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In this paper, a novel passive flexible leg joint method is proposed with the aim of enhancing the impact buffering capability as well as reducing energy consumption. The innovative structure cleverly incorporates micro-plate springs, offering significant stiffness adjustment capabilities. To meet the stiffness requirements, the relationships between foot-ground contact force and the deformation force of the elastic component, as well as the influence of elastic component deformation and foot cushioning amplitude are comprehensively analyzed. With the aid of finite element optimization analysis, a single-leg experimental platform is designed, and the effectiveness and applicability of the novel structure are validated through experiments including unloaded free swinging, freely falling body motion and ground squats experiments. Comparative experiments results show the evident superiorities of the passive compliance joint.

Purpose Force and torque production of human muscles depends upon their lengths and contraction velocity. However, these factors are widely assumed to be independent of each other and the few studies that dealt with interactions of torque, angle and angular velocity are based on isolated single-joint movements. Thus, the purpose of this study was to determine force/torque–angle and force/torque–angular velocity properties for multi-joint leg extensions. Methods Human leg extension was investigated ( n  = 18) on a motor-driven leg press dynamometer while measuring external reaction forces at the feet. Extensor torque in the knee joint was calculated using inverse dynamics. Isometric contractions were performed at eight joint angle configurations of the lower limb corresponding to increments of 10° at the knee from 30 to 100° of knee flexion. Concentric and eccentric contractions were performed over the same range of motion at mean angular velocities of the knee from 30 to 240° s −1 . Results For contractions of increasing velocity, optimum knee angle shifted from 52 ± 7 to 64 ± 4° knee flexion. Furthermore, the curvature of the concentric force/torque–angular velocity relations varied with joint angles and maximum angular velocities increased from 866 ± 79 to 1,238 ± 132° s −1 for 90–50° knee flexion. Normalised eccentric forces/torques ranged from 0.85 ± 0.12 to 1.32 ± 0.16 of their isometric reference, only showing significant increases above isometric and an effect of angular velocity for joint angles greater than optimum knee angle. Conclusions The findings reveal that force/torque production during multi-joint leg extension depends on the combined effects of angle and angular velocity. This finding should be accounted for in modelling and optimisation of human movement.

In insect exoskeletons, articular membranes connect the sclerotized hard segments within joints, ensuring protection, mobility, and resilience to mechanical stresses. During exoskeletal movement, these membranes experience tensile and compressive forces, leading to either stretching or the formation of cuticular folds. The mechanisms underlying cuticular folding remain unclear, particularly whether folds are regular (specific) or irregular (non-specific) and how cuticle ultrastructure influences folding patterns. To address these questions, we examined the femur–tibia joints in the mesothoracic legs of locusts (Locusta migratoria) using non-destructive micro-CT, histological methods, and scanning electron microscopy. The joints were analyzed at different flexion angles and maturity stages to characterize membrane folding. Our findings reveal distinct scales of cuticular folds in the femur–tibia joint: macrofolds associated with internal structures such as muscle attachment sites and microfolds potentially linked to cuticle ultrastructure, surface properties, or membrane thickness differences.

The force maintained following stretching of an active muscle exceeds the isometric force at the same muscle length. This residual force enhancement (RFE) is different for various muscles. It is currently unknown whether training induces changes in RFE. Weightlifters perform a large number of eccentric contractions during training, and RFE might be functionally relevant. The aim of this study was to examine whether there is increased RFE in weightlifters versus a reference group. Therefore, we measured external reaction forces during a multi-joint leg extension in weightlifters (n=10) and a reference group (n=11) using a motor driven leg press dynamometer (ISOMED 2000). Steady state isometric forces after stretching were compared to the corresponding forces obtained during isometric reference contractions. Statistical analyses yielded a significant RFE for both groups (p<0.001), but there were no RFE differences between the groups (p=0.320). However, RFE tends to decrease slower in the weightlifting group versus the reference group. We conclude that long-term weightlifting has only a minor influence on RFE. We speculate that the specific training including a combination of eccentric and concentric exercises induced almost no changes in titin-isoform expression which may be responsible for generation of RFE after active muscle stretching.

This study investigated the change in the joint angles of the lower limb during gait by heating the tip of the insole to make a conscious push-off with the warm part. Fifteen healthy males performed treadmill walking under three different conditions: CONTROL walked as usual, INST was instructed to extend the stride with a push-off from the ball of foot to the toe, and HEAT was asked to walk while attempting to push off the warm area, which was attached to the disposable warmer to the area from the ball of foot to the toe of the insole. A 3D-motion capture system with infrared cameras was used to analyze the gait. The hip joint angle increased significantly under the INST and HEAT. Although the ankle dorsi-flexion at heel strike did not differ significantly for these conditions, ankle plantar-flexion significantly increased at toe-off under the INST and HEAT. Especially, effect size (d) in increased plantar-flexion was large in HEAT (=1.50), whereas it was moderate in INST (=0.68). These results suggest that a heated stimulus during gait enhanced the consciousness of push-off and increased leg swing and ankle plantar-flexion during the terminal stance phase, which may increase the stride length.

The rapid development in offshore wind energy makes it imperative to have safe and environmentally sustainable installation vessels for long-term renewable energy installations. In the architecture and design of wind turbine installation vessels (WTIVs), the leg–spudcan joint is important. It contributes to the stability performance of a jack-up WTIV under harsh marine conditions. In this work, the fatigue behaviour of leg–spudcan connections under cyclic environmental and operational loads is studied. A hot spot stress (HSS)-based finite element model according to the requirements of China Classification Society (CCS) is used for assessment of the stress distributions, fatigue damage ratios, and the safety margins under realistic wave loading directions. At the minimum estimated fatigue life of 260 years, the results confirm that the structural system is capable of a service design life of 20 years and reinforce the importance of stress concentration associated with certain joints as a significant impact on the fatigue durability. Sensitivity analyses also show the influence of weld geometry, plate thickness, and S–N curve choice on fatigue predictions. The findings of the current study offer an engineering base for the improvement of the reliability and sustainability of the offshore wind turbine installation vessel, which contributes to the resilience of marine renewable energy infrastructure.

Locomotion of insects is exceptionally efficient and this efficiency is partially due to the kinematics within leg joints, which in different movement scenarios depends on their inner contacting conditions. The investigation of functionality of the leg joints can potentially provide new innovative problem solutions in robotics. The previously published information about the shape of the joints is not sufficient, because without knowledge about the movements of the articulating surfaces within the joint, the kinematics cannot be understood. To understand the joint movements, we have performed motion tracking experiments in the beetle Pachnoda marginata (Scarabaeidae, Cetoniinae) in different locomotory scenarios. We aimed at understanding the range of motion within single leg joints depending on their function in the entire leg movement scenario. For this purpose, we combined the motion analysis of living beetles with the results of the simulation of a multi-body system. The results of the multi-body simulation allowed the kinematic characterization of articulating joints by their degrees of freedom and the identification of the rotation axes. The simulated range of motion predicted by the limitations of the exoskeleton of the joints partially matched those obtained from the motion analysis of the living beetle. We showed that the range of motion of the single leg joints depends strongly on the type of the beetle locomotory scenario. It is also concluded that the simulation of multi-body systems is a powerful tool for the kinematic analysis of insect tribological systems.

Based on the spectral representation method of random function and combined with memoryless nonlinear translation theory, this paper analyzes the transformation relationship between potential Gaussian random process and non-Gaussian random process, and successfully generates a stationary non-Gaussian random process that conforms to the target non-Gaussian random process. For the non-stationary non-Gaussian random process simulation, on the basis of the stationary Gaussian random process, the intensity non-stationary uniform modulation model is used to modulate it, and combined with the nonlinear translation theory, the non-stationary non-Gaussian random process conforming to the target non-Gaussian random process is obtained. Aiming at the single-leg bouncing model based on the flexible rotary hip joint, the stability of its bouncing motion under passive motion is studied, and the influence of the flexible hip rotary joint on the motion stability is analyzed by comparing the single-leg bouncing motion characteristics of the free rotary hip joint. Based on the inverse dynamic control of the air phase, the fixed point distribution of the single-leg bounce of the flexible rotary hip joint was improved, and the function of the flexible rotary hip joint in the energy conversion of the bouncing motion was studied by establishing the energy consumption evaluation function. The kinematic performance verification, dynamic performance verification, dynamic parameter identification verification, and modal experiment simulation analysis were carried out for the built experimental platform, and the comparison and analysis with its theoretical model were carried out. The results show that the theoretical motion trajectory of the test mobile platform is basically consistent with the actual motion trajectory in the X and Y directions, and there is a small error in the Z-axis direction, and the error is within an acceptable range, indicating that the experimental platform system can be used to simulate the human hip joint. There is a large error between the theoretical value of the driving torque calculated by the theoretical value of the dynamic parameters and the measured value, and the dynamic theoretical model cannot accurately predict the driving torque. The predicted value of the driving torque calculated by using the identification value of the dynamic parameters is in good agreement with the measured torque, and its confidence is increased by 10–16%, indicating that the dynamic parameter identification method in this paper has a high degree of confidence.

Background: Lower limb malalignment has been associated with osteochondritis dissecans (OCD). However, the location of the OCD lesion often is not concordant with the mechanical leg axis. Other potentially modifiable alignment parameters may influence the propensity for impingement of the femoral condyles. Purpose: To assess differences in lower limb alignment (LLA) and relative tibiofemoral position between patients with medial (MFC-OCD) or lateral OCD (LFC-OCD) of the femoral condyle. Study Design: Cohort study; Level of evidence, 3. Methods: Patients ≤30 years old who were diagnosed with unicondylar OCD between January 2010 and January 2020 were eligible for this study. Included were 55 patients (age, 20.8 ± 4.5 years)—46 with MFC-OCD and 9 with LFC-OCD. Preoperative standing long-leg radiographs were studied to obtain primary outcomes—including LLA and mechanical alignment analyses—and secondary outcomes—including knee joint obliquity angle; rotation angle; medial, central (c-subluxation), and lateral subluxation (L-subluxation) of the tibia relative to the femur in the coronal plane; and tibiofemoral joint line center distance (TFJCD). Results: With regard to primary outcomes, LLA was significantly different between MFC-OCD (1.7°± 3.1° varus) and LFC-OCD (2.7 ± 3.1° valgus) (P < .001), and 78% (36/46) of patients with MFC-OCD had varus alignment, whereas 78% (7/9) of patients with LFC-OCD had valgus alignment (P < 0.002). With regard to secondary outcomes, patients with MFC-OCD had a more medial tibial position in relation to the femur, with a significantly smaller rotation angle (5.6°± 2.4° vs 9.6°± 3.6°; P < .001), a smaller C-subluxation (7.2 ± 6.6 vs 14.9 ± 8.8 mm; P < .01), a smaller L-subluxation (2.3 ± 2.6 vs 4.4 ± 2.7 mm; P < .05), and reduced TFJCD (3.5 ± 1.7 vs 6.6 ± 1.8 mm; P < .001) compared with the LFC-OCD group. For patients with MFC-OCD, the size of the OCD was significantly correlated with C-subluxation (r = 0.412; P = .006). Conclusion: LLA was significantly different according to OCD location. In patients with MFC-OCD, the tibia was subluxated medially, resulting in a change of joint geometry by approximation of the medial tibial eminence toward the medial femoral condyle, potentially causing excessive pressure overload and microtrauma of the cartilage. Interestingly, the extent of subluxation was correlated with OCD size.

Background This study investigates the influence of postoperative leg length discrepancy (LLD) on the temporomandibular system (TMS) after total hip or knee replacement (THR/TKR), focusing on long-term effects and functional or positional changes in the temporomandibular joint (TMJ). Methods A total of 45 patients (31 THR, 14 TKR) from Leipzig University Hospital were prospectively examined preoperatively and after 8–12 weeks. LLD was measured and categorized. A control group of 20 subjects without surgical interventions was used to compare the initial situation, and oral health was assessed using OHIP-G14 questionnaires. Statistical analysis was performed using SPSS version 24. Level of significance was accepted at p  < 0.05. Results While no patient developed temporomandibular disorders (TMD), functional and positional changes in the TMS were observed postoperatively, particularly in patients with a LLD ≥ 15 mm. Significant changes included increased mouth opening (+ 4.3 mm) and decreased left laterotrusion (-1.98 mm) in the high compensation group. Shifts in condylar position were noted in all spatial axes. No significant changes in function were observed in the control group and in patients with a LLD ≤ 10 mm. The subjective oral health-related quality of life remained unchanged. Conclusions Postoperative LLD after THR or TKR leads to measurable changes in TMJ position and mandibular function. However, these changes did not lead to clinical TMD within the study period. Trial registration This study involved examinations only and did not include any intervention. Therefore, trial registration was not required and was not performed. Clinical trial number: not applicable.