The Role of Ligaments in Arm Extension in Feather Stars (Echinodermata: Crinoidea)

It has long been thought that feather star arms flex due to muscular contraction and extend due to an opposing elastic force supplied by the ligaments, however, in 1985, Candia Carnivali and Saita (J. Morph. 185 , 59–74) proposed that extension was due not to elastic ligaments, but to hydraulic pressure within the coelomic canals of the arm. We tested this new proposal experimentally by destroying the coelomic canals along the proximal halves of all ten arms of a feather star and then inducing it to swim. The wave form of the swimming arms was recorded on cine film for frame analysis. While the animal was swimming even the arm regions without coelomic canals were able to extend vigorously. Therefore, hydraulic pressure in the coeloms is not required for arm extension in feather stars. Our results are consistent with the classical idea that elastic ligaments extend the arms of crinoids.     

Mechanical analysis of the sea-urchin lantern: the overall system in Paracentrotus lividus

The dental apparatus or Aristotle's lantern of sea-urchins is a complex system of interacting skeletal ossicles, joints, muscles and ligaments arranged in a rigorous geometry and involved in a variety of activities. In this paper we study the movement of the whole lantern system modelled as a rigid body. The model lantern is constrained at its apex by the peristomial membrane and its movement is controlled by five pairs of antagonistic forces (retractor and protractor muscles). The other main forces applied to the lantern are the elastic reactions of both muscles and ligamental structures (compass depressors and peristomial membrane). The lantern is allowed to perform vertical movements and lateral inclinations but cannot rotate around its main axis. The equilibrium conditions of the system have been found by means of a numerical iterative procedure for solving non-linear equations. The results of the present analysis allow simulation of the overall mechanical activity of the lantern taking into account the experimental data regarding active and passive muscular forces and the tensile constraints due to ligaments.     

Mutual influences of upper and lower extrimities during cyclic movements

The possibility of muscle activation of passive arm during its cyclic movements, imposed by active movements of contralateral arm or by experimenter was studied, as well as the influence of lower extremities cyclic movements onto arm muscles activity. In addition to that the activity of legs muscles was estimated in dependence on motor task condition for arms. Ten healthy supine subjects carried out opposite movements of arms with and without stepping-like movements of both legs. The experiment included three conditions for arm movements: 1) the active movements of both arms; 2) the active movements of one arm, when other entirely passive arm participated in the movement by force; 3) passive arm movement caused by experimenter. In the condition 2) additional load on active arm was applied (30 N and 60 N). In all three conditions the experiment was carried out with arms movements only or together with legs movements. The capability of passive moving arm muscles activation depended on increasing afferent inflow from muscles of contralateral arm was demonstrated. Emerging electrical activity was modulated in the arms movements cycle and depended on the degree of active arm loading. During combined active movements of arms and legs the reduction of activity in the flexor muscles of shoulder and forearm was observed. Concomitant arms movements increased the magnitude ofelectromiographic bursts during passive stepping-like movements in the most of recorded muscles, and the same increasing was only observed in biceps femoris and tibialis anterior muscles during active legs movement. The increasing of loading of one arm caused essential augmentation of EMG-activity in the majority of recording legs muscles. The data obtained are the additional proof of existence of functionally significant neuronal interaction both between arms and between upper and lower extremities, which is evidently depend on the intraspinal neuronal connections.     

Mutual influences of upper and lower extremities during cyclic movements

The possibility for the activation of muscles in a passive arm during its cyclic movements imposed by active movements of the contralateral arm or by an experimenter and the effect that the movements of lower extremities have on the activity of the arm muscles have been studied. In addition, the activity of the leg muscles was studied as dependent on the motor task performed by the arms. Ten healthy subjects performed antiphase arm movements with and without stepping-like movements of both legs in the supine position. The experiment was performed under three conditions for the arm movements: (1) both arms performed active movements; (2) one arm performed active movements, and the contralateral arm, being entirely passive, was forced to participate in movements; (3) the movement of the passive arm was caused by an experimenter. Under condition (2), additional loadings of 30 and 60 N were applied to the active arm. Under all conditions, the arm movements were performed with and without leg movements. The possibility for the activation of muscles in the arm performing passive movements has been demonstrated. To a large extent, this is possible due to an increase in the afferent inflow from the muscles of the contralateral arm. The electrical activity was modulated during cyclic arm movements and depended on the level of loading of the active arm. During the combined active movements of the arms and legs, the reduction in the activity of the flexor muscles of the shoulder and forearm was observed. In the case of passive stepping-like movements, the concomitant arm movements increased the magnitude of electromyographic bursts in most of the examined leg muscles. During active leg movements, a similar increase in electromyographic bursts was observed only in the m. biceps femoris (BF) and the anterior tibial muscle. An increase in the loading of one arm caused a significant increase in the EMG activity in most examined muscles of the legs. The data obtained provide additional proof for the existence of a functionally significant neuronal interaction between the arms, as well as between the upper and lower extremities, which is probably due to intraspinal neuronal connections.     

Abnormalities of mutual influences of the upper and lower limbs after a stroke

The common pattern of muscle activation and specifics of interlimb neuronal connections during the performance of rhythmic separate and simultaneous arm and leg movements in the lying position in healthy subjects, which reflected functionally significant interlimb neuronal interactions, were shown. The study was designed to investigate these mutual influences of the upper and lower limbs during the performance of similar motor tasks by stroke patients. Sixteen poststroke patients with different degrees of hemiparesis performed active and passive arm movements simultaneously with stepping leg movements or without them while lying supine. It was demonstrated that the patients had a disordered common pattern of distribution of muscle activity when they performed voluntary cyclic movements with both arms. Passive movements of both paretic and nonparetic arms led to different degrees of activation of their muscles, depending on the degree of paresis: in patients with mild paresis, muscle activation was similar to that in healthy subjects; in patients with severe paresis, it was insignificant. The loading of the nonparetic arm resulted in an increase in the activity in the paretic arm shoulder flexor muscles in patients with mild paresis (which was typical of healthy subjects), while loading did not influence significantly patients with severe paresis. The combination of cyclic arm movements and stepping leg movements in diagonal synergy decreased the activity in the proximal muscles of both arms, irrespective of the degree of paresis, as it was observed in healthy subjects. Simultaneous arm and leg movements did not change the muscle activity in nonparetic legs in either groups of patients, but the activity in the paretic leg muscles even decreased. The results obtained revealed important features of poststroke motor disturbances, which caused changes in interlimb interactions and largely depended on the degree of paresis. The data could be useful for developing new methods for the performance of rehabilitative procedures in poststroke patients.     

Abnormalities in mutual influences of upper and lower limbs in patients with stroke

Previously, in healthy subjects the common pattern of muscle activation and specifics of interlimb neuron connections during performance of rhythmic separate and simultaneous movements of arms and legs in the lying position, which reflect functional meaningful of interlimb interactions, were shown. The aim of this research was to investigate such mutual influences of upper and lower limbs during the execution of similar motor tasks by patients with stroke. In sixteen poststroke patients with different stage of hemiparesis arms movements together with or without legs movements were performed, while lying supine. It was demonstrated that the common pattern of muscle activity distribution under the execution of voluntary cyclic movements by both arms was disordered. Passive rhythmic movements of each arm caused the phased EMG activity in shoulder muscles in patients with mild hemiparesis, but no activation was observed in patients with severe paresis. The loading of nonparetic arm resulted in an increasing of activity in shoulder flexor muscles of paretic arm in patients with weak paresis (which was typical for healthy subjects), while it not exerted essential influences in patients with severe paresis. Under connecting the cyclic movements of arms with stepping movements of legs in diagonal synergy the activity in proximal muscles of both arms was decreased irrespective of the paresis degree, as it was seeing in healthy subjects. Simultaneous arms and legs movements did not change the muscle activity in non-paretic leg in both groups of patients, but in some muscles of paretic leg the activity even decreased. The results obtained revealed important features of poststroke motor disturbances, which caused the changes of interlimb interaction and in great degree depended on the level of paresis. The data of investigation can be of a great importance for developing the new methods for rehabilitative procedure in patients with stroke.     

Interlimb interactions during cyclic in-phase and antiphase movements of arms and legs and their dependence on afferent influences

Coordinated arm and leg movements imply neural interactions between the rhythmic generators of the upper and lower extremities. In ten healthy subjects in the lying position, activity of the muscles of the upper and lower extremities was recorded during separate and joint cyclic movements of the arms and legs with different phase relationships between the movements of the limbs and under various conditions of the motor task. Antiphase active arm movements were characterized by higher muscle activity than during the inphase mode. The muscle activity during passive arm movements imposed by the experimentalist was significantly lower than muscle activity during passive arm movements imposed by the other arm. When loading one arm, the muscle activity in the other, passively moving, arm increased independently from the synergy of arm movements. During a motor task implementing joint antiphase movements of both upper and lower extremities, compared to a motor task implementing their joint in-phase movements, we observed a significant increase in activity in the biceps brahii muscle, the tibialis anterior muscle, and the biceps femoris muscle. Loading of arms in these motor tasks has been accompanied by increased activity in some leg muscles. An increase in the frequency of rhythmic movements resulted in a significant growth of the muscle activity of the arms and legs during their cooperative movements with a greater rate of rise in the flexor muscle activity of the arms and legs during joint antiphase movements. Thus, both the spatial organization of movements and the type of afferent influences are significant factors of interlimb interactions, which, in turn, determine the type of neural interconnections that are involved in movement regulation.     

Contraction and stiffness changes in collagenous arm ligaments of the stalked crinoid Metacrinus rotundus (Echinodermata)

Shortening and stiffness were measured simultaneously in the aboral ligament of arms of sea lilies. Arm pieces were used from which oral tissues (including muscles) were removed, leaving only collagenous ligaments connecting arm ossicles. Chemical stimulation by means of artificial seawater with an elevated concentration of potassium caused both a bending movement and stiffness changes (either softening or stiffening). The movement lasted for 1.5-10 min, and bent posture was maintained. The observation that contraction was not necessarily associated with softening provided evidence against the hypothesis that the shortening of the aboral ligaments was driven by the elastic components that had been charged by the oral muscles and released their strain energy at the softening of the aboral ligaments. The speed of ligamental shortening was slower by at least one order of magnitude than that of muscles. Acetylcholine (10(-5)-10(-3) M) caused both contraction and softening. We conclude that the aboral ligament shows two mechanical activities based on different mechanisms: one is active contraction and the other is connective tissue catch in which passive mechanical properties show mutability. We suggest that there is neural coordination between the two mechanisms.     

Kinematics and dynamics of the temporomandibular joint and of the movements of the mandible

In order to analyze the complicated movements of the mandible as the open-closing movement and the protrusio are, it is useful to evaluate the basic kinematic principles and reduce them to simple technical constructions. Both the open-closing movement and the protrusio could be reduced to 4-bar links, which were used to simulate the movements with help of a computer. Besides, the polodes and the curves of points in the muscular attachments could be constructed. The 2 entirely different 4-bar links have 3 things in common: The resting system - cranium, the moving system - mandibula, and 1 of the 2 arms connecting these 2 systems - the ligamentum laterale. As this ligament is taut during movements it can be considered a "guiding ligament" representing 1 of the 3 determining components of the mandibular movements. The other of the 2 arms has no anatomical equivalent; this arm, however, is "replaced" by the 2 other determining components of the mandibular movements: the joint and the muscles. The curves, which the Caput mandibulae describes, are practically identical for the open-closing movement and the protrusio despite of the different 4-bar links and these curves exactly correspond to the Discus articularis, taut by the upper part of the M. pterygoideus lateralis. The muscles do not only just move the mandibula, but they are also the component, which can choose between the different mandibular movements. By means of the curves, which points in the muscular attachments describe, the function of the masticatory muscles could be analyzed exactly.     

Nonsomatotopic Organization of the Higher Motor Centers in Octopus

Hyperredundant limbs with a virtually unlimited number of degrees of freedom (DOFs) pose a challenge for both biological and computational systems of motor control. In the flexible arms of the octopus, simplification strategies have evolved to reduce the number of controlled DOFs [1], [2] and [3]. Motor control in the octopus nervous system is hierarchically organized [4] and [5]. A relatively small central brain integrates a huge amount of visual and tactile information from the large optic lobes and the peripheral nervous system of the arms [6], [7], [8] and [9] and issues commands to lower motor centers controlling the elaborated neuromuscular system of the arms. This unique organization raises new questions on the organization of the octopus brain and whether and how it represents the rich movement repertoire. We developed a method of brain microstimulation in freely behaving animals and stimulated the higher motor centers—the basal lobes—thus inducing discrete and complex sets of movements. As stimulation strength increased, complex movements were recruited from basic components shared by different types of movement. We found no stimulation site where movements of a single arm or body part could be elicited. Discrete and complex components have no central topographical organization but are distributed over wide regions.     

Activation of interlimb interactions increases the motor output in legs of healthy subjects: Study under the conditions of arm and leg unloading

The effect of arm movements and movements of individual arm joints on the electrophysiological and kinematic characteristics of voluntary and vibration-triggered stepping-like leg movements was studied under the conditions of horizontal support of the upper and lower limbs. The horizontal support of arms provided a significant increase in the rate of activation of locomotor automatism by noninvasive impact on tonic sensory inputs. The addition of active arm movements during involuntary stepping-like leg movements led to an increase in the EMG activity of hip muscles and was accompanied by an increase in the amplitude of hip and shin movements. The movement of the shoulder joints led to an increase in the activity of hip muscles and was accompanied by an increase in the amplitude of hip and shin movements. Passive arm movements had the same effect on induced leg movements. The movement of the shoulder joints led to an increase in the activity of hip muscles and an increase in the amplitude of movements of knee and hip joints. At the same time, the movement of forearms and wrists had a similar facilitating effect on the physiological and kinematic characteristics of rhythmic stepping-like movements, but influenced the distal segments of legs to a greater extent. Under the conditions of subthreshold vibration of leg muscles, voluntary arm movements led to activation of involuntary rhythmic stepping movements. During voluntary leg movements, the addition of arm movements had a significantly smaller impact on the parameters of rhythmic stepping than during involuntary leg movements. Thus, the simultaneous movements of the upper and lower limbs are an effective method of activation of neural networks connecting the rhythm generators of arms and legs. Under the conditions of arm and leg unloading, the interactions between the cervical and lumbosacral segments of the spinal cord seem to play the major role in the impact of arm movements on the patterns of leg movements. The described methods of activation of interlimb interactions can be used in the rehabilitation of post-stroke patients and patients with spinal cord injuries, Parkinson’s disease, and other neurological diseases.     

The inactivation principle: mathematical solutions minimizing the absolute work and biological implications for the planning of arm movements

An important question in the literature focusing on motor control is to determine which laws drive biological limb movements. This question has prompted numerous investigations analyzing arm movements in both humans and monkeys. Many theories assume that among all possible movements the one actually performed satisfies an optimality criterion. In the framework of optimal control theory, a first approach is to choose a cost function and test whether the proposed model fits with experimental data. A second approach (generally considered as the more difficult) is to infer the cost function from behavioral data. The cost proposed here includes a term called the absolute work of forces, reflecting the mechanical energy expenditure. Contrary to most investigations studying optimality principles of arm movements, this model has the particularity of using a cost function that is not smooth. First, a mathematical theory related to both direct and inverse optimal control approaches is presented. The first theoretical result is the Inactivation Principle, according to which minimizing a term similar to the absolute work implies simultaneous inactivation of agonistic and antagonistic muscles acting on a single joint, near the time of peak velocity. The second theoretical result is that, conversely, the presence of non-smoothness in the cost function is a necessary condition for the existence of such inactivation. Second, during an experimental study, participants were asked to perform fast vertical arm movements with one, two, and three degrees of freedom. Observed trajectories, velocity profiles, and final postures were accurately simulated by the model. In accordance, electromyographic signals showed brief simultaneous inactivation of opposing muscles during movements. Thus, assuming that human movements are optimal with respect to a certain integral cost, the minimization of an absolute-work-like cost is supported by experimental observations. Such types of optimality criteria may be applied to a large range of biological movements.     

Finger Muscle Attachments for an OpenSim Upper-Extremity Model

We determined muscle attachment points for the index, middle, ring and little fingers in an OpenSim upper-extremity model. Attachment points were selected to match both experimentally measured locations and mechanical function (moment arms). Although experimental measurements of finger muscle attachments have been made, models differ from specimens in many respects such as bone segment ratio, joint kinematics and coordinate system. Likewise, moment arms are not available for all intrinsic finger muscles. Therefore, it was necessary to scale and translate muscle attachments from one experimental or model environment to another while preserving mechanical function. We used a two-step process. First, we estimated muscle function by calculating moment arms for all intrinsic and extrinsic muscles using the partial velocity method. Second, optimization using Simulated Annealing and Hooke-Jeeves algorithms found muscle-tendon paths that minimized root mean square (RMS) differences between experimental and modeled moment arms. The partial velocity method resulted in variance accounted for (VAF) between measured and calculated moment arms of 75.5% on average (range from 48.5% to 99.5%) for intrinsic and extrinsic index finger muscles where measured data were available. RMS error between experimental and optimized values was within one standard deviation (S.D) of measured moment arm (mean RMS error = 1.5 mm < measured S.D = 2.5 mm). Validation of both steps of the technique allowed for estimation of muscle attachment points for muscles whose moment arms have not been measured. Differences between modeled and experimentally measured muscle attachments, averaged over all finger joints, were less than 4.9 mm (within 7.1% of the average length of the muscle-tendon paths). The resulting non-proprietary musculoskeletal model of the human fingers could be useful for many applications, including better understanding of complex multi-touch and gestural movements.     

Anticipatory postural adjustments to arm movement reveal complex control of paraspinal muscles in the thorax

Anatomical and empirical data suggest that deep and superficial muscles may have different functions for thoracic spine control. This study investigated thoracic paraspinal muscle activity during anticipatory postural adjustments associated with arm movement. Electromyographic (EMG) recordings were made from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 levels using fine-wire electrodes. Ten healthy participants performed fast unilateral and bilateral flexion and extension arm movements in response to a light. EMG amplitude was measured during 25 ms epochs for 150 ms before and 400 ms after deltoid EMG onset. During arm flexion movements, multifidus and longissimus had two bursts of activity, one burst prior to deltoid and a late burst. With arm extension both muscles were active in a single burst after deltoid onset. There was differential activity with respect to direction of trunk rotation induced by arm movement. Right longissimus was most active with left arm movements and right multifidus was most active with right arm movements. All levels of the thorax responded similarly. We suggest that although thoracic multifidus and longissimus function similarly to control sagittal plane perturbations, these muscles are differentially active with rotational forces on the trunk.     

Influence of Vibration on Motor Responses in the Upper Arm Muscles under Stationary Conditions and during Voluntary and Evoked Arm Movements under Limb Unloading Conditions

Locomotion of mammals, including humans, is based on the rhythmic activity of spinal cord circuitries. The functioning of these circuitries depends on multimodal afferent information and on supraspinal influences from the motor cortex. Using the method of transcranial magnetic stimulation (TMS) of arm muscle areas in the motor cortex, we studied the motor evoked potentials (MEP) in the upper arm muscles in stationary conditions and during voluntary and vibration-evoked arm movements. The study included 13 healthy subjects under arm and leg unloading conditions. In the first series of experiments, with motionless limbs, the effect of vibration of left upper arm muscles on motor responses in these muscles was evaluated. In the second series of experiments, MEP were compared in the same muscles during voluntary and rhythmic movements generated by left arm m. triceps brachii vibration (the right arm was stationary). Motionless left arm vibration led to an increase in MEP values in both vibrated muscle and in most of the non-vibrated muscles. For most target muscles, MEP was greater with voluntary arm movements than with vibration-evoked movements. At the same time, a similar MEP modulation in the cycle of arm movements was observed in the same upper arm muscles during both types of arm movements. TMS of the motor cortex significantly potentiated arm movements generated by vibration, but its effect on voluntary movements was weaker. These results indicate significant differences in the degree of motor cortex involvement in voluntary and evoked arm movements. We suppose that evoked arm movements are largely due to spinal rather than central mechanisms of generation of rhythmic movements.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 1: Theoretical Construction

A three-dimensional model of the knee is developed to study the interactions between the muscles, ligaments, and bones during activity. The geometry of the distal femur, proximal tibia, and patella is based on cadaver data reported for an average-size knee. The shapes of the femoral condyles are represented by high-order polynomials: the tibial plateaux and patellar facets are approximated as flat surfaces. The contacting surfaces of the femur and tibia are modeled as deformable, while those of the femur and patella are assumed to be rigid. Interpenetration of the femur and tibia is taken into account by modeling cartilage as a thin, linear, elastic layer, mounted on rigid bone. Twelve elastic elements describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit modeled as a three-element muscle in series with tendon. The path of each muscle is approximated as a straight line, except where it contacts and wraps around bone and other muscles; changes in muscle paths are taken into account using data obtained from MRI. In the first part of this paper, the model is used to simulate passive knee flexion. Quantitative comparisons of the model results with experimental data reported in the literature indicate that the relative movements of the bones and the geometry of the ligaments and muscles in the model are similar to those evident in the real knee. In Part II, the model is used to describe knee-ligament function during anterior-posterior draw, axial rotation, and isometric knee-extension and knee-flexion exercises.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 1: Theoretical Construct

A three-dimensional model of the knee is developed to study the interactions between the muscles, ligaments, and bones during activity. The geometry of the distal femur, proximal tibia, and patella is based on cadaver data reported for an average-size knee. The shapes of the femoral condyles are represented by high-order polynomials; the tibial plateaux and patellar facets are approximated as flat surfaces. The contacting surfaces of the femur and tibia are modeled as deformable, while those of the femur and patella are assumed to be rigid. Interpenetration of the femur and tibia is taken into account by modeling cartilage as a thin, linear, elastic layer, mounted on rigid bone. Twelve elastic elements describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit modeled as a three-element muscle in series with tendon. The path of each muscle is approximated as a straight line, except where it contacts and wraps around bone and other muscles; changes in muscle paths are taken into account using data obtained from MRI. In the first part of this paper, the model is used to simulate passive knee flexion. Quantitative comparisons of the model results with experimental data reported in the literature indicate that the relative movements of the bones and the geometry of the ligaments and muscles in the model are similar to those evident in the real knee. In Part II, the model is used to describe knee-ligament function during anterior-posterior draw, axial rotation, and isometric knee-extension and knee-flexion exercises.     

Assessment of neuromuscular activation of the upper limbs in children with spastic hemiparetic cerebral palsy during a dynamical task

This study compared the intensity, co-activity and frequency content of the electromyography (EMG) signals recorded bilaterally from six muscles of the upper limbs in children with spastic hemiparetic cerebral palsy (SHCP) and typically developing (TD) children during a bilateral movement. It was found that children with SHCP executed the bimanual circular movement with higher intensities of mean neuromuscular activity in both arms compared to TD children. Furthermore, the movement was performed with longer phases of concentric and eccentric activity in children with SHCP, indicating more co-activation, especially in the more impaired arm. The EMG signals yielded a higher mean power frequency in all the muscles of the more impaired arm and the wrist and elbow flexors of the less impaired arm, which was interpreted as a relatively higher contribution of type II muscle fibres compared to TD children. These observations suggest that in children with SHCP bimanual coordination requires higher neuromuscular activation in the muscles of both arms. Furthermore, SHCP also seems to involve structural changes to the muscle properties, which differ between arms.     

Trunk Muscle Activation at the Initiation and Braking of Bilateral Shoulder Flexion Movements of Different Amplitudes

The aim of this study was to investigate if trunk muscle activation patterns during rapid bilateral shoulder flexions are affected by movement amplitude. Eleven healthy males performed shoulder flexion movements starting from a position with arms along sides (0°) to either 45°, 90° or 180°. EMG was measured bilaterally from transversus abdominis (TrA), obliquus internus (OI) with intra-muscular electrodes, and from rectus abdominis (RA), erector spinae (ES) and deltoideus with surface electrodes. 3D kinematics was recorded and inverse dynamics was used to calculate the reactive linear forces and torque about the shoulders and the linear and angular impulses. The sequencing of trunk muscle onsets at the initiation of arm movements was the same across movement amplitudes with ES as the first muscle activated, followed by TrA, RA and OI. All arm movements induced a flexion angular impulse about the shoulders during acceleration that was reversed during deceleration. Increased movement amplitude led to shortened onset latencies of the abdominal muscles and increased level of activation in TrA and ES. The activation magnitude of TrA was similar in acceleration and deceleration where the other muscles were specific to acceleration or deceleration. The findings show that arm movements need to be standardized when used as a method to evaluate trunk muscle activation patterns and that inclusion of the deceleration of the arms in the analysis allow the study of the relationship between trunk muscle activation and direction of perturbing torque during one and the same arm movement.