Load-lifting Task Research Articles

A Framework for Modeling, Optimization, and Musculoskeletal Simulation of an Elbow–Wrist Exosuit

The light weight and compliance of exosuits are valuable benefits not present rigid exoskeleton devices, yet these intriguing features make it challenging to properly model and simulate their interaction with the musculoskeletal system. Tendon-driven exosuits adopt an electrical motor combined with pulleys and cable transmission in the actuation stage. An important aspect of the design of these systems for the load transfer efficacy and comfort of the user is the anchor point positioning. In this paper, we propose a framework, whose first purpose is as a design methodology for the synthesis of an exosuit device, achieved by optimizing the anchor point location. The optimization procedure finds the best 3D position of the anchor points based on the interaction forces between the exosuit and the upper arm. The computation of the forces is based on the combination of a mathematical model of a wrist–elbow exosuit and a dynamic model of the upper arm. Its second purpose is the simulation of the kinematic and physiological effects of the interaction between the arm, the exosuit, and the complex upper limb musculoskeletal system. It offers insights into muscular and exoskeleton loading during operation. The presented experiments involve the development and validation of personalized musculoskeletal models, with kinematic, anthropometric, and electromyographic data measured in a load-lifting task. Simulation of the exosuit operation—coupled with the musculoskeletal model—showed the efficacy of the suit in assisting the wrist and elbow muscles and provided interesting highlights about the impact of the assistance on shoulder muscles. Finally, we provide a possible design of an elbow and wrist exosuit based on the optimized results.

Mechanomyographic Analysis for Muscle Activity Assessment during a Load-Lifting Task.

The purpose of this study was to compare electromyographic (EMG) with mechanomyographic (MMG) recordings during isometric conditions, and during a simulated load-lifting task. Twenty-two males (age: 25.5 ± 5.3 years) first performed maximal voluntary contractions (MVC) and submaximal isometric contractions of upper limb muscles at 25%, 50% and 75% MVC. Participants then executed repetitions of a functional activity simulating a load-lifting task above shoulder level, at 25%, 50% and 75% of their maximum activity (based on MVC). The low-frequency part of the accelerometer signal (<5 Hz) was used to segment the six phases of the motion. EMG and MMG were both recorded during the entire experimental procedure. Root mean square (RMS) and mean power frequency (MPF) were selected as signal extraction features. During isometric contractions, EMG and MMG exhibited similar repeatability scores. They also shared similar RMS vs. force relationship, with RMS increasing to 75% MVC and plateauing to 100%. MPF decreased with increasing force to 75% MVC. In dynamic condition, RMSMMG exhibited higher sensitivity to changes in load than RMSEMG. These results confirm the feasibility of MMG measurements to be used during functional activities outside the laboratory. It opens new perspectives for future applications in sports science, ergonomics and human-machine interface conception.

Robot Formation Performing a Collaborative Load Transport and Delivery Task by Using Lifting Electromagnets

This paper presents a practical validation of a heterogeneous formation of mobile robots in performing a load lifting, transportation, and delivery task. Assuming that an unmanned ground vehicle (UGV) is unable to perform a mission by itself due to the presence of an obstacle in the navigation route, an unmanned aerial vehicle (UAV) is then assigned to lift the cargo over this UGV, transport the obstacle, and deliver over another UGV. The UAV uses an electromagnetic actuator supported by a cable to pick up the load, the mass of which is 32% of that of the UAV. Experimental results demonstrate that the developed system is capable of performing cargo transport missions and can be scalable for applications such as package delivery in urban or remote areas and supply delivery in conflict or disaster zones.

Comparison of the Dynamic Postural Control During Lifting and Lowering an External Load in Low Back Pain: A Cross-Sectional Study

ObjectiveThis study aimed to compare dynamic postural control between individuals with and without chronic low back pain (LBP) through load lifting and lowering. MethodsThis cross-sectional study included 52 male patients with chronic LBP (age: 33.37 ± 9.23 years) and 20 healthy male individuals (age: 31.75 ± 7.43 years). The postural control parameters were measured using a force plate system. The participants were instructed to stand barefoot (hip-width apart) on the force plate and lift a box (10% of the weight of the participants) from the waist height to overhead and then lower it from overhead to waist height. The interaction between the groups and tasks was determined using a 2-way repeated-measures analysis of variance. ResultsThere was no significant interaction between the groups and tasks. Regardless of the groups, postural control parameters including amplitude (P = .001) and velocity (P < .001) in anterior-posterior (AP) direction, phase plane in medial-lateral (ML) direction (P = .001), phase plane in AP-ML direction (P = .001), and the mean total velocity (P < .001) were lesser during the lowering compared with lifting. The results indicated that, regardless of the tasks, the postural control parameters including velocity (P = .004) and phase plane in AP direction (P = .004), velocity in ML direction (P < .001), phase plane (AP-ML) (P = .028), and mean total velocity (P = .001) in LBP were lesser compared with the normal group. ConclusionDifferent tasks affected postural control differently in patients with LBP and healthy individuals. Moreover, postural control was more challenged during the load-lowering than the load-lifting task. This may have been a result of a stiffening strategy. It may be that the load-lowering task might be considered as a more influential factor for the postural control strategy. These results may provide a novel understanding of selecting the rehabilitation programs for postural control disorders in patients.

An Integrated Dynamic Closed Loop Simulation Platform for Elbow Flexion Augmentation Using an Upper Limb Exosuit Model

Wearable robotic devices are designed to assist, enhance or restore human muscle performance. Understanding how a wearable robotic device changes human biomechanics through complex interaction is important to guide its proper design, parametric optimization and functional success. The present work develops a human-machine-interaction simulation platform for closed loop dynamic analysis with feedback control and to study the effect of soft-robotic wearables on human physiology. The proposed simulation platform incorporates Computed Muscle Control (CMC) algorithm and is implemented using the MATLAB -OpenSim interface. The framework is generic and will allow incorporation of any advanced control strategy for the wearable devices. As a demonstration, a Gravity Compensation (GC) controller has been implemented on the wearable device and the resulting decrease in the joint moments, muscle activations and metabolic costs during a simple repetitive load lifting task with two different speeds is investigated.

The Effect of Predictability of the Perturbation Magnitude on Anticipatory and Compensatory Postural Adjustments during a Bimanual Load-Lifting Task

Background: To minimize the potential postural disturbance induced by external or self-initiated perturbations, humans generate anticipatory postural adjustments based on their perceived consequences of the body disturbance. Lifting is a common activity that induces a self-initiated perturbation that can compromise balance control. Aim: To assess anticipatory (APAs) and compensatory (CPAs) postural adjustments generated in response to a self-initiated perturbation induced by lifting objects of uncertain mass. Methods: Ten young adults lifted the tray with either light or heavy object placed in it. Electromyographic activity of eight trunk and leg muscles, and center-of-pressure (COP) displacements were recorded and analyzed during the APAs and CPAs phases. Results: When the object mass changed unpredictably, the participants generated APAs based on the most recent experience of lifting and needed three trials of lifting to generate optimal APAs and CPAs. Conclusions: Young adults were able to predict the perturbation magnitude during self-initiated perturbations induced by lifting objects. The outcome provides a foundation for future studies focusing on the role of predictability of perturbation consequences in postural control of older adults and individuals with balance deficit.

Neurodevelopment of Posture-movement Coordination from Late Childhood to Adulthood as Assessed From Bimanual Load-lifting Task: An Event-related Potential Study

In a bimanual task, proprioception provides information about position and movement of upper arms. Developmental studies showed improvement of proprioceptive accuracy and timing adjustments of muscular events from childhood to adulthood in bimanual tasks. However, the cortical maturational changes related to bimanual coordination is not fully understood. The aim of this study was to investigate cortical correlates underlying motor planning and upper limb stabilization performance at left (C3) and right (C4) sensorimotor cortices using event-related potential (ERP) analyses. We recruited 46 participants divided into four groups (12 children: 8–10 years, 13 early adolescents: 11–13 years, 11 late adolescents: 14–16 years and 10 young adults: 20–35 years). Participants performed a bimanual load-lifting task, where the left postural arm supported the load and the right motor arm lifted the load. Maximal amplitude of elbow rotation (MA%) of the postural arm, reaction time (RT) and EMG activity of biceps brachii bilaterally were computed. Laplacian-transformed ERPs of the electroencephalographic (EEG) signal response-locked to motor arm biceps EMG activity onset were analyzed over C3 and C4. We found a developmental effect for behavioral and EEG data denoted by significant decrease of MA% and RT with age, earlier inhibition of the biceps brachii of the postural arm in adults and earlier EEG activation/inhibition onset at C3/C4. Amplitude of the negative wave at C4 was higher in children and early adolescents compared to the other groups. In conclusion, we found a maturational process in cortical correlates related to motor planning and upper limb stabilization performance with interhemispheric lateralization appearing during adolescence. Findings may serve documenting bimanual performance in children with neurodevelopmental disorders.

Comparative assessment of manual load lifting tasks by three methods: KIM-LHC, WISHA and Snook tables: A case study in printing industry

Introduction: today, musculoskeletal disorders are considered as a serious threat for workers, and one of the main activities, which lead to these problems, is lifting. Moreover, workers in printing industry are widely involved in inappropriate postures and lifting loads. The aim of this study was to compare the results of assessment of lifting tasks with KIM-LHC, WISHA and Snook tables in printing industry. Materials and Methods: In this cross-sectional study, a total number of 58 employees (64 tasks in total) from a printing industry staff in Tehran were evaluated with three observational methods of KIM-LHC, WISHA and Snook tables, and the final scores and necessary action levels were determined for them. Furthermore, statistical data were analyzed by SPSS (ver.22) software using Chi-square and Fisher exact tests. Results: Results showed that the prevalence of lower limbs musculoskeletal discomforts was high. Comparing the results of load lifting assessment with WISHA and KIM-LHC methods showed that there was a significant relationship between these two methods (p=0.005). Moreover, there was a significant relationship between the results of assessment through the WISHA and Snook tables methods (p=0.006), and finally the comparison of load lifting assessment results with KIM-LHC and Snook tables showed a significant relationship between these two methods (p=0.046). Conclusion: According to the results of this study, there was a high correlation between the results of these three methods, and they can be used as an alternative in printing industry for assessment of the load lifting task.

Immediate effects of using insoles with various wedges on activation and co-contraction indices of selected trunk muscles during load lifting

Trunk muscles play an important role during load lifting and contract to control trunk stability. The aim of present study was to investigate immediate effects of using various insole wedges on activation and co-contraction indices of selected trunk muscles during load lifting. Thirty able-bodied males completed load lifting task using nine various insole wedges. The results showed these significant differences: for normalized mean amplitude of RA muscle between posterior and anterior-medial wedges and for QL muscle between posterior and lateral wedges, for normalized peak amplitude of RA muscle between posterior and anterior-medial wedges, for median frequency of LES muscle between anterior-medial and anterior-lateral wedges, and for co-contraction of RA/TES, RA/LES and RA/MU between posterior and anterior-medial wedges (P = 0.001). These findings should be considered during designation of shoe or insole for work environments. Future studies need to assess other biomechanical aspects of using various insole wedges during work-related tasks.

Anticipatory postural adjustments during joint action coordination

There is a current claim that humans are able to effortlessly detect others’ hidden mental state by simply observing their movements and transforming the visual input into motor knowledge to predict behaviour. Using a classical paradigm quantifying motor predictions, we tested the role of vision feedback during a reach and load-lifting task performed either alone or with the help of a partner. Wrist flexor and extensor muscle activities were recorded on the supporting hand. Early muscle changes preventing limb instabilities when participants performed the task by themselves revealed the contribution of the visual input in postural anticipation. When the partner performed the unloading, a condition mimicking a split-brain situation, motor prediction followed a pattern evolving along the task course and changing with the integration of successive somatosensory feedback. Our findings demonstrate that during social behaviour, in addition to self-motor representations, individuals cooperate by continuously integrating sensory signals from various sources.

Tracking the acquisition of anticipatory postural adjustments during a bimanual load-lifting task: A MEG study.

During bimanual coordination, that is, manipulating with the dominant hand an object held by the postural hand, anticipatory postural adjustments are required to cancel the perturbations and ensure postural stabilization. Using magnetoencephalography (MEG), we investigated changes mediating the acquisition of anticipatory postural adjustments during a bimanual load-lifting task. Participants lifted a load with their right hand, hence triggering the fall of a second load fixed to their left (postural) forearm. During Acquisition, the onset of load-lifting and the fall of the second load were experimentally delayed after few trials. During Control, load-lifting triggered the fall of the second load without delay. Upward elbow rotation decreased with trial repetition during Acquisition, hence attesting the ongoing acquisition of anticipatory postural adjustments. Bilateral event-related desynchronisation (ERD) of the alpha rhythm (8-12 Hz) was recorded. Generators of the mu rhythm were found within central and associative motor regions. Their spatial distribution within the hemisphere contralateral to the load-lifting arm was less refined and circumscribed during Acquisition compared to Control. Regression analyses emphasized the specific involvement of the precuneus in the right hemisphere contralateral to the postural forearm, and a medial prefrontal region in the left hemisphere. Analyses of the time course power showed that an increase in preunloading activation within the precuneus and a decrease in postunloading inhibition within the medial prefrontal region were associated with the acquisition of anticipatory postural adjustments. The study provides original insights into cortical activations mediating the progressive tuning of anticipatory postural adjustments during the acquisition stage of motor learning.

Lumbar Facet Joint Kinematics and Load Effects During Dynamic Lifting.

To examine the lumbar facet joint kinematics in vivo during dynamic lifting and the effects of the load lifted. Although extensive efforts have been dedicated to investigating the risk factors of low back pain (LBP) associated with load handling in the workplace, the biomechanics of lumbar facet joints during such activities is not well understood. Fourteen healthy participants performed a load-lifting task while a dynamic stereo-radiography system captured their lumbar motion continuously. Data from 11 participants were included for subsequent analysis. A randomized block design was employed to study the load effect (4.5 kg, 9.0 kg, and 13.5 kg) on bilateral facet joint motions at approximately 60°, 40°, 20°, and 0° trunk-flexion postures. The facet orientations were also examined. Significant load effects were found for the flexion and lateral bending and superior-inferior translation of the facet joints. The L5-S1 displayed greater lateral bending and twisting, which was due to its more posterolateral orientation than the L2-L3, L3-L4, and L4-L5 facet joints. The left-right asymmetry in facet orientation was observed, most prominently at L3-L4 and L5-S1 facet joints. The lumbar facet joint kinematics are affected by the magnitude of the lifted load and are dependent on the orientations of articulating adjacent facets. This study provided new insights into the role of lumbar facet joints in vivo during lifting. Alterations in the facet joint kinematics due to vigorous functional demand can be one of the primary but overlooked mechanical factors in the causation of LBP.

Load Lifting and the Risk of Work-Related Musculoskeletal Disorders among Cabin Crews

Lifting and loading passengers’ hand-carry luggage into the overhead compartment in the flight cabin is one of the tasks performed by the cabin crews. The hand-carry luggage weight varies and can be up to 10 kg. The task involved load lifting over the head, awkward posture and repetitive that could lead to the risk of work-related musculoskeletal disorders (WMSDs). Hence, further investigation of those factors stimulates this study. An industrial survey was conducted and WMSDs symptom data were collected using Nordic Musculoskeletal Questionnaire (NMQ). Rapid Upper Limb (RULA) assessment was performed to analyse the posture during the load lifting task. The results of the industrial survey indicated that 88.3% of the workers experienced WMSD symptoms in various regions of the body. The highest symptoms reported at lower back (80.0%), followed by the neck (68.0%) and shoulder (59.0%). The result is supported with the result of RULA with final score 7, which indicated the load lifting task performed involved awkward posture, needs changes and further improvement should be immediately implemented. In conclusion, the cabin crews exposed to the risks of WMSDs and the results of this study can be used as references by the aviation industry to mitigate WMSDs issues among the cabin crews specifically and contribute to the improvement of the society well-being generally.

Mu-oscillation changes related to the development of anticipatory postural control in children and adolescents.

Anticipatory postural adjustments (APAs) cancel the destabilizing effects of movement on posture. Across development, the maturation of APAs is characterized by an accurate adjustment of the timing parameters of electromyographic (EMG) response. The study aimed at investigating the maturation of cortical oscillations involved in the improvement of APAs efficiency. Thirty-six healthy participants (8-16 yr) performed the bimanual load-lifting task in which subjects are instructed to lift a load, placed on the left forearm, with the right hand. EMG data were acquired over the biceps brachii on the postural arm to the determine EMG response onset. Electroencephalographic signals were analyzed in the time-frequency domain by convolution with complex Gaussian Morlet wavelets. Electrophysiological signature of APAs in children and adolescents consisted of a mu-rhythm desynchronization over the sensorimotor cortex contralateral to the postural arm. Across development, the mu-rhythm desynchronization was characterized by a progressive shift forward of the onset of the desynchronization, lower amplitude, and velocity. These changes occurred along with an alteration of the timing of the EMG response, as shown by an earlier onset of the flexor inhibition with increasing age. The maturational changes in the Mu-oscillations might sustain the development of APAs. A possible role of the Mu-oscillation in the generation of postural command is discussed. NEW & NOTEWORTHY Across development, our study showed a progressive shift forward of the parameters of the mu-rhythm desynchronization. These changes occurred along with an alteration of the timing parameters of the electromyographic response, as shown by an earlier onset of the flexor inhibition with increasing age. The progressive development of APAs during childhood and adolescence might therefore be sustained by maturational electrophysiological changes that include mu-rhythm oscillation modifications in the postural sensorimotor cortex.

Load-embedded inertial measurement unit reveals lifting performance

Manual lifting of loads arises in many occupations as well as in activities of daily living. Prior studies explore lifting biomechanics and conditions implicated in lifting-induced injuries through laboratory-based experimental methods. This study introduces a new measurement method using load-embedded inertial measurement units (IMUs) to evaluate lifting tasks in varied environments outside of the laboratory. An example vertical load lifting task is considered that is included in an outdoor obstacle course. The IMU data, in the form of the load acceleration and angular velocity, is used to estimate load vertical velocity and three lifting performance metrics: the lifting time (speed), power, and motion smoothness. Large qualitative differences in these parameters distinguish exemplar high and low performance trials. These differences are further supported by subsequent statistical analyses of twenty three trials (including a total of 115 total lift/lower cycles) from fourteen healthy participants. Results reveal that lifting time is strongly correlated with lifting power (as expected) but also correlated with motion smoothness. Thus, participants who lift rapidly do so with significantly greater power using motions that minimize motion jerk.

Capturing Three-Dimensional In Vivo Lumbar Intervertebral Joint Kinematics Using Dynamic Stereo-X-Ray Imaging

Availability of accurate three-dimensional (3D) kinematics of lumbar vertebrae is necessary to understand normal and pathological biomechanics of the lumbar spine. Due to the technical challenges of imaging the lumbar spine motion in vivo, it has been difficult to obtain comprehensive, 3D lumbar kinematics during dynamic functional tasks. The present study demonstrates a recently developed technique to acquire true 3D lumbar vertebral kinematics, in vivo, during a functional load-lifting task. The technique uses a high-speed dynamic stereo-radiography (DSX) system coupled with a volumetric model-based bone tracking procedure. Eight asymptomatic male participants performed weight-lifting tasks, while dynamic X-ray images of their lumbar spines were acquired at 30 fps. A custom-designed radiation attenuator reduced the radiation white-out effect and enhanced the image quality. High resolution CT scans of participants' lumbar spines were obtained to create 3D bone models, which were used to track the X-ray images via a volumetric bone tracking procedure. Continuous 3D intervertebral kinematics from the second lumbar vertebra (L2) to the sacrum (S1) were derived. Results revealed motions occurring simultaneously in all the segments. Differences in contributions to overall lumbar motion from individual segments, particularly L2-L3, L3-L4, and L4-L5, were not statistically significant. However, a reduced contribution from the L5-S1 segment was observed. Segmental extension was nominally linear in the middle range (20%-80%) of motion during the lifting task, but exhibited nonlinear behavior at the beginning and end of the motion. L5-S1 extension exhibited the greatest nonlinearity and variability across participants. Substantial AP translations occurred in all segments (5.0 ± 0.3 mm) and exhibited more scatter and deviation from a nominally linear path compared to segmental extension. Maximum out-of-plane rotations (<1.91 deg) and translations (<0.94 mm) were small compared to the dominant motion in the sagittal plane. The demonstrated success in capturing continuous 3D in vivo lumbar intervertebral kinematics during functional tasks affords the possibility to create a baseline data set for evaluating the lumbar spinal function. The technique can be used to address the gaps in knowledge of lumbar kinematics, to improve the accuracy of the kinematic input into biomechanical models, and to support development of new disk replacement designs more closely replicating the natural lumbar biomechanics.

Influence of snow shovel shaft configuration on lumbosacral biomechanics during a load-lifting task

Lower-back injury from snow shovelling may be related to excessive joint loading. Bent-shaft snow shovels are commonly available for purchase; however, their influence on lower back-joint loading is currently not known. Therefore, the purpose of this study was to compare L5/S1 extension angular impulses between a bent-shaft and a standard straight-shaft snow shovel. Eight healthy subjects participated in this study. Each completed a simulated snow-lifting task in a biomechanics laboratory with each shovel design. A standard motion analysis procedure was used to determine L5/S1 angular impulses during each trial, as well as peak L5/S1 extension moments and peak upper body flexion angle. Paired-samples t-tests (α = 0.05) were used to compare variables between shovel designs. Correlation was used to determine the relationship between peak flexion and peak moments. Results of this study show that the bent-shaft snow shovel reduced L5/S1 extension angular impulses by 16.5% (p = 0.022), decreased peak moments by 11.8% (p = 0.044), and peak flexion by 13.0% (p = 0.002) compared to the straight-shaft shovel. Peak L5/S1 extension moment magnitude was correlated with peak upper body flexion angle (r = 0.70). Based on these results, it is concluded that the bent-shaft snow shovel can likely reduce lower-back joint loading during snow shovelling, and thus may have a role in snow shovelling injury prevention.

Neuromagnetic imaging reveals timing of volitional and anticipatory motor control in bimanual load lifting

During bimanual load lifting, the brain not only contends with muscle activations in the load-lifting arm, but also has to pre-emptively modulate muscle activations in the load-bearing arm with temporal precision in order to minimize upward arm deflection. Premature or late inhibition in the load-bearing arm activity would result in augmented arm deflection. Little is currently known about the timing operation of motor systems subserving coordinated, bimanual actions. In this study, we measured neuromagnetic brain activity with whole-head magnetoencephalography while 15 participants performed a bimanual load-lifting task. To investigate neural processes prior to load lifting, a beamformer was applied to 6 contiguous 200ms time epochs spanning the entire premovement phase of the motor task. The sequence of neural activations, following a signal to lift the weight, was chronologically ordered: firstly, the primary motor cortex contralateral to the load-lifting arm was activated, then the cerebellum, and lastly, the basal ganglia, thalamus and primary-/pre- motor areas contralateral to the load-bearing arm. The current data extend our understanding of the neural underpinnings of bimanual coordination. A model is proposed to account for the central organization of volitional and anticipatory motor control in bimanual load lifting.

Neuromagnetic brain activity associated with anticipatory postural adjustments for bimanual load lifting

During bimanual load lifting, the brain must anticipate the effects of unloading upon the load-bearing arm. Little is currently known about the neural networks that coordinate these anticipatory postural adjustments. We measured neuromagnetic brain activity with whole-head magnetoencephalography while participants performed a bimanual load-lifting task. Anticipatory adjustments were associated with reduction in biceps brachii muscle activity of the load-bearing arm and pre-movement desynchronization of the cortical beta rhythm. Beamforming analyses localized anticipatory brain activity to the precentral gyrus, basal ganglia, supplementary motor area, and thalamus, contralateral to the load-bearing arm. To our knowledge this is the first human neuroimaging study to directly investigate anticipatory postural adjustments and to explicitly partition the anticipatory and volitional aspects of brain activity in bimanual load lifting. These data contribute to our understanding of the neural systems supporting anticipatory postural adjustments in healthy adults.

Development of action representation during adolescence as assessed from anticipatory control in a bimanual load-lifting task

The aim of this study was to explore, during adolescence, alterations in the use of a sensori-motor representation as unveiled by the measurement of anticipatory postural control in a bimanual load-lifting task. We hypothesised that adolescence constitutes a period of refinement of anticipatory postural control due to on-going updates of the body schema and sensori-motor representations. The anticipatory postural control was assessed using a bimanual load-lifting paradigm in which subjects stabilise their left postural forearm, which is supporting an object, while they use their right hand to lift up the object. Kinematics and electromyographic data were recorded in two groups of adolescents (11–13 and 14–16years of age) and a group of adults. Age and gender effects were tested. During voluntary unloading, the postural forearm stabilisation in adolescents was still different from the adult one, suggesting that further improvement of the postural forearm stabilisation must take place after the age of 16. No differences occur in the two adolescent groups. Moreover, girls presented a better stabilisation of the postural forearm than boys, indicating an earlier refinement of anticipatory postural control. The decrease of activity over postural flexors, which ensure postural stabilisation, appeared later in adolescents with respect to adults. Delayed timing adjustments and increased variability could reflect intense developmental processes underlain by an intense period of CNS maturation during adolescence. We discuss the role of brain maturation in the refinement of sensori-motor representations and the update of body schema.