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Summary This study investigated risk factors for osteonecrosis involving multiple joints (MJON) among glucocorticoid-treated patients. The best predictor of MJON was cumulative oral glucocorticoid dose. Risk of MJON was 12-fold higher in patients who had a second risk factor for osteonecrosis. Further research is needed into strategies for prevention of MJON. Introduction Osteonecrosis (ON) is a debilitating musculoskeletal condition in which bone cell death can lead to mechanical failure. When multiple joints are affected, pain and disability are compounded. Glucocorticoid treatment is one of the most common predisposing factors for ON. This study investigated risk factors for ON involving multiple joints (MJON) among glucocorticoid-treated patients. Methods Fifty-five adults with glucocorticoid-induced ON were prospectively enrolled. MJON was defined as ON in ≥ three joints. Route, dose, duration, and timing of glucocorticoid treatment were assessed. Results Mean age of enrolled subjects was 44 years, 58% were women. Half had underlying conditions associated with increased ON risk: systemic lupus erythematosus (29%), acute lymphoblastic leukemia (11%), HIV (9%), and alcohol use (4%). Mean daily oral dose of glucocorticoids was 29 mg. Average cumulative oral dose was 30 g over 5 years. The best predictor of MJON was cumulative oral glucocorticoid dose. For each increase of 1,000 mg, risk of MJON increased by 3.2% (95% CI 1.03, 1.67). Glucocorticoid exposure in the first 6 months of therapy, peak dose (oral or IV), and mean daily dose did not independently increase risk of MJON. The risk of MJON was 12-fold in patients who had a second risk factor (95% CI 3.2, 44.4). Conclusions Among patients with glucocorticoid-induced ON, cumulative oral dose was the best predictor of multi-joint disease; initial doses of IV and oral glucocorticoids did not independently increase risk. Further research is needed to better define optimal strategies for prevention and treatment of MJON.

Resistance-training exercises can be classified as either single- or multi-joint exercises and differences in surface electromyography (EMG) amplitude between the two training methods may identify which muscles can benefit from either training modality. This study aimed to compare the surface EMG amplitude of five hip- and knee extensors during one multi-joint (leg press) and two single-joint exercises (knee extension and kickback). Fifteen resistance-trained men completed one familiarization session to determine their unilateral six repetitions maximum (6RM) in the three exercises. During the following experimental session, EMG amplitudes of the vastus lateralis, vastus medialis, rectus femoris, gluteus maximus and biceps femoris of the left leg were measured while performing three repetitions on their respective 6RM loads. The multi-joint exercise leg press produced higher EMG amplitude of the vastus lateralis (ES = 0.92, p = 0.003) than the single-joint exercise knee extension, whereas the rectus femoris demonstrated higher EMG amplitude during the knee extension (ES = 0.93, p = 0.005). The biceps femoris EMG amplitude was higher during the single-joint exercise kickback compared to the leg press (ES = 2.27, p < 0.001), while no significant differences in gluteus maximus (ES = 0.08, p = 0.898) or vastus medialis (ES = 0.056, p = 0.025 were observed between exercises. The difference in EMG amplitude between single- and multi-joint exercises appears to vary depending on the specific exercises and the muscle groups tested. Leg press is a viable and time-efficient option for targeting several hip- and knee extensors during resistance training of the lower limbs, but the single-joint exercises may be preferable for targeting the rectus femoris and biceps femoris.

de Camargo, JBB, Braz, TV, Batista, DR, Germano, MD, Brigatto, FA, and Lopes, CR. Dissociated time course of indirect markers of muscle damage recovery between single-joint and multi-joint exercises in resistance-trained men. J Strength Cond Res XX(X): 000-000, 2020-This study compared the time course of indirect markers of muscle damage after multi-joint and single-joint exercises. Ten resistance-trained men (years: 26.9 ± 3.0; total body mass: 83.2 ± 13.8 kg; height: 176 ± 7.0 cm; resistance training [RT] experience: 5.5 ± 2.4 years; RT frequency: 5.3 ± 0.7 sessions; relative squat 1 repetition maximum: 1.4 ± 0.3) performed, in a random order, 5 sets of 8 repetition maximum of the back squat (BS) and knee extension (KE) exercises. Rectus femoris muscle thickness (MTRF), leg circumference (LC), and muscle soreness (MS) were recorded at baseline (pre), 0, 12, 24, and 36 hours after each exercise protocol. There was a significant increase (p < 0.05) in dependent variables at every time point after both the multi-joint and single-joint exercise sessions. However, MTRF and LC were greater at 0 and 36 hours, and MS was greater at 24 and 36 hours after BS when compared with KE (all p < 0.05). This study shows that resistance-trained individuals can experience significant higher levels of indirect markers of muscle damage when performing a multi-joint lower-limb exercise compared with a single one.

This study examined if acute multi-joint resistance exercises (RE; back squat, bench press, and deadlift) to volitional failure elicited a postexercise increase in the circulating response of biomarkers associated with neuroprotection. Thirteen males (age: 24.5 ± 3.8 years, body mass: 84.01 ± 15.44 kg, height: 173.43 ± 8.57 cm, training age: 7.1 ± 4.2 years) performed 4 sets to failure at 80% of a 1-repetition maximum on the squat, bench press, and deadlift in successive weeks. The measured biomarkers were brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), cathepsin B (CatB), and interleukin 6 (IL-6). Biomarkers were assessed immediately before and 10-min after exercise. There was a main time effect (pre-exercise: 24.00 ± 0.61 to postexercise: 27.38 ± 0.48 ng/mL; p < 0.01) for BDNF with increases in the deadlift (p = 0.01) and bench press (p = 0.01) conditions, but not in the squat condition (p = 0.21). There was a main time effect (pre-exercise: 0.87 ± 0.16 to postexercise: 2.03 ± 0.32 pg/mL; p < 0.01) for IL-6 with a significant increase in the squat (p < 0.01), but not the bench press (p = 0.88) and deadlift conditions (p = 0.24). No main time effect was observed for either CatB (p = 0.62) or IGF-1 (p = 0.56). In summary, acute multi-joint RE increases circulating BDNF. Further, this investigation is the first to report the lack of a transient change of CatB to an acute RE protocol. Novelty Low-volume RE to failure can increase BDNF. Resistance training does not confer an acute Cat B response.

Most strength and conditioning coaches deal with the question in the training plan, how to supplement specific exercises, or which non-specific exercises would be the most suitable for achieving the set purpose. This study aims to assess what strength transfer with a focus on the lower limbs is projected from the selected strength intervention program (the right leg exercises only single-joint exercises: leg extension on machine and leg curl; the left leg exercises only multi-joint exercises: deadlift and leg press) to the force of the knee joint flexors and extensors during the eccentric and the concentric contraction. In one training session, the participants repeated every exercise five times in four series. The load intensity was around 90% of 1RM and was increased by 5% after the first and the fifth week. The rest interval was always three minutes long. For the left lower limb, the highest transfer (0.20) was from the leg press to the knee joint extensor at the eccentric contraction and from the deadlift was the highest transfer (0.19) to the knee joint extensor at the eccentric contraction. For the right lower limb, the highest transfer (0.53) was from the leg extension on a machine to the knee joint flexor at the concentric contraction and from the lying leg curl was the highest transfer (0.47) to the knee joint flexor at the concentric contraction.

Although many previous studies have investigated the shear behaviour of single rock joints, few of them have focused on the shear behaviour of multi-joint rock specimens under constant normal stiffness boundary conditions. This study describes the manufacture of a series of rock specimens containing multiple parallel rough joints and estimates the role of surface roughness and spacing of joints during shearing. The results show that the upper joint is crushed while the lower joint is scratched after shearing for a two-joint specimen. The middle joint is more significantly damaged/scratched than the upper and lower joints after shearing for a three-joint specimen. The joint surface roughness plays a clearer role on the variations in shear stress, normal displacement and normal stress for a three-joint specimen than that for a two-joint specimen. With the increment of shear displacement, the surface resistance index (SRI) defined as the ratio of shear stress to normal stress exhibits peak values and residual values. As the spacing of joints increases, the peak SRI generally increases at a rate in the range of 0·15–0·22/cm, except for one specimen containing three joints with a relatively rough surface.

Brandão, L, de Salles Painelli, V, Lasevicius, T, Silva-Batista, C, Brendon, H, Schoenfeld, BJ, Aihara, AY, Cardoso, FN, de Almeida Peres, B, and Teixeira, EL. Varying the order of combinations of single- and multi-joint exercises differentially affects resistance training adaptations. J Strength Cond Res 34(5): 1254-1263, 2020-Our study aimed to compare the effects of multi-joint (MJ) and single-joint (SJ) exercises, either isolated or in combination, and in different orders, on cross-sectional area (CSA) of the pectoralis major (PM) and different heads of the triceps brachii (TB), as well as on the one-repetition maximum (1-RM) in the bench press and lying barbell triceps press. Forty-three young men were randomly assigned to one of 4 possible RT protocols: barbell bench press plus lying barbell triceps press (MJ + SJ, n = 12); lying barbell triceps press plus barbell bench press (SJ + MJ, n = 10); barbell bench press (MJ, n = 10); or lying barbell triceps press (SJ, n = 11). Results showed significant within-group increases in 1-RM bench press for MJ, MJ + SJ, and SJ + MJ but not for SJ. Conversely, significantly greater within-group increases in elbow extension 1-RM were noted for SJ, MJ + SJ, and SJ + MJ but not for MJ. Significantly greater increases in PM CSA were observed for MJ, MJ + SJ, and SJ + MJ compared with SJ. Significant increases in TB CSA were noted for SJ, MJ + SJ, and SJ + MJ, but not for MJ, without observed between-group differences. Individual analysis of TB heads showed significantly greater CSA increases in the lateral head for MJ, MJ + SJ, and SJ + MJ compared with SJ. Alternatively, significantly greater increases in the long head were observed for SJ, MJ + SJ, and SJ + MJ compared with MJ. CSA increases for the medial head were statistically similar between conditions. Our findings indicate that muscular adaptations are differentially affected by performance of MJ and SJ exercises.

Uncertainties and fault signals usually exist in the real systems and it is difficult to maintain stability and tracking performance for the real applications. Therefore, it is important to study the robust fault tolerant tracking control (RFTTC) for uncertain nonlinear feedback systems (NFS). Generally, the RFTTC schemes are designed for the uncertain NFS by using operator theory based robust right coprime factorization (ORRCF) method. In details, firstly, one novel RFTTC scheme is proposed for the uncertain NFS, wherein the fault tolerant controllers as well as the tracking one are designed based on the internal model. Secondly, the other new RFTTC scheme is proposed where the robust fault tolerant controllers are combined with the compensation operator and the tracking controller. By the proposed two design schemes, the impacts induced by the faults on the system is eliminated, and the entire nonlinear feedback system holds strong robustness and perfect tracking performance. Finally, simulation results of the multi-joint manipulator are used to indicate the validity of proposed two design schemes.

Background The impact that mechanical factors might have on gait reorganization was evaluated by the relationship between muscle mechanical capacity of isolated leg muscle groups and transition speed in previous studies. However, until now there are no studies that explored the relationship between muscle mechanical properties measured in cyclic multi-joint movements and gait transition speed. Research question What is the nature of the relationship between gait transition speed and muscle mechanical capacities measured in cyclic multi-joint movements? Methods The sample included 18 physically active male adults, stratified by anthropometric dimensions. Individual walk-to-run (WRT) and run-to-walk transition speed (RWT) were determined using the standard incremental protocol. Mechanical capacities of leg muscles were assessed by linear force-velocity models obtained during treadmill locomotion and on bicycle-ergometer. Results The results revealed inverse correlation between WRT and RWT and maximal force assessed on treadmill (F0; r = -0.57 and r = -0.54, respectively), as well with F0 (r = -0.65 and r = -0.58, respectively) and maximal power (Pmax; -0.66 and -0.65, respectively) collected on bicycle-ergometer. Significance This study confirmed that mechanical muscle capacities are important physical limitation factors of transition speed, explaining over 36 % of the variance. The findings showed that a novel approach, with high biomechanical similarities with natural locomotion, revealed different results (negative correlations) in comparison to previous studies.

Industrial robots have received enormous attention due to their widespread uses in modern manufacturing. However, due to the frictional discontinuous and other unknown dynamics in a robotic system, existing researches are limited to simulation and single- or double-joint robot. In this paper, we introduce a semiparametric controller combined with a radial basis function neural network (RBFNN) and a complete physical model considering joint friction. First, to extend the neural network (NN) controller to real-world problems, the continuously differentiable friction (CDF) model is adopted to bring physical information into the learning process. Then, RBFNN is employed to approximate the model error and other unmolded dynamics, and the parameters of the CDF model are updated online according to its learning ability. The stability of the robot system can be guaranteed by the Lyapunov theory. The primary parameters of the CDF model are determined by the identification experiment and subsequently iteratively updated by the NN. Real-time tracking tasks are performed on a six-degree-of-freedom (DoF) manipulator to follow the desired trajectory. Experimental results demonstrate the effectiveness and superiority of the proposed controller, especially at low speed.

How to improve the walking efficiency while ensuring the wearability is an important issue of lower limb exoskeletons. Active devices can provide greater forces, while the passive devices have advantage in weight. We presented a multi-joint exoskeleton with active hip extension assistance and passive ankle plantarflexion assistance in this work. An admittance controller based on a feedforward model was proposed to track the desired active force of the hip extension. An underfoot clutch mechanism was adapted to realize the passive ankle plantarflexion assistance. To assess the efficacy of the multi-joint exoskeleton in assisting walking, we conducted comprehensive experiments to evaluate the force tracking performance, lower limb muscle activities and metabolic cost. The results demonstrated that: (i) The average tracking error of the peak hip extension assistance force from three subjects was less than 3%. (ii) The reductions of normalized root-mean-square EMG in the lateral soleus, medial soleus and gluteus maximus of eight subjects achieved 15.33%, 11.11%, and 3.74%, respectively. (iii) The average metabolic cost of six subjects was reduced by 10.41% under exoskeleton on (EO) condition comparing to the condition of walking with no exoskeleton (NE). This work proved that the concept of the multi-joint exoskeleton with active-passive assistance can improve the walking efficiency.

Movements are reportedly controlled through the combination of synergies that generate specific motor outputs by imposing an activation pattern on a group of muscles. To date, the smallest unit of analysis has been the muscle. In this human study, we decoded the spiking activities of spinal motor neurons innervating six lower limb muscles during an isometric multi-joint task. We identified their common low-frequency components, from which networks of common synaptic inputs to the motor neurons were derived. The vast majority of the identified motor neurons shared common inputs with other motor neuron(s). In addition, groups of motor neurons were partly decoupled from their innervated muscle, such that motor neurons innervating the same muscle did not necessarily receive common inputs. Conversely, some motor neurons from different muscles – including distant muscles – received common inputs. Our results provide evidence of a synergistic control of a multi-joint motor task at the spinal motor-neuron level.TeaserThe generation of movement involves the activation of many spinal motor neurons from multiple muscles. A central and unresolved question is how these motor neurons are controlled to allow flexibility for adaptation to various mechanical constraints. Since the computational load of controlling each motor neuron independently would be extremely large, the central nervous system presumably adopts dimensionality reduction. We identified networks of functional connectivity between spinal motor neurons based on the common synaptic inputs they receive during a multi-joint task. Our findings revealed functional groupings of motor neurons in a low dimensional space. These groups did not necessarily overlap with the muscle anatomy. We provide a new neural framework for a deeper understanding of movement control in health and disease.

Pathological tremor can be a disabling condition that affects millions of people worldwide. Tremor reduction strategies based on peripheral electrical stimulation of afferent pathways are a promising alternative minimizing the adverse effects of traditional solutions, although a better understanding of the targeted mechanisms is required. Here, we performed a pilot study with two stimulation strategies based on bilateral and multi-joint stimulation below motor threshold, which were tested in two patients with Essential Tremor.

Lightweighting and cost reduction are overarching research themes in aerospace and automotive industries, leading to the exploration of new materials, advanced manufacturing methods, and design optimization algorithms. Multi-material topology optimization is an important tool that can generate unconventional designs leveraging the differing mechanical properties of multiple material types to increase performance. However, these approaches do not consider joining design during optimization, which can ultimately result in higher cost, worse performance, and unrealistic designs that must be altered in the interpretation stage. This work presents a multi-material and multi-joint topology optimization methodology that models joints at the interfaces between dissimilar materials, controls the joining pattern using joint design variables, and reduces cost through the addition of a joining cost constraint. Design variable interpolation schemes, interface detection for unstructured meshes, and sensitivity analysis are outlined in detail in this paper. The approach is applied to a real-world rocker arm geometry to demonstrate the importance of considering joints during multi-material topology optimization. The results of the numerical example indicate that the methodology can successfully detect interfaces in unstructured meshes and strategically place joints to maximize stiffness of the structure. A parameter study of various joining cost constraint levels illustrates how the optimizer alters part topology and joining design to reduce cost.

As a popular control rhythm of the multi-joint robotic fish, Center Pattern Generators (CPGs) plays an important role for motion performance. However, its optimal parameters are tough to seek through traditional methods. In order to address this problem, we propose an online optimization method for CPG parameters, including a novel normalized CPGs (N-CPGs) and a learning-based optimization algorithm. Via N-CPGs, the network parameters can be fully decoupled, which provides a great convenience for model parameter optimization. In particular, by applying the established dynamic model of the robotic fish, we use the deep Q network (DQN) to optimize the N-CPGs, aiming at improving the speed performance. Finally, extensive simulation results verify the effectiveness of proposed method, laying a solid foundation for real-time online control optimization of versatile motion modes in complex application scenarios.

Purpose The aim of the current meta-analysis was to examine the extent to which there are differences in upper extremity\ud motor synergies across different age groups in manipulative tasks.\ud Methods The studies that used the uncontrolled manifold method to examine the effect of age on motor synergies in multijoint\ud and multi-finger tasks were selected. Sixteen relevant studies from 1154 articles were selected for the meta-analysis—4\ud and 12 studies considered multi-joint kinematics and multi-finger kinetic tasks respectively.\ud Results The results of the meta-analysis suggested reduced strength of synergies in multi-finger task in older adults, but\ud this was not the case for synergies in multi-joint task. Part of this age-related difference in finger function is related to the\ud increased variability in total force in grasping tasks. However, reductions in the strength of multi-finger synergies in hand\ud functions following ageing appear to depend on the characteristics of the task.\ud Conclusions These findings indicate that the cooperation among fingers to stabilise the total required force to apply for\ud grasping and other fine motor skills is less efficient in older adults that might affect the quality of manipulative tasks.

BACKGROUND: The use of various single-joint proprioception measurements has resulted in contradictory findings after knee arthroplasty. The use of balance as a surrogate measure to assess knee proprioception post-operation has resulted in further confusion. The aim of this study was to measure single joint knee proprioception in participants after unilateral knee arthroplasty, and compares it to multi-joint balance. METHODS: Eleven participants at 1 year after unilateral total knee arthroplasty and twelve age-matched controls were enrolled. The threshold to detect passive motion and the sensory organization test were used to measure single joint knee proprioception and multi-joint balance respectively. Two-way ANOVA and independent t-tests were used to measure differences between and within groups. Regression analysis was used to measure the association between proprioception and balance measurements. FINDINGS: Surgical knees demonstrated significantly more deficient proprioception compared to the non-surgical knees and both knees of the control groups during flexion (P < 0.01) and extension (P < 0.05). Non-surgical knees showed similar proprioception to both knees of the control group during flexion and extension. Within the knee arthroplasty group, only deficiencies during flexion showed significant correlation with Sensory Organization Test visual ratio. No additional differences between both groups during balance measurements, nor any correlations between local joint proprioception and balance were seen. INTERPRETATION: These findings indicate deficient surgical knee proprioception in participants one year after unilateral total knee arthroplasty. Limited associations between measurements indicate that balance may be a poor measure of single-joint proprioception.

Isometric tests have been used to assess rate of force development (RFD), however variation in testing methodologies are known to affect performance outcomes. The aim of this study was to assess the RFD in the isometric squat (ISqT) using two test protocols and two testing angles. Eleven participants (age: 26.8 ± 4.5 years, strength training experience: 7.1 ± 3.03 years) completed test and retest sessions one week apart, whereby two test protocols with respect to duration and instructions were compared. Isometric peak force (ISqT

The purposes of the present study were (a) to determine whether a self-reported dominant leg was consistent with a dominant leg of force generation by using the isometric mid-thigh pull (IMTP) tests and (b) identify the features of bilateral IMTP (IMTPBi) and unilateral IMTP (IMTPUni) in terms of detecting strength imbalance of athletes. Fifteen male collegiate athletes performed IMTPUni and IMTPBi. The ground reaction force and surface electromyography were sampled with 1000Hz to assess force generation and neuromuscular activities in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus (ST), biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL) during IMTP. Legs were separated into dominant and non-dominant leg categories in accordance with two types of definitions including self-reported dominance of kicking leg and dominance of force generation in IMTP. In force generation and neuromuscular activity of IMTPBi and IMTPUni, there was no significant difference between self-reported dominant and non-dominant leg. However, results for a self-reported dominant leg were not consistent with results for dominant leg determined by force generation. In addition, the dominant leg of force generation exerted significantly larger PF than non-dominant leg, and the magnitude of asymmetry in IMTPBi was significantly larger than that of IMTPUni. Moreover, in IMTPBi, the neuromuscular activity of the VL of the dominant leg of force generation was significantly larger than that of the non-dominant leg. Therefore, it was suggested the necessity to distinguish the two types of IMTP tests because of the possibility that the strength imbalances detected by IMTPBi and IMTPUni would have different connotations.

Multi-joint snake robot is a vital reconnaissance, surveillance and attack weapon in national defence and military in the future. To study the trajectory tracking problem of a multi-joint snake robot with high redundancy and multi-degree of freedom in the plane, an adaptive trajectory tracking controller of a multi-joint snake robot considering non-holonomic constraints is proposed in this paper. The adaptive trajectory tracking controller replaces unknown parameters in the environment wi t h estimated values, which effectively solves the negative effects caused by uncertain and time-varying environmental parameters in the process of the robot movement and realizes the stability of the controller. Firstly, a new dynamical model of a multi-joint snake robot is established through coordinate transformation. Secondly, the control objective of the controller of the multi-joint snake robot is established. Thirdly, the proposed controller of the multi-joint snake robot is designed by the Backsteppi n g method to realize the control of the joint angle tracking error, link angle tracking error, actuator torque error and motion speed error of the robot. Then, a suitable Lyapunov function is found to verify the stability of the controller. Finally, through the MATLAB simulation and prototype experiment, the motion process of the multi-joint snake robot is observed, the trajectory tracking performance of the robot is analyzed, and the effectiveness of the adaptive trajectory tracking controller is verified.

Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip-knee-ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking for three participants. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26% and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance. Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible. Two-joint assistance reduced the metabolic cost of walking by between 34% and 42%, with the largest improvements coming from hip-ankle assistance. Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance. Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

To determine the effect of arm-raising pattern on upper limb proprioceptive accuracy for movements made to overhead targets.Sixteen healthy young adults were tested in standing with arms at the sides, made dominant arm-raising movements to an unseen overhead stop, randomly placed at one of five different overhead targets. Movements were made either as a uni-joint shoulder flexion movement in an arc, or as an unconstrained arm raising that was a series of multi-joint movements involving the shoulder, elbow, and wrist.Overall proprioceptive accuracy for discrimination between the five unseen overhead targets was not different after arm-raising with either a uni-joint or mult-joint pattern (Proprioceptive accuracy did not differ between simple uni-joint and more complex multi-joint arm-raising movement patterns, and the further the extent of the overhead target movement, the worse proprioceptive discrimination sensitivity for both movement patterns. Upper limb proprioceptive accuracy was therefore movement extent dependent, but movement pattern independent.

In order to improve the tip force and controllability of soft pneumatic actuator (SPA), this paper presents the design principle and mathematical modeling method of a multi-joint reinforced soft pneumatic actuator (MRSPA). The MRSPA is composed of an equivalent three driven joints and a spring leaf on the bottom of the MRSPA. Through finite element analysis (FEA), the influence of different chamber distribution on the bending performance of a single joint under the same length is explored. In addition, a mathematical model is established to explore the relationship between pressure, load and bending angle of the driven joints and to estimate the curved configuration of the MRSPA. The FEA results show that the uniform chamber distribution is easier to enable the two-way bending of the SPA. The mathematical model of the MRSPA is validated by comparing the simulation results based on the mathematical model with the FEA results.

Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip–knee–ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26 and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance (N = 3). Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible (N = 3). Two-joint assistance reduced the metabolic cost of walking by between 33 and 42%, with the largest improvements coming from hip-ankle assistance (N = 3). Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance (N = 4). Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

More classification patterns are needed if we want to get a better interaction. It means we need much more training data because of the mapping relationship between classification results and training data. And it may cause an increased burden or a secondary injury for the users who has a certain degree of motor impairment. To solve this question, this paper proposes a method using lower limb single-joint motions to estimate unlearned multiple-joint motions based on muscle synergy combinations. The method proposed using lower limb basic flexion extension motion to predict some complex motion which doesn't collect the complex motion surface EMG data. The experiment showed 4 unlearned combine motions predicted using 6 single motion and result in an average accuracy of 84.83%. Moreover, experiment results are given to illustrate that the solution is more efficient in real time control for lower limb exoskeleton. And these results are important for lower limb exoskeleton users with a lower limb motor dysfunction.

According to the neuromuscular model of virtual trajectory control, the postures and movements of limbs are performed by shifting the equilibrium positions determined by agonist and antagonist muscle activities. In this study, we develop virtual trajectory control for the reaching movements of a multi-joint arm, introducing a proportional-derivative feedback control scheme. In virtual trajectory control, it is crucial to design a suitable virtual trajectory such that the desired trajectory can be realized. To this end, we propose an algorithm for updating virtual trajectories in repetitive control, which can be regarded as a Newton-like method in a function space. In our repetitive control, the virtual trajectory is corrected without explicit calculation of the arm dynamics, and the actual trajectory converges to the desired trajectory. Using computer simulations, we assessed the proposed repetitive control for the trajectory tracking of a two-link arm. Our results confirmed that when the feedback gains were reasonably high and the sampling time was sufficiently small, the virtual trajectory was adequately updated, and the desired trajectory was almost achieved within approximately 10 iterative trials. We also propose a method for modifying the virtual trajectory to ensure that the formation of the actual trajectory is identical even when the feedback gains are changed. This modification method makes it possible to execute flexible control, in which the feedback gains are effectively altered according to motion tasks.

Successful execution of daily activities requires accurate perception of the torques one generates about multiple joints. Even so, previous studies are mostly limited to an individual’s perception when torques are generated about a single joint. Consequently, this study investigates how accurately individuals judge torques at their arm during a multi-joint task. The accuracy of fifteen right-hand dominant participants (age: 60 ± 10 years) in matching isometric elbow torques, within the same arm, was quantified during single- and/or multi-joint tasks. Participants generated and matched elbow torques when the shoulder was: (1) not abducted (single-to-single-joint), (2) abducted (multi-to-multi-joint), and (3) abducted and then not abducted (multi-to-single-joint). The constant error for the multi-to-single-joint condition (dominant: 6.9 ± 5.9 Nm, non-dominant: 6.0 ± 5.5 Nm) was greater than that for the single-to-single-joint condition (dominant: 2.7 ± 3.1 Nm, non-dominant: 3.4 ± 2.8 Nm) (p < 0.001) and multi-to-multi-joint condition (dominant: 3.0 ± 2.8 Nm, non-dominant: 3.9 ± 2.7 Nm) (p < 0.001). The constant error for the multi-to-multi-joint condition did not significantly differ from that of the single-to-single-joint condition (p $$=$$ = 0.780). Findings indicate that in older adults the perception of a self-generated torque during a 2-degree-of-freedom (DOF), multi-joint task is largely influenced by the motor commands associated with the 2-DOF task and is not specific to the DOF at each joint.

Safety and automatic control are extremely important when operating manipulators. For large engineering manipulators, the main challenge is to accurately recognize the posture of all arm segments. In classical sensing methods, the accuracy of an inclinometer is easily affected by the elastic deformation in the manipulator's arms. This results in big error accumulations when sensing the angle of joints between arms one by one. In addition, the sensing method based on machine vision is not suitable for such kind of outdoor working situation yet. In this paper, we propose a novel posture positioning method for multi-joint manipulators based on wireless sensor network localization. The posture sensing problem is formulated as a Nearest-Euclidean-Distance-Matrix (NEDM) model. The resulting approach is referred to as EDM-based posture positioning approach (EPP) and it satisfies the following guiding principles: (i) The posture of each arm segment on a multi-joint manipulator must be estimated as accurately as possible; (ii) The approach must be computationally fast; (iii) The designed approach should not be susceptible to obstructions. To further improve accuracy, we explore the inherent structure of manipulators, i.e., fixed-arm length. This is naturally presented as linear constraints in the NEDM model. For concrete pumps, a typical multi-joint manipulator, the mechanical property that all arm segments always lie in a 2D plane is used for dimension-reduction operation. Simulation and experimental results show that the proposed method provides efficient solutions for posture sensing problem and can obtain preferable localization performance with faster speed than applying the existing localization methods., 7 pages, 8 figures

To achieve vertical profile exploration of deep-sea hybrid structures, a multi-joint autonomous underwater vehicle (MJ-AUV) with the orthogonal joints structure was designed, and its virtual prototype was built using Automatic Dynamic Analysis of Mechanical Systems (ADAMS). This paper focuses on the attitude control of the designed MJ-AUV which is a nonlinear system with strong coupling, big hysteresis, large inertia, and time-varying disturbance. According to the special structure of the MJ-AUV, an error based variable gain linear active disturbance rejection controller (EVG-LADRC) was proposed and compared with the traditional proportional-integral-derivative (PID) controller and LADRC. Simulation results demonstrated that EVG-LADRC outperformed the PID and LADRC in terms of rapidity, anti-interference, and accuracy.

Minimally invasive percutaneous needle-based procedures such as brachytherapy, ablation, and biopsy are standard clinical procedures in cancer interventions. Active needle steering increases the target placement accuracy, and consequently improves the clinical outcome. In this work, dynamical characteristic analysis and FEM modeling of flexible joints of a 3D steerable active flexible needle, when actuated by three Shape Memory Alloy (SMA) actuators, are studied. The Shape Memory Effect (SME) and Pseudoelasticity (PE) of the SMA actuators, their biocompatibility, and high corrosion resistance have made them appropriate alternatives in biomedical applications. Modelling the dynamics and FEM analyses of the flexible active needle during actuation is essential before predicting the active needle’s behavior inside tissue.

Resistance-training of the lower limbs can be performed using exercises moving one (single-joint exercises) or several joints (multi-joint exercises). This study compared the effects of training one multi-joint exercise (leg press) or two single-joint exercises (leg extension and kickback) on dynamic and isometric strength and the transferability of dynamic strength between exercises. Fifty-three physically active women were randomized to a multi-joint (MJ) training group (age = 21.95±0.82 years, mass = 64.85±5.76 kg, height = 167.35±2.47 cm; n = 20), single-joint (SJ) training group (age = 22.56±1.66 years, mass = 64.85±5.76 kg, height = 165.94±2.84 cm; n = 18), or a control (CON) group (age = 21.27±0.68 years, mass = 68.43±4.86 kg, height = 168.63±2.84 cm; n = 15). The training groups participated in an 8-week supervised single- or multi-joint lower limb training consisting of 18 sessions. Pre- and post-training, six repetitions maximum (RM) and maximal voluntary isometric contraction in the three exercises were assessed, along with electromyography of the superficial quadriceps muscles. Improvements in all dynamic exercises were greatest after training the specific exercises (ES = 1.26–2.14, P

StartReact is the ability of the startle reflex to involuntarily release a planned movement in the presence of a loud acoustic stimulus resulting in muscle activity patterns and kinematics that are tightly regulated and scaled with the intended action. Previous studies demonstrated startReact's robustness during simple single-joint reaching tasks and found no difference between startReact and voluntary movements for movement kinematics and muscle activation patterns. However, startReact has not been evaluated during multi-joint reaching movements with multiple degrees of freedom. It is unclear if startReact would evoke accurate and precise multi-joint reaching movements in an unrestricted workspace. Furthermore, if tested more rigorously, multi-joint startReact movement kinematics and muscle activation patterns might not be truly equivalent despite showing no difference through traditional ANOVAs. A previous study found multi-joint startReact was possible during unrestricted elbow and shoulder movement when reaching to a forward target. Therefore, we hypothesized that startReact would evoke similar multi-joint reaching movements for movement accuracy and muscle activation patterns when compared to voluntary movements in a multi-directional workspace. Expanding upon the previous study, our study uses a larger workspace and fully evaluates movement kinematics and muscle activations patterns. Results confirmed our hypothesis and found startReact movements were readily evoked in all directions. StartReact responses presented stereotypically earlier muscle activation, but the relative timing of agonist/antagonist firing pairs between startReact and voluntary movements remained similar. Results demonstrate that startReact is robustly present and equivalent in multi-joint reaching tasks and has potential clinical use for evaluating healthy and impaired movement.

Joint coordination during locomotion and how this coordination changes in response to perturbations remains poorly understood. We investigated coordination among forelimb joints during the swing phase of skilled locomotion in the cat. While cats walked on a horizontal ladder, one of the cross-pieces moved before the cat reached it, requiring the cat to alter step size. Direction and timing of the cross-piece displacement were manipulated. We found that the paw was transported in space through body translation and shoulder and elbow rotations, whereas the wrist provided paw orientation required to step on cross-pieces. Kinetic analysis revealed a consistent joint control pattern in all conditions. Although passive interaction and gravitational torques were the main sources of shoulder and elbow motions for most of the movement time, shoulder muscle torque influenced movement of the entire limb at the end of the swing phase, accelerating the shoulder and causing interaction torque that determined elbow motion. At the wrist, muscle and passive torques predominantly compensated for each other. In all perturbed conditions, although all joints and the body slightly contributed to changes in the step length throughout the entire movement, the major adjustment was produced by the shoulder at the movement end. We conclude that joint coordination during the swing phase is produced mainly passively, by exploiting gravity and the limb’s intersegmental dynamics, which may simplify the neural control of locomotion. The use of shoulder musculature at the movement end enables flexible responses to environmental disturbances. NEW & NOTEWORTHY This is the first study to investigate joint control during the swing phase of skilled, accuracy-dependent locomotion in the cat and how this control is altered to adapt to known and unexpected perturbations. We demonstrate that a pattern of joint control that exploits gravitational and interaction torques is used in all conditions and that movement modifications are produced mainly by shoulder muscle torque during the last portion of the movement.

The purpose of the present study was to look at lower extremity force generation and neuromuscular activation by comparing isometric mid-thigh pull in the unilateral stance (IMTPUni) and bilateral stance (IMTPBi), and identifying the characteristics of IMTPUni. Fifteen male collegiate athletes (age: 20.60 ± 1.50 years, height: 1.74 ± 0.05 m, mass: 69.04 ± 4.23 kg) performed IMTPUni and IMTPBi as multi-joint isometric exercise. Ground reaction force (GRF) was measured to assess force generation during IMTP. Surface electromyography (EMG) was used to measure neuromuscular activation in the gluteus maximus (Gmax), gluteus medius (Gmed), semitendinosus, biceps femoris (BF), rectus femoris (RF) and vastus lateralis (VL), which were represented as average rectified values (ARVs). The EMG of the muscles during IMTPUni was normalized by IMTPBi to compare relative change among muscles. The co-contraction index (CI) during IMTPUni was also calculated by using normalized EMG. As a result, IMTPBi was significantly higher in BF than IMTPUni. However, in IMTPUni, although only one leg contributed to produce force, GRF of IMTPUni reached 80% of neuromuscular activity relative to IMTPBi. While the neuromuscular activation of Gmax, Gmed, BF, RF and VL was significantly higher proportionately in IMTPUni compared to IMTPBi, neuromuscular activation was even greater in Gmax and Gmed. The co-contraction index (CI) was increased in IMTPUni. The features of neuromuscular activation during IMTPUni were similar to the single leg squat and step-up exercise examined in previous studies due to the necessity to support the body with a single leg.

In this paper, a novel compliant passive joint with two torsion springs is designed for a multi-joint robotic fish to improve propulsive performance. The motion of the multi-joint robotic fish is governed by the central pattern generator (CPG) control method. Using this multi-joint robotic fish as a testbed, the effect of compliant passive joint on swimming speed with changes in spring constant and CPG parameters such as oscillation frequency and phase difference is explored. As for the multi-joint robotic fish with a compliant passive joint, the swimming speed increases directly with the increase of oscillation frequency and the swimming speed achieved at maximum oscillation frequency increases with the decrease of phase difference. In addition, the comparison of swimming performance between robotic fish with a compliant passive joint and a fixed passive joint is made. Remarkably, the maximum swimming speed after improvement increases approximately 9.43 cm/s, corresponding to 0.17 BL/s. Experimental results reveal that adding an extra compliant passive joint can not always bring an improvement in swimming performance. Appropriate stiffness of passive joint and control parameters are needed to achieve better swimming performance.

The aim of the present study was to compare muscular performance and body composition changes following low-volume resistance-training programs consisting of multi-joint (MJ) exercises (cable chest press and seated row) versus a combination of multi- and single-joint (MJ+SJ) exercises (cable chest press, seated row, biceps curl, and triceps extension). Thirty untrained healthy aging adults were randomly assigned to 3 groups: MJ (n = 11), MJ+SJ (n = 11), and control (n = 8). Twelve-repetition maximums (12-RMs) for the cable chest press and seated row, localized muscular endurance for the elbow flexors handgrip strength, and body composition were assessed before and after the 8-week training program. All comparisons were analyzed via a mixed-model analysis with repeated measures (group × time) and the Bonferroni post hoc test (p < 0.05). The MJ and MJ+SJ groups increased performance in the 12-RM cable chest press (MJ = 61.5% ± 24.6% and MJ+SJ = 71.1% ± 25.6%), 12-RM seated row (MJ = 46.4% ± 26.3% and MJ+SJ = 51.5% ± 21.0%), localized muscular endurance (MJ = 24.7% ± 16.7% and MJ+SJ = 37.0% ± 11.4%), and handgrip strength (MJ = 9.3% ± 10.4% and MJ+SJ = 16.6% ± 25.3%) after the intervention. Body composition (i.e., trunk and upper limb fat and lean mass) did not change for any groups. No significant differences were observed between the MJ versus the MJ+SJ protocols after the intervention for any variables. In conclusion, for aging adults, either MJ or MJ+SJ low-volume resistance training resulted in similar increases in 12-RM, localized muscular endurance, and handgrip strength, without changes in body composition after 8 weeks of training.

Previous research has investigated synergies involved in locomotion and balance reactions; however, there is limited insight into the emergence of skilled balance control with practice of challenging tasks. We explored motor learning of tandem and single leg stance on an unstable surface-a slackline. Balance was tested in 10 naïve healthy adults at four time points: baseline, after one slackline practice session, after 1 week of practice, and 1 week following the final practice session. We recorded kinematics of the upper and lower arms bilaterally, trunk, and thigh and foot unilaterally while participants balanced in tandem and single leg stance on a slackline and narrow rigid beam (transfer task). When participants first attempted to stand on the slackline, they exhibited fast and frequent movements across all joints with actions along the frontal plane (particularly the hip) and fell after a short period (~3 seconds). Performance improved rapidly (fewer falls), and this was accompanied by dampened trunk and foot oscillations and the development of coordinated movement patterns with a progressive emphasis on more distal upper body segments. Continuous relative phase angles between joint pairs began to cluster around either 0° (indicating in-phase movement) or 180° (indicating anti-phase movement). Participants also began to demonstrate coordinated upper body synergies and performance improvements (fewer falls) on the transfer task, while a control group (n = 10) did not exhibit similar synergies or performance improvements. Our findings describe the emergence of coordinated movement synergies involving the upper body as healthy adults learn a challenging balance task.