@article{dubois2025JcvPCA,

title = {JcvPCA and JsvCRP: A set of metrics to evaluate changes in joint coordination strategies},

author = {Oc\'{e}ane Dubois and Agn\`{e}s Roby-Brami and Ross Parry and Nathana\"{e}l Jarrass\'{e}},

url = {https://doi.org/10.1371/journal.pone.0325792},

doi = {10.1371/journal.pone.0325792},

year  = {2025},

date = {2025-01-01},

urldate = {2025-01-01},

journal = {PLOS ONE},

volume = {20},

number = {8},

pages = {1-22},

publisher = {Public Library of Science},

abstract = {Characterizing changes in inter-joint coordination presents significant challenges, as it necessitates the examination of relationships between multiple degrees of freedom during movements and their temporal evolution. Existing metrics are inadequate in providing physiologically coherent results that document both the temporal and spatial aspects of inter-joint coordination. In this article, we introduce two novel metrics to enhance the analysis of inter-joint coordination. The first metric, Joint Contribution Variation based on Principal Component Analysis (JcvPCA), evaluates the variation in each joint’s contribution during series of movements. The second metric, Joint Synchronization Variation based on Continuous Relative Phase (JsvCRP), measures the variation in temporal synchronization among joints between two movement datasets. We begin by presenting each metric and explaining their derivation. We then demonstrate the application of these metrics using simulated and experimental datasets involving identical movement tasks performed with distinct coordination strategies. The results show that these metrics can successfully differentiate between unique coordination strategies, providing meaningful insights into joint collaboration during movement. These metrics hold significant potential for fields such as ergonomics and clinical rehabilitation, where a precise understanding of the evolution of inter-joint coordination strategies is crucial. Potential applications include evaluating the effects of upper limb exoskeletons in industrial settings or monitoring the progress of patients undergoing neurological rehabilitation.},

keywords = {Kinematics},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Design and Control of a Climbing Robot for Autonomous Vertical Gardening},

author = {Marko Jam\v{s}ek and Gal Sajko and Jurij Krpan and Jan Babi\v{c}},

doi = {10.3390/machines12020141},

issn = {2075-1702},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Machines},

volume = {12},

issue = {2},

pages = {141},

abstract = {This paper focuses on the development of a novel climbing robot that is designed for autonomous maintenance of vertical gardens in urban environments. The robot, designed with a unique five-legged structure, is equipped with a range of electrical and mechanical components, enabling it to autonomously navigate and maintain a specially designed vertical garden wall facilitating interactive maintenance and growth monitoring. The motion planning and control of the robot were developed to ensure precise and adaptive movement across the vertical garden wall. Advanced algorithms were employed to manage the complex dynamics of the robot’s movements, optimizing its efficiency and effectiveness in navigating and maintaining the garden structure. The operation of the robot in maintaining the vertical garden was evaluated during a two-week trial where the robot successfully performed nearly 8000 leg movements, with only 0.6% requiring human intervention. This demonstrates a high level of autonomy and reliability. This study concludes that the pentapod robot demonstrates significant potential for automating the maintenance of vertical gardens, offering a promising tool for enhancing urban green spaces.},

keywords = {Compliance and Impedance Control, Kinematics, Robot Design},

pubstate = {published},

tppubtype = {article}

}

@article{dubois2024Short,

title = {Short term after-effects of small force fields applied by an upper-limb exoskeleton on inter-joint coordination},

author = {Oc\'{e}ane Dubois and Agn\`{e}s Roby-Brami and Ross Parry and Nathana\"{e}l Jarrass\'{e}},

doi = {10.1109/ICRA57147.2024.10610645},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {IEEE International Conference on Robotics and Automation},

pages = {959-965},

abstract = {Exoskeleton technologies have numerous potential applications, ranging from improving human motor skills to aiding individuals in their daily activities. While exoskeletons are increasingly viewed, for example, as promising tools in industrial ergonomics, the effect of using them on human motor control, particularly on inter-joint coordination, remains relatively uncharted. This paper investigates the effects of generic low-amplitude force fields applied by an exoskeleton on motor strategies in asymptomatic users. The force fields mimic common perturbations encountered in exoskeletons, such as residual friction, over/under-tuned assistance, or structural elasticity. Fifty-five participants performed reaching tasks while connected to an arm exoskeleton, experiencing one of five tested force fields. Their movements before and after exposure to the exoskeleton force field were compared. The study focuses both on spatial and temporal changes in coordination using specific metrics. The results reveal that even brief exposure to a low- amplitude force field, or to uncompensated residual friction and dynamic forces, applied at the joint level can alter the interjoint coordination, while task performance remains unaffected. The tested force fields induced varying degrees of changes in joint contributions and synchronization. This study highlights the importance of monitoring coordination changes to fully understand the impact of exoskeletons on human motor control and thus enable safe and widespread adoption of those devices.},

keywords = {Human Motor Control, Kinematics, Physical Human Robot Interaction},

pubstate = {published},

tppubtype = {article}

}

@article{segas2023intuitive,

title = {Intuitive movement-based prosthesis control enables arm amputees to reach naturally in virtual reality},

author = {Effie Segas and S\'{e}bastien Mick and Vincent Leconte and Oc\'{e}ane Dubois and R\'{e}mi Klotz and Daniel Cattaert and Aymar Rugy},

editor = {Kianoush Nazarpour and Tamar R Makin},

url = {https://doi.org/10.7554/eLife.87317},

doi = {10.7554/eLife.87317},

issn = {2050-084X},

year  = {2023},

date = {2023-10-01},

urldate = {2023-10-01},

journal = {eLife},

volume = {12},

pages = {RP87317},

publisher = {eLife Sciences Publications, Ltd},

abstract = {Impressive progress is being made in bionic limbs design and control. Yet, controlling the numerous joints of a prosthetic arm necessary to place the hand at a correct position and orientation to grasp objects remains challenging. Here, we designed an intuitive, movement-based prosthesis control that leverages natural arm coordination to predict distal joints missing in people with transhumeral limb loss based on proximal residual limb motion and knowledge of the movement goal. This control was validated on 29 participants, including seven with above-elbow limb loss, who picked and placed bottles in a wide range of locations in virtual reality, with median success rates over 99% and movement times identical to those of natural movements. This control also enabled 15 participants, including three with limb differences, to reach and grasp real objects with a robotic arm operated according to the same principle. Remarkably, this was achieved without any prior training, indicating that this control is intuitive and instantaneously usable. It could be used for phantom limb pain management in virtual reality, or to augment the reaching capabilities of invasive neural interfaces usually more focused on hand and grasp control.},

keywords = {Human-in-the-Loop Control, Kinematics, Machine Learning},

pubstate = {published},

tppubtype = {article}

}

@article{dubois2023Guide,

title = {A guide to inter-joint coordination characterization for discrete movements: a comparative study},

author = {Oc\'{e}ane Dubois and Agn\`{e}s Roby-Brami and Ross Parry and Mahdi Khoramshahi and Nathana\"{e}l Jarrass\'{e}},

url = {https://doi.org/10.1186/s12984-023-01252-2},

doi = {10.1186/s12984-023-01252-2},

issn = {1743-0003},

year  = {2023},

date = {2023-09-30},

urldate = {2023-09-30},

journal = {Journal of NeuroEngineering and Rehabilitation},

volume = {20},

number = {1},

pages = {132},

abstract = {Characterizing human movement is essential for understanding movement disorders, evaluating progress in rehabilitation, or even analyzing how a person adapts to the use of assistive devices. Thanks to the improvement of motion capture technology, recording human movement has become increasingly accessible and easier to conduct. Over the last few years, multiple methods have been proposed for characterizing inter-joint coordination. Despite this, there is no real consensus regarding how these different inter-joint coordination metrics should be applied when analyzing the coordination of discrete movement from kinematic data. In this work, we consider 12 coordination metrics identified from the literature and apply them to a simulated dataset based on reaching movements using two degrees of freedom. Each metric is evaluated according to eight criteria based on current understanding of human motor control physiology, i.e, each metric is graded on how well it fulfills each of these criteria. This comparative analysis highlights that no single inter-joint coordination metric can be considered as ideal. Depending on the movement characteristics that one seeks to understand, one or several metrics among those reviewed here may be pertinent in data analysis. We propose four main factors when choosing a metric (or a group of metrics): the importance of temporal vs. spatial coordination, the need for result explainability, the size of the dataset, and the computational resources. As a result, this study shows that extracting the relevant characteristics of inter-joint coordination is a scientific challenge and requires a methodical choice. As this preliminary study is conducted on a limited dataset, a more comprehensive analysis, introducing more variability, could be complementary to these results.},

keywords = {Dynamic Motion, Kinematics},

pubstate = {published},

tppubtype = {article}

}

@article{Eiken2022,

title = {Effects of vision on energy expenditure and kinematics during level walking},

author = {Ola Eiken and Igor B. Mekjavi\'{c} and Jan Babi\v{c} and Ulf Danielsson and Magnus Hallberg and Stylianos N. Kounalakis},

url = {https://link.springer.com/10.1007/s00421-022-04914-6},

doi = {10.1007/s00421-022-04914-6},

issn = {1439-6319},

year  = {2022},

date = {2022-05-01},

urldate = {2022-05-01},

journal = {European Journal of Applied Physiology},

volume = {122},

number = {5},

pages = {1231--1237},

abstract = {Purpose We have previously observed substantially higher oxygen uptake in soldiers walking on terrain at night than when performing the same walk in bright daylight. The aims of the present study were to investigate the influence of vision on mechanical efficiency during slow, horizontal, constant-speed walking, and to determine whether any vision influence is modified by load carriage. Methods Each subject (n = 15) walked (3.3 km/h) for 10 min on a treadmill in four different conditions: (1) full vision, no carried load, (2) no vision, no carried load, (3) full vision with a 25.5-kg rucksack, (4) no vision with a 25.5-kg rucksack. Results Oxygen uptake was 0.94 ± 0.12 l/min in condition (1), 1.15 ± 0.20 l/min in (2), 1.15 ± 0.12 l/min in (3) and 1.35 ± 0.19 l/min in (4). Thus, lack of vision increased oxygen uptake by about 19%. Analyses of movement pattern, by use of optical markers attached to the limbs and torso, revealed considerably shorter step length (12 and 10%) in the no vision (2 and 4) than full vision conditions (1 and 3). No vision conditions (2 and 4) increased step width by 6 and 6%, and increased vertical foot clearance by 20 and 16% compared to full vision conditions (1 and 3). Conclusion The results suggest that vision has a marked influence on mechanical efficiency even during entrained, repetitive movements performed on an obstacle-free horizontal surface under highly predictable conditions.},

keywords = {Kinematics, Postural Balance},

pubstate = {published},

tppubtype = {article}

}

@article{Sever2021,

title = {Postural responses to sudden horizontal perturbations in tai chi practitioners},

author = {Jernej Sever and Jan Babi\v{c} and \v{Z}iga Kozinc and Nejc \v{S}arabon},

doi = {10.3390/ijerph18052692},

issn = {16604601},

year  = {2021},

date = {2021-01-01},

urldate = {2021-01-01},

journal = {International Journal of Environmental Research and Public Health},

volume = {18},

number = {5},

pages = {1--12},

abstract = {Tai Chi has been shown to elicit numerous positive effects on health and well-being. In this study, we examined reactive postural control after sudden unloading horizontal perturbations, which resembled situations encountered during Tai Chi. The study involved 20 participants, 10 in the Tai Chi group (age: 37.4 ± 7.8 years), who had been regularly training the push-hand technique for at least 7 years, and 10 in the control group, consisting of healthy adults (age: 28.8 ± 5.0). Perturbations were applied at three different positions (hips, shoulders, and arms) via the load-release paradigm. Twenty measurements were carried out for each perturbation position. We measured peak vertical and horizontal forces on the ground (expressed percentage of body mass (%BM)), peak center of pressure displacement and peak horizontal and vertical velocities at the knee, hip and shoulder joints. The Tai Chi group exhibited smaller increases in vertical ground reaction forces when perturbations were applied at the hips (11.5 ± 2.1 vs. 19.6 ± 5.5 %BW; p = 0.002) and the arms (14.1 ± 4.2 vs. 23.2 ± 8.4 %BW; p = 0.005). They also responded with higher horizontal force increase after hip perturbation (16.2 ± 3.2 vs. 13.1 ± 2.5 %BW; p \< 0.001). Similar findings were found when observing various outcomes related to velocities of vertical movement. The Tai Chi group also showed lower speeds of backward movement of the knee (p = 0.005\textendash0.009) after hip (0.49 ± 0.13 vs. 0.85 ± 0.14 m/s; p = 0.005) and arm perturbations (0.97 ± 0.18 vs. 1.71 ± 0.29 m/s; p = 0.005). Center of pressure displacements were similar between groups. Our study demonstrated that engaging in Tai Chi could be beneficial to reactive postural responses after sudden perturbations in a horizontal direction; however, future interventional studies are needed to directly confirm this. Moreover, because of the age difference between the groups, some confounding effects of age cannot be ruled out.},

keywords = {Kinematics, Neuromusculoskeletal Modelling, Postural Balance, Sport},

pubstate = {published},

tppubtype = {article}

}

@article{Maurice2020b,

title = {Objective and Subjective Effects of a Passive Exoskeleton on Overhead Work},

author = {Pauline Maurice and Jernej \v{C}amernik and Da\v{s}a Gorjan and Benjamin Schirrmeister and Jonas Bornmann and Luca Tagliapietra and Claudia Latella and Daniele Pucci and Lars Fritzsche and Serena Ivaldi and Jan Babi\v{c}},

url = {https://ieeexplore.ieee.org/document/8856265/},

doi = {10.1109/TNSRE.2019.2945368},

issn = {1534-4320},

year  = {2020},

date = {2020-01-01},

journal = {IEEE Transactions on Neural Systems and Rehabilitation Engineering},

volume = {28},

number = {1},

pages = {152--164},

address = {Nancy},

abstract = {Overhead work is a frequent cause of shoulder work-related musculoskeletal disorders. Exoskeletons offering arm support have the potential to reduce shoulder strain, without requiring large scale reorganization of the workspace. Assessment of such systems however requires to take multiple factors into consideration. This paper presents a thorough in-lab assessment of PAEXO, a novel passive exoskeleton for arm support during overhead work. A list of evaluation criteria and associated performance metrics is proposed to cover both objective and subjective effects of the exoskeleton, on the user and on the task being performed. These metrics are measured during a lab study, where 12 participants perform an overhead pointing task with and without the exoskeleton, while their physical, physiological and psychological states are monitored. Results show that using PAEXO reduces shoulder physical strain as well as global physiological strain, without increasing low back strain nor degrading balance. These positive effects are achieved without degrading task performance. Importantly, participants' opinions of PAEXO are positive, in agreement with the objective measures. Thus, PAEXO seems a promising solution to help prevent shoulder injuries and diseases among overhead workers, without negatively impacting productivity.},

keywords = {Ergonomy, Exoskeleton Design and Control, Kinematics, Physical Human Robot Interaction, Postural Balance},

pubstate = {published},

tppubtype = {article}

}

@article{Gorjan2019,

title = {Small, movement dependent perturbations substantially alter postural control strategy in healthy young adults},

author = {Da\v{s}a Gorjan and Jan Babi\v{c} and Nejc \v{S}arabon and Zrinka Potocanac},

url = {http://www.sciencedirect.com/science/article/pii/S0021929018307292},

doi = {10.1016/j.jbiomech.2018.09.008},

issn = {18732380},

year  = {2019},

date = {2019-01-01},

journal = {Journal of Biomechanics},

volume = {91},

pages = {1--6},

abstract = {Postural control is commonly investigated by observing responses to perturbations. We developed a perturbation paradigm mimicking self-generated errors in weight shifting, which are a common cause of falling among older adults. Our aim was to determine the effects of this small, but complex, perturbation on postural sway of healthy young adults and evaluate the role of vision and cognition during movement dependent perturbations. Fifteen participants stood hip-width apart with their eyes open, closed and while performing two different cognitive tasks. Participants were continuously perturbed by medial-lateral (ML) support surface translations corresponding to, and hence doubling, their own center of mass sway. We analyzed the standard deviation (SD), root mean square (RMS), range, and mean power frequency (MPF) of center of pressure displacements. ML postural sway increased due to the perturbation (SD p ≤ .001, range p \< .001, RMS p ≤ .001, MPF p \< .001). Cognitive load increased the ML sway range (p = .048). Lack of vision increased ML MPF (p = .001) and anterior-posterior (AP) range (p \< .001), SD (p \< .001), and RMS (p = .001). Significant interaction of vision with the perturbation was found for the ML range (p = .045) and AP SD (p = .018). The perturbation specifically affected ML postural sway. Increased MPF is indicative of a postural control strategy change, which was insufficient for fully controlling the increased sway. Despite being small, this type of perturbation appears to be challenging for young adults.},

keywords = {Kinematics, Muscle Mechanics, Postural Balance},

pubstate = {published},

tppubtype = {article}

}

@article{\v{C}amernik2019b,

title = {Staying on your feet: the effectiveness of posture and handles in counteracting balance perturbation},

author = {Jernej \v{C}amernik and Morteza Azad and Luka Peternel and Zrinka Poto\v{c}anac and Jan Babi\v{c}},

url = {https://doi.org/10.1080/00140139.2018.1559363 https://www.tandfonline.com/doi/full/10.1080/00140139.2018.1559363},

doi = {10.1080/00140139.2018.1559363},

issn = {0014-0139},

year  = {2019},

date = {2019-01-01},

journal = {Ergonomics},

volume = {62},

number = {5},

pages = {657--667},

publisher = {Taylor \& Francis},

abstract = {Stairways, public transport and inclined walkways are often considered as sites with higher likelihood of falls due to a sudden loss of balance. Such sites are usually marked with warning signs, equipped with non-slip surfaces and handles or handrails to avert or decrease this likelihood. Especially, handles are supposed to provide additional support in cases of a sudden loss of balance. However, the mechanisms of using handles for balance at different heights are not yet fully disclosed. We simulated full body perturbations by applying an anterior force to the waist and investigated effectiveness and mechanisms of balance recovery in five different postures: step stance and normal stance with or without holding handles at different heights. Results indicate that both step stance and holding handles at different vertical positions sufficiently assist balance recovery, compared to normal stance. While there was no significant effect of handle in CoM displacement, the shoulder height handle required the lowest handle force, indicating a difference in using the handle. Practitioner summary: To investigate handle use for balance recovery, we perturbed healthy young adults in different standing positions. Even though the use of different handles had a similar effect, the lowest forces were exerted on the shoulder height handle indicating a preferred handle position for balance recovery. Abbreviation: AP: antero-posterior; CNS: Central nervous system; CoM: Center of Mass; CoMmax: Maximal displacement of the center of mass; CoP: Center of pressure; FHmax: Maximal resultant force exerted on the handle; hFHmax: Maximal horizontal force exerted on the handle; vFHmax; Maximal vertical force exerted on the handle; M1-M8: Perturbation force magnitude.},

keywords = {Human Motor Control, Kinematics, Postural Balance},

pubstate = {published},

tppubtype = {article}

}

@article{Petric2011a,

title = {On-line frequency adaptation and movement imitation for rhythmic robotic tasks},

author = {Tadej Petri\v{c} and Andrej Gams and Auke J Ijspeert and Leon \v{Z}lajpah},

url = {http://journals.sagepub.com/doi/10.1177/0278364911421511},

doi = {10.1177/0278364911421511},

issn = {0278-3649},

year  = {2011},

date = {2011-01-01},

journal = {The International Journal of Robotics Research},

volume = {30},

number = {14},

pages = {1775--1788},

abstract = {In this paper we present a novel method to obtain the basic frequency of an unknown periodic signal with an arbitrary waveform, which can work online with no additional signal processing or logical operations. The method originates from non-linear dynamical systems for frequency extraction, which are based on adaptive frequency oscillators in a feedback loop. In previous work, we had developed a method that could extract separate frequency components by using several adaptive frequency oscillators in a loop, but that method required a logical algorithm to identify the basic frequency. The novel method presented here uses a Fourier series representation in the feedback loop combined with a single oscillator. In this way it can extract the frequency and the phase of an unknown periodic signal in real time and without any additional signal processing or preprocessing. The method determines the Fourier series coefficients and can be used for dynamic Fourier series implementation. The proposed method can be used for the control of rhythmic robotic tasks, where only the extraction of the basic frequency is crucial. For demonstration several highly non-linear and dynamic periodic robotic tasks are shown, including also a task where an electromyography (EMG) signal is used in a feedback loop.},

keywords = {Dynamic Motion, Kinematics},

pubstate = {published},

tppubtype = {article}

}