Load-lifting Task Research Articles

Time-frequency and ERP analyses of EEG to characterize anticipatory postural adjustments in a bimanual load-lifting task

Anticipatory postural adjustments (APAs) compensate in advance for the destabilizing effect of a movement. This study investigated the specific involvement of each primary motor cortex (M1) during a bimanual load-lifting task in which subjects were required to maintain a stable forearm position during voluntary unloading. Kinematics, electromyographic, and electroencephalographic (EEG) data were recorded in eight right-handed healthy subjects lifting a load placed on their left forearm. Two EEG analyses were performed: a time–frequency (TF) analysis and an event-related potential (ERP) analysis. The TF analysis revealed a mean power decrease in the mu rhythm over the left and right M1 concomitant with lifting onset. Each decrease showed specific features: over the right M1, contralateral to the postural forearm, there was a steeper slope and a greater amplitude than over the left M1. Although a mu rhythm desynchronization has until now been the signature of cortical activity related to a motor component, we show that it can also be related to postural stabilization. We discuss the involvement of the mu rhythm desynchronization over the postural M1 in the high temporal precision enabling efficient APAs. ERP analysis showed a negative wave over the left M1 and a concomitant positive wave over the right M1. While the negative wave classically reflects M1 recruitment related to the forthcoming lifting, the novelty here is that the positive wave reflects the transmission of inhibitory commands toward the postural forearm.

Premovement brain activity in a bimanual load-lifting task

Even the simplest volitional movements must be precisely coordinated with anticipatory postural adjustments. Little is currently known about the neural networks that coordinate these adjustments in healthy adults. We measured brain activity prior to movement during a bimanual load-lifting task, designed to elicit anticipatory adjustments in a restricted and well-defined set of musculature in the arm. Electroencephalography and magnetoencephalography brain measurements were obtained from eleven participants while they performed a bimanual load-lifting task that required precise inter-limb coordination. Anticipatory biceps brachii inhibition in the loaded arm was associated with a robust desynchronization of the beta rhythm. Beamforming analyses localized beta band responses to the parietal lobules, pre- and post-central gyri, middle and medial frontal gyri, basal ganglia and thalamus. The current study shows that premovement brain activity in a bimanual load-lifting task can be imaged with magnetoencephalography. Future experiments will partition out brain activity associated with anticipatory postural adjustments and volitional movements. The experimental paradigm will also be useful in the study of motor function in patients with developmental or degenerative disorders.

Anticipatory postural adjustments in a bimanual load‐lifting task in children with developmental coordination disorder

Postural control is a fundamental component of action in which deficits have been shown to contribute to motor difficulties in children with developmental coordination disorder (DCD). The purpose of this study was to examine anticipatory postural adjustments (APAs) in children with DCD in a bimanual load-lifting task. Sixteen children with reported motor problems (two females, 14 males; mean age 9 y; SD 2 y) and 16 typically developing, age-matched children (six females, 10 males; mean age 9 y; SD 2 y) took part in the study. The task required the children to maintain a stable elbow angle, despite imposed or voluntary unloading of the forearm. APAs were assessed using electromyography and kinematics analysis. Although children with DCD could compensate for the consequences of unloading, the results demonstrated that APAs were less efficient in children with DCD than in typically developing children. A positive and significant coefficient of regression between the flexor inhibition latency and the postural stabilization was only found in typically developing children. The impaired fine-tuning of the muscle contribution and the poor stabilization performances demonstrate poor predictive modelling in DCD.

Effects of local and core body temperature on grip force modulation during movement-induced load force fluctuations

Impaired manual functioning often occurs when the hands are exposed to cold temperatures, but the underlying mechanism is not clearly understood. Tactile feedback is thought to provide important information during object manipulations in order to scale and regulate grip forces; however, topical anaesthetic-induced tactile sensation impairments may not realistically simulate the systemic neuromuscular impairment of the whole hand that could occur during cold temperature exposure. In two experiments, we studied the impact of (1) local hand cooling [thermoneutral finger skin temperature, cold (<8 degrees C)] and (2) core body temperature (thermoneutral core body temperature, pre-heated by 0.5 degrees C, pre-cooled by 0.5 degrees C) with cold hands on manual dexterity and the ability to control and co-ordinate grip forces during a cyclical load-lifting task. In Experiment 1 (n = 10), hand cooling significantly decreased Purdue Pegboard performance (P = 0.002), while increasing grip force by approximately 5 N during the cyclical load-lifting task compared to thermoneutral (P = 0.037). The temporal co-ordination of grip and load forces was unaffected by hand cooling. In Experiment 2 (n = 11), pegboard performance was impaired following hand cooling (P < 0.001), and to a greater extent when the body was pre-cooled (p < 0.001). However, neither grip force (P = 0.99) nor the temporal co-ordination of grasping and lifting forces (P = 0.85) were affected by core body temperature. These data support the existence of a robust centrally controlled feedforward system able to anticipate the dynamics of manual manipulations and accordingly regulate the temporal co-ordination of fingertip forces during object manipulation. This centrally controlled mechanism appears to differ from the mechanisms governing other aspects of manual dexterity.

Anticipatory postural adjustments in a bimanual load-lifting task in children with Duchenne muscular dystrophy

We investigated the consequences of a progressive damage to the muscular system on the organization of anticipatory postural adjustments (APA) in children with Duchenne muscular dystrophy (DMD). We used a bimanual load-lifting task requiring the stabilization of the forearm position despite its voluntary or imposed unloading. Eight children with DMD from 4 to 11 years of age were compared to eight typically developing (TD) children. Elbow angle and multiple surface EMGs were recorded and assessed the use of APA. The muscle weakness did not impair (1) the proprioceptive afference and the motor efference constituting the unloading reflex; and (2) the use of an anticipatory function in children with DMD. However, APA used for the forearm stabilization were less efficient in the group of children with DMD. We conclude that in DMD the muscular weakness could be a restraint to the efficiency of APA with respect to TD children.

Impairment of a cortical event-related desynchronisation during a bimanual load-lifting task in children with autistic disorder

In autism, the abilities of communication are affected, associated with abnormalities of cognitive, sensorial and motor development. In a previous study based on a load-lifting task, we showed impairment of anticipation in children with autism as evidenced by kinematics and eletromyographic recordings [Neurosci. Lett. 348 (2003) 17]. In the present study, we assessed the cortical counterparts of the use of anticipatory postural adjustments in a group of control children and in a group of children with autism. The tasks required maintaining a stable forearm position despite imposed or voluntary lifting of an object placed either on the controlateral forearm or on a support. We investigated the differences between the two groups of children on the Event-Related Desynchronisation (ERD) which precedes movement onset in adults [Electroencephalogr. Clin. Neurophysiol. 46 (1979) 138]. Electroencephalogram (EEG) power evolution of a 6–8-Hz frequency band was averaged before and after imposed or voluntary movement onset. EEG reactivity of control and autistic children did not differ during the imposed unloading condition, but significant differences appeared in the voluntary unloading situations. Before lifting the object, control children showed an ERD above the left motor areas. An ERD also occurred above the right motor areas when the object was placed on their forearm. This indicates that the ERD can also translate the use of anticipatory postural adjustments. By contrast, children with autism did not show an ERD in the two voluntary situations. This suggests a central deficit of anticipation in both postural and motor control in children with autism.

Motor control and children with autism: deficit of anticipatory function?

This study aims at investigating how do anticipatory postural adjustments develop in children with autism, during a bimanual load-lifting task that required maintaining the stabilisation of the forearm despite imposed or voluntary unloading. Elbow angle and electromyographic were recorded on the child forearm supporting the load. The forearm stabilisation was as good in children with autism as in the control group. However, in children with autism, the latencies for both kinematics and muscular events indicated an increase of the duration of unloading. These results indicate the use of a feedback rather than a feed-forward mode of control. Impairments in both the building of internal representations and the mastering of timing parameters, could explain the deficient postural anticipation reported in children with autism.

Developmental sequence in the acquisition of anticipation during a new co-ordination in a bimanual load-lifting task in children

The aim of this experiment was to test the capacity of children to develop anticipation at various stages of their growth. We studied the learning process of an artificial co-ordination by means of a procedure of double unloading in two groups of children, and a group of adults. Elbow-joint angle measurement was used to assess for the improvement of the forearm stabilization through the six learning sessions. The main results report a developmental sequence of the acquisition of anticipatory postural adjustments (APA) similar to the one established for the ontogenesis of APA. A difference in learning dynamics, but also in the final level of performance, is reported between children aged 5–6 and children aged 7–8 years. The improvement occurring at the age of 7 years probably indicates maturation of internal representations, favourable to the faster setting up of operational anticipated control.

Building anticipatory postural adjustment during childhood: a kinematic and electromyographic analysis of unloading in children from 4 to 8 years of age.

The present study addressed the question of how do anticipatory postural adjustments (APA) develop during childhood, in the range from 4 to 8 years, during a bimanual load-lifting task. This task required maintaining the stabilisation of the forearm position despite imposed or voluntary unloading of the forearm. Elbow angle and multiple surface EMG were recorded on the child postural forearm supporting a load. During voluntary unloading, the elbow flexion of the postural forearm was calculated as a percentage of the elbow flexion measured during the imposed situation. Improvement of the forearm stabilisation was observed mainly between 4--6 and 7--8 years of age, but the oldest children did not reach the adult level of stabilisation of the postural forearm. Moreover, a clear developmental sequence in the acquisition of APA was reported: first the selection of an efficient EMG pattern underlying the forearm stabilisation, and second the mastering of timing adjustments. In fact, regression of the co-contraction pattern was observed with age, together with selection of the adult-like reciprocal pattern. Mastering of the timing adjustments of the reciprocal pattern, characterised in adults by a well-synchronised co-ordination between onset of the flexor muscle contraction of the manual arm and onset of the flexor muscle inhibition of the postural forearm, progressively improves during development. Moreover, these results suggest that the internal representation of the consequences of unloading on the forearm stabilisation, underlying anticipatory function during a bimanual co-ordination task, slowly build up during childhood.

Acquisition of anticipatory postural adjustments in a bimanual load-lifting task: normal and pathological aspects.

Anticipatory adjustments of forearm posture are associated with a voluntary load-lifting movement in bimanual load-lifting tasks. Three aspects of these adjustments are analyzed: their goal, their central organization, and their acquisition. The goal of the anticipatory adjustment in this task is to minimize the perturbation of forearm posture that occurs during unloading. The central organization is based on two parallel controls responsible, respectively, for the lifting movement of the moving forearm and the anticipatory postural adjustment of the postural forearm, their coordination depending on a central timing signal. The acquisition of the anticipatory postural adjustment was tested using a paradigm where the voluntary movement performed by one hand triggered, via an electronic switch, the load release of the postural forearm. It was achieved after 40-60 trials and was not graded as a function of the voluntary movement parameters, but of the disturbance of the postural arm about to occur. The learned anticipation was not transferred when, after a first acquisition session with one forearm as the postural forearm, a second learning session was performed with the other forearm as the postural forearm. The acquisition was tested in Parkinsonian and in hemiparetic patients with capsular lesion. The highest acquisition deficit was observed in hemiparetic patients, when the contralateral forearm was the postural forearm; the deficit was less important when the ipsilateral arm was postural. Surprisingly, the anticipatory postural adjustments in hemiparetic patients were rather well preserved when the natural load-lifting task was tested. These results suggest that the basal-ganglia SMA circuit and M1 premotor areas are important in the acquisition process.

Development of anticipatory postural adjustments in a bimanual load-lifting task in children.

Anticipatory postural adjustments (APA) are needed to perform a movement without perturbing posture. We investigated the development of APA in 3- to 4-year-old children during a bimanual load-lifting task. The task required maintaining a stable elbow position despite imposed or voluntary unloading of the forearm. Although children can compensate the consequences of unloading by using APA, their performance did not reach an adults' level. In addition, children showed high intra-individual variability in the voluntary situation, revealed by the coexistence of both adult-like and immature patterns in kinematic and electromyographic data. In conclusion, the present study reports that APA, associated with a bimanual load-lifting task, are still being set up in 3- to 4-year-old-children. The intra-individual variability should decrease with age and be associated with a progressive mastering of the timing parameters characterizing APA.

Multiple correspondence analysis of biomechanical signals characterized through fuzzy histograms

Data characterizing is considered the first and main stage of the statistical analysis. Rather than characterizing each biomechanical signal through one or few global indicators, such as the mean or the root mean square, this paper suggests first to cut the scale into several fuzzy windows and to summarize the data within each window through an occurrence indicator. These indicators become the analysis variables. They can be analyzed through the multiple correspondence analysis, which shows the most discriminant variables, connections between them, empirical situation classes and correspondences between these classes and the most discriminant variables. An example is considered for arguing our point of view; it concerns characterizing and analysis of forces situated at the hand, foot and back level in a load lifting task.

Coordination between posture and movement in a bimanual load-lifting task: is there a transfer?

The present experimental series was designed to test the possibility that an anticipatory postural adjustment learned during the performance of a bimanual load lifting task may be transferred between the upper extremities. Eight seated subjects were asked to maintain horizontally one forearm (postural arm) loaded with a 1-kg load, which was fixed to the arm by means of an electromagnet. The unloading was triggered either by the experimenter pressing a switch (control) or by the subjects making a voluntary movement with their other arm (moving arm). In the latter case, the subject lifted a 1-kg load resting on a force platform with the moving hand, and the switching off was triggered when the force level reached a threshold of 0.5 kg. The maximum amplitude (MA) and the maximum velocity (MV) of the postural forearm elbow joint rotation occurring after the unloading were measured at each trial. The learning process was estimated by performing a regression analysis on each series of trials, using an exponential model, and from the intercept of the regression curve with the ordinate. 1. During the original learning session (three series of 20 trials), a decrease in MA and MV was found to occur both within the series and between the series during a session. 2. After the initial learning session, the sides of the postural and moving arm were interchanged to test whether any transfer had occurred. The first series of trials in the second session (transfer) and the last series of trials in the original learning session were compared and found to be significantly different in terms of the intercept (seven subjects in the case of MA, five subjects in the case of MV) and the slope (five subjects), indicating a lack of transfer. 3. The data recorded during the second transfer learning session indicated that learning occurred in all eight subjects in the case of MA and in six subjects in the case of MV. It was observed that the original learning session did not facilitate the second one. 4. The lack of transfer of the anticipatory postural adjustment observed in this task is discussed with reference to the data in the literature.

Postural effects on biomechanical and psychophysical weight-lifting limits

Many believe that biomechanical models and data are not sufficiently refined and validated to be used as the basis for setting 'safe' population load lifting limits. Rather, they advocate that such limits should be based on what a sample of the population demonstrate to be 'maximum acceptable weight limits' (MAWL) resulting from psychophysical tests performed with different populations. Yet, biomechanical models are becoming more robust and valid. Computerized versions of these models are readily available, and these models now can provide a more complete understanding of the pathophysiology of a person's spinal column and supporting structures, thereby providing a means to predict the risk of tissue trauma in given lifting situations for large size populations. NIOSH has recognized the validity of both biomechanics and psychophysics for establishing a Recommended Weight Limit (RWL) in the United States. The implications of using both types of methods and data are explored in this paper. Three case studies are presented that involve infrequent lifting of varied size boxes from near floor level to explore how MAWL and biomechanically determined limits differ. The cases include symmetric, sagittal plane lifting using a freestyle posture, a similar lift but with freestyle and squat lift postures, and an asymmetric load lifting task. In all three case comparisons it is shown that a recommended load to be lifted based solely on a spinal disc compression force tolerance of 3400 N would be much lower than published MAWL values representing 75% or even 90% of young males under 40 years old (i.e. MAWL values may not be protective of some young males). It also is shown that MAWL values do not have as much population variance as the spinal motion segment failure values. Hence, many younger males would be expected to have spinal columns that can tolerate the highest published MAWL values. Several mitigating factors, including load lifting trajectories, lifting dynamics, and biomechanical modeling limitations are discussed, as well as differences in compressive force tolerances and MAWLs associated with age and gender.

Coordination between posture and movement in a bimanual load lifting task: putative role of a medial frontal region including the supplementary motor area.

The aim of the present experimental series was to investigate the role of the medial frontal region including the supplementary motor area in the coordination between posture and movement in a bimanual load lifting task. The seated subject was instructed to maintain in a horizontal position one forearm (postural arm) which was loaded with a 1 kg weight. The unloading was performed either by the experimenter (imposed unloading) or by a voluntary movement of the other arm (voluntary unloading). In normal individuals, with the voluntary unloading, the movement control was accompanied by an anticipatory adjustment of the postural forearm flexor activity, which resulted in the maintenance of the forearm position despite the unloading. The anticipatory postural adjustments were impaired in 4 out of 5 patients with unilateral lesion of the SMA region; the defect was observed mainly when the postural forearm was contralateral to the lesion. No change in the anticipatory postural adjustment was observed in one patient with complete callosal section. This finding indicates that the coordination between the posture and movement in this task is not organized through callosal fibers linking the cortices on both sides but rather at a subcortical level. The anticipatory postural adjustments were abolished in two patients with spastic hemiparesis when the postural forearm was the spastic arm. It is suggested that the SMA region contralateral to the postural forearm, together with other premotor or motor areas, may select the circuits responsible for the phasic postural adjustments which are necessary to ensure postural maintenance, whereas the motor cortex contralateral to the voluntary movement controls both the movement and, via collaterals, the preselected circuits responsible for the associated postural adjustments.

Acquisition of co-ordination between posture and movement in a bimanual task.

The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the experimenter (control) or by the subject voluntarily moving the other arm. In the latter case, the movement involved the elbow joint (load lifting (A), isometric force change at the wrist level (B), elbow rotation (C) and pressing a button with the wrist (D] or the fingers (grip isometric force change). We recorded the maximal amplitude and maximal velocity of the rotation of the postural forearm, the EMG of the forearm flexors on both sides and the force exerted either by the load on the postural arm or by the isometric contraction of the moving arm. The maximal forearm angular velocity after unloading was known to be related to the level of muscle contraction before unloading. 1. In the control situation, repetition of the imposed unloading test resulted in a progressive reduction in the maximal forearm rotation without any decrease in the maximal velocity. The amplitude and duration of the unloading reflex were found to increase in parallel. These results suggest that an adaptive mechanism took place which increased the gain of the unloading reflex loop and reduced the mechanical effect of the perturbation. This mechanism was found to come into play not only in the control situation but also in other paradigms where the perturbation was expected by the subjects. 2. A decrease in both maximal amplitude and velocity of forearm rotation together with a weak "anticipatory" deactivation of the forearm postural flexors was observed when the unloading was caused by an elbow movement (situations A, B, C) which indicates that a feedforward postural control took place. An interlimb coordination was built up and stabilized after 40-60 trials. Pressing a button with the wrist (weak force and displacement) was a less effective means of inducing an anticipatory control of the flexors of the postural forearm, which indicates that the intensity of the central control plays a role in the building up of the coordination. 3. A distal grip action exerting either weak (100 g) or a high (1 kg) force was able to reduce the maximal amplitude of the forearm rotation, but not the maximal velocity, which indicates that an improved reflex action takes place, but not a feedforward anticipatory postural control.(ABSTRACT TRUNCATED AT 400 WORDS)

Performance of a bimanual load-lifting task by parkinsonian patients.

Normal subjects and Parkinsonian patients performed a bimanual load lifting task. In this task, one "postural" forearm, held in a horizontal position while supporting a 1 kg weight, was unloaded either by the experimenter's hand (imposed unloading) or by the subject's other hand in response to a tone burst (voluntary unloading). The variables recorded were reaction time (RT: time interval between the tone and beginning of unloading) and movement time (MT: duration of the change in force measured by a force platform on the "postural" forearm). Elbow angle changes were also measured with a potentiometer. The EMG activity from brachioradialis of the "postural" arm and that from the biceps of the "active" arm were recorded. The Parkinsonian patients showed an increase in both RT and MT and an impairment of the co-ordination between movement and posture which was reflected in an increase in amplitude of the elbow rotation after voluntary unloading. Moreover, the decrease in EMG activity in the brachioradialis of the postural arm during unloading was less in Parkinsonian patients than in the normal group. This disorder of postural command was often accompanied by a lack of anticipatory EMG changes. Comparison between treated and non-treated patients showed that dopamine agonists brought about recovery of both RT and MT but did not improve postural co-ordination. The co-ordination was less impaired when the voluntary unloading was performed by the preferred hand. Several hypotheses are discussed concerning the mechanism underlying this impaired co-ordination.