). CONCLUSIONS: Sarcopenia is associated with low BMD(a) and osteoporosis in middle-aged and elderly men. Further studies are necessary to assess whether maintaining muscle mass contributes to prevent osteoporosis.

Determining the optimal gait modification strategy for patients with knee osteoarthritis: Trunk lean or medial thrust?

BACKGROUND: The gait modification strategies Trunk Lean and Medial Thrust have been shown to reduce the external knee adduction moment (EKAM) in patients with knee osteoarthritis which could contribute to reduced progression of the disease. Which strategy is most optimal differs between individuals, but the underlying mechanism that causes this remains unknown. RESEARCH QUESTION: Which gait parameters determine the optimal gait modification strategy for individual patients with knee osteoarthritis? METHODS: Forty-seven participants with symptomatic medial knee osteoarthritis underwent 3-dimensional motion analysis during comfortable gait and with two gait modification strategies: Medial Thrust and Trunk Lean. Kinematic and kinetic variables were calculated. Participants were then categorized into one of the two subgroups, based on the modification strategy that reduced the EKAM the most for them. Multiple logistic regression analysis with backward elimination was used to investigate the predictive nature of dynamic parameters obtained during comfortable walking on the optimal modification gait strategy. RESULTS: For 68.1 % of the participants, Trunk Lean was the optimal strategy in reducing the EKAM. Baseline characteristics, kinematics and kinetics did not differ significantly between subgroups during comfortable walking. Changes to frontal trunk and tibia angles correlated significantly with EKAM reduction during the Trunk Lean and Medial Thrust strategies, respectively. Regression analysis showed that MT is likely optimal when the frontal tibia angle range of motion and peak knee flexion angle in early stance during comfortable walking are high (R2Nagelkerke = 0.12). SIGNIFICANCE: Our regression model based solely on kinematic parameters from comfortable walking contained characteristics of the frontal tibia angle and knee flexion angle. As the model explains only 12.3 % of variance, clinical application does not seem feasible. Direct assessment of kinetics seems to be the most optimal strategy for selecting the most optimal gait modification strategy for individual patients with knee osteoarthritis.

The effectiveness of exercise and physical activity programs on fatigue and sleep in people with arthritis - A systematic review with meta-analysis.

This systematic review aimed to systematically investigate the literature on the effectiveness of exercise and physical activity programs on fatigue and sleep in people with arthritis. For that, seven databases were searched for relevant randomized controlled trials. After the searches, 36 studies investigating 2281 participants were included. Risk of bias assessments were done by two independent reviewers using the Cochrane Risk of Bias tool 2. Random-effects meta-analyses were performed, and the Grading of Recommendations Assessment, Development and Evaluation framework was used to judge the certainty of evidence. The evidence on benefits of exercise and physical activity programs on fatigue and sleep parameters in people with osteoarthritis and psoriatic arthritis was either lacking or inconclusive. There was very low to low certainty evidence for a slight benefit of exercise and physical activity programs on fatigue at short-term in people with ankylosing spondylitis and rheumatoid arthritis. However, the evidence was very uncertain for the medium- and long-term as well as for any sleep parameters. The results indicate that exercise and physical activity programs may offer some benefits on fatigue for people with arthritis in the short-term, although the best type of exercise remains uncertain. The available evidence on improvements in sleep was insufficient to draw strong conclusions.

Role of Y(2) receptors in the regulation of gastric tone in rats.

We set out to determine the effect of peptide YY(3-36) (PYY(3-36)) on the gastric muscle tone in conscious rats by measuring intragastric pressure (IGP) during intragastric nutrient drink infusion. After an overnight fast, a chronically implanted gastric fistula was connected to a custom-made nutrient drink infusion system and a catheter to measure IGP. IGP was measured before and during the infusion of a nutrient drink (Nutridrink; 0.5 ml/min) until 10 ml was infused. Rats were treated with PYY(3-36) (0, 33, and 100 pmol·kg(-1)·min(-1)) in combination with a subcutaneous injection of the Y(2) receptor antagonists JNJ31020028 (10 mg/kg) or BIIE0246 (2 mg/kg). Experiments were also performed after subdiaphragmatic vagotomy and after pretreatment with 3 ml of nutrient drink (to mimic a fed state). IGP was compared as the average IGP during nutrient infusion, represented as means ± SE and compared using ANOVA. PYY(3-36) dose dependently increased the IGP during nutrient infusion (4.7 ± 0.3, 5.7 ± 0.5 and 7.3 ± 0.7 mmHg; P < 0.01) while JNJ31020028 and BIIE0246 could block this increase [4.4 ± 0.5 (P < 0.001) and 4.8 ± 0.4 (P < 0.05) mmHg, respectively]. Also in vagotomized rats, PYY(3-36) was able to significantly increase the IGP during, an effect attenuated by JNJ31020028. BIIE0246 and JNJ31020028 were not able to decrease the IGP when no PYY(3-36) was administered. PYY(3-36) increased gastric tone through an Y(2) receptor-mediated mechanism that does not involve the vagus nerve. Y(2) receptor antagonists were not able to decrease gastric tone without exogenous administration of PYY(3-36), indicating that Y(2) receptors do not play a crucial role in the determination of gastric tone in physiological conditions.

Musculoskeletal frailty: a geriatric syndrome at the core of fracture occurrence in older age.

A progressive decline in physiologic reserves inevitably occurs with ageing. Frailty results from reaching a threshold of decline across multiple organ systems. By consequence, frail elderly experience an excess vulnerability to stressors and are at high risk for functional deficits and comorbid disorders, possibly leading to institutionalization, hospitalization and death. The phenotype of frailty is referred to as the frailty syndrome and is widely recognized in geriatric medical practice. Although frailty affects both musculoskeletal and nonmusculoskeletal systems, sarcopenia, which is defined as age-related loss of muscle mass and strength, constitutes one of the main determinants of fracture risk in older age and one of the main components of the clinical frailty syndrome. As a result, operational definitions of frailty and therapeutic strategies in older patients tend to focus on the consequences of sarcopenia.

Reporting whole-body vibration intervention studies: recommendations of the International Society of Musculoskeletal and Neuronal Interactions.

Whole-body vibration (WBV) is receiving increasing interest as a therapeutic modality to improve neuromuscular performance or to increase bone mass or density. In order to help improve the quality of reports about WBV treatment studies, the International Society of Musculoskeletal and Neuronal Interactions (ISMNI) invited experts in the field to provide suggestions on how the intervention should be described in such reports. The recommendations are presented here.

Superimposed vibration confers no additional benefit compared with resistance training alone.

Eighteen participants (22-43 years) were randomly allocated to one of two groups: resistance training combined with vibration (VIB; five males, four females) or resistance training alone (CON; five males, four females). Each participant trained three sessions per week (three sets of 10 seated calf raises against a load, which was increased progressively from 75% of one repetition maximum (1RM) to 90% 1RM for 4 weeks. For the VIB group, a vibratory stimulus (30 Hz, 2.5 mm amplitude) was applied to the soles of the feet by a vibration platform. The two groups did not differ significantly with respect to the total amount of work performed during training. Both groups showed a significant increase in maximum voluntary contraction and 1RM (P<0.01) with training. There were no significant changes in measures that assessed the rate at which force was developed. Countermovement jump height increased for the CON (P<0.01) but not for the VIB group. Comparisons between the groups revealed that they did not differ significantly from one another with respect to any measure of performance, before or following training. It appears that vibration superimposed upon resistance training does not alter or augment the increase in strength induced by resistance training alone.

Balancing between the two: Are freezing of gait and postural instability in Parkinson's disease connected?

Postural instability and freezing of gait (FoG) are key features of Parkinson's disease (PD) closely related to falls. Growing evidence suggests that co-existing postural deficits could influence the occurrence and severity of FoG. To date, the exact nature of this interrelationship remains largely unknown. We analyzed the complex interaction between postural instability and gait disturbance by comparing the findings available in the posturographic literature between patients with and without FoG. Results showed that FoG and postural instability are intertwined, can influence each other behaviorally and may coincide neurologically. The most common FoG-related postural deficits included weight-shifting impairments, and inadequate scaling and timing of postural responses most apparent at forthcoming postural changes under time constraints. Most likely, a negative cycle of combined and more severe postural deficits in people with FoG will enhance postural stability breakdown. As such, the wide brain network deficiencies involved in FoG may also concurrently influence postural stability. Future work needs to examine whether training interventions targeting both symptoms will have extra clinical benefits on fall frequency.

Altered Achilles tendon function during walking in people with diabetic neuropathy: implications for metabolic energy saving.

The Achilles tendon (AT) has the capacity to store and release elastic energy during walking, contributing to metabolic energy savings. In diabetes patients, it is hypothesized that a stiffer Achilles tendon may reduce the capacity for energy saving through this mechanism, thereby contributing to an increased metabolic cost of walking (CoW). The aim of this study was to investigate the effects of diabetes and diabetic peripheral neuropathy (DPN) on the Achilles tendon and plantarflexor muscle-tendon unit behavior during walking. Twenty-three nondiabetic controls (Ctrl); 20 diabetic patients without peripheral neuropathy (DM), and 13 patients with moderate/severe DPN underwent gait analysis using a motion analysis system, force plates, and ultrasound measurements of the gastrocnemius muscle, using a muscle model to determine Achilles tendon and muscle-tendon length changes. During walking, the DM and particularly the DPN group displayed significantly less Achilles tendon elongation (Ctrl: 1.81; DM: 1.66; and DPN: 1.54 cm), higher tendon stiffness (Ctrl: 210; DM: 231; and DPN: 240 N/mm), and higher tendon hysteresis (Ctrl: 18; DM: 21; and DPN: 24%) compared with controls. The muscle fascicles of the gastrocnemius underwent very small length changes in all groups during walking (~0.43 cm), with the smallest length changes in the DPN group. Achilles tendon forces were significantly lower in the diabetes groups compared with controls (Ctrl: 2666; DM: 2609; and DPN: 2150 N). The results strongly point toward the reduced energy saving capacity of the Achilles tendon during walking in diabetes patients as an important factor contributing to the increased metabolic CoW in these patients. NEW & NOTEWORTHY From measurements taken during walking we observed that the Achilles tendon in people with diabetes and particularly people with diabetic peripheral neuropathy was stiffer, was less elongated, and was subject to lower forces compared with controls without diabetes. These altered properties of the Achilles tendon in people with diabetes reduce the tendon's energy saving capacity and contribute toward the higher metabolic energy cost of walking in these patients.

Differences in knee adduction moment between healthy subjects and patients with osteoarthritis depend on the knee axis definition.

OBJECTIVE: This study, firstly, investigates the effect of using an anatomical versus a functional axis of rotation (FAR) on knee adduction moment (KAM) in healthy subjects and patients with knee osteoarthritis (KOA). Secondly, this study reports KAM for models with FAR calculated using weight-bearing and non-weight-bearing motion. DESIGN: Three musculoskeletal models were created using OpenSim with different knee axis of rotation (AR): transepicondylar axis (TEA); FAR calculated based on SARA algorithm using a weight-bearing motion (wFAR) and a non-weight-bearing motion (nwFAR). KAM were calculated during gait in fifty-nine subjects (n=20 healthy, n=16 early OA, n=23 established OA) for all models and groups. RESULTS: Significant differences between the three groups in the first peak KAM were found when TEA was used (p=0.038). However, these differences were no longer present when using FAR. In subjects with established OA, KAMs were significantly reduced when using nwFAR compared to TEA models but also compared to wFAR models. CONCLUSION: The presence of excessive KAM in subjects with established KOA showed to be dependent on the definition of the AR: anatomical versus functional. Therefore, caution should be accounted when comparing KAM in different studies on KOA patients. In patients with end-stage knee OA where increased passive knee laxity is likely to exist, the use of weight-bearing motions should be considered to avoid increased variability in the location and orientation of a FAR obtained from activities with only limited joint loading.

Lateral trunk lean and medializing the knee as gait strategies for knee osteoarthritis.

OBJECTIVE: To determine (1) if Medial Thrust or Trunk Lean reduces the knee adduction moment (EKAM) the most during gait in patients with medial knee osteoarthritis, (2) if the best overall strategy is the most effective for each patient and (3) if these strategies affect ankle and hip kinetics. DESIGN: Thirty patients with symptomatic medial knee osteoarthritis underwent 3-dimensional gait analysis. Participants received verbal instructions on two gait strategies (Trunk Lean and Medial Thrust) in randomized order after comfortable walking was recorded. The peaks and impulse of the EKAM and strategy-specific kinematic and kinetic variables were calculated for all conditions. RESULTS: Early stance EKAM peak was significantly reduced during Medial Thrust (-29%). During Trunk Lean, early and late stance EKAM peak and EKAM impulse reduced significantly (38%, 21% and -25%, respectively). In 79% of the subjects, the Trunk Lean condition was significantly more effective in reducing EKAM peak than Medial Thrust. Peak ankle dorsi and plantar flexion, knee flexion and hip extension and adduction moments were not significantly increased. CONCLUSIONS: Medial Thrust and Trunk Lean reduced the EKAM during gait in patients with knee osteoarthritis. Individual selection of the most effective gait modification strategy seems vital to optimally reduce dynamic knee loading during gait. No detrimental effects on external ankle and hip moments or knee flexion moments were found for these conditions.

Knee contact forces are not altered in early knee osteoarthritis.

OBJECTIVE: This study calculated knee contact forces (KCF) and its relations with knee external knee adduction moments (KAM) and/or flexion moments (KFM) during the stance phase of gait in patients with early osteoarthritis (OA), classified based on early joint degeneration on Magnetic Resonance Imaging (MRI). We aimed at assessing if altered KCF are already present in early structural degeneration. DESIGN: Three-dimensional motion and ground reaction force data in 59 subjects with medial compartment knee OA (N=23 established OA, N=16 early OA, N=20 controls) were used as input for a musculoskeletal model. KAM and KFM, and KCF were estimated using OpenSim software. RESULTS: No significant differences were found between controls and subjects with early OA. In early OA patients, KAM significantly explained 69% of the variance associated with the first peaks KCF but only KFM contributed to the second peaks KCF. The multiple correlation, combining KAM and KFM, showed to be higher. However, only 20% of the variance of second peak KCF was explained by both moments in established OA. CONCLUSION: KCF are not increased in patients with early OA, suggesting that knee joint overload is more a consequence of further joint degeneration in more advanced stages of OA. Additionally, our results clearly show that KAM is not sufficient to predict joint loading at the end of the stance, where KFM contributes substantially to the loading, especially in early OA.

Is the metabolic cost of walking higher in people with diabetes?

People with diabetes walk slower and display biomechanical gait alterations compared with controls, but it remains unknown whether the metabolic cost of walking (CoW) is elevated. The aim of this study was to investigate the CoW and the lower limb concentric joint work as a major determinant of the CoW, in patients with diabetes and diabetic peripheral neuropathy (DPN). Thirty-one nondiabetic controls (Ctrl), 22 diabetic patients without peripheral neuropathy (DM), and 14 patients with moderate/severe DPN underwent gait analysis using a motion analysis system and force plates and treadmill walking using a gas analyzer to measure oxygen uptake. The CoW was significantly higher particularly in the DPN group compared with controls and also in the DM group (at selected speeds only) compared with controls, across a range of matched walking speeds. Despite the higher CoW in patients with diabetes, concentric lower limb joint work was significantly lower in DM and DPN groups compared with controls. The higher CoW is likely due to energetic inefficiencies associated with diabetes and DPN reflecting physiological and biomechanical characteristics. The lower concentric joint work in patients with diabetes might be a consequence of kinematic gait alterations and may represent a natural strategy aimed at minimizing the CoW.

Combined oral contraceptives, thrombophilia and the risk of venous thromboembolism: a systematic review and meta-analysis.

UNLABELLED: Essentials We performed a meta-analysis on thrombosis risk in thrombophilic oral contraceptive (COC)-users. The results support discouraging COC-use in women with a natural anticoagulant deficiency. Contrary, additive risk of factor V Leiden (FVL) or prothrombin-G20210A (PT) mutation is modest. Women with a FVL/PT-mutation as single risk factor can use COCs if alternatives are not tolerated. SUMMARY: Background Combined oral contraceptives (COCs) are associated with an increased risk of venous thromboembolism (VTE), which is shown to be more pronounced in women with hereditary thrombophilia. Currently, WHO recommendations state that COC-use in women with hereditary thrombophilias (antithrombin deficiency, protein C deficiency, protein S deficiency, factor V Leiden and prothrombin-G20210A mutation) is associated with an unacceptable health risk. Objective To perform a meta-analysis evaluating the additional risk of VTE in COC-users with thrombophilia. Methods The MEDLINE and EMBASE databases were searched on 10 February 2015 for potential eligible studies. A distinction was made between 'mild' (factor V Leiden and prothrombin-G20210A mutation) and 'severe' thrombophilia (antithrombin deficiency, protein C deficiency, protein S deficiency, double heterozygosity or homozygosity of factor V Leiden and prothrombin-G20210A mutation). Results We identified 12 case-control and three cohort studies. In COC-users, mild and severe thrombophilia increased the risk of VTE almost 6-fold (rate ratio [RR], 5.89; 95% confidence interval [CI], 4.21-8.23) and 7-fold (RR, 7.15; 95% CI, 2.93-17.45), respectively. The cohort studies showed that absolute VTE risk was far higher in COC-users with severe thrombophilia than in those with mild thrombophilia (4.3 to 4.6 vs. 0.49 to 2.0 per 100 pill-years, respectively), and these differences in absolute risks were also noted in non-affected women (0.48 to 0.7 vs. 0.19 to 0.0), but with the caveat that absolute risks were estimated in relatives of thrombophilic patients with VTE (i.e. with a positive family history). Conclusion These results support discouraging COC-use in women with severe hereditary thrombophilia. By contrast, additive VTE risk of mild thrombophilia is modest. When no other risk factors are present, (e.g. family history) COCs can be offered to these women when reliable alternative contraceptives are not tolerated.

Dynamic position sense during a cyclical drawing movement: effects of application and withdrawal of tendon vibration.

The present study addressed the stability of dynamic position sense across time as well as the resetting of position sense following its disturbance by means of tendon vibration. Blindfolded subjects drew circles within a specific location of the workspace for a duration of 28 s and at a repetition rate of 1 s(-1). To study the stability of dynamic position sense, the changes in circle drawing performance across time were studied (control condition). Resetting of dynamic position sense was studied by application and subsequent withdrawal of biceps tendon vibration during movement (vibration condition). The results showed that the spatial characteristics of circle drawing in the control condition did not change significantly over the course of the 28 s trial, suggesting that dynamic position sense does not drift systematically across time. Whereas vibration leads to a decrease in diameter, a deterioration of the circularity of the pattern, and a drift of the hand movement toward the body, a restoration of these features was obtained during withdrawal of vibration. This suggests that subjects are able to reset dynamic position sense to reasonable values without the help of vision during active cyclical movement.

Exploring interlimb constraints during bimanual graphic performance: effects of muscle grouping and direction.

Past studies on bimanual coordination have revealed a general preference to move the limbs in a symmetrical fashion, also denoted as the in-phase mode. Its counterpart, the asymmetrical or anti-phase mode, is performed with lower degrees of accuracy and stability. This ubiquitous tendency to activate the homologous muscle groups is referred to as the muscle grouping constraint (egocentric constraint). The present study confirmed the generalizability of this constraint across various coordination patterns, performed in the horizontal plane. In addition, evidence was generated that movement direction in extrinsic space also constrains bimanual coordination (allocentric constraint). Overall, the present observations suggest that direction is an important movement parameter that is encoded in the central nervous system and that is subject to interactions between the neural specifications of both limbs.