Physical Activity Levels, Correlates, and All-Cause Mortality Risk in People Living With Different Health Conditions.

BACKGROUND: To better understand physical activity behavior and its health benefits in people living with health conditions, we studied people with and without 20 different self-reported health conditions with regard to (1) their physical activity levels, (2) factors correlated with these physical activity levels, and (3) the association between physical activity and all-cause mortality. METHODS: We used a subsample (n = 88,659) of the Lifelines cohort study from the Netherlands. For people living with and without 20 different self-reported health conditions, we studied the aforementioned factors in relation to physical activity. Physical activity was assessed with the Short Questionnaire to Assess Health-Enhancing Physical Activity Questionnaire, and mortality data were obtained from the Dutch death register. RESULTS: People with a reported health condition were less likely to meet physical activity guidelines than people without a reported health condition (odds ratios ranging from 0.55 to 0.89). Higher body mass index and sitting time, and lower self-rated health, physical functioning, and education levels were associated with lower odds of meeting physical activity guidelines across most health conditions. Finally, we found a protective association between physical activity and all-cause mortality in both people living with and without different health conditions. CONCLUSION: People living with different health conditions are generally less physically active compared with people living without a health condition. Both people living with and without self-reported health conditions share a number of key factors associated with physical activity levels. We also observed the expected protective association between physical activity and all-cause mortality.

Effectiveness and therapeutic validity of physiotherapeutic exercise starting within one year following total and unicompartmental knee arthroplasty for osteoarthritis: a systematic review.

BACKGROUND: To determine the effectiveness and therapeutic validity of physiotherapeutic exercise after total and unicompartmental knee arthroplasty for osteoarthritis. It was hypothesized that interventions of high therapeutic validity result in superior functional recovery after total and unicompartmental knee arthroplasty versus interventions of low therapeutic validity. METHODS: A systematic review incorporating a comprehensive database search of five major databases relevant to the topic was conducted. Randomized controlled trials were reviewed if they included studies that compared postoperative physiotherapeutic exercise with usual care or compared two types of postoperative physiotherapeutic interventions. All included studies were assessed for risk of bias (using the Cochrane Collaboration's tool) and therapeutic validity (using the Consensus on Therapeutic Exercise Training scale). The characteristics of the included articles and their results on joint and muscle function, functional performance, and participation were extracted. RESULTS: Of the 4343 unique records retrieved, 37 articles were included. Six of them showed good therapeutic validity, suggesting low therapeutic validity in 31 studies. Three articles showed a low risk of bias, 15 studies scored some concerns for risk of bias and 19 studies scored high risk of bias. Only one article scored well on both methodological quality and therapeutic validity. CONCLUSION: Due to heterogeneity of outcome measures and length of follow-up, as well as limited reporting of details of the physiotherapeutic exercises and control interventions, no clear evidence was found on effectiveness of physiotherapeutic exercises after total and unicompartmental knee arthroplasty. Homogeneity in intervention characteristics and outcome measures would enhance comparability of clinical outcomes between trials. Future studies should incorporate similar methodological approaches and outcome measures. Researchers are encouraged to use the Consensus on Therapeutic Exercise Training scale as a template to prevent insufficient reporting.

Implementing Exercise = Medicine in routine clinical care; needs for an online tool and key decisions for implementation of Exercise = Medicine within two Dutch academic hospitals.

BACKGROUND: There is much evidence to implement physical activity interventions for medical reasons in healthcare settings. However, the prescription of physical activity as a treatment, referring to as 'Exercise is Medicine' (E = M) is currently mostly absent in routine hospital care in The Netherlands. To support E = M prescription by clinicians in hospitals, this study aimed: (1) to develop an E = M-tool for physical activity advice and referrals to facilitate the E = M prescription in hospital settings; and (2) to provide an E = M decision guide on key decisions for implementation to prepare for E = M prescription in hospital care. METHODS: A mixed method design was used employing a questionnaire and face-to-face interviews with clinicians, lifestyle coaches and hospital managers, a patient panel and stakeholders to assess the needs regarding an E = M-tool and key decisions for implementation of E = M. Based on the needs assessment, a digital E = M-tool was developed. The key decisions informed the development of an E = M decision guide. RESULTS: An online supportive tool for E = M was developed for two academic hospitals. Based on the needs assessment, linked to the different patients' electronic medical records and tailored to the two local settings (University Medical Center Groningen, Amsterdam University Medical Centers). The E = M-tool existed of a tool algorithm, including patient characteristics assessed with a digital questionnaire (age, gender, PA, BMI, medical diagnosis, motivation to change physical activity and preference to discuss physical activity with their doctor) set against norm values. The digital E = M-tool provided an individual E = M-prescription for patients and referral options to local PA interventions in- and outside the hospital. An E = M decision guide was developed to support the implementation of E = M prescription in hospital care. CONCLUSIONS: This study provided insight into E = M-tool development and the E = M decision-making to support E = M prescription and facilitate tailoring towards local E = M treatment options, using strong stakeholder participation. Outcomes may serve as an example for other decision support guides and interventions aimed at E = M implementation.

Facilitators and barriers for the implementation of exercise are medicine in routine clinical care in Dutch university medical centres: a mixed methodology study on clinicians' perceptions.

OBJECTIVES: Despite the many proven advantages of a physically active lifestyle in patient populations, prescription of exercise is currently not widely implemented in routine clinical practice. The aims of this study were twofold: (1) to assess perceptions of clinicians on the current practice of exercise is medicine (E=M) prescription in two Dutch university medical centres and (2) to determine their perceived barriers and facilitators for the implementation of E=M in routine clinical care in Dutch university medical centres. DESIGN: A mixed methodologies study, using both online questionnaires and semi-structured interviews. SETTING: Dutch university medical centres. PARTICIPANTS: Clinicians working within the departments of medical oncology, orthopaedics and rehabilitation medicine of two university medical centres. RESULTS: Forty-five clinicians (response rate of 51%) completed the questionnaire, and 19 clinicians were interviewed. The results showed that even though clinicians had a positive attitude towards prescribing E=M, only a few reported to regularly prescribe E=M to their patients. The 52 identified facilitators and barriers for implementation of E=M were categorised into four main themes: (1) beliefs toward the implementation of E=M (eg, clinicians knowledge and skills, and social support), (2) factors related to the patient perspective (eg, patient priorities or motivation), (3) factors related to the referral options (eg, knowledge of and trust in local referral options) and (4) practical considerations when implementing E=M (eg, time constraints). CONCLUSIONS: Our study showed that even though many clinicians have a positive attitude toward an active lifestyle, many are not prescribing E=M on a regular basis. In order for clinicians to effectively implement E=M, strategies should focus on increasing clinicians E=M referral skills, improving clinicians knowledge of E=M referral options and develop a support system to ensure that E=M is high on the priority list of clinicians.

Self-report Versus Measured Physical Activity Levels During Outpatient Cardiac Rehabilitation.

PURPOSE: Many patients with coronary artery disease (CAD) do not achieve the recommended physical activity (PA) levels during and after cardiac rehabilitation (CR). The aim of this study was to analyze moderate to vigorous physical activity (MVPA) levels and the differences between perceived (self-reported) and measured (activity monitor) MVPA in CAD patients during CR. The second aim was to analyze which patient characteristics were associated with this difference. METHODS: A two-center observational-sectional study was conducted within the Department of Rehabilitation Medicine of the University Medical Center Groningen between January and April 2018. Adults with CAD, following an outpatient CR program, were included. Perceived MVPA was assessed with the Short Questionnaire to Assess Health-enhancing Physical Activity and compared with ActivPAL3 activity monitor outcomes over a period of 7 d. RESULTS: Fifty-one patients with CAD (age 59.4 ± 7.1 yr, eight females) were recruited. Four patients (8%) did not achieve the recommended guideline level of ≥150 min/wk of MVPA. Patients spent ≥80% of the week in sedentary activities. Patients overestimated MVPA with a median of 805 (218, 1363) min/wk (P< .001). The selected patient characteristics (age, body mass index, type of CAD, type of CR, social support, and self-efficacy) were not associated with this overestimation. CONCLUSIONS: Most patients with CAD, participating in an outpatient CR program, do achieve MVPA exercise recommendations but spend simultaneously too much time in sedentary activities.

Rehabilitation: mobility, exercise & sports; a critical position stand on current and future research perspectives.

BACKGROUND: Human movement, rehabilitation, and allied sciences have embraced their ambitions within the cycle of "RehabMove" congresses over the past 30 years. This combination of disciplines and collaborations in the Netherlands has tried to provide answers to questions in the fields of rehabilitation and adapted sports, while simultaneously generating new questions and challenges. These research questions help us to further deepen our understanding of (impaired) human movement and functioning, with and without supportive technologies, and stress the importance of continued multidisciplinary (inter)national collaboration. METHODS: This position stand provides answers that were conceived by the authors in a creative process underlining the preparation of the 6th RehabMove Congress. RESULTS: The take-home message of the RehabMove2018 Congress is a plea for continued multidisciplinary research in the fields of rehabilitation and adapted sports. This should be aimed at more individualized notions of human functioning, practice, and training, but also of performance, improved supportive technology, and appropriate "human and technology asset management" at both individual and organization levels and over the lifespan. CONCLUSIONS: With this, we anticipate to support the development of rehabilitation sciences and technology and to stimulate the use of rehabilitation notions in general health care. We also hope to help ensure a stronger embodiment of preventive and lifestyle medicine in rehabilitation practice. Indeed, general health care and rehabilitation practice require a healthy and active lifestyle management and research agenda in the context of primary, secondary, and tertiary prevention.IMPLICATIONS FOR REHABILITATIONContinued multidisciplinary (international) collaboration will stimulate the development of rehabilitation and human movement sciences.Notions from "human and technology asset management and ergonomics" are fundamental to rehabilitation practice and research.The rehabilitation concept will further merge into general health care and the quality there-off.

Implementing Individually Tailored Prescription of Physical Activity in Routine Clinical Care: Protocol of the Physicians Implement Exercise = Medicine (PIE=M) Development and Implementation Project.

BACKGROUND: The prescription of physical activity (PA) in clinical care has been advocated worldwide. This "exercise is medicine" (E=M) concept can be used to prevent, manage, and cure various lifestyle-related chronic diseases. Due to several challenges, E=M is not yet routinely implemented in clinical care. OBJECTIVE: This paper describes the rationale and design of the Physicians Implement Exercise = Medicine (PIE=M) study, which aims to facilitate the implementation of E=M in hospital care. METHODS: PIE=M consists of 3 interrelated work packages. First, levels and determinants of PA in different patient and healthy populations will be investigated using existing cohort data. The current implementation status, facilitators, and barriers of E=M will also be investigated using a mixed-methods approach among clinicians of participating departments from 2 diverse university medical centers (both located in a city, but one serving an urban population and one serving a more rural population). Implementation strategies will be connected to these barriers and facilitators using a systematic implementation mapping approach. Second, a generic E=M tool will be developed that will provide tailored PA prescription and referral. Requirements for this tool will be investigated among clinicians and department managers. The tool will be developed using an iterative design process in which all stakeholders reflect on the design of the E=M tool. Third, we will pilot-implement the set of implementation strategies, including the E=M tool, to test its feasibility in routine care of clinicians in these 2 university medical centers. An extensive learning process evaluation will be performed among clinicians, department managers, lifestyle coaches, and patients using a mixed-methods design based on the RE-AIM framework. RESULTS: This project was approved and funded by the Dutch grant provider ZonMW in April 2018. The project started in September 2018 and continues until December 2020 (depending on the course of the COVID-19 crisis). All data from the first work package have been collected and analyzed and are expected to be published in 2021. Results of the second work package are described. The manuscript is expected to be published in 2021. The third work package is currently being conducted in clinical practice in 4 departments of 2 university medical hospitals among clinicians, lifestyle coaches, hospital managers, and patients. Results are expected to be published in 2021. CONCLUSIONS: The PIE=M project addresses the potential of providing patients with PA advice to prevent and manage chronic disease, improve recovery, and enable healthy ageing by developing E=M implementation strategies, including an E=M tool, in routine clinical care. The PIE=M project will result in a blueprint of implementation strategies, including an E=M screening and referral tool, which aims to improve E=M referral by clinicians to improve patients' health, while minimizing the burden on clinicians.

Rhythmic neural activity is comodulated with short-term gait modifications during first-time use of a dummy prosthesis: a pilot study.

BACKGROUND: After transfemoral amputation, many hours of practice are needed to re-learn walking with a prosthesis. The long adaptation process that consolidates a novel gait pattern seems to depend on cerebellar function for reinforcement of specific gait modifications, but the precise, step-by-step gait modifications (e.g., foot placement) most likely rely on top-down commands from the brainstem and cerebral cortex. The aim of this study was to identify, in able-bodied individuals, the specific modulations of cortical rhythms that accompany short-term gait modifications during first-time use of a dummy prosthesis. METHODS: Fourteen naïve participants walked on a treadmill without (one block, 4 min) and with a dummy prosthesis (three blocks, 3 × 4 min), while ground reaction forces and 32-channel EEG were recorded. Gait cycle duration, stance phase duration, step width, maximal ground reaction force and, ground reaction force trace over time were measured to identify gait modifications. Independent component analysis of EEG data isolated brain-related activity from distinct anatomical sources. The source-level data were segmented into gait cycles and analyzed in the time-frequency domain to reveal relative enhancement or suppression of intrinsic cortical oscillations. Differences between walking conditions were evaluated with one-way ANOVA and post-hoc testing (α = 0.05). RESULTS: Immediate modifications occurred in the gait parameters when participants were introduced to the dummy prosthesis. Except for gait cycle duration, these modifications remained throughout the duration of the experimental session. Power modulations of the theta, mu, beta, and gamma rhythms, of sources presumably from the fronto-central and the parietal cortices, were found across the experimental session. Significant power modulations of the theta, beta, and gamma rhythms within the gait cycle were predominately found around the heel strike of both feet and the swing phase of the right (prosthetic) leg. CONCLUSIONS: The modulations of cortical activity could be related to whole-body coordination, including the swing phase and placing of the prosthesis, and the bodyweight transfer between legs and arms. Reduced power modulation of the gamma rhythm within the experimental session may indicate initial motor memories being formed. Better understanding of the sensorimotor processes behind gait modifications may inform the development of neurofeedback strategies to assist gait rehabilitation.

Standing task difficulty related increase in agonist-agonist and agonist-antagonist common inputs are driven by corticospinal and subcortical inputs respectively.

In standing, coordinated activation of lower extremity muscles can be simplified by common neural inputs to muscles comprising a functional synergy. We examined the effect of task difficulty on common inputs to agonist-agonist (AG-AG) pairs supporting direction specific reciprocal muscle control and agonist-antagonist (AG-ANT) pairs supporting stiffness control. Since excessive stiffness is energetically costly and limits the flexibility of responses to perturbations, compared to AG-ANT, we expected greater AG-AG common inputs and a larger increase with increasing task difficulty. We used coherence analysis to examine common inputs in three frequency ranges which reflect subcortical/spinal (0-5 and 6-15 Hz) and corticospinal inputs (6-15 and 16-40 Hz). Coherence was indeed higher in AG-AG compared to AG-ANT muscles in all three frequency bands, indicating a predilection for functional synergies supporting reciprocal rather than stiffness control. Coherence increased with increasing task difficulty, only in AG-ANT muscles in the low frequency band (0-5 Hz), reflecting subcortical inputs and only in AG-AG group in the high frequency band (16-40 Hz), reflecting corticospinal inputs. Therefore, common neural inputs to both AG-AG and AG-ANT muscles increase with difficulty but are likely driven by different sources of input to spinal alpha motor neurons.

In Standing, Corticospinal Excitability Is Proportional to COP Velocity Whereas M1 Excitability Is Participant-Specific.

Reductions in the base of support (BOS) make standing difficult and require adjustments in the neural control of sway. In healthy young adults, we determined the effects of reductions in mediolateral (ML) BOS on peroneus longus (PL) motor evoked potential (MEP), intracortical facilitation (ICF), short interval intracortical inhibition (SICI) and long interval intracortical inhibition (LICI) using transcranial magnetic stimulation (TMS). We also examined whether participant-specific neural excitability influences the responses to increasing standing difficulty. Repeated measures ANOVA revealed that with increasing standing difficulty MEP size increased, SICI decreased (both p < 0.05) and ICF trended to decrease (p = 0.07). LICI decreased only in a sub-set of participants, demonstrating atypical facilitation. Spearman's Rank Correlation showed a relationship of ρ = 0.50 (p = 0.001) between MEP size and ML center of pressure (COP) velocity. Measures of M1 excitability did not correlate with COP velocity. LICI and ICF measured in the control task correlated with changes in LICI and ICF, i.e., the magnitude of response to increasing standing difficulty. Therefore, corticospinal excitability as measured by MEP size contributes to ML sway control while cortical facilitation and inhibition are likely involved in other aspects of sway control while standing. Additionally, neural excitability in standing is determined by an interaction between task difficulty and participant-specific neural excitability.

Predicting mobility outcome in lower limb amputees with motor ability tests used in early rehabilitation.

STUDY DESIGN: Retrospective cohort study. BACKGROUND: Persons with a lower limb amputation can regain mobility using a prosthetic device. For fast and adequate prescription of prosthetic components, it is necessary to predict the mobility outcome early in rehabilitation. Currently, prosthetic prescription is primarily based on empirical knowledge of rehabilitation professionals. OBJECTIVE: In this study, we explored motor ability tests, to be completed without a prosthetic device, which have predictive value for mobility outcome at the end of rehabilitation. METHODS: For this study, data of 82 patients with a lower limb amputation were included. The Single-limb standing balance test (Balance test), the Lower-Extremity Motor Coordination Test and the Amputee Mobility Predictor Assessment Tool (AMPnoPRO) were used as measures for motor ability. Mobility outcome was measured using the Timed Up and Go Test, the Two-Minute Walking Test and K levels were used. RESULTS: The explained variance of the Balance test, the Lower-Extremity Motor Coordination Test and the AMPnoPRO was, respectively, 0.603, 0.534 and 0.649 on the Two-Minute Walking Test (linear regression); 0.597, 0.431 and 0.624 on the Timed Up and Go Test (linear regression); and 0.432, 0.420 and 0.526 on the K levels (logistic regression). CONCLUSION: The AMPnoPRO predicted mobility outcome statistically (largest amount of explained variance). Clinical relevance This study explored the possibility of statistically predicting mobility outcome in lower limb amputees at the end of rehabilitation, using motor ability tests conducted in early rehabilitation. This study suggests the use of the AMPnoPRO to predict mobility outcome in lower limb amputees.

Postural challenge affects motor cortical activity in young and old adults.

When humans voluntarily activate a muscle, intracortical inhibition decreases. Such a decrease also occurs in the presence of a postural challenge and more so with increasing age. Here, we examined age-related changes in motor cortical activity during postural and non-postural contractions with varying levels of postural challenge. Fourteen young (age 22) and twelve old adults (age 70) performed three conditions: (1) voluntary contraction of the soleus muscle in sitting and (2) leaning forward while standing with and (3) without being supported. Subthreshold transcranial magnetic stimulation was applied to the soleus motor area suppressing ongoing EMG, as an index of motor cortical activity. The area of EMG suppression was ~60% smaller (p<0.05) in unsupported vs. supported leaning and sitting, with no difference between these latter two conditions (p>0.05). Even though in absolute terms young compared with old adults leaned farther (p=0.018), there was no age effect or an age by condition interaction in EMG suppression. Leaning closer to the maximum without support correlated with less EMG suppression (rho=-0.44, p=0.034). We conclude that the critical factor in modulating motor cortical activity was postural challenge and not contraction aim or posture. Age did not affect the motor control strategy as quantified by the modulation of motor cortical activity, but the modulation appeared at a lower task difficulty with increasing age.

Immersive virtual reality improves movement patterns in patients after ACL reconstruction: implications for enhanced criteria-based return-to-sport rehabilitation.

PURPOSE: The purpose of this study was to evaluate the influence of immersion in a virtual reality environment on knee biomechanics in patients after ACL reconstruction (ACLR). It was hypothesized that virtual reality techniques aimed to change attentional focus would influence altered knee flexion angle, knee extension moment and peak vertical ground reaction force (vGRF) in patients following ACLR. METHODS: Twenty athletes following ACLR and 20 healthy controls (CTRL) performed a step-down task in both a non-virtual reality environment and a virtual reality environment displaying a pedestrian traffic scene. A motion analysis system and force plates were used to measure kinematics and kinetics during a step-down task to analyse each single-leg landing. RESULTS: A significant main effect was found for environment for knee flexion excursion (P = n.s.). Significant interaction differences were found between environment and groups for vGRF (P = 0.004), knee moment (P < 0.001), knee angle at peak vGRF (P = 0.01) and knee flexion excursion (P = 0.03). There was larger effect of virtual reality environment on knee biomechanics in patients after ACLR compared with controls. CONCLUSION: Patients after ACLR immersed in virtual reality environment demonstrated knee joint biomechanics that approximate those of CTRL. The results of this study indicate that a realistic virtual reality scenario may distract patients after ACLR from conscious motor control. Application of clinically available technology may aid in current rehabilitation programmes to target altered movement patterns after ACLR. LEVEL OF EVIDENCE: Diagnostic study, Level III.

Validation and User Evaluation of a Sensor-Based Method for Detecting Mobility-Related Activities in Older Adults.

Regular physical activity is essential for older adults to stay healthy and independent. However, daily physical activity is generally low among older adults and mainly consists of activities such as standing and shuffling around indoors. Accurate measurement of this low-energy expenditure daily physical activity is crucial for stimulation of activity. The objective of this study was to assess the validity of a necklace-worn sensor-based method for detecting time-on-legs and daily life mobility related postures in older adults. In addition user opinion about the practical use of the sensor was evaluated. Twenty frail and non-frail older adults performed a standardized and free movement protocol in their own home. Results of the sensor-based method were compared to video observation. Sensitivity, specificity and overall agreement of sensor outcomes compared to video observation were calculated. Mobility was assessed based on time-on-legs. Further assessment included the categories standing, sitting, walking and lying. Time-on-legs based sensitivity, specificity and percentage agreement were good to excellent and comparable to laboratory outcomes in other studies. Category-based sensitivity, specificity and overall agreement were moderate to excellent. The necklace-worn sensor is considered an acceptable valid instrument for assessing home-based physical activity based upon time-on-legs in frail and non-frail older adults, but category-based assessment of gait and postures could be further developed.

Controlling horizontal deceleration during gait termination in transfemoral amputees: measurements and simulations.

In this study we investigated how leading limb angles combined with active ankle moments of a sound ankle or passive stiffness of a prosthetic ankle, influence the center of mass (CoM) velocity during the single limb support phase in gait termination. Also, we studied how the trailing limb velocity influences the CoM velocity during this phase. We analyzed force plate data from a group of experienced transfermoral (TF) amputee subjects using a prosthetic limb, and the outcome from a two-dimensional mathematical forward dynamics model. We found that when leading with the sound limb, the subjects came almost to a full stop in the single limb support phase, without the use of the prosthetic limb. When leading with the prosthetic limb, the CoM deceleration was less in a relatively short single limb support phase, with a fast forward swing of the trailing sound limb. Slowing down the heavier trailing sound limb, compared to the prosthetic limb, results in a relatively larger braking force at the end of the swing phase. The simulations showed that only narrow ranges of leading limb angle and ankle moments could be used to achieve the same CoM velocities with the mathematical model as the average start and end velocities of the prosthetic limb user. We conclude that users of prosthetic limbs have a narrow range of options for the dynamics variables to achieve a target CoM velocity. The lack of active control in the passive prosthetic ankle prevents the TF amputee subjects from producing sufficient braking force when terminating gait with the prosthetic limb leading, forcing the subjects to use both limbs as a functional unit, in which the sound limb is mostly responsible for the gait termination.

[Sport performance with a prosthesis]. / Sporten met een prothese.

Technology is a contributory factor to sporting success in many Paralympic sports. This article is about upper and lower limb prostheses that are used in sports. The characteristics of lower limb prosthesis can be modified to respond to predictable leg movements such as with running. Conventional mechanical lower limb prostheses do not respond well to unexpected movements. There are upper limb prostheses that have been adapted for a broad range of sports including fishing, cycling, kayaking, skiing, baseball and even mountain climbing. Techniques are being developed that enable a more natural movement of the prosthesis to occur, such as targeted muscle reinnervation. These techniques are currently still in the experimental stage. The training schedule of the sportsperson must be balanced against his or her tolerance level to avoid mechanical overstrain, not only around the stump but also on the unaffected side. Lower limb prostheses that lead to top sporting successes, such as with running, have resulted in discussions about distorted competition. No upper limb prostheses have led to similar discussions.

Postural control of elderly: moving to predictable and unpredictable targets.

Impaired postural control with muscle weakness is an important predictor of falls within the elderly population.Particular daily activities that require weight shifting in order to be able to reach a specific target (a cup on a table) require continuous adjustments to keep the body's center of mass balanced. In the present study postural control was examined in healthy elderly and young subjects during a task in which subjects had to move the body's center of mass towards a virtual target on a screen that appeared at predictable and unpredictable locations. Postural control decreased with unpredictable targets, e.g. movement time was larger, trajectories more irregular. The results indicate that even though older individuals clearly benefitted from the early release of target location information, young individuals improved even more when target information became available.This indicates that the young were better able to use this information prospectively for executing the target directed movement quickly and accurately.

Stabilizing moments of force on a prosthetic knee during stance in the first steps after gait initiation.

In this study, the occurrences of stabilizing and destabilizing external moments of force on a prosthetic knee during stance, in the first steps after gait initiation, in inexperienced users were investigated. Primary aim was to identify the differences in the external moments during gait initiation with the sound leg leading and the prosthetic leg leading. A prosthetic leg simulator device, with a flexible knee, was used to test able-bodied subject, with no walking aid experience. Inverse dynamics calculations were preformed to calculate the external moments. The subjects learned to control the prosthetic leg within 100 steps, without walking aids, evoking similar patterns of external moments of force during the steps after the gait initiation, either with their sound leg loading or prosthetic leg leading. Critical phases in which a sudden flexion of the knee can occur were found just after heelstrike and just before toe off, in which the external moment of force was close to the internal moment produced by a knee extension aiding spring in the opposite direction.

Principles of obstacle avoidance with a transfemoral prosthetic limb.

In this study, conditions that enable a prosthetic knee flexion strategy in transfemoral amputee subjects during obstacle avoidance were investigated. This study explored the hip torque principle and the static ground principle as object avoidance strategies. A prosthetic limb simulator device was used to study the influence of applied hip torques and static ground friction on the prosthetic foot trajectory. Inverse dynamics were used to calculate the energy produced by the hip joint. A two-dimensional forward dynamics model was used to investigate the relation between obstacle-foot distance and the necessary hip torques utilized during obstacle avoidance. The study showed that a prosthetic knee flexion strategy was facilitated by the use of ground friction and by larger active hip torques. This strategy required more energy produced by the hip compared to a knee extension strategy. We conclude that when an amputee maintains enough distance between the distal tip of the foot and the obstacle during stance, he or she produces sufficiently high, yet feasible, hip torques and uses static ground friction, the amputee satisfies the conditions for enable stepping over an obstacle using a knee flexion strategy.