Biomechanics

Background/Objectives: Upper-limb loss represents a critical clinical and socioeconomic challenge globally. While myoelectric devices offer multi-articulated grasping, their high cost restricts access in low-resource settings. This work presents the preliminary biomechanical design, Fused Deposition Modeling (FDM) manufacturing, and proof-of-concept evaluation of a custom transradial prosthesis (EVA) with a manual, incremental ratchet-type tensioning mechanism. Methods: Virtual CAD assembly was parametrically customized from user anthropometry. Finite Element Analysis (FEA) incorporating transversely isotropic material models (E_x = E_y = 2150 MPa, E_z = 1620 MPa) and transient dynamic impact simulations evaluated structural stresses and contact transitions. Physical prototypes were FDM-printed in Polyethylene Terephthalate Glycol (PETG) and Thermoplastic Polyurethane (TPU). Grip forces were experimentally measured using piezoresistive sensors, while transmission torque (M_knob = 1.37 N·m) was analytically derived. Ratchet reliability was tested over 1000 continuous cycles, and an able-bodied simulator pilot study (N = 5) evaluated usability (Box and Block Test, Donning/Doffing, System Usability Scale). Results: Peak static von Mises stress (45.0 MPa) remained below the PETG yield limit (47–60 MPa), whereas transient impact stress reached 53.8 MPa. Safe grip thresholds without slippage were established up to 5.3 kg for wood, 3.4 kg for iron, and 2.1 kg for glass. Experimental grip force measured 122.5 ± 4.2 N. Failure at 7.5 kg followed a two-stage sequence: hinge micro-delamination (6.5 kg) followed by internal return spring snapping. Cyclic ratchet testing showed 0.08 mm pawl wear and 0.2–0.4 mm back-slip with 90.9% retained grip force. Simulator testing yielded a Box and Block score of 14.2 ± 1.8 blocks/min, donning time of 28.5 ± 4.2 s, and a SUS score of 78.5/100. Conclusions: The manual ratchet mechanism provides an ultra-lightweight (344 g) and affordable (~$50 USD) assistive alternative. However, manual contralateral actuation occupies the sound hand (100% involvement during adjustment), precluding true bimanual independence. Near-term mitigations, including shoulder-driven pull-cables and sEMG solenoids, are proposed.

Background/Objectives: Wheelchair fencing requires effective trunk coordination because athletes cannot use the lower limbs for propulsion. This exploratory study investigated whether coach-guided scapular-control instruction was associated with differences in spinal kinematics during fencing lunges. Methods: Seven competitive wheelchair fencers performed six lunges under Natural and Coach-guided conditions. Four inertial measurement units were positioned at C7–Th1, Th6–Th7, Th12–L1, and L5–S1. Eight kinematic outcomes were analyzed using linear mixed-effects models with Condition, Segment, and their interaction as fixed effects and Participant as a random intercept. Repeated lunges were averaged within participant, condition, and segment, resulting in 56 observations. Benjamini–Hochberg FDR correction was applied across 24 omnibus tests, followed by Holm correction for post hoc segment comparisons. Results: Three effects remained significant after FDR correction. RMS angular acceleration differed between conditions (F(1,42) = 17.00, p < 0.001, q = 0.004, η²p = 0.288). Significant Segment effects were observed for peak angular jerk (F(3,42) = 5.00, p = 0.005, q = 0.038, η²p = 0.263) and time to peak angular velocity (F(3,42) = 5.33, p = 0.003, q = 0.038, η²p = 0.276). Holm-adjusted comparisons showed significant differences between L5–S1 and Th6–Th7 for peak angular jerk (pHolm = 0.010) and time to peak angular velocity (pHolm = 0.004). No Condition × Segment interaction survived FDR correction. Conclusions: The findings indicate condition-associated differences in RMS angular acceleration and segment-related differences in peak angular jerk and timing of peak angular velocity. Given the small sample and fixed condition order, these findings should be interpreted as exploratory associations rather than evidence of a causal coaching effect.

Background: The jump shot is a critical technical element in modern handball, requiring the complex integration of speed, power, and precision. As the game evolves toward higher intensities, traditional coaching models require validation against objective biomechanical data. This study aimed to investigate the kinematic characteristics of the jump shot in elite players and establish a methodological framework for transitioning raw kinematic parameters into expert-based performance models. Methods: Kinematic analysis was conducted on five elite male handball players (n = 5, 15 total trials), focusing on the approach, flight, and release phases. Additionally, ten highly qualified handball experts (N = 10) independently established a theoretical performance model. To enable direct comparison between objective measurements and expert assessments, kinematic frequencies were linearly normalized onto a five-point ordinal continuum. The relationship between the kinematic model and the hypothetical expert model was determined using Spearman’s rank correlation coefficient. “Kinematic analysis was conducted on elite handball players, focusing on the approach, flight, and release phases. Results: Elite players predominantly utilize a two-step approach, with the first step slightly longer than the second to optimize the kinematic chain. Kinematic data and expert evaluations showed high congruency regarding body posture, highlighting the necessity of diagonally aligned shoulders and a forward-leaning trunk during the flight phase. A statistically significant correlation was observed between objective kinematic parameters and expert ratings, confirming the model’s validity. Conclusions: This study demonstrates a novel approach for evaluating technical performance by bridging the gap between biomechanical data and expert intuition. These findings provide a valuable exploratory foundation for automated technical evaluation systems and offer practical insights into contemporary technical trends for elite-level coaching in the rapid tempo of modern handball.