FUNCTIONAL ROLE OF PROPRIOCEPTIVE FEEDBACK IN BALANCE AND IN REACTIVE MOVEMENT

Human movement is generated either by internal muscle forces, or by external forces that are attached to the body system. Most of our muscles act via lever arms on the bone system, thus generating rotational forces that produce consequently torques and joint moments. Therefore, studies dealing with control strategies of joint moments to achieve a desired movement or an intended task are addressing one of the most interesting topics. In several papers the constraints and relative importance of sensory feedback are investigated. It seems that in a given task a complex interaction of feed-forward- and feed-back-mechanisms adjust the actual joint stiffness. By means of the H-reflex methodology, the spinal excitability for muscles can be determined. Under selective conditions, the inhibitory or facilitatory behavior of spinal reflex contribution can be investigated. Quite recently, the transcranial magnetic stimulation (TMS) has been developed to assess corticospinal excitability during human movement. Selective stimulation of the neurons in the motor cortex allows the determination of the relative contribution of corticospinal activation during movement. Application of both techniques, H-reflex and TMS, allows differentiation of spinally and centrally organized muscle activation. The present paper highlights recent findings about neuromuscular control in balance and stretch-shortening cycle movements and reflects adaptations induced by balance training. For both type of movements, the stiffness properties of the involved joint complexes are modulated by spinal and central modulation of the neuromuscular activation. Training adjusts/adapts this motor control specifically for balance tasks and for reactive movements. Longitudinal training studies in which postural control (balance training) was exercised showed that the spinal and the cortical contributions were reduced after the training. Thus it was assumed that motor control was shifted towards supraspinal centers (Taube et al. 2007). From stretch shortening cycle (SSC) it is known that high muscular stiffness is a prerequisite to enable proper performances and that feed-forward activation of the extensor muscles prior to ground contact is modulated by effective stretch reflex contributions (feed-back activation). This modulation, however, is largely dependent on the individual stretch load tolerance of the neuromuscular system. Recent results indicate that the “stereotyped” reflexes are much more modulated than expected previously. It has been shown that modulation of spinal circuitry is achieved by presynaptic inhibition

MOTION OF THE BOW DURING AIMING AND RELEASING THE SHOT

The range of motion of a recurve bow during aiming and releasing the shot is very small. Thus on-target-trajectories are used. To measure the on-target-trajectories of bows a system originally designed for gun shooting was modified. The system can be fitted onto the archer’s personal bow. 15 highly skilled archers of the German National Teams of women and men participated in the study. Two intraindividual typical strategies of aiming were found: 11 archers try to hold the aim on sight for at least 2 seconds whereas 4 archers tend to “slide” on the target and release the shot at once when the target is on sight. For 14 of 15 archers the “hold boxes” disclose an asymmetry in aiming: The horizontal magnitude of the hold box is larger than the vertical dimension. From release to when the arrow leaves the string, the right handed archers tend to move to the left and the left handed archers tend to move right

IN VIVO EVALUATION OF ANKLE LIGAMENT FORCES USING A FIBER OPTIC TRANSDUCER

INTRODUCTION: Successful injury prevention, treatment and rehabilitation require a clear understanding of ligament function and forces acting on these ligaments, especially for injuries to the lateral ankle ligaments, which are very common in many kinds of sports. Several authors (Bahr et al. 1998; Renström, et al., 1988; Sauer et al., 1978) investigated forces or tensile strength of the ligament talofibulare anterior (LTFA) in vitro. There is, however, a lack of information of investigations with direct measurement of forces in this structure. The aim of this study was to apply a fiber optic transducer in vivo in order to register forces in the LTFA during different natural movements of the ankle joint under varied load conditions

PREVENTIVE ANKLE TAPING -EVALUATION OF MECHANICAL, NEUROMUSCULAR AND THERMAL EFFECTS BEFORE AND AFTER EXERCISE

INTRODUCTION: . Athletes and coaches in different sport disciplines use preventive adhesive tape or bandages in order to avoid ankle sprains since Paul Beiersdorf has invented tape about 100 years ago. Many authors tried to evaluate the main effects of taping in respect to its mechanical support to the ankle joint and its preventive effect concerning injuries in high risk sports like basketball, football, athletics or gymnastics. Clinical studies have shown that ankle taping reduces the risk of injury although it has been demonstrated that the mechanical support does decrease even after a few minutes of practise. The aim of the study was to investigate the mechanical as well as the neuromuscular influence of different tape materials and techniques before and after exercise. Method: 12 subjects underwent different trials in a randomized order with two materials (B,C) and two taping techniques (D,E) and without tape (A). This sense of exercises were used to stress the ankle: 5 Drop jumps (36 cm Height) 10 minutes running (tread mill) 3 minutes jumping using a special “jump-device” with slope surfaces ( increased inversion/eversion and dorsal/plantar flexion during the landing phase). The course was performed two times. The main test was the simulated ankle inversion injury by using a special tilt device to apply randomized ankle movements (300 inversion + 150 Plantarflexion) while the subject is standing on the tilt platform. Magnitude and velocity of ankle joint motion was recorded from 2axial goniometers (Penny&Giles). EMG activity was measured from the mm. peroneus 1., tibialis a., gastrocnemius and vastus medialis. Skin temperature alterations beneath the adhesive tape were recorded after each exercise by thermocouples with an accuracy of 0.1 K. RESULTS: Amplitude and velocity (relative to value without tape) of simulated inversion injury was initially reduced by all tapes significantly: Inversion angle relativ to the trial without tapeJA): If no tape was used then EMG -activity during simulation was reduced up to 12% after 20 minutes of exercise. If the ankle was taped -the EMG reduction after 20 minutes was at a lower level ( 5%). Skin temperature under the tape increased significantly compared to untaped ankle. DISCUSSION: The preventive effect of adhesive taping is achieved at the intitial exercise phase by the mechanical stabilization properties of the material. In the later exercise phase (when the mechanical support decreases) the risc of injury could be reduced by the proprioceptive effect, which can be concluded by the increased EMG-activities. REFERENCES: Fumich, R. M., et al. The measured effect of taping on combined foot and ankle motion before and after exercise. AMJSM, 9(1981):165-170

IN VITRO AND IN VIVO DETERMINATION OF ANKLE JOINT AND SUBTALAR JOINT AXES USING THE HELICAL AXIS METHOD

INTRODUCTION: In the kinematic analysis of most human joints continuous motion can be simulated by a sequence of finite motion steps of one part of the joint relative to the other part. In previous studies different experimental setups were used in vitro to determine the subtalar joint axis (talo- alcaneo-navicularaxis), and great variability could be shown for both orientation and position. The orientation of the axis can be described as a projection to anatomical planes in terms of deviation – that is, the projection to the transversal plane and as an inclination that is the projection to the sagittal plane. The study objective was to verify the application of the helical axis method to the ankle and subtalar joint in vitro and to transform the method for in vivo investigations. METHODS: In vitro: one fresh frozen ankle specimen was thawed preexperimentally and then fixed in a laboratory frame. The lower leg was fixed about 15 cm proximal to the ankle joint. In the first series we used stereo photogrammetry to determine optimal marker positions. In a second series with ankle, 2 specimen’s stress x-rays were used to compare talar tilt and the helical axis. In vivo: the marker system was fixed to the tibia using adhesive double- sided tape and with a special shoe construction to fix it to the calcaneus. 3D calculation of marker coordinates in finite positions were performed from a four-camera setup using the Peak Performance® system. Twelve subjects were tested in sitting position without foot-ground contact. They moved their feet from a neutral position into dorsiflexion and (while maintaining dorsiflexion) to eversion and inversion position. RESULTS: The in vitro investigation revealed a mean deviation from repeated measurements of 10.6 degrees (± 4.6) and an inclination of 45.7 (± 5.6). The correlation of x-ray talar tilt with the helical axis method was r = 0.86 for the intact joint and 0.9 with ankle joint ligaments cut. From 12 subjects a mean deviation of 23 (± 13) and an inclination of 46 (± 10) were calculated. The correlation of deviation and inclination was r = 0.8. DISCUSSION: This method is applicable to determine subtalar joint axis in vivo. However, the parameters are highly susceptible to measurement errors and noise. The mean results were in accord with previous studies, but the differences among subjects were remarkable. From the correlation of the angles and the relationship of the axis to the other ankle joint stabilizing structures (muscles, tendons) one could conclude that this complex may play an important role with respect to sudden inversion injuries CONCLUSION:. If the axis of the subtalar joint could be identified as risk factor to ankle sprains then in vivo determination of the axis could be used for prevention

Editorial: Neuromechanics in Movement and Disease With Physiological and Pathophysiological Implications: From Fundamental Experiments to Bio-Inspired Technologies.

SCOPUS: ed.jinfo:eu-repo/semantics/publishe

Optimization of Muscle Activity for Task-Level Goals Predicts Complex Changes in Limb Forces across Biomechanical Contexts

Optimality principles have been proposed as a general framework for understanding motor control in animals and humans largely based on their ability to predict general features movement in idealized motor tasks. However, generalizing these concepts past proof-of-principle to understand the neuromechanical transformation from task-level control to detailed execution-level muscle activity and forces during behaviorally-relevant motor tasks has proved difficult. In an unrestrained balance task in cats, we demonstrate that achieving task-level constraints center of mass forces and moments while minimizing control effort predicts detailed patterns of muscle activity and ground reaction forces in an anatomically-realistic musculoskeletal model. Whereas optimization is typically used to resolve redundancy at a single level of the motor hierarchy, we simultaneously resolved redundancy across both muscles and limbs and directly compared predictions to experimental measures across multiple perturbation directions that elicit different intra- and interlimb coordination patterns. Further, although some candidate task-level variables and cost functions generated indistinguishable predictions in a single biomechanical context, we identified a common optimization framework that could predict up to 48 experimental conditions per animal (n = 3) across both perturbation directions and different biomechanical contexts created by altering animals' postural configuration. Predictions were further improved by imposing experimentally-derived muscle synergy constraints, suggesting additional task variables or costs that may be relevant to the neural control of balance. These results suggested that reduced-dimension neural control mechanisms such as muscle synergies can achieve similar kinetics to the optimal solution, but with increased control effort (≈2×) compared to individual muscle control. Our results are consistent with the idea that hierarchical, task-level neural control mechanisms previously associated with voluntary tasks may also be used in automatic brainstem-mediated pathways for balance

Effects and moderators of exercise on quality of life and physical function in patients with cancer:An individual patient data meta-analysis of 34 RCTs

This individual patient data meta-analysis aimed to evaluate the effects of exercise on quality of life (QoL) and physical function (PF) in patients with cancer, and to identify moderator effects of demographic (age, sex, marital status, education), clinical (body mass index, cancer type, presence of metastasis), intervention-related (intervention timing, delivery mode and duration, and type of control group), and exercise-related (exercise frequency, intensity, type, time) characteristics. Relevant published and unpublished studies were identified in September 2012 via PubMed, EMBASE, PsycINFO, and CINAHL, reference checking and personal communications. Principle investigators of all 69 eligible trials were requested to share IPD from their study. IPD from 34 randomised controlled trials (n=4,519 patients) that evaluated the effects of exercise compared to a usual care, wait-list or attention control group on QoL and PF in adult patients with cancer were retrieved and pooled. Linear mixed-effect models were used to evaluate the effects of the exercise on post-intervention outcome values (z-score) adjusting for baseline values. Moderator effects were studies by testing interactions. Exercise significantly improved QoL (β=0.15, 95%CI=0.10;0.20) and PF (β=0.18,95%CI=0.13;0.23). The effects were not moderated by demographic, clinical or exercise characteristics. Effects on QoL (βdifference_in_effect=0.13, 95%CI=0.03;0.22) and PF (βdifference_in_effect=0.10, 95%CI=0.01;0.20) were significantly larger for supervised than unsupervised interventions. In conclusion, exercise, and particularly supervised exercise, effectively improves QoL and PF in patients with cancer with different demographic and clinical characteristics during and following treatment. Although effect sizes are small, there is consistent empirical evidence to support implementation of exercise as part of cancer care

The effect of whole body vibration on the H-reflex, the stretch reflex, and the short-latency response during hopping

The effect of whole body vibration (WBV) on reflex responses is controversially discussed in the literature. In this study, three different modalities of reflex activation with increased motor complexity have been selected to clarify the effects of acute WBV on reflex activation: (1) the electrically evoked H-reflex, (2) the mechanically elicited stretch reflex, and (3) the short-latency response (SLR) during hopping. WBV- induced changes of the H-reflex, the stretch reflex, and the SLR during hopping were recorded in the soleus and gastrocnemius muscles and were analyzed before, during (only the H-reflex), immediately after, 5 min and 10 min after WBV. The main findings were that (1) the H-reflexes were significantly reduced during and at least up to 5 min after WBV, (2) the stretch reflex amplitudes were also significantly reduced immediately after WBV but recovered to their initial amplitudes within 5 min, and (3) the SLR during hopping showed no vibration-induced modulation. With regard to the modalities with low motor complexities, the decreased H- and stretch reflex responses are assumed to point toward a reduced Ia afferent transmission during and after WBV. However, it is assumed that during hopping, the suppression of reflex sensitivity is compensated by facilitatory mechanisms in this complex motor task