Transfer and retention effects of gait training with anterior-posterior perturbations to postural responses after medio-lateral gait perturbations in older adults.

BACKGROUND: Gait perturbations, occurring in any direction in daily life, may result in a fall. In fall prevention, gait perturbation training is a promising approach. Treadmill perturbations in anterior-posterior direction can easily be applied by accelerations or decelerations of the belt, but it is unknown whether training effects transfer to reactive recovery in medio-lateral direction. We aimed to evaluate the transfer and retention effects of gait training with treadmill perturbations in anterior-posterior direction to medio-lateral reactive recovery. METHODS: 30 community dwelling older adults (>65 years) participated in this study. They were randomly assigned to a treadmill training session either with 16 anterior-posterior perturbations or with treadmill walking. The assessments contained a walking trial with 4 anterior-posterior and 4 medio-lateral perturbations. Deviations in trunk velocity from unperturbed walking were summed over the first three strides after perturbation as a measure of recovery. FINDINGS: An exposure to gait perturbations during the baseline assessment led to significant improvement of recovery responses. For anterior-posterior perturbations, both groups showed better recovery immediately and 1-week post-intervention, and no group x time interaction was found.. For medio-lateral perturbations, both groups showed better recovery immediately and 1-week post-intervention, and again no group × time interaction. INTERPRETATION: Baseline assessment with perturbations in anterior-posterior and medio-lateral directions caused significant improvements that were retained. Short-term training can be effective in dynamic stabilization of one's trunk, but our findings do not exclude that multi-directional perturbations may be needed.

The validity and usability of an eight marker model for avatar-based biofeedback gait training.

BACKGROUND: Virtual reality presents a platform for therapeutic gaming, and incorporation of immersive biofeedback on gait may enhance outcomes in rehabilitation. Time is limited in therapeutic practice, therefore any potential gait training tool requires a short set up time, while maintaining clinical relevance and accuracy. The aim of this study was to develop, validate, and establish the usability of an avatar-based application for biofeedback-enhanced gait training with minimal set up time. METHODS: A simplified, eight marker model was developed using eight passive markers placed on anatomical landmarks. This allowed for visualisation of avatar-based biofeedback on pelvis kinematics, hip and knee sagittal angles in real-time. Retrospective gait analysis data from typically developing children (n = 41) and children with cerebral palsy (n = 25), were used to validate eight marker model. Gait outcomes were compared to the Human Body Model using statistical parametric mapping. Usability for use in clinical practice was tested in five clinical rehabilitation centers with the system usability score. FINDINGS: Gait outcomes of Human Body Model and eight marker model were comparable, with small differences in gait parameters. The discrepancies between models were <5°, except for knee extension where eight marker model showed significantly less knee extension, especially towards full extension. The application was considered of 'high marginal acceptability' (system usability score, mean 68 (SD 13)). INTERPRETATION: Gait biofeedback can be achieved, to acceptable accuracy for within-session gait training, using an eight marker model. The application may be considered usable and implemented for use in patient populations undergoing gait training.

Gait stability in response to platform, belt, and sensory perturbations in young and older adults.

Perturbation-based gait assessment has been used to quantify gait stability in older adults. However, knowledge on which perturbation type is most suitable to identify poor gait stability is lacking. We evaluated the effects of ipsi- and contra-lateral sway, belt acceleration and deceleration, and visual and auditory perturbations on medio-lateral (ML) and anterior-posterior (AP) margins of stability (MoS) in young and older adults. We aimed to evaluate (1) which perturbation type disturbed the gait pattern substantially, (2) how participants recovered, and (3) whether recovery responses could discriminate between young and older adults. Nine young (25.1 ± 3.4 years) and nine older (70.1 ± 7.6 years) adults walked on the CAREN Extended (Motek BV, The Netherlands). The perturbation effect was quantified by deviation in MoS over six post-perturbation steps compared to baseline walking. Contra-lateral sway and deceleration perturbations resulted in the largest ML (1.9-4 times larger than other types) and AP (1.6-5.6 times larger than other types) perturbation effects, respectively. After both perturbation types, participants increased MoS by taking wider, shorter, and faster steps. No differences between young and older adults were found. We suggest to evaluate the potential of using contra-lateral sway and deceleration perturbations for fall risk identification by including both healthy and frail older adults. Graphical abstract Margins of stability during steady state (left) and perturbed (right) gait to quantify reactive gait stability in response to various perturbation types in young and older adults.

Glenohumeral stability in simulated rotator cuff tears.

Rotator cuff tears disrupt the force balance in the shoulder and the glenohumeral joint in particular, resulting in compromised arm elevation torques. The trade-off between glenohumeral torque and glenohumeral stability is not yet understood. We hypothesize that compensation of lost abduction torque will lead to a superior redirection of the reaction force vector onto the glenoid surface, which will require additional muscle forces to maintain glenohumeral stability. Muscle forces in a single arm position for five combinations of simulated cuff tears were estimated by inverse dynamic simulation (Delft Shoulder and Elbow Model) and compared with muscle forces in the non-injured condition. Each cuff tear condition was simulated both without and with an active modeling constraint for glenohumeral stability, which was defined as the condition in which the glenohumeral reaction force intersects the glenoid surface. For the simulated position an isolated tear of the supraspinatus only increased the effort of the other muscles with 8%, and did not introduce instability. For massive cuff tears beyond the supraspinatus, instability became a prominent factor: the deltoids were not able to fully compensate lost net abduction torque without introducing destabilizing forces; unfavorable abductor muscles (i.e. in the simulated position the subscapularis and the biceps longum) remain to compensate the necessary abduction torque; the teres minor appeared to be of vital importance to maintain glenohumeral stability. Adverse adductor muscle co-contraction is essential to preserve glenohumeral stability.

Pathological muscle activation patterns in patients with massive rotator cuff tears, with and without subacromial anaesthetics.

A mechanical deficit due to a massive rotator cuff tear is generally concurrent to a pain-induced decrease of maximum arm elevation and peak elevation torque. The purpose of this study was to measure shoulder muscle coordination in patients with massive cuff tears, including the effect of subacromial pain suppression. Ten patients, with MRI-proven cuff tears, performed an isometric force task in which they were asked to exert a force in 24 equidistant intervals in a plane perpendicular to the humerus. By means of bi-polar surface electromyography (EMG) the direction of the maximal muscle activation or principal action of six muscles, as well as the external force, were identified prior to, and after subacromial pain suppression. Subacromial lidocaine injection led to a significant reduction of pain and a significant increase in exerted arm force. Prior to the pain suppression, we observed an activation pattern of the arm adductors (pectoralis major pars clavicularis and/or latissimus dorsi and/or teres major) during abduction force delivery in eight patients. In these eight patients, adductor activation was different from the normal adductor activation pattern. Five out of these eight restored this aberrant activity (partly) in one or more adductor muscles after subacromial lidocaine injection. Absence of glenoid directed forces of the supraspinate muscle and compensation for the lost supraspinate abduction torque by the deltoideus leads to destabilizating forces in the glenohumeral joint, with subsequent upward translation of the humeral head and pain. In order to reduce the superior translation force, arm adductors will be co-activated at the cost of arm force and abduction torque. Pain seems to be the key factor in this (avoidance) mechanism, explaining the observed limitations in arm force and limitations in maximum arm elevation in patients suffering subacromial pathologies. Masking this pain may further deteriorate the subacromial tissues as a result of proximal migration of the humeral head and subsequent impingement of subacromial tissues.